Chairs
Dibakar Bhattacharyya C. Jeffrey Brinker
Dept of Chemical & Materials Engr Dept of Ceramic Synth & Inorg Chem
Univ of Kentucky Sandia National Labs
Lexington, KY 40506 Albuquerque, NM 87106
606-257-2794 505-272-7627
David Needham
Dept of Mech Engr & Matls Sci
Duke Univ
Hudson Hall
Durham, NC 27708-0300
919-660-5355
* Invited paper
SESSION GG1: INORGANIC MEMBRANES
Chair: C. Jeffrey Brinker
Tuesday Morning, April 6, 1999
Salon 14 (M)
8:30 AM GG1.1
TEMPERATURE AND PRESSURE DEPENDENCE OF LIGHT GAS MIXTURE
PERMEATION THROUGH SAPO-34 MEMBRANES. Joseph C. Poshusta, Eric A. Pape,
Vu A. Tuan, John L. Falconer, Richard D. Noble , Univ of Colorado, Dept
of Chemical Engineering, Boulder, CO.
Zeolite membranes are composed of inorganic microporous
crystals that are attractive for gas separation because their pore sizes
are uniform and typically less than 1 nm. Because zeolites are inorganic,
they have excellent thermal stability and chemical resistance making them
an ideal material as membranes for the separation of gas mixtures in a
variety of applications. The silicoaluminophosphate analog of chabazite,
SAPO-34, is an attractive membrane material for the separation of light
gases, because the pore size of SAPO-34 crystals (0.4 to 0.45 nm) is close
to the kinetic diameters of light gases. Continuous layers of SAPO-34 crystals
were synthesized on the inside surface of porous alumina support tubes.
Single gas and binary mixture permeances were measured as functions of
temperature and pressure with pressure drop as the driving force for diffusion
(i.e. no sweep gas was used). Single gas permeation through SAPO-34 membranes
decreased with molecular size for H2, CO2, N2,
CH4, and n-C4H10. The permeance of CO2
decreased as pressure increased with a constant pressure drop, and this
behavior is consistent with the surface diffusion mechanism. Binary mixtures
of CO2/CH4, N2/CH4, and H2/CH4
were separated using SAPO-34 membranes supported on porous alumina tubes.
The room temperature CO2/CH4 composition based selectivity
was 5.5 at 270 kPa feed pressure with a 138 kPa pressure drop. Below room
temperature (229 K), the CO2/CH4 selectivity increased
to 7.5. The room temperature selectivities of N2/CH4
and H2/CH4 were 1.8 and 3.8, respectively. Increasing
temperature and pressure decreased the CO2/CH4 and
N2/CH4 selectivities, but the H2/CH4
selectivity was constant up to 470 K, and decreased to 3.4 at 520 K. The
temperature dependence of the CO2/CH4 and N2/CH4
selectivities is consistent with separation by competitive adsorption.
Size selectivity controls the H2/CH4 separation,
however, because high selectivity is observed at 520 K.
8:45 AM GG1.2
MICROPOROUS SILICA MEMBRANE FOR CO2 REMOVAL
FROM NATURAL GAS. Chung-Yi Tsai 1, Siu-Yue Tam1,
C. Jeffrey Brinker2, The University of New Mexico, NSF Center
for Micro-Engineered Materials1,2, Sandia National Laboratories2,
The Advanced Materials Laboratory, Albuquerque, NM.
For the removal of carbon dioxide from natural gas prior
to delivery to a pipeline, membranes are more advantageous than conventional
amine adsorption processing for use on offshore platforms, high CO2
content wells, small gas streams or environmentally sensitive areas. Unlike
conventional polymeric membranes, porous silica membranes with higher permeance
and selectivity are applicable at high wellhead pressures and do not suffer
from CO2 plasticization, representing an alternative for CO2/CH4
separation. We processed ultramicroporous silica membranes with reproducible
high permeances and high separation factors (3 x 10-4 cm3(STP)/s/cm2/cmHg
and 160, respectively) exceeding that of the best-known membranes for separation
of a 50/50 (v/v) CO2/CH4 gas mixture. The asymmetric
membrane, composed of three major layers (ultramicropore layer, mesopore
layer, and macropore layer) is further simulated by a two-dimensional mathematical
model. This model, accounting for mass transfer in both the solid and the
gas phases, is used to assess the influence of a number of operating parameters
(temperature, pressure, and feed flow rates) for a tube-and-shell configuration,
membrane separator. The model predictions compared to experimental results
will be addressed in this presentation. This work was performed at Sandia
National Laboratories and supported by the U.S. Department of Energy under
Contract No. DE-AC04-94AL85000 and the Electric Power Research Institute.
9:00 AM *GG1.3
SYNTHESIS AND PERMEATION PROPERTIES OF CERAMIC-SUPPORTED
ORIENTED MFI-TYPE MEMBRANES. Michael Tsapatsis , George Xomeritakis Department
of Chemical Engineering, University of Massachusetts, Amherst, MA.
The technique of secondary (seeded) growth has been used
to prepare highly intergrown and oriented MFI-type membranes with thickness
in the range 5-30 micron on the surface of a-Al2O3 porous support disks.
Initially the porous support surface is coated with colloidal silicalite-1
seed nanocrystals ( 100 nm in diameter) by dip coating the disks in a stable
aqueous suspension of the nanocrystals. Subsequently the disks are brought
in contact with a clear synthesis solution under hydrothermal conditions
at various temperatures and times for the purpose of regrowing the seed
nanocrystals to a continuous zeolite layer covering the entire support
surface. The separation potential of the membranes was studied by single-component
and binary permeation experiments using N2, SF6 and butane isomers. For
the most successful preparations, the N2:SF6 single-component ratio was
above Knudsen but rather modest (8-10) while the permeation flux of n-C4H10
and the n-C4H10:i-C4H10 ratio from 50/50 mixtures at 22°C was in the
range 1.5-4.5x10-3 mol m-2 s-1 and 25-60, respectively. The n-C4H10:i-C4H10
ratio remained high up to about 100-140°C but decreased drastically
to <10 at higher temperatures. The permeation results indicate that
the membranes at hand exhibit shape-selective properties comparable to
other in-situ grown MFI-type zeolite membranes reported in the literature.
9:30 AM GG1.4
DEFECT FREE MOLECULAR SIEVE COMPOSITE MEMBRANES. Tina
M. Nenoff , Steven G. Thoma, Daniel Trudell, Alejandra V. Chavez, Phillip
Pohl, Sandia National Labs, Albuquerque, NM.
Inorganic thin film membranes for catalysis and separations
processes have been prepared by direct growth of molecular sieve crystals
onto alumina supports and metal oxide disks. Molecular modeling methods
have been employed to predict and design pore size and shapes for shape
selectivity. Silica based systems employed a composite matrix of crystalline
and amorphous coatings that create a defect free membrane. The choice of
amorphous coating is highly dependent upon substrate, due to adhesion factors.
The resulting membrantes consist of mono- to bi-layer, intergrown oriented
crystals. Zinc based systems are synthesized under mild conditions which
result in defect free membranes. Permeation results on the silica- and
zinc-based membranes indicate molecular sieving capabilities for small
gas molecules and organic molecules, respecively.
9:45 AM GG1.5
``ZEOLITE-LIKE'' SOL-GEL SILICA MEMBRANE. Sujit Naik
1, Chung-Yi Tsai1, C. Jeffrey Brinker1,2,
Roger Assink2; 1The University of New Mexico, NSF
Center for Micro-Engineered Materials and 2Sandia National Laboratories,
Advanced Materials Laboratory, Albuquerque, NM.
A `molecular templating' technique was used for creating
microporous amorphous silica with pore size comparable to that of zeolite
ZSM-5. The tetrapropylammonium (TPA) cation, used as a structure-directing
agent in ZSM-5 synthesis, was incorporated as a template within an inorganic
sol-gel silica matrix and subsequently removed to create pores with molecular
dimensions (pore size 5-6 ).
This approach exploits the high drying stresses that develop in sol-gel
silica to form organic-inorganic hybrid materials that upon calcination
result in microporous silica. We describe the synthesis and characterization
of microporous silica membranes for separation of isomers such as n-butane
and isobutane. Microporous TPA-templated sol-gel silica was characterized
using gas adsorption, TGA and XRD. 1H-29Si CP NMR
and 2H NMR were used to determine the efficiency of templating
in the organic-inorganic hybrid materials. The corresponding membranes
are ultrathin, defect-free and have excellent processability. Single gas
permeation experiments indicate that such membranes exhibit a molecular
sieving behavior. The membranes show a high flux of 210-4
cm3(STP)/s/cm2/cm-Hg for n-butane and ideal selectivity
of 450 for N-2/SF-6 and 20 for n-butane/isobutane at 80C.
Dual gas permeation experiments with a n-butane/isobutane mixture gave
results consistent with the single gas measurements.
10:30 AM GG1.6
IN-SITU COUNTER DIFFUSION CVD FOR PORE SIZE CONTROL OF
INORGANIC POROUS MEMBRANE. Yasuyuki Egashira , Nobuhiko Mori, Yasushi Funakoshi
and Korekazu Ueyama, Osaka Univ., Graduate School of Engineering Science,
Division of Chemical Engineering, Osaka, JAPAN.
Combing a chemical vapor deposition (CVD) and catalytic
reaction, a novel pore size control method for inorganic porous membrane,
so called counter
diffusion CVD is proposed and its mechanism is modeled theoretically and
availability examined experimentally. Basically,
counter diffusion CVD is one of the contour diffusion CVD, where two reactant
gases, highly reactive each other, diffuse from both sides of the porous
membrane and react inside the membrane, and high reactivity of the reactants
results a thin deposition region. Counter diffusion CVD method has advantage
of thin deposition region with low resistance for permeation, however,
this method requires somewhat complicated reactor configuration, especially,
separated feed of two reactants is necessarily. In
counter diffusion CVD, catalytic reaction is utilized to produce one of
the reactant gas from source gases which do not react with the other reactant
gas. On one side of the membrane covered to avoid gas diffusion and catalyst
inserted between this cover and membrane. Then, source gases for the reactant
diffuse from the other side of the membrane to produce the reactant gas
over catalyst at covered side of the membrane, and this reactant back diffuses
to react with the other reactant gas. In such configurations, counter diffusion
CVD can achieved without feed separation. A reactor model of this
counter diffusion CVD method was developed and it describes relationship
between reaction condition and deposition position. Availability of this
CVD method was demonstrated experimentally applying to TiCl4/H2/CO2
reaction system. Using Cu based catalyst, H2O produced from
H2 and CO2, then with TiCl4 to deposit
TiO2 within porous media, such as Vycor Glass.
10:45 AM GG1.7
MOLECULAR SIEVE MEMBRANES VIA LASER ABLATION. Kenneth
J. Balkus, Jr. , Ashley Scott, Trindad Munoz, University of Texas at Dallas,
Department of Chemistry, Richardson, TX.
Pulsed laser ablation has been employed to deposit thin
films of nanoporous metal oxides onto porous substrates. After a brief
hydrothermal treatment highly crystalline continuous and some times oriented
molecular sieve membranes are obtained. Recent results for the preparation
of oriented silica molecular sieves UTD-1 and MCM-41 on stainless steel
frits will be presented. The separation of linear paraffins and aromatics
by a UTD-1 membrane shows enhanced permeation of the alkanes. Results using
Ti-UTD-1 in a catalytic membrane reactor will also be presented.
11:00 AM GG1.8
MICROFABRICATED INORGANIC MEMBRANES FOR PROTEIN SEPARATION
AND IMMUNOISOLATION. Tejal A. Desai , Dept. of Bioengineering, University
of Illinois at Chicago, IL; Derek Hansford and Mauro Ferrari, University
of California, Berkeley, CA.
The application of microfabrication technology to create
precise separation and isolation membranes for biomedical applications
is described. By utilizing fabrication techniques commonly employed in
the microelectronics industry (MEMS), membranes were fabricated with well-controlled
and uniform pore sizes, allowing the optimization of membrane parameters
for cell immunoisolation and viral filtration. The membrane-forming process
employs bulk and surface micromachining to define chambers within single
crystalline silicon wafers that interface with the surrounding biological
environment through polycrystalline silicon filter membranes with thicknesses
less than ten microns. Pore sizes down to 18 nanometers have been attained
through deposition and subsequent etching of sacrificial layers. Membranes
were fabricated to present a high density of uniform pores to allow sufficient
permeability to biomolecules such as oxygen, glucose, and insulin. The
ability of the membranes to exclude the passage of larger proteins such
as immunoglobulin G and albumin has also been characterized. The semipermeability
of microfabricated membranes, their biocompatibility, ease in sterilization,
along with their thermal and chemical stability, may provide an significant
advantages for biomedical applicaions. Microfabrication technology may
be applied to other materials of interest for the development of highly
controlled membranes.
11:15 AM GG1.9
STEAM-RESISTANT -ALUMINA
MEMBRANES. Arian Nijmeijer, Henk Kruidhof, Henk Verweij and Manon Timmerman-Oude
Wolbers , Inorganic Materials Science, University of Twente, Enschede,
NETHERLANDS.
For application in process industry membranes which are
stable against aggressive environments are needed. State of the art mesoporous -alumina
membranes suffer heavily from steam atmospheres. Phenomena like pore-growth
and moreover blistering off of the mesoporous layer occur during steam-treatment.
This makes these membranes unsuitable for many industrial applications.
With the use of an anchoring agent this problem can be largely solved.
11:30 AM GG1.10
FABRICATION OF UF MEMBRANES BY LAMINATION TECHNIQUE USING
NANOPARTICLE DERIVED CERAMIC FOILS. R. Nonninger , B. Walter, O. Binkle,
H. Schmidt, Institut fuer Neue Materialien gem. GmbH, Saarbruecken, GERMANY.
A fabrication techniques of flat ceramic ultrafiltation
membranes has been developed which is based on two steps, first a tape
casting step to produce a porous thin film undependently of the substrate,
followed by laminating the free-standing film on to the top of the porous
ceramic substrate in order to fabricate an asymmetric ultrafiltration ceramic
membrane module. The ultrathin ( 15 m)
tape casted ceramic films contained 16 wt.
binder and could be directly laminated on an already sintered porous Al2O3
support with a average pore size of 3 m
without using any intermediate layers. For the ceramic tape fabrication
a tape casting process using a nanoscaled zirconia powder which particle
size ranges between 20 and 50 nm has been developed. In order to obtain
stable aqueous slurries with a solid content of 50 wt.
the surface of the ZrO2 powder had to be modified with a carboxylic
acid in order to stabilize the zirconia particles electrostatically. A
minimum of the viscosity (20 mPas)
and a minimum of the particle size distribution (d50: 55 nm)
was achieved with 4 wt. of the surface
modifier. The laminated ZrO2 tapes were sintered 2 h at 1000C
on the porous Al2O3 supports. In correlation of the
investigated slurry properties a homogeneous sintered microstructure of
the UF-membrane with a narrow pore size distribution (average diameter
30 nm) and a porosity of 54 were obtained.
The 1-20 m thick sintered zirconia
layer is characterized by a defect free top layer. The develloped synthesis
route is a usefull techniques to produce flat ceramic UF elements with
ultrathin active membranes.
11:45 AM GG1.11 A CO2 GAS SENSOR OF
La2O3 - LOADED SiO2-SnO2 MEMBRANE
BY SOL-GEL TECHNIQUE. Nishengliang , Chen Yuquan, Luo Wei, Pan Min, Dept.
of BME, Zhejiang University, Hangzhou, P.R.CHINA.
Detecting the concentration of CO2 at ppm level
by a simple method is desirable not only in various industrial processes
but also in environmental technology. The preparation of La2O3
- loaded SiO2 - SnO2 membrane materials, which starting
materials are SnCl4 and tetraethyl orthosilicate (TEOS), used
the sol-gel technique, is described. The CO2 sensitive properties
of the SiO2 - SnO2 element, effected by the sol-gel
processing and its different microstructures, La2O2
- loaded amount and the processing gas conditions, were investigated. The
results show that the La2O3 - loaded SiO2
- SnO2 membrane gas sensor has quick response to ppm-levels
CO2, and the sensitivity monotonically increases with the concentration
of dry CO2 in range 300-3000 ppm. Here we have studied the sensitive
property of the La2O3 - loaded SiO2 -
SnO2 element by sol-gel technique in more detail.
SESSION GG2: POLYMER MEMBRANES
Chair: Dibakar Bhattacharyya
Tuesday Afternoon, April 6, 1999
Salon 14 (M)
1:30 PM *GG2.1
GAS SEPARATION MEMBRANE MATERIALS: NEW DEVELOPMENTS AND
FUTURE NEEDS. W.J. Koros , Chemical Engineering Department, The University
of Texas at Austin, TX.
The lack of fundamental materials science understanding
often prevents the use of a membrane-based approach for solving important
practical problems. Given this fact, the minimal interaction between the
traditional membrane and materials science communities is surprising. One
inhibiting factor that complicates effective interaction between the two
communities is the diversity of potential applications of membrane technology.
While this diversity makes membranes an exciting field, it also complicates
the identification of which problems should be given priority attention
by the materials science community. The membrane-based gas separation sub-area
will be used to illustrate a recommended strategy for more active participation
by the materials science community across the board in the membrane field.
To narrow down the diverse array of areas for analysis, market size was
used as a measure to select three important applications: air separation,
natural gas separation and olefin-paraffin separations. Key challenges
will be identified in each case, and constraints currently preventing unfettered
approaches to meet these challenges will be discussed. Traditional organic
polymer membranes, liquid membranes and even molecular sieving membranes
are candidates for these applications. By better understanding the differences
and similarities between these three applications, competitive technologies,
and the basis for current constraints in membrane formation, avenues around
these constraints will be considered. Materials science topical areas and
approaches most likely to have a significant impact for each of the three
applications will first be suggested. By also analyzing similarities in
needs that transcend the specific applications, a strategy for promoting
interactions between the membrane and materials science communities will
be suggested. Such a strategy could be extended to encompass the full spectrum
of gas, vapor and liquid separation applications and help advance the interests
of both communities.
2:00 PM GG2.2
NANOPOROUS GAS TRANSPORT IN SEMICRYSTALLINE BLOCK COPOLYMERS.
Peter Kofinas , Peter L. Drzal, Sufi R. Ahmed, University of Maryland,
Dept of Materials and Nuclear Engineering, College Park, MD.
The shear-induced orientation textures produced by plane
strain compression of semicrystalline ethylene/ethylene-propylene (E/P
and E/EP/E) diblock and triblock copolymers and their blends with amorphous
EP homopolymers were investigated. Two dimensional small angle x-ray scattering
(SAXS) was used to determine the domain spacing and lamellar orientation
relative to the specimen boundaries. The SAXS experiments indicated that
depending on the processing conditions orientation textures parallel, perpendicular
and transverse to the plane of shear can be produced. Gas permeability
coefficients were obtained for several gases at room temperature in these
block copolymer systems and their blends with homopolymers. It was found
that the gas transport properties of these semicrystalline systems were
influenced by changes in processing conditions and solvent treatments to
produce anisotropic gas transport properties and porous membranes. The
separation properties of these polymer membranes was altered by changing
the mechanism of gas transport. A selective solvent was used to remove
the homopolymer and develop a uniform nanoporous structure in the oriented
blend morphologies. Depending on the choice of solvent, various degrees
of porosity could be induced in the polymeric membrane. The orientation
texture produced from channel die processing was not disrupted by the introduction
of the pores. It was shown that the induced porosity increased the permeability
of the block copolymer membrane, while retaining some selectivity due to
the confinement of the pores within the block copolymer self-assembled
microphase separated morphology. The permeability results coupled with
small angle x-ray scattering (SAXS) data, provide a direct connection between
changes in microstructure to the observed changes in gas transport properties.
2:15 PM GG2.3
PERMEATION OF NOBLE GASES THROUGH POLYMER MEMBRANES STUDIED
WITH A MASS SPECTROMETER. Holger Norenberg , G.D.W. Smith, G.A.D. Briggs,
University of Oxford, Department of Materials, Oxford, UNITED KINGDOM;
T. Miyamoto, Y. Tsukahara, Technical Research Institute, Toppan Printing
Company, Sugito Takanodai, JAPAN.
Polymer membranes are used in a number of applications
to prevent the permeation of certain gas species (barrier films) or to
separate individual components of gas mixtures from each other. In order
to improve these properties a much better understanding of the process
of gas permeation through membranes is required. We have developed a new
method of measuring gas permeation through thin polymer membranes. This
method uses a mass spectrometer to measure the partial pressure of the
permeated gas species, which originates from a confined volume of gas,
as function of time [1]. The method works on very small amples (4 mm diameter)
and is inherently calibration free. It can be used to study the permeation
of individual components in a gas mixture. In a simple mathematical model
an exponential decay of the partial pressure as function of time is predicted.
The permeation of inert gases is useful for understanding mechanisms of
gas transport through membranes in the absence of chemical interactions.
Our experiments with light noble gases (He, Ne, Ar) confirm the predicted
exponential behaviour. Experiments carried out with Krypton which has a
much higher m/q ratio showed that only a fit with two exponential functions
is satisfactory. We will show a number of examples with noble gases permeating
through PET and OPP and discuss advantages and limitations of the method
and the mathematical model. [1] Holger N{orenberg, T. Miyamoto, N. Fukugami
Y. Tsukahara, G. D. W. Smith and G. A. D. Briggs, accepted for publication
in Vacuum.
2:30 PM *GG2.4
BASIS OF PERMEABILITY/SELECTIVITY TRADEOFF RELATIONS
IN POLYMERIC GAS SEPARATION MEMBRANES. Benny D. Freeman , NC State Univ,
Dept of Chemical Engineering, Raleigh, NC.
Gas separation properties of polymer membrane materials
follow distinct tradeoff relations: more permeable polymers are generally
less selective and vice versa. Robeson (J. Membrane Sci. 62, p. 165, 1991)
identified the best combinations of permeability and selectivity for important
binary gas pairs pairs (O2/N2, CO2/CH4,
H2/N2, etc.) and represented these permeability/selectivity
combinations empirically as: =*P,
where P is the more permeable gas permeability, alpha is selectivity, and
lamdba and beta are adjustable parameters. This presentation gives a fundamental
theory for this observation. In the theory, lamdba depends only on gas
size. beta depends on lamdba, gas condensability, and one adjustable parameter.
Excellent agreement for these parameters with the published slope and intercept
of the so-called upper bound permeability/selectivity tradeoff lines is
demonstrated.
3:30 PM GG2.5
STRUCTURE-PROPERTY RELATIONSHIPS IN PROTON-CONDUCTING
MEMBRANES: QUANTIFICATION OF CROSSLINKING AND CORRELATION WITH SWELLING
AND OTHER PROPERTIES. Hans-Peter Brack , Guenther G. Scherer, Paul Scherrer
Institute, Electrochemistry, Villigen PSI, SWITZERLAND; Daniel Fischer,
Gustav Peter, Zuercher Hochschule Winterthur, Chemistry Department, Winterthur,
SWITZERLAND.
We are preparing proton-conducting membranes by using
the radiation-grafting method to introduce polystyrene-based grafted chains
into fluoropolymer films. The polystyrene chains are sulfonated in a subsequent
step to introduce proton conductivity. We reported earlier that introducing
crosslinking into our radiation-grafted membranes by adding divinylbenzene
(DVB) and/or triallylcyanurate into our grafting solutions leads to significant
changes in membrane properties important for their application in Polymer
Electrolyte Fuel Cells including: (1) swelling in water and resultant dimensional
changes, (2) mechanical properties, (3) proton conductivity, (4) gas crossover,
and (5) resistance to degradation. Unfortunately, the analysis of the DVB
content of membranes is quite complex because technical grade DVB is typically
a mixture of both meta- and para-DVB with the intermediates in the DVB
production, 3- and 4-ethylvinylbenzene (EVB), still present in significant
quantities. All four monomers, meta- and para-DVB and meta- and para-EVB,
are radically polymerizable and thus capable of being incorporated during
grafting. We report here on an infrared analysis of the content of both
the para- and meta-isomers and styrene in our radiation-grafted films.
This analysis indicates that the para isomers are preferentially introduced
during grafting, even though the meta isomers are present in excess in
the technical grade DVB used. More para-isomers are systematically introduced
as the DVB content of the grafting mixture increases; however, the ratio
of the para-/meta-isomers incorporated into the films increases with increasing
DVB content in the grafting solution. Raman analysis of the grafted films
indicates that in all cases very little of the DVB is actually fully reacted
and thus functioning as crosslinks. Taken together with the swelling properties
of these membranes, these results indicate that low levels of DVB incorporation
reduce water swelling significantly and that further increases in DVB content
do not lead to further reduction of swelling or hydration levels (H2O/-RSO3H).
3:45 PM GG2.6
THERMAL DEGRADATION OF RADIATION-GRAFTED FILMS AND MEMBRANES.
Hans-Peter Brack , Gunther G. Scherer, Paul Scherrer Institute, Electrochemistry
Dept, Villigen PSI, SWITZERLAND; Denise Ruegg, Heiner G. Bührer, Zurcher
Hochschule Winterthur, Chemistry Dept, Winterthur, SWITZERLAND.
The thermal degradation under N2 has been investigated
of some fluoropolymer films before and after: (1) gamma or electron beam
irradiation, (2) subsequent grafting with styrene and, in some cases, (3)
sulfonation of the grafted polystyrene component. The films investigated
include: (a) polytetrafluoroethylene or PTFE, (b) poly(tetrafluoroethylene-co-hexafluoropropylene)
or FEP, (c) polyvinylidenefluoride or PVDF, (d) poly(ethylene-alt-tetrafluoroethylene)
or ETFE, and (e) polyethylene. The thermal degradation temperatures and
activation energies for degradation decreased and the rates of weight loss
increased as the fluorine content of the starting films decreased. Irradiation
with a total dose of 20 kGy did not significantly affect the thermal degradation
temperatures, rates of weight loss, or activation energies of the three
film types studied: FEP, PVDF, and ETFE. The thermal degradation temperatures
and activation energies of the grafted polystyrene component of the three
grafted film types, FEP-g-PS, PVDF-g-PS, and ETFE-g-PS varied systematically
as: PVDF < ETFE < FEP. It is proposed that the more highly fluorinated
FEP matrix exerts a protecting effect on the grafted PS domains. For the
grafted films based on a particular fluoropolymer type (FEP, ETFE, or PVDF),
the activation energies were found to increase as the graft level (polystyrene
content) increased. This increase in activation energy may result from
longer grafted chain lengths and thus lower relative concentration of end
groups. Thermal degradation is believed to begin at the end groups in many
polymer systems. All of our films were irradiated with the same dose and
grafted for the same period of time. Lower graft levels were obtained here
by diluting the styrene used for grafting in toluene. Thus the grafted
films based on the same fluoropolymer type are expected to have the same
number of active radical sites and thus grafted PS chains, but they likely
differ in the lengths of these chains.
4:00 PM GG2.7
PSEUDOCROWN ETHERS AS FIXED SITE CARRIERS IN FACILITATED
TRANSPORT MEMBRANES. Brian J. Elliott , W. Brinson Willis and Christopher
N. Bowman, University of Colorado, Dept. of Chemical Engineering, Boulder,
CO.
Polymeric membranes were synthesized by modifying porous
polyethylene membrane supports for separations of metal ions in aqueous
sources. A polymerization synthesis technique was used to form pseudocrown
ethers (polymeric networks that contain crown ether-like moieties) in the
pores of the membrane support. The pseudocrown ethers were formed in situ
during free radical photopolymerization of poly(ethylene glycol) diacrylates
with the use of templating ions. The templating ions were used to induce
the poly(ethylene glycol) diacrylate monomers into a circular conformation
prior to the photopolymerization, thus bringing the two reactive endgroups
into close proximity. The degree of pseudocrown ether formation was found
to be a function of the metal ion / monomer complex geometry, strength
and abundance, and this pseudocrown ether formation occurred with a reduction
in the amount of autoacceleration as compared to the bulk polymerization
(i.e. non-templated). This reduction in autoacceleration was due to the
decreased crosslinking in the pseudocrown ether network relative to the
non-templated network. The possible crown structures obtained from the
monomeric poly(ethylene glycol 200) diacrylate were 21-pseudocrown-6 and/or
18-pseudocrown-5. Pseudocrown ether membranes used in facilitated transport
separations were selective for potassium over sodium which is consistent
with results obtained from membranes that contain dibenzo-18-crown-6 as
a fixed site carrier. By maximizing the concentration of pseudocrown ethers
a selectivity for potassium over neodymium of 3,700 was obtained with a
flux of potassium several orders of magnitude higher than typical fixed
site carrier membranes. Pseudocrown ether membranes that are synthesized
from poly(ethylene glycol) diacrylate analogs that contain nitrogen or
sulfur in replace of some or all of the oxygen atoms in the ethylene glycol
chain should exhibit selectivity for certain transition metals which are
of greater interest with regard to pollution prevention and purification
of water.
4:15 PM GG2.8
Transferred to GG6.3
4:30 PM GG2.9
ELECTROCHEMICALLY PRODUCED MEMBRANES FOR ULTRAFILTRATION
AND REVERSE-OSMOSIS. Lidia Kolzunova , Inst of Chemistry, Far East Dept,
Russian Academy of Sciences, Vladivostok, RUSSIA.
Numerous problems of water purification and organic and
biological moleculs separation can be solved by ultrafiltration and reverse-osmosis
and need diverse membranes and various formation methods. Progressive,
one-stage (2-30 min) and cheap technology of polymer permselective membrane
production is formation of porous films by electrochemically initiated
polymerization of aqueous vinyl monomers (Pat. RF 1560280). The method
allows to control copolymer composition, macromolecule cross-linking, microstructure
development, pore configuration and size, membrane thickness by change
of electrolysis conditions and bath compounds. Membranes have high polymer
matrix homogeneity in consequence of monomer molecules orientation in electric
field perpendicularly to electrode surface and synthesis of polymer with
narrow molecular mass distribution.
Formation conditions of films and composite membranes
and modules were determined and influence of them on structure, properties,
penetration and selectivity were researched. The dense film structures
are formed by -(1.16-1.20) V. These membranes have low penetration and
high selectivity (99.9%). Pore size and framework friability of polymer
films increase with growth of electropolymerization velocity (>-1.3 V).
Membranes are formed by potentiostatic electrolysis have higher penetration
than produced by galvanostatically. Polymer cross-linking by bifunction
monomers allows to form hard polymer structures with both low friability
and small swelling. Pore deformation of these membranes by pressure is
insignificant. Membranes are stable during exploitation and possess high
filtration velocity.
The properties and exploitation characteristics of ultrafilter
and reverse-osmotic membranes are studied. All membranes have small area
of hysteresis loop that testify high elasticity, hardness and deformation
stability of membrane structure. Membranes are stable in acids and alkalis
(pH 1-14). Using of formaldehyde not only as copolymerizing and cross-linking
but anticeptic component permits to prevent microbiological membrane desintegration.
These membranes can be used for cleaning of aggressive solutions and biological
mediums.
4:45 PM GG2.10
POLYMER MEMBRANES AS SENSITIVE ELEMENTS OF IMMUNOSENSORS.
Tetyana Panasyuk, Sergiy Piletisky, Ganna Eliska, Inst of Molecular Biology
and Genetics, Dept of Translational Mechanisms of Genetic Information,
Kyiv, UKRAINE; Rinat Nigmatullin, Inst of Colloid and Water Chemistry,
Dept of Physical Chem of Membranes, Kyiv, UKRAINE; Mikhaylo Bryk , National
Univ `Kyiv-Mohyla Academia', Dept of Chemistry, Kyiv, UKRAINE.
Biosensors are analytical devices that respond selectively
to analytes in an appropriate sample and convert the results into an electrical
or other signals via a combination of a biological recognition system and
a physico-chemical transducer. Data presented in this report indicates
that bioaffinity membranes could be responsible for both molecular recognition
and signal generation. The immunosensors discussed use porous polymeric
membranes as a support for the antibody and at the same time as an active
part of the transducer, such a sensor system with a bioaffinity polymeric
membrane (with immobilized Ab) is able to change its ion permeability during
immunochemical reaction.
The methods of obtaining of bioaffinity membranes based
on acrylonitrile-co-acrylic acid and polyvinylchloride have been developed.
The influence of porous structure on effectiveness of immunochemical reaction
at bioaffinity membranes have been studied.
Using of hydrophobic polyvinylchloride membranes allow
to prepare membranes with a hydrophilic outer surface and hydrophobic pores
or partially hydrophilised pores through the width of the membrane thickness.
It is essential to localize the antigen-antibody (Ag-Ab) reaction in pores
so that surface immobilisation is avoided. In such a way, even small quantities
of Ag in solution could influence membrane permeability which would allow
the improvement of the sensor response. The modification of polyvinylchloride
membranes by non-ionogenic detergent has been studied. The effectiveness
immunoreagent sorption by PVC membranes is time dependent on treatment
in detergent solution. The conditions of partial hydrophilization of PVC
membrane for best immunoreagent sorption have been established.
The conductometric system was used for sensor response
determination. Response of immunosensors correlates with effectiveness
of immunochemical reaction. Both immusensor based on bioaffine acrylonitrile-co-acrylic
acid membranes and polyvinylchloride membranes exhibit higher sensitivity
to rabbit IgG (Ag) (5 ng/ml) and a higher rate compared with the ELISA-method
(the response time is 5-6 min).
SESSION GG3: BIOMEMBRANES
Chair: David Needham
Wednesday Morning, April 7, 1999
Salon 14 (M)
8:30 AM GG3.1
THE MECHANOCHEMISTRY OF LIPID VESICLES EXAMINED BY MICROPIPET
MANIPULATION TECHNIQUES. David Needham , Department of Mechanical Engineering
and Materials Science, Duke University, Durham, NC.
The lipid bilayer membrane is a truly remarkable engineering
material, - it surrounds every cell on the planet providing a mechanical,
chemical, and electrical barrier for the cell. It also acts as a 2 dimensional
solvent for the protein components of the cell membrane. It is however
only 5 nm thick, and, with an area compressibility that is equivalent to
bulk compressibilities between ordinary liquids and gases, and a bending
stiffness of only a few kT, the lipid bilayer is one of the thinnest and
softest materials known. As a consequence, it is both fragile and inherently
difficult to resolve optically. Because of these physical limitations,
direct measurements of the full range of material and interactive properties
of lipid membranes have only been possible by the development of sensitive
micropipet manipulation techniques and the creation of appropriate preparative
procedures that produce large (20 to 30 micron) single-walled lipid vesicles
that can be seen in the optical microscope.
The glass micropipet provides a unique way of applying
well defined stresses to a vesicle capsule whilst at the same time acting
as a sensitive transducer of vesicle membrane area and volume change. Using
a suction pipet, a single lipid vesicle can be manipulated, and several
mechanochemical experiments can be performed that characterize: membrane
area expansion, tensile failure and bending; adsorption, uptake and desorption
of various membrane-soluble components; membrane permeability coefficient
and pore formation; thermal bilayer transitions; membrane yield shear and
shear viscosity for gel phase bilayers; intermembrane adhesion energy that
results from the cumulation of several attractive and repulsive colloidal
potentials.
This overview will focus on the various micropipet methods
that have been specifically developed since 1980 to study the mechanochemical
features of lipid bilayer vesicles (Needham, D. and D. V. Zhelev. Vesicles.,
eds. Rosoff, Marcel Dekker, New York and Basel, 1996 p.373-444). The information
gained from such studies not only characterizes the membrane and its intermembrane
interactions from a fundamental materials science perspective, it also
provides essential materials property data that are required for the successful
design and deployment of lipid vesicle capsules in applications such as
drug delivery.
8:45 AM GG3.2
FOLDING AND RESPREADING IN LUNG SURFACTANT - INFLUENCE
OF CHAIN LENGTH OF LIPIDS AND PRESENCE OF PROTEINS. Karlheinz Graf , Anja
von Nahmen, Joseph A. Zasadzinski, Dept of Chemical Engineering, University
of California, Santa Barbara, CA; Gerhard Schwarz, Dept of Biophysical
Chemistry, Biocenter of the University, Basel, SWITZERLAND; Alan J. Waring,
Dept of Pediatrics, Drew University-King Medical Center and University
of California, Los Angeles, CA.
Lung surfactant, a mixture of saturated lecithins, phospatidylglycerols,
fatty acids, and four specific proteins plays an important role in the
ability of higher developed, living organisms to breathe. During volume
change in the aveolar interface the surfactant maintains aveolar stability
by lowering the surface tension during expiration [1]. Langmuir isotherms
and fluorescence microscopy show the corresponding structural changes within
a monolayer of the lung surfactant as the films are compressed [2]. It
has been shown that processes like bilayer formation, folding and respreading
of lipids and protein are essential to viable lung surfactant during compression
and expansion. These processes are mainly influenced by the presence of
charged lipid compounds and lung surfactant proteins.
We present investigations on the chain length of the
lipid compounds which is known to affect the stiffness of the film and
therefore might affect the collapse behaviour of the membrane. Here we
concentrate on a model lipid mixture with the proteins SP-B and SP-C on
a buffered subphase at pH
6.9 to mimic the biological system.
The proteins are responsible for all processes to occur.
In order to explain this general behaviour on the base of theoretical models,
it is a crucial point to know how much of the proteins actually is in the
monolayer. This can be achieved by studying the partitioning of proteins
between monolayer and subphase by a simple thermodynamic study [3].
References
[1] Ka Yee Lee, Michael M. Lipp, Joseph A. Zasadzinski,
Alan J. Waring, Coll. Surf. A, 128 (1997) 255-242.
[2] Michael M. Lipp, Ka Yee Lee, Alan J. Waring, Joseph
A. Zasadzinski, Biophys. J., 72 (1997) 2783-2804.
[3] Gerhard Schwarz, Susanne E. Taylor, Langmuir, 11
(1995) 4341-4346.
9:00 AM GG3.3
VESOSOMES - A NEW DRUG DELIVERY SYSTEM. Edward Kisak
, Bret Coldren, Michael Kennedy, Dirk Trommeshauser, Joseph A. Zasadzinski,
Univeristy of California at Santa Barbara, Dept of Chemical Engineering,
Santa Barbara, CA.
Vesosomes consist of a sized aggregate of unilamellar
vesicles attached to each other due to the interaction between ligand -
receptor combinations. These aggregates are encapsulated by a second bilayer
again using the ligand-receptor interaction. The aggregated vesicles can
be of similar or varied membrane and interior composition. The vesosomes
can incorporate a variety of water soluble or lipid soluble drugs within
the interior vesicles, or the exterior capsule, or both. We studied the
effects of using different ligand-receptor combinations and ratios to rapidly
prepare vesicle aggregates of a fixed sized. The stability of these aggregates
was also tested. Research into a variety of methods of aggregate encapsulation
has also been carried out.
9:15 AM GG3.4
THE PRODUCTION OF LIPID VESICLES BY EXTRUSION THROUGH
POLYCARBONATE MEMBRANES. P. Patty, C. Asman, D.G. Hunter and B.J. Frisken
, Burnaby, CANADA.
The production of lipid vesicles is an important aspect
of the application of vesicle systems to drug delivery technologies. One
popular production method involves pushing or extruding a lipid suspension
through the cylindrical pores of polycarbonate membranes1. However,
the actual mechanism by which the polydisperse, multilamellar lipid suspension
breaks up into a relatively monodisperse population of vesicles is not
well understood. We have characterized vesicles produced under different
extrusion parameters and from different lipids. We find that vesicles are
only produced above a threshold extrusion pressure and that the lysis tension
of the membrane can be estimated from this minimum pressure. We also find
that the final size of the vesicles decreases as the applied pressure increases.
We have shown that the final size of the vesicles produced depends directly
on the pressure applied, rather than the flowrate or shear that result
from it.
1M.J. Hope, M.B. Bally, G. Webb, and P.R.
Cullis, Biochim. Biophys. Acta. 812, 55-65 (1985).
9:30 AM GG3.5
ELASTIC PROPERTIES AND MICROSTRUCTURES OF CATANIONIC
SURFACTANTS. Hee-Tae Jung , J.A. Zasadzinski, Department of Chemical Engineering
and Materials, University of California, Santa Barbara, CA; Dan Iampietro,
E.W. Kaler, Department of Chemical Engineering, University of Delaware,
Newark, DE.
Spontaneous equilibrium vesicles can be prepared from
aqueous mixtures of single tailed cationic and anionic surfactants. Bending
elastic constants of mixtures of two surfactants were determined by cryo
TEM of vesicle phases followed by image analysis in order to determine
the vesicle size distribution. The experimental results are in a good agreement
with the thermodynamic theory of aggregation. We compare the bending constants
and microstructures of the fluorinated mixtures with the hydrogenated mixture.
The hydrogenated vesicles are about kT, the longer fluorinated is about
10 kT. The replacement of long chain fluorinated molecules by short ones
dramatically reduce bending modulus from 10kT to kT. The microstructure
and morphology of the surfactants are also discussed.
9:45 AM GG3.6
REVERSIBLE COLLAPSE PROCESSES IN MIXED LIPID-PROTEIN-FILMS.
Anja von Nahmen , Dawn Takamoto, Karlheinz Graf, Junqi Ding, Joseph Zasadzinski,
University of California at Santa Barbara, Dept. of Chemical Engineering,
Santa Barbara, CA; Ka Yee C. Lee, University of Chicago, Dept. of Chemistry,
Chicago, IL; Alan Waring, University of California at Los Angeles, CA;
MLK, Drew University Medical Center and Perinatal Labs, Los Angeles, CA.
A complex mixture of lipids and proteins - commonly known
as lung surfactant - lines the alveolar air-water-interface. It reduces
the surface tension of the interface and thereby the work of breathing.
A low surface tension is generally assigned to saturated and rigid lipids.
To insure reduction of the surface tension during inhalation lung surfactant
needs sufficient respreading kinetics. Unsaturated and fluid lipids are
essential to ensure a good respreadability, but do not form stable monolayer
at low surface tension. Recent studies suggest that the key to ensure both
- low surface tension and good respreadability - is a reversible transition
from a two-dimensional monomolecular layer to a partionally three-dimensional
system. The nature of this collapse process strongly depends on film composition.
In this study we investigate complex model systems of saturated, unsaturated,
and charged lipids that also contain surfactant proteins B and C. Using
Langmuir technique in combination with fluorescence microscopy as well
as atomic force microscopy allows for detailed investigation of the phase
behavior and morphology of the model systems. We find that addition of
surfactant proteins makes the collapse process more reversible. Two different
collapse mechanisms can be observed: the formation of stacked protein-rich
lipid bilayers and a long range buckling of the film. We assign the observed
morphology to single compounds or specific lipid-protein or lipid-lipid
interactions.
10:30 AM *GG3.7
MICROMECHANICS OF A RELATIVELY SIMPLE AND NATURAL BIOMEMBRANE
COMPOSITE. D. Discher , J. Lee, D. Wong, C. Picart, University of Pennsylvania,
Philadelphia, PA.
In a material sense, biomembranes are interconnecting
lamellar composites with fluid as well as solid like characteristics. The
fluidity primarily arises from the lipid bilayer, but on the cell's inner
face one often finds a sparse, sometimes ordered network of proteins. The
red blood cell provides a simple yet classic example of this. Short (relative
to a persistence length, Lp) actin filaments are intertriangulated by non-covalent
association with the protein spectrin which, in turn, has a contour length
Lc Lp. We have simulated coarse-grained
versions of such a polymeric structure at multiple scales by Metropolis
Monte Carlo and in both nano- and meso-scale ensembles. The theoretical
results demonstrate several features which we have partially confirmed
by direct experiment. First, the statistical mechanics of this soft, wet
network is borne out by constrained fluctuations of attached nanoparticles
that, by equipartition, also yield a very simple and local estimate for
network elasticity. Second, despite such thermal motion, micropatterned
photobleaching shows the network can sustain very large strains with material
stretching at least of order 200%;
further, the network's in-plane compressibility appears much softer than
that of the overlying lipid bilayer. Third, in such large deformation,
fluorescence polarization shows that the actin nanofilaments tend to stably
reorient in the maximum strain direction, consistent with an ordered but
distorted microstructure. Thus, in comparison with the fluid lipid bilayer,
the network is softer in many respects, but still maintains a solid-like
character.
11:00 AM GG3.8
POLYMOSOMES: NOVEL CAPSULAR STATES OF DI-BLOCK COPOLYMERS.
D. Discher , B. Discher, J. Lee, Y. Won*, D. Ege, F. Bates*,
D. Hammer, University of Pennsylvania, Philadelphia, PA; *University
of Minnesota, MN.
Lipid-based vesicles find application in various products
ranging from pharmaceuticals where they are used in drug delivery, to cosmetics,
to paints and coatings. The amphiphillic character of lipids has been synthetically
mimicked in the last several years with di-block copolymers, some of which
are well known to form lamellar phases in water. Using polyethylethylene/polyethyleneoxide
(PEE-PEO; 3.9 kD with 10% polydispersity), we have been able to form soft,
unilamellar vesicular capsules, or `polymosomes'. We have studied these
vesicles by micromanipulation and found some unique properties. Polymosome
membranes reproducibly have a surface area compressibility and a bending
modulus which approximate those of lipid membranes, and yet vesicle pressurization
shows that the polymosome wall is far tougher, with areal strains at failure
estimated to be almost 20% in comparison to the few%
for lipids. The polymosomes also appear to be an order of magnitude less
permeable to water than liposomes, but osmotic adjustment of polymosome
volume is still possible and generates a range of vesicle shapes that compare
well with phase diagrams of lipid vesicle morphology. Such behavior is,
in theory, predicated on a bilayer structure and a lack of molecular flip-flop
between layers. These and additional results suggest that capsular states
of diblock copolymers may, in some cases, provide performance improvement
over lipid capsules.
11:15 AM GG3.9
MASS-ELECTRO ANALYSIS OF LIPID MEMBRANES FOR CHINESE
WINE TASTING SENSING MODEL. Chen Yuquan, Pan Min , Dept of BME, Zhejiang
Univ, Hangzhou, P.R.CHINA.
The Lipid membrane is ubiquitous in biology. Olfaction
is one of the important senses of human being. Lipids are important not
only in life processes but also in making membranes for artificial olfaction
and taste sensors. Recently mass and electrical property of lipids is investigated
separately using PYE electrical chip and IDT (interdigital electrodes)
or potential measurement etc to analysis the relationship between lipid
membrane structure and the sensing property. This paper describes a new
compound mass-electron analysis method of lipid model. A novel compound
sensor with the lipid membrane was developed; it can get the mass responses
and electrical responses separately and simultaneously with one lipid membrane.
The results of analysis and experiment will be employed to optimize tasting
sensor array design for Chinese wine measurement. Different lipid membranes,
such as polyvinyl chloride and dioctyl phenylphosphonate(DOP) or trioctyl
methyl ammonium chloride(TOMA) or the compound lipid material with different
ratio of DOP and TOMA or the cholesterol oleic acid, prepare processing
and their deposition method and membrane thickness and bass chip preprocessing
are also studied. As a system, later 8 kinds Chinese wine and their grades
with a lipid sensor array with 7 kinds lipid membranes were measured by
an advanced dynamic regression technique, it shows the precise is better
than the normal method.
11:30 AM GG3.10
VARIABLE TEMPERATURE FLUID STAGE FOR AFM. Srinivas Manne,
Richard K. Workman , University of Arizona, Dept of Physics, Tucson, AZ.
The design of a simple variable temperature fluid stage
for an Atomic Force Microscope is presented. The stage is based on a thermoelectric
heating/cooling element which allows control of sample and fluid temperature
from -4C to 130C. This allows the study of phase transitions and other
temperature dependent phenomena. While this fliud cell is useful for imaging
in gas or fluids, we will present results on micelle phase transistions
at the solid liquid interface.
11:45 AM GG3.11 INTERACTIONS BETWEEN POLY(2-ETHYLACRYLIC
ACID) AND LIPID BILAYER MEMBRANES: EFFECTS OF CHOLESTEROL AND GRAFTED POLY(ETHYLENE
GLYCOL). David Needham, Jeff Mills and Gary Eichenbaum, Department of Mechanical
Engineering and Materials Science, Duke University, Durham, NC.
The inclusion of cholesterol in lipid bilayer membranes
causes a condensation of the interface and a dramatic decrease in elastic
area compressibility of the bilayer as well as its permeability to water.
The presence of PEG grafted to the bilayer interface, via the incorporation
of PEG-lipids into the bilayer, can inhibit the close approach of globular
macromolecules and micelles. It is of interest then to determine if these
two different kinds of barriers can hinder the approach and interaction
of a water-soluble polymer that can be triggered to undergo a conformational
transition due to a lowering of solution pH making it less soluble in aqueous
media and more soluble in lipid bilayers, which it can then permeabilize.
We have studied the exchange of the protonatable polymer, poly (2-ethylacrylic
acid) (PEAA), with vesicle membranes containing cholesterol from 0 to 60
mol% or PEG2000-lipid (5 mol%). The release of an entrapped dye from 100
nm extruded liposomes was used as an assay for membrane perturbation by
the polymer as a function of pH. The inclusion of cholesterol was found
to reduce the pH at which the polymer caused release of internal contents
from the lipid vesicles, and the degree of polymer protonation (i.e., hydrophobicity)
correlated well with the increase in elastic expansion modulus of the vesicle.
The results are discussed in terms of a balance between polymer solubility
and membrane expansion. With respect to the PEG barrier, the presence of
5 mol% PEG2000, which represents full surface coverage, did not prevent
PEAA from inducing contents release, demonstrating that highly hydrated
polymeric layers are not effective barriers for other water soluble polymers,
and may point to some association between the two polymers.
SESSION GG4: HYBRID MEMBRANES
Chair: Benny D. Freeman
Wednesday Afternoon, April 7, 1999
Salon 14 (M)
1:30 PM GG4.1
CHALLENGING PERVAPORATION SEPARATIONS USING POLYMERIC
AND ZEOLITE MEMBRANES. Dhaval S. Shah , Dibakar Bhattacharyya, University
of Kentucky, Dept. of Chemical and Materials Engineering, Lexington, KY;
Ajit Ghorpade, SmithKline Beecham Corporation, King of Prussia, PA.
The separation and recovery of solvents is of major interest
to many industries ranging from pharmaceuticals to electronic materials.
Pervaporation is a membrane-based process used for the separation of solvents.
Based on material properties, pervaporation membranes can be mainly classified
into two types; polymeric and ceramic membranes. This research concentrates
on separation studies of various solvent systems using these membranes.
In polymeric membranes, depending on the nature of the polymer, a particular
species will preferentially permeate through the membrane. Experiments
were performed with alcohol-water mixtures in the presence and absence
of inorganic salts using hydrophilic PVA-based polymeric membranes. The
flux for ethanol-water mixture increased from 0.05 to 1.2 kg/m2/hr as the
feed water concentration was increased from 3 to 70 wt % at 333 K. The
importance of plasticization and coupling effects, in alcohol-water separation
using PVA membranes, will be discussed. Silicone-based organophilic polymeric
membranes were also used to study the separation of various solvent mixtures.
High selectivities (100-200) were obtained for ethyl acetate-water and
tetrahydrofuran-water mixtures because of the strong affinity of these
compounds for the polydimethylsiloxane (PDMS) active layer of the membrane.
The main drawbacks of polymeric membranes are their low resistance to solvents
like dimethylformamide (DMF) and dimethylsulfoxide (DMSO) and low selectivities
in dilute solutions. Inorganic membranes help overcome this limitation
of polymeric membranes. Zeolite membranes were used to study the separation
characteristics of several solvent-water mixtures. Zeolites are crystalline,
hydrated aluminosilicates of group I and group II elements which have a
very narrow pore size distribution. A partial/total exclusion of a particular
species and a high sorption of aqueous species may be achieved in zeolite
membranes leading to high selectivities. For 30 wt % ethanol solution,
zeolite membrane selectivity (>1000) was found to be 2 orders of magnitude
higher than that for the PVA membrane (7).
1:45 PM GG4.2
HYBRID POLYIMIDE-SILICA MEMBRANES FOR GAS SEPARATION.
Eva Marand , Chris J. Cornelius, Nicolas G. Vidonic, Virginia Polytechnic
Institute and State University, Department of Chemical Engineering, Blacksburg,
VA.
Hybrid polyimide-silica membranes were fabricated using
a functionalized hexafluorinated polyimide and alkoxysilane precursors,
reacted under sol-gel conditions, forming an interpenetrating network of
silica within a polymer matrix. The covalent linkages between these two
components drive mixing on a molecular level, leading to a highly homogeneous
system. Gas permeability results show a maximum in permeability as a function
of silica content at about 10 weight percent silica, even though the membrane
density continuously increases with silica content. Simultaneous increase
in gas selectivities with silica content suggests that the packing of the
polyimide chains is indeed affected by the presence of the silica phase.
The presence of the inorganic component constrains the polymer chains,
decreasing their conformational entropy, which leads to more open chain
packing. However, the packing arrangements must be quite uniform since
the selectivity also increases. At high silica concentrations the inorganic
component starts to phase separate, acting more as a filler, lowering the
overall permeability. This behavior has been examined for a number of different
alkoxysilane precursors including tetraethoxysilane, dimethyldiethoxy silane
and phenyltriethoxysilane, which give rise to different cross-link densities
and different morphologies due to molecular compatibility differences between
the components and different reaction rates under sol-gel conditions. The
permeability results are also correlated with the dynamic mechanical response,
results of wide-angle X-ray diffraction studies and electron microscopy
images for these materials.
2:00 PM GG4.3
MONOLAYERS OF AMPHIPHILIC FULLERENE DERIVATIVES CONTAINING
AN AZOBENZENE CHROMOPHORE. Kei Oishi , Masahito Sano, Seiji Shinkai, Chemotransfiguration
Project, JST, Fukuoka, JAPAN.
One of the problems of producing stable monolayers of
fullerene [60] at the air-water interface was the tendency of fullerene
to form 3D aggregates. Here, we have synthesized an amphiphilic fullerene
derivative giving Langmuir-Blodgett films with monolayer domains of uniform
thickness extending over tens of microns. The derivative has an azobenzene
chromophore and an ammonium head group. It gives an expanded surface pressure-area
isotherm with a limiting area of 0.95 nm2/molecule. This area compares
well with the limiting area of an ideal monolayer. The UV-VIS reflection
spectroscopy on the water surface shows no specific exciton peaks. These
results indicate a significant hydration of the azobenzene segment and
suggest a model of dangling monolayers that all parts of the molecule other
than the fullerene head are submerged into the water phase.
2:15 PM GG4.4
PROPERTIES OF COMPOSITE MEMBRANES PREPARED FROM PVDF
AND INORGANIC PARTICLES. Aldo Bottino, Gustavo Capannelli, Valentina D'Asti,
Paolo Piaggio , Genova Univ, Genova, ITALY.
The use of composite materials can play an important role
for the preparation of novel membranes with controlled properties which
can be widely used in the traditional separation processes (e.g. gas separation
and ultrafiltration) as well as in emerging and innovative applications,
like catalytic membrane reactors and devices. The interest of this preparative
route derives from the well known point that polymeric-inorganic composites
can combine in a favourable manner the properties of the separate organic
and inorganic materials or can even exhibit new properties that are not
found in the separate one-phase materials. On this basis it would be therefore
possible to produce membranes with chemical and physical properties tailored
for a given application. In order to verify this statement we have studied
the properties of asymmetric membranes prepared by the phase inversion
technique from blends of polyvinylidene fluoride (PVDF), i.e. a polymer
widely used in membrane science and technology, and inorganic particles
like silica and zeolites. The results obtained for these composite membranes
will be shown with regard to their permeability, porosity, hydrophilicity
and compared to those observed for the corresponding PVDF membranes. Moreover
the insertion of a catalist into some of these membranes has been investigated
and first results of their catalitic activity in some standard reactions
will be shown. The effect induced on the membrane morphology by different
preparative conditions have been analysed by vibrational spectroscopy and
electron microscopy. In this way the role played in the formation of the
asymmetric structure of the membrane by the type of solvent, the nature
of the inorganic particles, the temperature and the air exposure time,
has been investigated. In particular the analysis of the FTIR-ATR and PAS
spectra allowed an effective characterisation of both surfaces of the membranes.
2:30 PM GG4.5
ORGANIC-INORGANIC MEMBRANES PREPARED FROM POLYETHERDIAMINE
AND EPOXY-CONTAINING INORGANIC PRECURSORS. S.P. Nunes , K.V. Peinemann,
E. Rikowski, GKSS-Research Center, Geesthacht, GERMANY; M.L. Sforca, I.V.P.
Yoshida, University of Campinas, BRAZIL.
Dense membranes with organic and inorganic polymer segments
were prepared by reacting polymeric diamines contaning ethylene glycol
and propylene glycol blocks with epoxy modified inorganic precursors. Polymeric
diamines with molecular weight 900 and 2000 g/mol were used as organic
segments. For the first part of this work the inorganic precursor was glycidoxypropyl
trimethoxy silane (GPTMS) or mixtures of GPTMS and tetraethoxysilane (TEOS).
The hybrid was prepared by mixing different proportions of epoxysilane
and diamine in tetrahydrofurane, followed by hydrolysis and condensation
of the alkoxy groups by dropping 0.15 M HCl into the solution and stirring
during about 20 hours. Dense films, after drying at 80 C, under vacuum,
were characterized by nuclear magnetic resonance and dynamic mechanical
analysis. The rigidity of the films increased with increasing epoxy content
and also with addition of TEOS. Since the hybrid polymer contains long
polyether segments, the films are quite hydrophilic. The water absorption
was measured as a function of time to give values of water diffusivity
(D) and solubility (S). The water solubility in the films prepared from
diamine with molecular weight 900 g/mol was about twice that of films prepared
from diamines with molecular weight 2000 g/mol. Increasing the TEOS content,
the water diffusivity decreased, but the water solubility increased. Composite
membranes were prepared by coating an asymmetric porous poly(vinylidene
fluoride) support with a dense layer of the organic-inorganic hybrids.
The membranes were then tested for nanofiltration. Membranes with cut off
2300 g/mol and water flow 4.4 l/h m2 bar were obtained from
amines with longer polyether segments; the cut off could be decreased to
860 g/mol by addition of TEOS, keeping the water flow around 2.5 l/h m2
bar. The dense membranes were tested for gas permeation. The presence of
amine groups as well as polyether segments contributes to high CO2
permeabilities (up to 125 Barrer), relative to other gases. Membranes with
carbon dioxide/nitrogen selectivity up to 85 were obtained. Just few polymeric
materials have been reported in the literature with such high values both
for permeability and carbon dioxide/nitrogen selectivity. As a second epoxy
modified inorganic precursor, polyhedral silsesquioxanes with cube-octameric
R8 Si8 O12 (R = epoxy) were synthesized,
dissolved in tetrahydrofurane and further reacted with the same diamines
used above to form dense membranes for gas permeation. Beside their evaluation
as membranes, the films were also characterized by electron microscopy
and thermal analysis.
2:45 PM GG4.6
FABRICATION, CHARACTERIZATION AND UTILIZATION OF NEW
TYPES OF MEMBRANES. Younan Xia , Byron Gates, Univ of Washington, Seattle,
WA.
We have successfully fabricated two new types of membranes:
2-D membranes with tunable pore sizes and 3-D membranes with highly ordered
porous structures. Both membranes were prepared by molding against appropriate
template structures. We are going to present fabrication procedures and
characterization results, as well as several schemes for the funtionalzation
and utilization of these membranes.
SESSION GG5: BILAYER/MULTILAYER MEMBRANES AND SENSORS
Chair: Dennis E. Discher
Wednesday Afternoon, April 7, 1999
Salon 14 (M)
3:30 PM GG5.1
OIL-SWOLLEN BILAYERS BY A MYELIN TRANSMEMBRANE PROTEIN
AND BY SYNTHETIC PEPTIDES. N. Taulier, C. Nicot, M. Waks, LIP, CNRS 7623,
Universitè Paris VI, Paris, FRANCE; R. Ober, LPMC, CNRS 792, Collège
de France, Gif-sur-Yvette, FRANCE; T. Gulik-Krzywicki, CGM, CNRS 2420,
Gif-sur-Yvette, FRANCE; R.S. Hodges, P. Semchuk, PENCE Medical Center,
University of Alberta, CANADA; and W. Urbach , ENS, LPS, CNRS, Paris, FRANCE.
We have explored the interaction of the Myelin Proteolipid
with a nonionic lamellar (L) phase.
In contrast to water-soluble proteins, the spontaneous insertion of the
4 -helix transmembrane protein
induces a progressive expulsion of oil and a simultaneous squeezing of
the interlamellar space. The interlamellar distance is only function of
the protein-to-surfactant molar ratio (up to a maximum) and scales as C-0.5,
where C is the protein surface density. Above this limiting value, the
mean interlamellar distance is optimal and leads to a plateau. We have
investigated the mechanism of this unusual phenomenon with a series of
single -helical peptides of
increasing length (from 8 to 16 hydrophobic amino-acids). It depends among
others on the ratio of the peptide/surfactant length and peptide hydrophobicity.
The results are presented and discussed in terms of the Helfrich theory
applied to bilayers decorated with penetrating molecular inclusions, stabilized
by entropic forces. Since hydrophobic forces alone play a crucial role
in the insertion of transmembrane peptide chains into bilayers, the aim
of this work is to provide a simple model for the ``zipper like'' function
attributed to the myelin transmembrane protein in maintaining the multilamellar,
compact architecture of myelin. On freeze-fracture electron micrographs,
where proteins appear as membrane inclusions, we have determined the radial
distribution function of inclusions: g(r). Short-range correlation observed
in the transmembrane protein position is characteristic of two-dimensional
interacting particles in fluid state. Analysis of g(r) allows the determination
of interprotein forces.
3:45 PM GG5.2
PYROLYZED RESISTS FOR BIO-MEMS APPLICATIONS. Marc Madou
, Ohio State University, Department of Materials Science and Engineering
and Department of Chemistry, Columbus, OH.
Photopatterned resists pyrolyzed at different temperatures
and in different ambient gases can be used as a carbonaceous material for
micro electro mechanical systems (MEMS).The carbon films were characterized
by several analytical techniques, viz. profilometry, thermogravimetric
analysis, four-point probe measurements, SEM, TEM, AFM, XPS and Raman spectroscopy.
In addition cyclic voltammetry was performed on the carbon film electrodes,
and the carbon films have been compared to glassy carbon for their electrochemical
behavior.The carbon films prepared at the higher temperatures showed good
electrochemical reversibility similar to that of glassy carbon. The carbon
films thus produced have potential applications in MEMS, and as electrodes
in batteries, capacitors, sensors, etc. Two specific applications of this
new material will be discussed (I) complex shaped electrodes for specific
electrochemical sensors such as glucose sensors, (II) artificial muscle
with C-MEMS as valve seats. In the first application it is shown that carbon
surface modifications enable one to favor the desired reactions (e.g. with
glucose mediators) over interfering reactions (e.g. reactions with reducing
compounds such as ascorbic acid). In the second application it will be
demonstrated how polymeric artificial muscle (a blend of hydrogel with
redox polymer) can be grown electrochemically on a C-MEMS valve seat and
how this artificial muscle can be actuated electrochemically and chemically
to open and close the valve.
4:00 PM GG5.3
ORDERED ASSEMBLY OF PROTEINS ON SURFACES. Leonidas G.
Bachas , J. Wang, W. Huang, Department of Chemistry, University of Kentucky,
Lexington, KY; S. Viswanath, J. Liu, D. Bhattacharyya, Department of Chemical
& Materials Engineering, University of Kentucky, Lexington, KY.
Membrane materials with immobilized enzymes play a central
role in the development of biosensors, bioreactors and diagnostics. The
functional groups on the protein, that serve as sites for the attachment,
are generally distributed throughout the protein structure. Often this
results in a random orientation of protein molecules on the surface. In
this presentation, several approaches that facilitate the ordered assembly
of enzymes on a variety of materials, including membranes, will be described.
Biotinylation reactions performed under controlled conditions were used
to immobilize enzymes in a layer-by-layer fashion onto surfaces. For other
enzymes, a specific attachment site was introduced by gene fusion and site-directed
mutagenesis. These strategies were applied to achieve site-specific immobilization
of several enzymes including alkaline phosphatase, -galactosidase,
and subtilisin. The site-specific immobilization led to orientation of
the enzyme molecules on the surface of materials and to a higher activity
compared to the conventional immobilization methods.
4:15 PM GG5.4
CALMODULIN-MEDIATED REVERSIBLE IMMOBILIZATION OF ENZYMES.
Vesna Schauer-Vukasinovic, Greta Schrift, Sylvia Daunert , University of
Kentucky, Department of Chemistry, Lexington, KY.
Reversible immobilization of -lactamase
and glutathione S-transferase (GST) was performed using a system based
on the binding of calmodulin (CaM) to a modified surface containing phenothiazine.
Specifically, a fusion protein between the C-terminus of CaM and the N-terminus
of -lactamase was prepared,
and the fusion protein was immobilized in the presence of Ca2+
through the CaM part of the molecule to silica particles covalently modified
with phenothiazine. The immobilized fusion protein retains the -lactamase
enzymatic activity, as well as the ability of CaM to bind to phenothiazine.
The activity of the immobilized enzyme was determined using a continuous
flow method. The reversibility and reproducibility of the fusion protein
loading on the solid surface was evaluated by measuring the rate of reaction
of -lactamase after each consecutive
loading of the enzyme onto the particles. The versatility of this immobilization
approach was studied by reloading the column with a different enzyme, namely
glutathione S-transferase, which was fused to the N-terminus of CaM. The
activity of GST showed that GST immobilized through the CaM part of the
fusion protein is catalytically active for over one month. This approach
may find useful applications in the fields of biosensors and diagnostics.
4:30 PM GG5.5
COEXISTENCE OF BUCKLED AND FLAT MONOLAYERS: MORE EVIDENCES
FOR SURFACTANT PROTEINS TO KEEP MONOLAYERS STABLE. Junqi Ding 1,
Anja von Nahmen1, Alan Waring2, Joseph Zasadzinski1*,
Robert Notter3, 1Department of Chemical Engineering,
University of California, Santa Barbara, CA; 2MLK, Drew University
Medical Center and Perinatal Labs, Harbor, UCLA, CA; 3Department
of Pediatrics and Environmental Medicine, University of Rochester, Rochester,
NY.
Characteristic features of lung surfactants are the ability
to sustain low surface tension and good respreadability. Both are limited
by a two to three dimensional instability called collapse. In this study,
we use Brewster-Angle and Fluorescence Microscopy with Langmuir isotherm
to study collapse behaviors of Survanta
and Curosurf (natural lung surfactant
extracts). We supplement synthetic surfactant protein B to the natural
extracts which improves surfactant performance in animal models. On compression
to low surface tension, a large amplitude buckling occurs, especially with
the additional synthetic protein B. The elongated structures remain attached
to the interface and are reversibly reincorporated into the monolayer upon
expansion. These collapse behaviors keep the monolayer stable at low surface
tension and make the surfactants respread easily. The buckling structures
are identical to those seen in model lipid and SP-B protein mixtures.
4:45 PM GG5.6
Abstract Withdrawn.
SESSION GG6: POSTER SESSION:
MEMBRANES
Chair: C. Jeffrey Brinker
Wednesday Evening, April 7, 1999
8:00 P.M.
Salon 7 (M)
GG6.1
Abstract Withdrawn.
GG6.2
DEVELOPMENT OF ``NEW LIPID'' BY THE AGGREGATION OF SYNTHETIC
10-ALKYL ISOALLOXAZINES IN AQUEOUS MEDIA. Shveta Chaudhary , Abha Awasthi,
S.M.S. Chauhan, Department of Chemistry, University of Delhi, Delhi, INDIA.
Bioorganic approaches to design and construction of synthetic
cells have been focus of much current interest. The barrier that defines
the interior and exterior of a living cell is a cell membrane. Lipids being
predominent constituent of biological membranes, their important functions
are generally derived from their propensity to self organize. Such self
assembly due to amphiphilic nature of lipids provide internal mesophases
(smectic) with controlled sizes, shapes and microenviroments. Most of synthetic
amphiphilic molecules organize in the aqueous as well as organic solvents
depending upon their structure and polarity. The 10- substituted isoalloxazines,
FMN and FAD are present as prosthetic group in various flavoenzymes and
flavoprotein. The 10-substituted isoalloxazine is amphiphilic in nature.
The substitution of different alkyl groups at position 10 of isoalloxazine
ring increases the amphiphilicity of flavin nucleus. The sonic dispersal
of isoalloxazines of different chain length at 10 position in aqueous media
(5 methanol) formed vesicles of
varying sizes. The 10-alkyl isoalloxazine were synthesized by cyclocondensation
of o-chloro nitrobenzene with different amines followed by catalytic hydrogenation
and treatment with alloxan.The vesicle formation by the aggregation of
isoalloxazine are supported by different techniques like transmission electron
microscopy, quasielastic light scattering etc.. Thus, the synthetic 10-alkyl
isoalloxazines are behaving as an ideal amphiphiles or new lipid.
GG6.3 PRELIMINARY RESULTS ON IN VITRO AND IN VIVO
BIOCOMPATIBILITY OF CHITOSAN-XANTHAN POLYIONIC COMPLEX. Fatiha Chellat,
Maryam Tabrizian , Ecole Polytechnique, Biomedical Engineering Inst, Montreal,
Qc, CANADA; Severian Dumitriu, Estaban Chornet, Sherbrooke Univ, Dept of
Chemical Engineering, Sherbrooke, Qc, CANADA; Charles Hilaire Rivard, Ste
Justine Hospital, Montreal, Qc, CANADA; L'hocine Yahia, Ecole Polytechnique,
Biomedical Engineering Inst, Montreal, Qc, CANADA.
Biodegradable polymers are among the most widely used
materials in pharmaceutical sciences for drug delivery systems. Chitosan
and xanthan have been extensively studied for this purpose. Here, we focused
on Chitosan-Xanthan microspheres hydrogel-based obtained after chitosan
and xanthan complexation. The polycationic propeties of chitosan allows
the interaction with xanthan gum having polyanionic properties resulting
in a polyelectrolyte complex. In this study we report on the in vitro and
in vivo biocompatibility of the complex. For in vitro studies, we used
L-929 and J-774 cell lines, respectively fibroblastic and macrophages cells.
For the first one, we studied the influence of chitosan-xanthan microspheres
on cell viability using MTT test. The assessment of cytokines {IL-1b and
TNF-a} and nitric oxide secretion was performed on J-774 cell line. For
these studies, several concentrations of microspheres and their degradation
products were used. For in vivo studies, tablets with 1 cm in diameter
and 1 mm in thickeness were implanted subcutaneously in the back of male
Wistar rats at the interscapular level. The results showed no cytotoxic
effects of the microspheres on L-929 cells. An increase in nitric oxide
formation was observed when the concentration of microspheres increased.
TNF-a production increased significantly after macrophages incubation with
the macrospheres. A maximum cytokine production is reached for the concentration
of 1 mg/ml of microspheres. The degradation products affected the cytokines
secretion as a function of microspheres incubation time in culture medium.
In vivo studies showed a good biocompatibilty of chitosan-xanthan microspheres.
They also indicated that the degradation of the particles and their fragmentation
result in further normal foreign body reactions.