Synthesis of Shape-Controlled Polymer Nano/Microstructures Using Initiated Chemical Vapor Deposition (iCVD) Polymerization in Structured Liquids

The ability to synthesize functional polymer nano/microstructures with programmable shapes will benefit a wide range of applications such as particles for drug delivery with programmable pharmacokinetics, oriented fibers for efficient electrolytic capacitors and batteries, isoporous films for membrane separations, to name a few. Current synthesis approaches for polymer particles are laborious and insufficiently versatile. For example, driven by surface tension effects, polymer nano/microparticles are predominantly spheres and the obtainment of non-spherical shapes often require complete redesign of the synthesis procedure. Using a novel synthesis platform, where initiated chemical vapor deposition (iCVD) polymerization of divinylbenzene was performed in nematic liquid crystals (LC), we obtained a host of shape-controlled polymer particles ranging from nano spheres, hemispherical micro-domes, randomly oriented or directed macrogel, micro spheres, spheroids and micro discs simply by tuning the synthesis conditions such as the flowrates of monomer and LC alignment. That unprecedented versatility in shape control was enabled by a deep understanding of the mechanisms of reaction and transport in the dynamic LC, achieved using a novel assembly of in-situ long-focal range reflection-mode microscopy with the reactors. The in-situ imaging capability bridged a critical knowledge gap in liquid-templated polymerization, the mechanism of which remained elusive partially due to the depleting reactant concentrations and changing LC alignments over the course of polymerization. Applying the iCVD polymerization technique to LC, enabled continuous and controlled vapor-phase delivery to achieve concentrations below the structure-disrupting threshold of LC templates throughout the process with real-time monitoring. Nematic LC medium being a poorer solvent lead to the formation of nanospheres in bulk in contrast to microspheres obtained in conventional isotropic solvents used for precipitation polymerization of divinylbenzene. These precipitating nanospheres constituted as the building blocks, aggregating into shaped-macrogel clusters on the LC-solid interface. Guided by the LC-template near the interface, we obtained hemispherical domes in homeotropically aligned LC and, randomly oriented or directional clusters in two different hybrid templates. Further, we obtained microspheres, spheroids and unique disc-shaped particles desolvating from the macrogel clusters formed at the LC-solid interface at later stages. Additionally, we observed iCVD polymerization to cause lowering of LC-surface anchoring energy over the course of reaction. This is the first-time synthesis of such a wide variety of tunable shaped-polymeric particles have been demonstrated using a single synthesis platform compatible with a library of more than 70 functional monomers.