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Spider Silk Inspired PEBA/Goethite Nanocomposite for Stronger Triboelectrification
Andris Šutka1,Linards Lapčinskis1,Kaspars Mālnieks1,Artis Linarts1
Riga Technical University1
Polymer triboelectric charging takes a critical role in mechanical energy harvesting by triboelectric nanogenerator (TENG) devices . In order to boost the performance of TENG devices, the researchers aim to magnify the triboelectric charge on polymer surface. To enhance the polymer triboelectrification, several approaches have been used, such as surface functionalisation , choosing the proper polymer couple by taking the triboelectric series as guidance , or increasing the specific contacting area via nanostructuring [4, 5]. However, so far, many efforts have been driven by taking into consideration the electron transfer as a mechanism for polymer triboelectrification.
In recent studies, strong evidence for the heterolytic covalent bond break and material transfer as a mechanism for polymer triboelectrification has been provided [6-8]. Upon contacting the physical intermolecular bonds are formed and if the total energy of these physical bonds is larger than the energy of covalent bond in the macromolecule, the covalent bond scission happens along with material transfer. It has been shown that the higher surface charge value can be observed for soft and sticky polymers because the material transfer is promoted due to smaller mechanical integrity and stronger adhesion [6-8]. However, the softer materials with weak intermolecular bonding in bulk may result in material transfer without scission of covalent bonds. Thus, the optimal balance between softness, hardness and surface adhesion should be achieved. Accordingly, strong electrification may be expected in polymers possessing highly ordered macromolecular inclusions enclosed within a soft elastomeric matrix. A similar macromolecular structure can be observed in spider silk, which is known for its strong electrification in streams of air dusts, thus providing spider ballooning [9, 10]. Such structure can be engineered by adding nanoparticles to thermoplastic elastomers to induce formation of inclusions with a higher degree of macromolecular ordering.
In the present work, we use inorganic goethite α-FeO(OH) nanowires to promote formation of highly ordered macromolecular inclusions in soft elastomeric poly(ether-block-amide) (PEBA) matrix to obtain structure similar as in spider silk. The surface of goethite is densely covered by hydroxyl groups (–OH), thus ensuring sites for hydrogen bonding with PEBA as proven by DSC and FTIR. The increase in surface charge measured in contact-separation for more than order of magnitude is demonstrated after introduction of as little as 0.1 vol% of goethite. At the optimal content of goethite nanoparticles the charge density reaches 1.86 nC cm-2.
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