Tunable hygromorphism: structural implications of low molecular weight gels and electrospun nanofibers in bilayer composites

Abstract

This investigation highlights the potential for electrospun nanofiber mats and self-assembled nanofiber networks to be interfaced synergistically to induce hygromorphic behaviour. Control poly(vinyl alcohol) (PVA) electrospun active layers and 1,3:2,4-di-p-methylbenyliedene sorbitol (MDBS) self-assembled passive layers encapsulated in an ethylene oxide-epichlorohydrin (EO-EPI) copolymer matrix were fabricated to examine the influence of composition on the properties guiding hygromorphism, such as water transport, layer thickness, and layer modulus. Experimentally determined material constants were utilized in conjunction with mathematical modeling to determine ideal layer properties. It was revealed that the active layer with the highest PVA content exhibited the fastest water transport, and the passive layer with the highest MDBS content displayed the slowest water transport. However, the hygromorphic bilayer fabricated utilizing the lowest PVA content and the highest MDBS fraction was predicted to induce the highest change in curvature due to the lower modulus and thickness of the PVA nanofiber active layer. Decreasing the MDBS content reduced the passive layer modulus while increasing water transport, which theoretically reduced the overall bilayer curvature. The hygromorphic bilayer composites fabricated using these ideal control layers exhibited folding bias and response variations dependent upon active layer composition and imposed folding directions. By utilizing the favorable force balances between the active layer with the lower PVA content and the passive layer with the highest MDBS amount in conjunction with folding bias in a non-preferential direction, it was possible to achieve hygromorphic unfolding and refolding with hydration. Through modelling and individual layer examination, a unique platform built on two independent fiber networks has been designed to achieve biomimetic hygromorphism in synthetic bilayer composites.

Moisture absorption measurement and modelling of a cellulose acetate

“…The moisture absorption can cause swelling, shrinkage, deformation, as well as a change in the rigidity of a hygroscopic material. Although the moisture absorption in polymers has often been considered as a disadvantage because it could affect the performance of a product during its service life (Xiaosong Ma et al 2009;Wong 2010;Zhang et al 2010), humidity sensitive polymers allow the manufacturing of sensors or actuators able to respond to a change in the environment humidity level (Ramirez-figueroa et al 2016;Burgert and Fratzl 2009;Reyssat and Mahadevan 2009;Krieg et al 2013;Taccola et al 2015;Yao et al 2015;Menges and Reichert 2015;Holstov et al 2015;Wang et al 2016Wang et al , 2017Alexander and Korley 2017).…”

Intelligent Nanofiber Composites: Dynamic Communication between Materials and Their Environment

“…Our group demonstrated the ability to use fundamental concepts of bilayer curvature to fabricate a new generation of hygromorphic actuators . The utilization of a molecular gel (MG) (1,3:2,4‐di‐p‐methylbenyliedene sorbitol) in the solid state enhanced hydrophobicity and increased the passive layer moduli through the formation of a self‐assembled fiber network.…”

“…Experimentally determined material constants were utilized in conjunction with mathematical modeling to determine ideal layer properties. The hygromorphic bilayer composites fabricated using these ideal control layers exhibited folding bias and response variations dependent upon active layer composition and imposed folding directions . By utilizing the favorable force balances between the active layer with the lower fiber content and the passive layer with the highest gelator amount, in conjunction with folding bias in a nonpreferential direction, it was possible to achieve hygromorphic unfolding and refolding with hydration (Figure ).…”

“…Removal of solvent post‐gel/polymer introduction results in composites with embedded self‐assembled fiber networks. These fiber networks can enhance mechanics, be extracted to form porous membranes, influence small molecule and fluid transport, or be used to achieve stimuli responsiveness . Their solid‐state properties, though less explored than the gel state, have the potential to expand their applicability in the realm of functional environmentally responsive composites.…”

Low Molecular Weight Hydrogel for Super Efficient Separation of Small Organic Molecules Based on Size Effect

“…The hydrogel formed viscous flow under shear stress (shear thinning) and could rapidly recover when the applied stress was relaxed (self-healing) to ensure the application. , As new materials for depollution of the environment, LMWGs have the inherent advantages in controlling microstructure via the adjustment of interactions between gel nanofibers for selective absorbance and pollutants extraction . The tunable noncovalent interactions in LMWGs caused moldable networks with different properties from traditional chemically cross-linked hydrogels to meet the engineering requirements for diverse applications, from injection, pumping, or spraying. − Moreover, the easily changeable chemical structures of gelators ensured the LMWGs were recyclable and environment friendly. − …”