Self-growing nano-liquid-crystal film from dynamic swollen hydrogel substrates

A hydrogel which spontaneously swells in an aqueous polymer solution was observed to produce a new hydrogel film coated on its swollen surface. Here, inspired by this phenomenon, we theoretically formulate the dynamics of isotropic-to-nematic (I-N) phase transition caused by swelling a hydrogel substrate (HS) in a dilute nanoplatelet suspension, and quantitatively characterize a self-growing nano-liquid-crystal (NLC) film coated on the swollen HS surface. We show that as the HS gets softer, the resulting NLC film can form earlier and achieve greater thickness (up to hundreds of micrometers). Our results and the existing experiments confirm that the growth dynamics of the NLC film or hydrogel film is exclusively regulated by the swelling behaviors of the HS instead of suspension configurations, e.g., I-N phase transition or sol-gel transition, suggesting a universal signature for the solutes ranging from molecules to colloids. However, both the maximum thickness of the NLC film and the corresponding characteristic time rely highly on the inherent elasticity of the HS and nanoplatelet aspect ratio. We demonstrate that the swelling quasiequilibrium state rather than the equilibrium state of the HS is more qualified to formulate a condition which is practically significant in preestimating the moment when the maximum thickness of the NLC film appears. Our theoretical framework serves as a robust paradigm to extensively rationalize (bio)film coatings which self-integrate with diverse nanostructural configurations via swelling-induced phase transition.