Programmable helical twisting in oriented humidity-responsive bilayer films generated by spray-coating of a chiral nematic liquid crystal

A facile method is presented that generates humidity-driven helical twisting in thin, oriented polyamide 6 (PA6) films by spray-coating of a chiral nematic liquid crystal followed by photopolymerization into a network. The liquid crystal network (LCN) is self-aligned by the PA6 substrate, and the internal twist angle of the LCN provides the direction and extent of twisting for the expanding PA6 substrates. The handedness and extent of helical twisting in the bilayer film can be finely programmed by the degree of twist in the thin topping LCN layer. This straightforward spray-coating process and self-alignment of the liquid crystals (LCs) is compatible with high-throughput industrial manufacturing processes and is applicable to other stretched commodity polymers.