Surface-Induced Alignment of Liquid Crystal Elastomers on Commercial Polyimide-Based Films

Abstract

Liquid crystal elastomers (LCEs) are versatile materials capable of reversible, large-scale deformations in response to external stimuli. The orientation of the liquid crystal mesogens within the polymer network significantly impacts their performance in various applications, including soft robotics and actuators. Here, we present a simple, cost-effective surface-induced alignment technique using off-the-shelf, commercially available Kapton HN films, which—unlike previously reported custom PI coatings—inherently possess surface features capable of inducing mesogen alignment and can also be mechanically rubbed to enhance the density and uniformity of surface nanogrooves. This enables the fabrication of monodomain LCE films with controlled alignment through a straightforward mechanical rubbing process, representing a significant advancement in accessibility and scalability compared to prior methods. Atomic Force Microscopy (AFM) reveals that surface rubbing alters the topography of Kapton films, with rubbing in different directions resulting in distinct roughness profiles. Polarized optical microscopy (POM) analysis of LCE films aligned using this technique demonstrates that rubbing Kapton horizontally or vertically leads to varying degrees of mesogen alignment, with horizontal rubbing producing the highest alignment quality. Thermal actuation tests confirm that the alignment configuration significantly influences the LCE's actuation response, with the planar-aligned films exhibiting uniaxial contraction and twisted-aligned films demonstrating bending behavior due to through-thickness strain mismatch. This mechanistic correlation between surface morphology, mesogen orientation, and actuation behavior offers new insights into alignment-driven deformation in LCEs. This technique offers an accessible and reproducible method for fabricating aligned LCEs, which can be beneficial for early-stage research and educational purposes in soft material design and fabrication.