Wrinkle Formation and Optical Modulation in Ultrathin Liquid Crystalline Polymer Films on Soft Substrates

Ultrathin liquid crystalline polymer (LCP) films, with submicron thickness, are deposited onto polydimethylsiloxane (PDMS) substrates using initiated chemical vapor deposition (iCVD). These films are highly promising for adaptive optics, flexible sensors, and soft actuators due to their tunable optical properties and strain sensitivity. The iCVD process generates internal compressive strains, influenced by the PDMS substrate’s elastic modulus, which drives the formation of microstructures within the LCP films. When the strain surpasses a critical threshold, spontaneous surface wrinkling occurs, aligning the LCP molecules and enhancing their order parameter. Externally applied strains further align mesogenic units along the stretching direction, causing reversible birefringence changes due to the elasticity of the PDMS substrate. This elasticity ensures consistent optical responses under stress. Analysis of the local order parameter as a function of strain reveals a unified relationship with the PDMS modulus, offering insights into the intrinsic strain development in LCP films during the iCVD process.