Light-Fueled Nanoscale Surface Waving in Chiral Liquid Crystal Networks

Abstract

Nano-and micro-actuating systems are promising for application in microfluidics, haptics, tunable optics, and soft robotics. Surfaces capable to change their topography at the nano-and microscale on demand would allow control over wettability, friction, and surface-driven particle motility. Here, we show that light-responsive cholesteric liquid crystal (LC) networks undergo a waving motion of their surface topography upon irradiation with light. These dynamic surfaces are fabricated with a maskless one-step procedure, relying on the liquid crystal alignment in periodic structures upon application of a weak electric field. The geometrical features of the surfaces are controlled by tuning the pitch of the liquid crystal. Pitch control by confinement allows engineering one-dimensional (1D) and two-dimensional (2D) structures that wave upon light exposure. This work demonstrates the potential that self-organizing systems might have for engineering dynamic materials, and harnessing the functionality of molecules to form dynamic surfaces, with nanoscale precision over their waving motion.

Light‐Switching Surface Wettability of Chiral Liquid Crystal Networks by Dynamic Change in Nanoscale Topography

“…When a voltage is applied to a planar sample with certain confinement conditions, 1D or 2D periodic microstructures can form when voltage increases. [ 29,32,34 ] Owing to the competition and equilibrium of different forces caused by the electric field, surface anchoring, and elasticity of LCs, LC molecules are reoriented in the system with minimized free energy density, such that specific LC configurations can be formed under diverse conditions. To the best of our knowledge, such 1D and 2D microstructures occur in different mechanisms and exhibit different optical properties.…”

“…This result is consistent with a previous report where the CLC–monomer mixture with mobility crams the space as internal anisotropic stress is relaxed after the balancing of surface anchoring confinement and electric field before photopolymerization. [ 29 ] After photopolymerization and removal of the substrates, the polymer network increases the elastic modulus and restricts the deformation. The accumulated stress cannot be compensated when free energy is insufficient, and thus the freestanding LCN film has flat surface.…”

“…Creating surface patterns involves not only ameliorating material resolution but also developing a dedicated fabrication strategy. [29,30] LCNs have excellent tunability, maneuverability, and stability, and can be fabricated with convenient fabrication procedures. It can be modified into shape-like spheres, fibers, or 4D actuators through 3D printing technologies.…”

Regulating Surface Topography of Liquid‐Crystalline Polymers by External Stimuli

“…Reproduced with permission. [ 129 ] Copyright 2021, American Chemical Society. e) Schematic illustration of the switch of adhesion via light‐triggered topographical deformation.…”

“…This kind of motion control was explored computationally, [ 29 ] and the corresponding experiment has been carried out recently. [ 129 ] When the confinement ratio ( d / P 0 , where d is the thickness of the layer and P 0 is the pitch) is in a specific range, the cholesteric layer will exhibit 1D periodic structures perpendicular to the rubbing direction of the polyimide alignment layer. This is the so‐called HH‐perpendicular structure.…”