Dynamically morphing microchannels in liquid crystal elastomer coatings containing disclinations

Abstract

Liquid crystal elastomers (LCEs) hold a major promise as a versatile material platform for smart soft coatings since their orientational order can be predesigned to program a desired dynamic profile. In this work, we introduce temperature-responsive dynamic coatings based on LCEs with arrays of singular defects-disclinations that run parallel to the surface. The disclinations form in response to antagonistic patterns of the molecular orientation at the top and bottom surfaces, imposed by the plasmonic mask photoalignment. Upon heating, an initially flat LCE coating develops linear microchannels located above each disclination. The stimulus that causes a non-flat profile of LCE coatings upon heating is the activation force induced by the gradients of molecular orientation around disclinations. To describe the formation of microchannels and their thermal response, we adopt a Frank–Oseen model of disclinations in a patterned director field and propose a linear elasticity theory to connect the complex spatially varying molecular orientation to the displacements of the LCE. The thermo-responsive surface profiles predicted by the theory and by the finite element modeling are in good agreement with the experimental data; in particular, higher gradients of molecular orientation produce a stronger modulation of the coating profile. The elastic theory and the finite element simulations allow us to estimate the material parameter that characterizes the elastomer coating's response to the thermal activation. The disclination-containing LCEs show potential as soft dynamic coatings with a predesigned responsive surface profile.

Regulating Surface Topography of Liquid‐Crystalline Polymers by External Stimuli

“…[ 82 ] Indentations were formed because the material moved away from the center of the defect, whereas protrusions formed when the opposite situation appeared, as shown in Figure 7c,d. Then, one approach combining experiment with analysis and numerical modeling was proposed to describe the thermally induced surface topographical deformation of LCE coatings, [ 83 ] and the reason for the SRG formation was ascribed to the change of the order parameter controlled by temperature, which in turn led to the anisotropic expansion of LCE coatings.…”

Switching between 3D Surface Topographies in Liquid Crystal Elastomer Coatings Using Two‐Step Imprint Lithography

“…[ 2,3,15 ] In most cases, the initial rest state of the surface is flat and upon actuation surface structures appear; in other cases the sample presents an initial 3D surface topography, and upon actuation the topography changes in height. [ 2–4,16–21 ] LC elastomers (LCEs) with 3D surface pillar array microstructures exhibiting height and diameter changes with changing temperature were created using imprinting or molding methods. [ 22–27,28,29 ] By programming the LC directors inside the pillars, more complex motions could be achieved.…”