Microstructured Nematic Liquid Crystalline Elastomer Surfaces with Switchable Wetting Properties

Abstract

Inspired by the lotus leaf, scientists have developed many superhydrophobic surfaces, some of which show remarkable switching between hydrophobic and hydrophilic state under external stimuli. However, the switch usually relies on the change of chemical properties rather than on the modification of the topographic structure of the surface. In this paper, the roughness‐change‐related switchable wetting properties of microstructured responsive surfaces made of nematic liquid crystalline elastomers (LCEs) is reported. First, various carbonate LC monomers and side‐on LCEs are synthesized with low nematic‐to‐isotropic transition temperature, TNI. Then, LCEs prepared from 3″‐vinylcarbonyloxypropyl 2,5‐di(4′‐octyloxybenzoyloxy)benzoate monomer, with TNI of 76 °C and contraction of 34% are used to construct a surface covered with micropillar arrays by using a replica molding technique. The contraction of the micropillars induces a reversible roughness change of the microstructured surface. Water contact angle of this microstructured surface changed with temperature, indicating a successful approach at building a surface with switchable wetting properties.

Light Responsive Microstructured Surfaces of Liquid Crystalline Network with Shape Memory and Tunable Wetting Behaviors

“…The contraction of 25% is larger than that found in monodomain LCN film (14%), probably because the magnetic field is more efficient than rubbed surfaces in aligning the mesogens. [12a,20] As expected, the actuation of micropillars can also be stimulated by light irradiation (Figure d–f). With a similar process as that of LCN film, we can see that UV light irradiation for 1 h at 60 °C also drives 25% contraction of the pillars.…”

“…These results demonstrate that light responsive microstructured surfaces covered with micropillar arrays show variation of wetting property in mild conditions; the dimensions and spacing of micropillars also affect the wettability and variation of WCA of structured surfaces. [12a,b] The variations of WCA of light responsive surfaces are not as large as those of surfaces made of thermotropic LCN in our previous work,[12a,b] in which different monomers were used and the resulting thermotropic LCNs showed 70% contraction. In the current light responsive system with relatively small contraction, a better design of micropillar's size and spacing may help to amplify the variation of WCA and observe evident change of wettability …”

The first thiol–yne click chemistry approach for the preparation of liquid crystalline elastomers

“…All samples are able to undergo big deformations, up to 48%, and notably bigger than contractions previously reported for side-chain LCEs prepared using acrylate polymerization. 13 For E-CL 3 20 we also observed a relevant increase in length perpendicular to the contraction direction (188% of the original length). By cooling down the samples, only polymers containing CL1 recover their original shape (Fig.…”

“…perpendicular to the monomer alignment direction). 13 For E-CL 3 20 we observed also a relevant length increase perpendicular to contraction direction (188% of the original length). parallel to the monomer alignment direction), weak diffuse maxima can be distinguished at the low angle region, which arise from end-to-end monomer correlations in the nematic phase.…”

Controlling Liquid Crystal Orientations for Programmable Anisotropic Transformations in Cellular Microstructures

“…While previous studies have investigated the deformation of either cellular structures with the nematic director aligned along the plates [31] or simple shapes with an arbitrary nematic director, [33,36] the interplay between LCE molecular anisotropy and the constraints introduced by the interconnectivity typical of cellular structures can largely expand the range of achievable deformations. To first explore how LCE molecular anisotropy can affect the deformation and symmetry breaking of surfaceattached cellular structures, we conducted finite element (FE) simulations using the commercial package ABAQUS 2018/ Standard.…”