Oscillating Chiral‐Nematic Fingerprints Wipe Away Dust

Abstract

access to water is often limited and waterbased self-cleaning approaches are not applicable. We report here a new concept of a dry self-cleaning method without the aid of water. This will solve a problem for solar farms placed in deserts where accumulated dust and sand at the surfaces of the photovoltaic cells block the sun light, which might cut power production as a result of a sand storm by 40%. [12] For reference, contaminated solar panels in solar farms are still removed from deposited dust by manually brushing. In addition, dust mitigating technologies may be used to protect any mechanical/optical/electric systems that carry out Lunar/Mars missions against dust hazards.[13] The waterfree self-cleaning philosophy we propose here is based on an orchestrated change of the surface topography. The induced vibrations mechanically transport dusts and debris to the edges of the surface, eventually supported by gravity when the surface is tilted. In a previous publication, we reported on homeotropic nematic liquid crystal network (LCN) which we could bring into a volumetric vibration by a high-frequency AC electric field. [14] The dynamic topographies were irregular and rather small, in the order of 100 nm. In order to create larger deformations, we focus here on a chiralnematic LCN that is brought in the so-called fingerprint mode with periodically alternating planar and homeotropic molecular alignment. The electrically induced change of the order parameter, with periodic alternating contraction and expansion, is anticipated to enhance the surface deformation to dimensions capable to transport sand grains. In addition, the topographic periodicity will be determined by the pitch of the molecular helix rather than by electrode spacing.The particle-rejecting coating is made by in situ photopolymerization of a mixture of chiral reactive mesogens that forms a crosslinked LCN on top of interdigitated electrodes (IDE). We chose for the IDE as it provides an in-plane electrical field while the LC coating will form an electrical isolating shield protecting potential users. By controlling the surface conditions of this IDE substrate prior to polymerization as described in Experimental Section the rod-like mesogens in the LCN adapted a helicoidal organization with the helix axes parallel to the surface as schematically shown in Figure 1a. The helix axes take a worm-like configuration (Figure 1b) also known as fingerprint texture. The black area in Figure 1b corresponds to the molecules that are homeotropically aligned while the planar orientation is optically birefringent showing blue color. More fingerprints patterns are shown in Figures S1 and S2 of the Supporting Information.The underlying deformation mechanism is to decrease the LCN order parameter and bringing the LCN into oscillation by a lateral This work presents an approach to create mechanical undulations at a solid organic coating surface under the influence of an electric field. The coating is fabricated through polymerization of chiral reactive mesogens aligned ...

Surface Dynamics at Photoactive Liquid Crystal Polymer Networks

“…An alternative approach to transport matter is exploited through taking advantage of gravity by tilting the surface from its horizontal position . The continuous generation of surface undulations at the surface of LCNs has been demonstrated to successfully transport sand dust to the edge of the coating and to eventually slide them off.…”

“…a) The fingerprint reverses the surface topography in which the initial peaks become valleys and the valleys become peaks. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Oscillating Surfaces Fueled by a Continuous AC Electric Field

“…We demonstrate that the waves can be brought into motion at a frequency up to 5 Hz. This value is significantly larger than that of, for instance, LCN coatings which is generally in the range of 0.1 Hz . We envision that this newly proposed fast oscillating wave can be used for haptic applications, such as human–machine interface, refreshable braille display as well as used to interact with the environment, for instance, transporting materials and particles, mechanically de‐icing through surface vibrations, and regulating light.…”

“…Despite the viscous component, the maximum protrusion height is obtained within 100 ms by switching the polarity of E0 corresponding to a vertical displacement speed of 5 µm s −1 . In comparison, the surface deformation of coatings in other systems generally require 10 s or more …”

Photomobile Polymer Materials with Complex 3D Deformation, Continuous Motions, Self‐Regulation, and Enhanced Processability

“…Inkjet printing was also applied to prepare a microactuator showing complicated motion mimicking natural cilia . Moreover, surface properties of CLCP films, such as adhesion and friction, were controlled through switching of surface topography at the microscopic scale …”