Morphing of liquid crystal surfaces by emergent collectivity

Abstract

Liquid crystal surfaces can undergo topographical morphing in response to external cues. These shape-shifting coatings promise a revolution in various applications, from haptic feedback in soft robotics or displays to self-cleaning solar panels. The changes in surface topography can be controlled by tailoring the molecular architecture and mechanics of the liquid crystal network. However, the nanoscopic mechanisms that drive morphological transitions remain unclear. Here, we introduce a frequency-resolved nanostrain imaging method to elucidate the emergent dynamics underlying field-induced shape-shifting. We show how surface morphing occurs in three distinct stages: (i) the molecular dipoles oscillate with the alternating field (10–100 ms), (ii) this leads to collective plasticization of the glassy network (~1 s), (iii) culminating in actuation of the topography (10–100 s). The first stage appears universal and governed by dielectric coupling. By contrast, yielding and deformation rely on a delicate balance between liquid crystal order, field properties and network viscoelasticity.

Dynamical Landau–de Gennes theory for electrically-responsive liquid crystal networks

“…Thus, based on purely in-plane stimuli an out-of-plane expansion of the LCN is observed. Follow-up experiments by Van der Kooij et al on the same experimental system have since shown that there is a characteristic plasticization time associated with the initial macroscopic deformation of the LCN [36].…”

“…Although one might expect electrothermal or electrostrictive effects to play an important role here, it can be shown that neither can adequately account for the magnitude of the observed modulation [35][36][37][38]. Instead, Liu et al rationalise the observed behavior by remarking that, upon in-plane actuation by the electric field, the end-grafted liquid crystalline mesogens reorient slightly away from their as-prepared homeotropic alignment, increasing their mutual excluded volume with the mesogens that cannot reorient as easily due their incorporation in the background polymer network.…”

Artificial Organic Skin Wets Its Surface by Field-Induced Liquid Secretion

“…Under the appropriate conditions it translates into macroscopic effects such as mechanical morphing of the coating surfaces. 15 Based on this newly acquired knowledge, in this work we exploit the use of RF AC fields to alter the chemical properties at a coating surface through excreting and absorbing functional liquids. These functional artificial skins may administer medicine (e.g., for wound treatment), adjust tribology by controlled release of lubricants, or carefully dose chemicals for interfacial chemical reactions.…”

“…Under the appropriate conditions it translates into macroscopic effects such as mechanical morphing of the coating surfaces. 15 …”

Functional Liquid Crystal Polymer Surfaces with Switchable Topographies

“…Surface oscillation during electrical stimulation has also been revealed with laser speckle imaging in further studies. [ 103,104 ]…”