Protruding organic surfaces triggered by in-plane electric fields

Abstract

Coatings with a dynamic surface topography are of interest for applications in haptics, soft robotics, cell growth in biology, hydro- and air dynamics and tribology. Here we propose a design for creating oscillating surface topographies in thin liquid crystal polymer network coatings under an electric field. By applying an alternating electric field, the coating surface deforms, and pre-designed local corrugations appear. The continuous AC electric field further initiates oscillations superimposed on the formed topographies. This effect is based on microscopic free volume creation. By exciting the liquid crystal network at its resonance frequency, maximum free volume is generated and large surface topographies are formed. Molecular simulation is used to examine this behaviour in microscopic detail as a function of oscillation frequency. Surface topography formation is fast and reversible. Excess free volume is energetically unfavourable, thus the surface topographies disappear within seconds once the electric field is removed.

Travelling waves on photo-switchable patterned liquid crystal polymer films directed by rotating polarized light

“…The wave speed can be further enhanced by an increase in actuation frequency, which has been observed for a glassy azobenzene-embedded LC polymer by a slight addition of visible light and temperature increase, 38 attributed to a boosted cis-to-trans isomerization. Furthermore, a moderate addition of visible light is found to enhance the total lightinduced strains due to the additional effect of continuous transcis-trans isomerization cycles, 29,45,46 leading to wave amplitudes that can be a factor of 4 higher. Thus, we expect that the modulation and frequency can be further enhanced leading to larger wave speeds and amplitudes and thus a higher flow efficiency for peristaltic microfluidic propulsion.…”

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 …”

“…Considering also the surface area of our sample (1 cm 2 ), a remarkably low energy consumption of 168 mW m −2 is required to bring the surface to a mechanical oscillation. In comparison, electrically responsive LCN surface topographies require about 90 W m −2 and UV responsive LCN coatings 2–7 kW m −2 , more than five orders of magnitude higher …”

On the History of Reactive Mesogens: Interview with Dirk J. Broer

“…But a device surface can also communicate with people in a haptic‐like manner by altering its touch sensation. Depending on the application, the actuation can be either light‐driven or electrical‐field‐driven (Figure c) . The surfaces are capable of transporting particles, which, for instance, has been demonstrated for the removal of sand from solar panels .…”