Controlled Placement of Microparticles at the Water–Liquid Crystal Elastomer Interface

Abstract

Controlled placement of microparticles is of prime importance in production of microscale superstructures. In this work, we demonstrate the remote control of microparticle placement using a photoactivated surface profile of a liquid crystal elastomer (LCE) coating. We employ light-responsive LCEs with preimposed patterns of molecular orientation (director) in the plane of coating. Upon UV illumination, these in-plane director distortions translate into deterministic topographic change of the LCE coating. Microparticles placed at the interface between the LCE coating and water, guided by gravity, gather at the bottom of photoinduced troughs. The effect is reversible: when the substrates are irradiated with visible light, the coatings become flat and the microparticle arrays disorganize again. The proposed noncontact manipulation of particles by photoactivated LCEs may be useful in development of drug delivery or tissue engineering applications.

Design of nematic liquid crystals to control microscale dynamics

“…The displacements are deterministically related to the molecular orientation pattern. For example, upon heating, when the scalar order parameter of the LCE decreases, a circular bend of molecular orientation causes elevations, while a radial splay causes depressions of the coating (128,129). To understand the relationship, consider how the orientational order is coupled to rubber elasticity of an LCE, as mediated by cross-linking of the polymer network.…”

Morphing of liquid crystal surfaces by emergent collectivity

“…Bridging the gap between the molecular level and large-scale collective motion requires a method with access to a wide range in time and length scales. While digital holography microscopy (DHM) has proven successful at visualizing surface morphing in real time with high spatial resolution 5–9 , it remains superficial with limited time resolution. By contrast, conventional (polarized) optical microscopy can be very fast, yet the structural changes of deforming LC surfaces are often too subtle to resolve in detail.…”

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

“…This periodic splay-bend pattern has been experimentally realized in liquid crystal elastomers. 39 When the film is exposed to a uniform polarized light source, different regions have different trans-to-cis conversion levels due to the fact that the isomerization depends on the angle between the local director and the electric field of the polarized light. As a result, a periodic distribution of cis concentration is generated in the plane of the film and thus a surface undulation is formed.…”