Active Shape-Morphing Elastomeric Colloids in Short-Pitch Cholesteric Liquid Crystals

Abstract

Active elastomeric liquid crystal particles with initial cylindrical shapes are obtained by means of soft lithography and polymerization in a strong magnetic field. Gold nanocrystals infiltrated into these particles mediate energy transfer from laser light to heat, so that the inherent coupling between the temperature-dependent order and shape allows for dynamic morphing of these particles and well-controlled stable shapes. Continuous changes of particle shapes are followed by their spontaneous realignment and transformations of director structures in the surrounding cholesteric host, as well as locomotion in the case of a nonreciprocal shape morphing. These findings bridge the fields of liquid crystal solids and active colloids, may enable shape-controlled self-assembly of adaptive composites and light-driven micromachines, and can be understood by employing simple symmetry considerations along with electrostatic analogies.

Spatial organization of active particles with field-mediated interactions

“…This class of systems also encompasses synthetic objects that actively shape the medium in which they are confined. The latter include liquid crystal colloids endowed with a tunable degree of freedom [18], whose interactions have been experimentally explored [19] with a view to controling self-assembly at the micrometer scale.…”

Magnetically responsive gourd-shaped colloidal particles in cholesteric liquid crystals

“…Recent studies also showed the importance of size [18][19][20][21][22][23][24] and shape [24][25][26][27][28][29][30][31] in elastic interactions and ensuing assemblies of colloidal particles in nematics. On the other hand, colloidal dispersions in twisted nematic and cholesteric LCs (CLCs) have received less attention [32][33][34][35][36][37][38][39][40][41][42][43][44] because of the complexity of the problem caused by, for example, the screening of elastic interactions by periodic structure of cholesterics. 44 This complexity increases as the ratio between the particle's size and cholesteric periodicity increases.…”

Liquid Crystal Colloids

“…Particles shaped as letters of the Latin alphabet (Figure 7k,l), on the other hand, exhibit well-defined orientations with respect to n 0 and induce surface boojums with  i s i =correlated with their shapes. Other colloidal shapes studied recently include pyramids, spirals, shape-morphing elastomeric rods, gourd-shaped dimers, particles with nanoscale surface roughness, and so on (98)(99)(100)(101)(102)(103)(104)(105)(106)(107)(108)(109)(110)(111)(112)(113), in all cases demonstrating that the geometric shape pre-defines locations of topological defects and colloidal interactions. Facile control of nanoparticle and molecular organization and the ensuing composite properties can be achieved by applying electric, magnetic, and optical fields (80).…”