Wrinkling Labyrinth Patterns on Elastomeric Janus Particles

Abstract

We describe a novel, low-cost and low-tech method for the fabrication of elastomeric Janus particles with diameters ranging from micrometers to millimeters. This consists of UV-irradiating soft urethane/urea elastomer spheres, which are then extracted in toluene and dried. The spheres are thus composed of a single material: no coating or film deposition steps are required. Furthermore, the whole procedure is carried out at ambient temperature and pressure. Long, labyrinthine corrugations ("wrinkles") appear on the irradiated portions of the particles' surfaces, the spatial periodicity of which can be controlled by varying the sizes of particles. The asymmetric morphology of the resulting Janus particles has been confirmed by scanning electron microscopy, atomic force microscopy, and optical microscopy. We have also established that the spheres behave elastically by performing bouncing tests with dried and swollen spheres. Results can be interpreted by assuming that each sphere consists of a thin, stiff surface layer ("skin") lying atop a thicker, softer substrate ("bulk"). The skin's higher stiffness is hypothesized to result from the more extensive cross-linking of the polymer chains located near the surface by the UV radiation. Textures then arise from competition between the effects of bending the skin and compressing the bulk, as the solvent evaporates and the sphere shrinks.

Curvature delays growth-induced wrinkling

“…In this case a stability analysis can be used to determine the critical conditions for the onset of surface wrinkling. These ideas have been applied to different geometries such as planar films [11][12][13][14], cylindrical shells [15][16][17], and spherical layers [18][19][20][21]. Comparisons between planar and curved systems reveal that the surface curvature plays an important role in pattern formation and evolution.…”

Microfluidics Assisted Fabrication of Three-Tier Hierarchical Microparticles for Constructing Bioinspired Surfaces

“…The polymer templates can be synthesized using flow lithography, 39 electro-spraying, 40 or microfluidic techniques. 41−43 Subsequently, the exposed surfaces are modified by using additional material coating, 44 plasma etching, 45 surface chemical oxidation, 46 chemical modification, 47 solvent evaporation, 3,48 electron irradiation, 27 or UV irradiation. 49 Although effective, these fabrication methods are time-consuming and require complex processes.…”