Preparation of Asymmetric Porous Janus Particles Using Microfluidics and Directional UV Curing

Abstract

Asymmetric porous Janus particles of poly(tripropylene glycol diacrylate) poly(TPGDA)) are prepared from TPGDA/4‐cyano‐4′‐pentylbiphenyl (5CB) mixtures using microfluidics and directional ultraviolet (UV) curing. Droplets of the TPGDA/5CB mixtures, which have been prepared successfully in the microfluidics channel, are photo‐polymerized in the off‐chip reservoir with a focused UV beam irradiated from beneath the reservoir. The isotropic TPGDA/5CB single phase is phase‐separated into two phases during the photopolymerization of TPGDA. The relative rate of photopolymerization compared with phase separation is different according to which hemisphere of the droplet is exposed to the UV beam. Rapid polymerization on the UV‐exposed hemisphere of the droplet produces small 5CB‐rich phase‐separated domains leading to a close and smooth structure, whereas slow polymerization on the opposite hemisphere produces large 5CB‐rich domains that induce an open and rough porous structure. These asymmetric porous Janus particles of poly(TPGDA) cause asymmetric swelling, in which the UV‐exposed hemisphere swell more than the other in the solvents due to the large porous surface area made by the small‐phase‐separated domain, which prevents the formation of a compact cross‐linked network structure. The complete dried droplet after the extraction of 5CB has an acorn‐like appearance, in which the swelled UV‐exposed hemisphere shrinks more than the other leading to a wrinkled structure. This new method combining microfluidics and directional UV curing provides a simple and unique way of fabricating asymmetric porous Janus particles and their functionalization with metal nanoparticles.