Liquid Crystal Foams Generated by Pressure-Driven Microfluidic Devices

Thermotropic liquid crystals possess superior foaming capability without the aid of surfactants because of the anisotropic molecular structures. We developed a T-junction microfluidic device to inject gas bubbles of uniform size into a liquid crystal in the nematic and the smectic phases. The bubble size is primarily determined by the dimension of microfluidic channel regardless of the phase, and air bubbles of a few tens of micrometer diameter were stably injected at the rate up to 110 Hz to the close packing density with a polydispersity less than 4%. It is shown that an efficient path to fabricate stable liquid crystal foams is to inject bubbles in the nematic phase, where the highest injection rate is possible, and promptly cool it down to the smectic phase.