Surfactant-Driven Assembly of Poly(ethylenimine)-Coated Microparticles at the Liquid Crystal/Water Interface

Microparticles sitting at interfaces formed by a liquid crystal (LC) and water are known to self-assemble into distinct patterns. In this study, we observed that poly(ethylenimine)- (PEI-) coated microparticles are able to self-assemble at LC/water interfaces decorated with surfactants such as Tween 20 and sodium dodecyl sulfate (SDS). Interestingly, assemblies of microparticles strongly depend on the types of surfactants used and how surfactants adsorb on the PEI-coated microparticles. For example, adsorption of Tween 20 on the PEI-coated microparticles causes the microparticles to form short chains that follow the director field of the LC. In contrast, adsorption of SDS causes the microparticles to assemble into circular rings that encompass domains saturated with SDS. Such surfactant-driven assembly of microparticles offers a possible method for directing the assembly of microparticles. It can also be applied for the visual detection of lipases that hydrolyze Tween 20 in water.