Sol-gel-derived nanoparticles coated liquid entities: liquid marbles, liquid plasticine, and flat interface

Particle-coated liquid entities are the basis of many useful products, such as foams, emulsions, bijels, and liquid marbles (LMs). Particles stabilized at the liquid-air interface have been widely explored during the past two decades. Such interfaces usually consist of micro- to nano-sized particles that often tend to aggregate and lose transparency as well as the smoothness of the interface. Recently, these obstacles have been overcome by using sol-gel-derived silica nanoparticle coating. Sol-gel-derived nanoparticles offer a monolayer structure at the interface with high transparency and reproducibility. This paper critically reviews three sol-gel-derived liquid entities: LMs, liquid plasticine (LP), and nanoparticle-coated flat interface. LM, a particle-covered droplet, was significantly explored for its application as a container in many biological and chemical processes. Unlike powder-derived LM, sol-gel-derived LM can be formed into any desired shape, commonly known as LP. Monolayer-covered sol-gel entities also offer a simple physical platform for investigating many fundamental properties of particle-coated interfaces. In the present review, starting from its preparation to the application, all critical aspects are summarized. Some unaddressed issues compared to the powder LM are also discussed for future research.