(40c) A New Class of Colloidal Gel Based on the Solvent Segregation Assisted Particle Self-Assembly

In this work, a new type of thermally reversible gel is formed by a bottom-up approach using nanoparticles dispersed in a binary solvent similar to the well-studied bicontinuous interfacially jammed emulsion gel (bijel). However, unlike the particles in bigel that do not like either component of the binary solvent, nanoparticles in this new gel are prepared with a strong preference to one component of the binary solvent. As a result, preferential wetting to one liquid drives the particles into one liquid domain that is rich in one of the solvent components. The structure arrest of particles in one liquid domain cause the gel formation of the whole system, which is thus named as solvent segregation driven gel (SeedGel). The gelation mechanism is demonstrated by contrast matching experiments using small angle neutron scattering (SANS). The average domain size and gelation temperature have been also determined. It is found that the jammed nanoparticles render strong mechanical strength to the SeedGel. Free-standing nanoporous bulk materials that are centimeter in size could be obtained in different shapes by this method. The shape can be maintained even after removing the solvent from the SeedGel by heating. Dried SeedGel samples can be obtained without any micrometer or nanometer sized cracks as investigated by electron scanning microscopy (SEM). We believe that the SeedGel preparation method opens a door to self-assemble nanoparticles into porous materials, which is simple, yet useful for applications that require high surface areas.