Solvent structure controlled SeedGel formation investigated using miscible binary solvents

Abstract

Recently, a solvent segregation driven gel (SeedGel) has been demonstrated to be a tunable and versatile way to stabilize bicontinuous structures in a binary solvent. Here, the structure properties of the SeedGel prepared with two miscible solvents, 3-methylpyridine (3MP)/water and deuterated 3MP (d-3MP)/water, are systematically investigated using ultra-small angle neutron scattering (USANS), small angle X-ray and neutron scattering (SAXS and SANS). The structures of samples prepared with 3MP/water show similar behavior to one previous SeedGel prepared with lutidine/water. Interestingly, the deuteration of 3MP significantly shifts the gelation temperature of the SeedGel. The results also demonstrate that both components of the binary solvent can be exchanged between the formed two domains of a SeedGel when changing the temperature. Importantly, the binary solvent used for the SeedGel preparation does not have to undergo bulk phase transition as a function of temperature. Our results show that the correlation length due to the density fluctuation of the binary solvent is about the same at the gelation transition temperature for all studied SeedGels prepared with different binary solvents. Thus, this correlation length seems to be a key controlling parameter for SeedGel formation. It is noted that this observation not only holds in binary solvents that show a bulk phase separation but also exists in miscible binary solvents without bulk phase separation. The results here thus open a window to prepare SeedGels with a new set of binary solvents that may have been overlooked before and provide guidance for choosing appropriate miscible binary solvents that can be used to prepare SeedGels.