Solvophobicity-Driven Mesoscale Structures: Stabilizer-Free Nanodispersions

Solvophobicity-driven mesoscale structures that lack any stabilizers are perhaps the most common spontaneously formed stable colloidal objects (particles, droplets). In spite of this, they have been significantly overlooked for a long time and the knowledge on solvophobicity-driven mesoscale structures (SDMSs) is rather limited. Here, we follow up on our previous work on mesoscale solubility [Rak, D.; Sedlák, M. On the Mesoscale Solubility in Liquid Solutions and Mixtures. J. Phys. Chem. B 2019, 123, 1365-1374. 10.1021/acs.jpcb.8b10638] and aim at providing a fully consistent picture of the nature, formation, and stability of SDMSs. We investigate both aqueous and nonaqueous mixtures, showing that this phenomenon is universal and not limited to aqueous systems. An experimental regime diagram is constructed as a function of the concentration of the solvophobic component and the solvophobicity strength given by mixtures of various organic solvents. Aqueous mixtures are investigated using well-defined ternary systems comprising water, ethanol (or other organic solvents), and a series of linear alkanes serving as hydrophobes. This investigation covers unique long-time monitoring of SDMS stability (up to three years). Another parameter studied in detail is the temperature of the mixture. SDMSs are characterized in terms of their shape and size distributions obtained using orthogonal techniques. Last but not least, we bring some insights into the SDMS surface zeta potential─the key quantity behind the stability of SDMSs. We investigate zeta potential as a function of the mixture composition, pH, and temperature.