Perfluorinated Surfactant-Assisted Polar-in-Fluorous Nonaqueous Microemulsions: Formation and Solute Solvation

Nonaqueous microemulsions (MEs) are mandatory in several applications in which water is undesirable or incompatible. Due to the presence of high levels of oxygen in most fluorous solvents, MEs consisting of fluorous media may harness enormous potential in biomedical applications. Evidence for formation of MEs comprising pools of polar solvents, polar-protic ethanol (EtOH), ethylene glycol (EG), formamide (FA), and polar-aprotic N,N-dimethylformamide (DMF), within a bulk continuum of fluorous perfluoromethylcyclohexane (PFMC) under ambient conditions is presented. These nonaqueous MEs are stabilized by perfluoroheptanoic acid (PFHA) as the emulsifier. In the presence of PFHA, the intake of investigated polar solvents that are almost immiscible in neat PFMC becomes appreciable. The presence of the MEs is evidenced by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) and further characterized by Fourier-transform infrared (FTIR) absorbance data. The size of the ME pools is found to increase with polar solvent loading P_s, where P_s = [polar solvent]/[PFHA]. Two fluorescence probes, coumarin-102 (C102) and coumarin-153 (C153), which afford complementary information, are utilized to gain insight into solute solvation and diffusion within these ME systems. For this, steady-state fluorescence emission and excitation, excited-state intensity and anisotropy decay, and fluorescence correlation spectroscopy (FCS) are used. These PFHA-assisted polar solvent-in-fluorous solvent nonaqueous ME systems provide new organized media and offer opportunities for template-directed nanomaterial synthesis.