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Biocompatible and Biodegradable Surfactants for the Hydrofluoroalkane|Water Interface

Parthiban Selvam1, Libo Wu2, and Sandro R. P. da Rocha2. (1) ChE - Wayne State University, 5050 Anthony Wayne Dr., Detroit, MI 48202, (2) Chemical Engineering and Materials Science, Wayne State University, Detroit, MI 48201

Hydrofluoroalkanes (HFA) - HFA134a and HFA227 are used on a large scale as CFC substitutes, primarily for the refrigerants market, medical aerosols and fire extinguishers. Even though HFAs and CFCs have some similar physical properties, the most notable challenge in replacing CFCs with HFAs is their differing solvating power. HFAs are more polar than CFCs due to the presence of asymmetrically positioned H atoms in the molecules. Hence, the methyl-based surfactants and additives used in CFC-based formulations are not soluble in HFAs. This has created many challenges in the reformulation of HFA-containing systems.

In this work we investigate the interfacial activity of biocompatible and biodegradable nonionic block copolymer surfactants at the HFA-water (HFA|W) interface. A series of amphiphiles containing a biodegradable HFA-phile, with varying molecular weight and percentages of the hydrophile-to-HFA-phile (HFB), have been synthesized. The fundamental interfacial properties of these surfactants, including interfacial tension and micellization behavior, have been determined in situ, under pressure. Tension reduction of as much as 30 mN·m-1 was observed. An increase in the number of repeat units of the HFA-philic moiety is shown to cause further increase in interfacial activity, bringing the overall tension value close to zero. Spontaneous emulsification is observed with certain surfactants. These amphiphiles are shown to form aggregates in HFAs in the presence of water. Due to their high interfacial activity, these surfactants self-emulsify at very low water loadings. The results shown here are of relevance in the selection of highly interfacial active surfactants for the HFA|W and their applicability in emulsion formation for drug delivery and aerosol foams.