Surfactant dissolution and water solubilization in chlorine-free liquified gas propellants

The initial water content of a group of 15 pharmaceutically and toxicologically acceptable surfactants showed a tendency to increase with the surfactant hydrophilic-lipophilic balance (HLB) value. Surfactant solubility was determined in chlorine-free "alternative propellants" (n-butane, propane, dimethyl ether [DME], 1,1,1,2-tetrafluoroethane (HFA-134a), and 1,1,1,2,3,3,3-heptafluoropropane [HFA-227ea], and trichloromonofluoromethane [CFC-11] in the absence of cosolvents such as ethanol. Water-soluble surfactants such as Carbowax(R), Sentry(R), PEG 300, Tween(R) 20 and Brij(R) 30 with high HLB values showed appreciable solubility in HFA-134a and HFA-227ea. In systems containing greater than or equal to 80% propellant by weight, each single-phase propellant-surfactant blend was screened for its ability to solubilize iodine and dissolve or solubilize water with increasing surfactant concentration. This screening was performed to investigate the possibility of formulating high-volatility, single-phase systems with increased polarity and solvency from these conventional excipients and vehicles. Ternary-phase diagrams show the regions of apparent single and multiple phase behavior in each system. Despite the increased polarity of the hydrofluoroalkanes (HFAs), appreciable water solubility was seen only with these surfactants in DME and in the hydrocarbons (HCs) n-butane and propane.