Determination of density and surface tension in ethanol and HFA 134a mixtures

Recent publications of a transient aerodynamic atomization model have highlighted saturated vapor pressure, density, viscosity and surface tension as key properties governing pressurized metered dose inhaler (pMDI) droplet size1, 2, 3. Pharmaceutical pMDI formulations widely use mixtures of propellant and excipients, such as ethanol, but mixing rules for the aforementioned properties are not available in the literature. Hence, composition-dependent surface tension and density were experimentally determined for ethanol-HFA 134a mixtures. The expressions presented of density and surface tension are advantageous to understanding transient flows inside the actuator and atomization of pMDI formulations containing ethanol as a co-solvent 2