(748d) The Single Parameter Hygroscopicity of Biodegradeable Polymers

The water-uptake ability of different compounds determines the final size and the fate of the aerosols in a supersaturated environment. Hygroscopicity is an important physicochemical property that compares the water-uptake ability of different substances. The traditional single parameter hygroscopicity indicates that the water-uptake ability depends on the molecular volume of the solute. This is true for substances with molecular weight less than 200g/mol. The Flory-Huggins Kohler (FHK) theory can be applied to predict the growth of a larger molecular weight polymeric aerosol. FHK shows that the water uptake ability of the polymer no longer depends on the molar volume of the solute. In this study, we develop the expression for single parameter hygroscopicity from FHK, and show that the hygroscopicity depends on both the dry particle size and the water-polymer interaction parameter in the FHK model. We also measure the hygroscopicity of four different hydrophilic biodegradable compounds, mannitol, lactose, gelatin and polyethylene glycol. The molecular weight of the four compounds are all significantly different and range in the order of 50 to 10,000 g/mol. The hygroscopicity of the four compounds derived from both traditional Köhler and FHK is compared; for very large molecules traditional methods can underpredict hygroscopicity up to 200%. A new size-dependent parameterization for hygroscopicity of polymers is provided. In summary, the water affinity plays an important role of the water uptake of the organic nano-particles.