(480a) Control of Spreading and Drying of a Drug-Solvent Mixture From Marangoni Flows

We studied the drying process of dopamine solution drops put by means drop-on-demand tecnique on a wettable solvent cast biopolymeric films. Three stages can be identified. First, the droplet spreads until a maximum radius where evaporation becomes dominant. The second phase is characterized by a constant radius due to competition between spreading and evaporation of the solvent. Finally, the contact line recedes until complete evaporation of the solvent.

During evaporation process we have observed the transformation of a studied system from one phase to another. Furthermore, we have shown that the observed 1st order phase transition can be manipulated via interfacial characteristics of substrate to produce amorphous or crystalline structures upon droplet impingement. In general there exists three regions for which the structure of the splat will exist as either as a structure lacking long range order of the positions of the atoms, a semi crystalline structure with limited long range atomic structure at the peripheries, or an ordered structure where the API exists in a crystalline state. The three distinct structures of the splat observed upon and after impingement are due to differences in wetting phenomena, interaction at the interface of the splat and the substrate, and evaporation kinetics of the drop due to differences in temperature reduction.