Study of the organic solvent template double emulsions for porous microspheres production with adjustable structures

Abstract

In this study, the method of Hansen solubility parameters was applied to identify a solvent substitution less toxic than dichloromethane used in a microencapsulation process. A theoretical approach was developed to investigate the influence of solvent type on water permeation across the solvent film in w/o/w template double emulsions. Analysis showed that water solubility in the solvent was a key factor in deciding water permeability across the solvent film, which could vary significantly with different solvents. Besides high water permeability, experiments showed that dichloromethane and ethyl acetate films in double emulsion also featured very low film robustness due to their high water permeability and poor film robustness. To improve film robustness, the influence of polymer and surfactant concentration in the film phase was studied. Results showed that increased viscosity and non-Newtonian conversion induced by polymers dissolved in the film phase could significantly improve the stability of the template double emulsion; the addition of hydrophobic surfactant Span 80 in the film phase significantly destabilized double emulsion with twofold effects: at low concentration water permeation was promoted while at high concentration deformation and breakup of the oil film were facilitated. Further study showed that different internal structures, i.e., microspheres of single- and multi-compartments, could be effectively tailored by employing the water permeation characteristics as predicted by the permeation model. The large cavity of the hollow single-compartment microspheres makes them particularly suitable as delivery vehicle systems.