Mapping electrospray modes and droplet size distributions for chitosan solutions in unentangled and entangled concentration regimes

Abstract

Chitosan is a natural polymer that exists as a polyelectrolyte in acidic aqueous solutions. The solution viscosity strongly depends on the polymer’s molecular weight and concentration in the solution, and the solution pH. Microparticle production by electrospraying is of significant interest in the drug delivery applications of this biocompatible polymer. We report herein a study aimed at empirical understanding of the influence of electrospray process parameters on the size distribution of microdroplets of chitosan solutions with different molecular weights and concentrations. How the nature of interchain interactions in the solution affects the electrospray mode, was studied for different applied voltages, V, over a wide range of solution flow rates, Q. Stable cone-jets were observed only for solutions in the unentangled regime. Unlike solutions of non-polymeric electrolytes of comparable viscosities, the chitosan droplet size distribution generally showed a strong dependence not only on Q but also on V and the solution viscosity. Carrying out the electrospraying process at a higher voltage in the stable cone-jet mode resulted in smaller and more narrowly dispersed droplets. For the droplets produced in this mode, We∼Re1.79, where We and Re are the droplet Weber and Reynolds numbers, respectively. The order of dependence of the Sauter mean droplet diameter on Q was found to be 0.26. Diameters of droplets produced in (or close to) the precession mode exhibited a significantly weaker dependence on Q. For a given wt% concentration in solution, a polymer of lower molecular weight resulted in a lower droplet size polydispersity index.