Water-in-oil microemulsions with greener oil solvents as sustainable nanoreactors of biopolymer nanoparticles

Abstract

Microemulsions have been widely used in multidisciplinary fields, yet reverse water-in-oil microemulsions are traditionally dispersed in petroleum-based oil solvents. For greener approaches, it should be also feasible to use less toxic, bio-based hydrocarbon solvents as continuous oil phase. Herein, reverse microemulsions in different alkanes, middle-chain alkanols, middle-chain esters or combinations of nonpolar solvent with alkanol are compared, using Aerosol-OT as common surfactant. As model of bio-based solvents, ethyl caprylate, isoamyl acetate and isoamyl alcohol are proposed as a more sustainable approach of oil solvents. Various characterization techniques were used to compare the properties and stability of reverse microemulsions for the different oil phase compositions, ranging from ternary phase diagrams to conductometry and turbidity titrations, micro-Differential Scanning Calorimetry and cryo-Scanning Electron Microscopy. As sustainable application, these microemulsions in bio-based solvents were proved suitable as template phase for the synthesis of cross-linked chitosan nanoparticles. The sizes of the resulting biopolymer nanoparticles were characterized by Dynamic Light Scattering and Atomic Force Microscopy, so that the effect of different crosslinkers and different the oil phase compositions was also compared. Thus, the use bio-based alkyl esters can provide similar microemulsion properties as the conventional alkanes, especially when using a combination of nonpolar solvents with alkanols.