Mechanism of electrical percolation of w/o microemulsions formed by nonionic surfactants

摘要

A study was carried out on the mechanism of electrical conductivity percolation of H2O/C16EO20-butanol/heptane microemulsions. Electrical conductivity, UV-vis spectroscopy and FTIR spectra were used to study the diluted dry microemulsions with the mass ratio of C16EO20-butanol/heptane=3:3:4. The results of electrical conductivity showed that the percolation occurred around phi(w)=20wt% and the transition of w/o microemulsions to bicontinueous microemulsions happened when phi(w)=45wt%. From the UV-vis absorption spectra, it was found that the absorption of methyl orange (MO) in microemulsions shifted red than that of in oil phase, but the maximal absorption peak (lambda(max)) remained unchanged when phi(w)>20wt%. It implied that the position of MO solubilized in microemulsions was unvaried after free water appeared in the core. FTIR spectra revealed that the OH band of water in microemulsions moved to high frequency at low phi(w) (20wt%) and became broader at high phi(w). It indicated that the added water only caused the hydration of EO at low phi(w), the hydration completed when phi(w)>20wt% and then the residual water entered into the core with properties similar to bulk water. The presence of free water as ions exchange medium will cause the electrical conductance increased. The percolation appeared after the hydration of EO completed.