The Effect of Temperature on the Adsorption of Dodecane onto Nonionic and Ionic Surfactant Monolayers at the Air-Water Surface

摘要

We have measured the adsorption isotherms for dodecane adsorption at the solution-vapour surface for surfactant monolayer covered aqueous surfactant solutions at concentrations in excess of their critical micelle concentration (cmc) values. The temperature dependence of the adsorption have been determined for both a nonionic surfactant (H-(CH_2)_(12)-(OCH_2CH_2)_5-OH, abbreviated to C_(12)E_5) and an ionic surfactant (n-dodecyltrimethyl-ammonium bromide, abbreviated to DoTAB). For the nonionic surfactant, dodecane adsorption decreases with increasing temperature at low surface concentration of the oil whereas it increases at high surface concentrations. With the ionic surfactant DoTAB, the temperature effect shows a similar crossover in behaviour but the changes in adsorption are opposite in direction to those seen for the nonionic surfactant. The adsorption data are correlated to the effects of temperature on the microemulsion phase behaviour of ionic and nonionic surfactants and discussed in relation to the microstructures of the mixed oil/surfactant films as determined by neutron reflection methods.