Effect of Electrolyte Solutions on the Adsorption of Surfactants at PTFE-Water Interface

Adsorption of ionic and nonionic surfactants on low surface energy hydrophobic PTFE water interfaces in the absence and presence of electrolytes have been studied here. The objective of this study is to see the surfactant adsorption behavior in the presence of electrolytes that may reduce the consumption of surfactants. The kinetics of adsorption fits well pseudo-second-order kinetic model for the three surfactants studied here. Adsorption isotherms of TX-100 follow Langmuir type, whereas sodium dodecylbenzene sulfonate (SDBS) and cetylpyridinium bromide (CPB) follow Freundlich type. However, in the presence of electrolytes both the ionic surfactants show better fitting with Langmuir type isotherm. The effect of electrolytes on the surfactant concentration far below the CMC shows there is a linear increase in amount adsorbed with the increase in ionic strength of the electrolyte mainly due to reduction in headgroup repulsion and finally reaches a plateau level when the equilibrium concentration reaches CMC at that electrolyte concentration.