A study on the determination of the critical micelle concentration of surfactant solutions using contact angle data

Abstract

The critical micelle concentration (cmc) is an important parameter in colloidal and surface chemistry and a wide range of techniques have been devised for cmc determination. In this study, the determination of the cmc of surfactant solutions from the unique advancing and receding contact angle (CA) data was investigated. The sessile drop was formed from a pendant drop which had reached its equilibrium surface tension (ST) in a saturated atmosphere (~100% humidity). The CA was determined from the best-fit between the edge locations of drop and the Young-Laplace theoretical profile. The advancing and receding CAs were determined from the CA relaxation profiles of the sessile drops. It was observed that the breakpoints of the advancing and receding CAs of SDS solution drop coincided with the cmc determined from the ST data. However, the comparatively slower adsorption and bulk diffusion rates of TX-100 and C12E6 made the CA breakpoints deviate from that of ST. Thus, it was concluded that the approach of using the unique CA data for the determination of cmc could be applied only to those surfactants with a relatively high mass transport rate, such as SDS.