Fast estimation of the equilibrium adsorption constants of ionic surfactants with account for ion-specific effects

Understanding the factors contributing to the adsorption of surfactants to interfaces, without the need to carry out lengthy and meticulous experiments on every new surfactant system, is a pressing need in both industrial and academic research. A large group of the most widely used surfactants have aliphatic chains for their hydrophobic tails. Yet the variations in the length of the tail, the nature of the hydrophilic group, and the nature of the counterion (for ionic surfactants) make the exact adsorption capacity hard to predict. sent here a simple procedure for the fast and accurate estimation of the adsorption capacity of this large collection of surfactants by parameterizing the separate contributions of their components. We report the determination of the contribution from the polar heads by a model where it is the only free parameter and linear fits to experimental data. Uncertainty from experimental variations is decreased by fitting the results to another linear dependence for a series of homologous surfactants with different tail lengths where the incremental contribution of the tail is well established. The contributions from eight different polar heads (DMPO, DEPO, SO4−, OH, COOH, COO−, NH3+, and N(CH3)3+) are tabulated, as are contributions from 15 counter-ions (for ionic surfactants). The results allow immediate estimation of the adsorption strength of nearly 300 surfactant systems, for many of which the adsorption constants are not known. Comparisons of the calculated constants of randomly selected surfactant systems against their experimentally measured values yielded deviations of only about 3.5 ± 2%. Such quick calculation of a surfactantʹs adsorption constant based only on its molecular structure is a powerful tool for quantitative screening and cost-benefit analysis of surfactants for designing many industrial processes, including flotation of mineral particles, pharmaceutical foam fractionation, and de-emulsification in the oil industry. We point out techniques for expanding this method to other types of surfactant systems as well.