(629e) Novel Approach To Determine Equilibrium Adsorption Properties From Experimental Dynamic Surface Tension Data For Nonionic Surfactants

Moorkanikkara, S. N., Massachusetts Institute of Technology
Blankschtein, D., Massachusetts Institute of Technology

We explore a novel approach to determine equilibrium adsorption properties from experimental dynamic surface tension (DST) data and the known rate-limiting adsorption kinetics mechanism. Specifically, we develop a new methodology to determine the Equilibrium Surface Tension vs. bulk solution Concentration (ESTC) behavior of nonionic surfactants using experimental pendant-bubble DST data when the adsorption kinetics is diffusion-controlled. The new methodology requires the following three inputs: (1) experimental DST data measured at a single surfactant bulk solution concentration, Cb, (2) the diffusion coefficient of the surfactant molecule, D, and (3) a single equilibrium surface tension data point, to predict the entire ESTC curve applicable over a wide range of surfactant bulk solution concentration values which are less than, or equal to, Cb. We demonstrated the applicability of the new methodology by predicting the ESTC curves of two alkyl poly(ethylene) nonionic surfactants, C12E4 and C12E6, and validated the results by comparing the predictions with: (a) equilibrium surface tension measurements, (b) surface-expansion measurements, and (c) dynamic surface tension measurements for t < 100 - 200 s (when the assumption of diffusive transport of surfactant molecules in the bulk solution is valid). Very good agreement was obtained between the predictions and the measurements in (a), (b), and (c) for both C12E4 and C12E6. Based on these results, we conclude that the new methodology represents an efficient method to predict reliable ESTC curves for nonionic surfactants.