New methodology to determine equilibrium surfactant adsorption properties from experimental dynamic surface tension data.
In this paper, we explore a novel approach to predict equilibrium adsorption properties from experimental dynamic surface tension (DST) data and the known rate-limiting adsorption kinetics mechanism, an approach that has never been pursued in the DST literature. Specifically, we develop a new methodology to predict the equilibrium surface tension versus surfactant bulk solution concentration (ESTC) behavior of nonionic surfactants from experimental DST data when the adsorption kinetics rate-limiting mechanism 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 concentrations which are less than, or equal to, Cb. We demonstrate the applicability of the new methodology by predicting the ESTC curves of the two alkyl poly (ethylene oxide) nonionic surfactants C12E4 and C12E6, and validate the results by comparing the predictions with (a) equilibrium surface tension measurements, (b) surface-expansion measurements, and (c) pendant-bubble dynamic surface tension measurements for t<approximately 100-200 s (when the assumption of diffusive transport of surfactant molecules in the bulk solution is valid). Very good agreement is obtained between the predictions and the measurements in (a), (b), and (c) for both C12E4 and C12E6. On the basis of these results, we conclude that the new methodology presented here represents an efficient method to predict reliable ESTC curves for nonionic surfactants.
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Srinivas Nageswaran
SN
Moorkanikkara
Daniel
D
Blankschtein