Application of Polymer Adsorption Models to Dynamic Surface Tension

The Langmuir kinetics model and van Eijk and Cohen Stuart's spreading disk model were used to predict the dynamic surface tension of aqueous poly(N-isopropylacrylamide). Both published experimental results and calculations based on self-consistent field theory were used to convert the concentrations of adsorbed polymer to surface tension. The modeling could predict the slopes of surface tension versus log time curves; however, the times scales for surface tension lowering could not be modeled for a series of polymer concentrations using a single set of model parameters. Oscillating drop experiments in which the surface area of pendent drops was varied sinusoidally by pumping solution in and out of the drop were modeled. The experimental steady-state surface tension oscillations were less than the predicted values, indicating that the adsorbed layer could reconfigure to compensate for an expanding interface.