Prediction of Adsorption of Nonionic Polymers from Aqueous Solutions to Solid Surfaces

Abstract

In this paper, a model for predicting adsorption of nonionic polymers from aqueous solutions to solid surfaces has been presented. The model is based on continuum form of the self-consistent mean field theory. The model incorporates the effect of the hydrogen bond using Flory−Huggins model with a concentration-dependent Flory−Huggins parameter. The self-consistent field is derived using the Evans and Needham approach. The model has been validated using the reported experimental data on adsorption of poly(ethylene oxide) (PEO) from aqueous solution to silica. All the parameters of the model have been estimated from the reported data of the independent experiments specifically directed to obtain these parameters. Thus, the concentration-dependent Flory−Huggins parameter is estimated from the water activity in PEO solution, Kuhn length through the radius of gyration of PEO under ϑ conditions, and polymer−surface affinity parameter through the specific enthalpy of displacement of water by PEO in the limit of zero adsorption. The model quantitatively predicts the adsorbed amount in trains, loops, and tails and the hydrodynamic thickness of the adsorbed layer. It also correctly predicts the effect of pH and molecular weight of PEO on these quantities. The advantage of this approach is that it allows direct extension of models, describing thermodynamics of hydrogen bond in the bulk, to the interfacial region. The other important contribution of this work is that it shows that, for estimation of the adsorbed amount in the form of trains, the calorimetric technique yields results which are consistent with the NMR spin relaxation technique.