Dynamic surface tension of aqueous polymer solutions .1. Ethyl(hydroxyethyl)cellulose (BERMOCOLL cst-103)

The dynamic surface tension of aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) was measured using the pendant-drop method and digital-image analysis. The EHEC concentrations studied ranged from 3.2 . 10(-5) to 0.28% w/w. The time dependence of surface tension was analyzed using a diffusion-kinetics-controlled theory where the adsorption kinetics depended on the fraction of the total surface coverage. For EHEC concentrations less than or equal to 10(-3)% w/w, the isotherms showing surface tension vs log time follow a sigmoidal pattern. Three consecutive kinetic regions exist: the induction region, the surface-coverage region, and the mesophase region. The process of the adsorption of polymer segments is described in terms of relaxation times and the critical points of time, at the onset and at the end of the region of surface coverage. An extremely slow surface equilibration in the mesophase region indicates a progressive ordering of the polymer segments within the surface layer. (C) 1995 Academic Press, Inc.