Dynamic Surface Tension of Dilute Aqueous Solutions of Nonionic Cellulose Derivatives in Relation to Other...

The dynamic surface tension of 10 nonionic water soluble cellulose derivatives with molecular weights (M(w)) in the range 100,000-1,300,000 has been measured by the pendant drop method at the water/air interface. The surface tension measured after 11.7 h, gamma*, was taken as an apparent steady state surface tension. The gamma* at the highest concentration, 500 ppm, gamma*(500), showed values from 63 to 37 mN/m, and the value of gamma*(500) depends on the hydrophilic/hydrophobic balance of the polymer. The aim of the present work was to discuss the dynamic surface tension in relation to some other characterization parameters, like M(w), diffusion coefficient, intrinsic viscosity ([eta]), cloud point, and degree of hydrophilic/hydrophobic substitution. Dynamic surface tension was shown in a concentration range of 2-10 ppm. The time to reach (gamma(H2O)-gamma*)/2, defined as t(1/2), was found to be inversely correlated both to the diffusion coefficient and to the square of the bulk concentration, which can be expected for a diffusion controlled process. The time t(1/2) showed an approximately linear relationship against [eta](1/3). The pendant drop was found to decrease in volume with time due to the high vapor pressure caused by the curvature of the drop (DeltaP = 2gamma/r(drop)). Copyright 1999 Academic Press.