Measurements of the viscosity of thin fluid films between two surfaces with and without adsorbed polymers

Abstract

A new method has recently been introduced for making detailed measurements of hydrodynamic effects in very thin liquid films between two surfaces. The method is used to obtain viscosity profiles, i. e. the viscosity as a function of the separation, between surfaces with adsorbed polymer layers. Results are presented for pure cyclohexane between two mica surfaces and for polystyrene (M _w=9×10⁵) adsorbed onto mica from cyclohexane at 26°C (i. e. below theθ-temperature of 34.5°C). The range of distances over which the concept of an effective “hydrodynamic layer” is applicable is established, and a simple correspondence is found between the effective hydrodynamic thickness, the radius of gyration of the polymer and the range of the steric force between the two polymer-covered surfaces. Further experimental evidence is presented which suggests that, depending on the solvent conditions, similar correlations apply more generally to other polymer systems.