Abstract
The surface force technique, whereby the forces acting between two solid surfaces immersed in liquids or in adhesive contact are directly measured, represents a novel approach for both fundamental and application-oriented studies of the surface and colloid science of papermaking. The nature and measurement of surface forces are briefly discussed, and some results reported for mica surfaces are reviewed in order to illustrate the surface chemical information obtainable using a conventional Israelachvili-type surface force apparatus. In the case of cellulose surfaces immersed in water and aqueous electrolyte solutions the measured force vs. distance profile is characterized by three regimes. Significantly, conventional DLVO theory cannot explain the interaction forces measured between cellulose surfaces. Electrostatic double-layer forces, as anticipated, dominate the long-range interactions. However, as the two cellulose surfaces begin to “contact” each other, there is an interplay of steric and electrostatic forces due to dangling tails of cellulose chains. The observed force curves, therefore, are interpreted in terms of a new model — the “dangling tail” model — of the cellulose surface, namely, the water-swollen cellulose surface has long and weakly charged cellulose chains or “molecularfibrils” which extend into the aqueous solution. In addition, the application of the surface force technique to basic problems in the adsorption of polymers, both cationic polyelectrolytes and hemicelluloses, and the colloidal stability of kaolin suspensions is illustrated. The advantages of using a new type of surface force apparatus in future studies of surface and physicochemical phenomena relevant to paper manufacturing, coating and recycling are also briefly discussed.
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