Surface and friction forces between cellulose surfaces measured with colloidal probe microscopy

To better understand interactions that govern the micro-theological behavio r of pulp fiber suspensions, we used colloidal probe microscopy to study no rmal forces and sliding friction between model cellulose surfaces in polyel ectrolyte solutions. Hydrodynamic interactions must be accounted for in dat a analysis. Long-range interactions are governed by double layer forces, an d once surfaces contact, by osmotic repulsive forces and viscoelasticity. I ncreasing the ionic strength decreases surface potentials and increases adh esive forces. Polyelectrolytes cause strong steric repulsion at high surfac e coverage, where interactions are sensitive to probe velocity. Polymer bri dging occurs at low coverage. Regardless of scan size, friction exhibits irregular stick-slip behavior re lated to surface roughness. Above a critical scan size of about 100 nm - co rresponding to the average size of asperities on one of the model surfaces - lateral forces are independent of scan size but depend on the load. Hydro dynamic forces contribute little to friction. Even small amounts of high mo lecular weight polyelectrolytes decrease sliding friction between cellulose surfaces significantly.