Surface and friction forces between cellulose surfaces measured with colloidal probe microscopy
To better understand interactions that govern the micro-rheological behavior of pulp fiber suspensions, we used colloidal probe microscopy to study normal forces and sliding friction between model cellulose surfaces in polyelectrolyte solutions. Hydrodynamic interactions must be accounted for in data analysis. Long-range interactions are governed by double layer forces, and once surfaces contact, by osmotic repulsive forces and viscoelasticity. Increasing the ionic strength decreases surface potentials and increases adhesive forces. Polyelectrolytes cause strong steric repulsion at high surface coverage, where interactions are sensitive to probe velocity. Polymer bridging occurs at low coverage. Regardless of scan size, friction exhibits irregular stick-slip behavior related to surface roughness. Above a critical scan size of about 100 nm - corresponding to the average size of asperities on one of the model surfaces - lateral forces are independent of scan size but depend on the load. Hydrodynamic forces contribute little to friction. Even small amounts of high molecular weight polyelectrolytes decrease sliding friction between cellulose surfaces significantly.
Zauscher, S; Klingenberg, DJ
Nordic Pulp and Paper Research Journal
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