Polyelectrolyte Adsorption on Solid Surfaces: Theoretical Predictions and Experimental Measurements

This work utilizes a combination of theory and experiments to explore the adsorption of two different cationic polyelectrolytes onto oppositely charged silica surfaces at pH 9. Both polymers, poly(diallyldimethylammonium chloride), PDADMAC, and poly(4-vinyl N-methylpyridinium iodide), PVNP, are highly charged and highly soluble in water. Another important aspect is that a silica surface carries a relatively high surface charge density at this pH level. This means that we have specifically chosen to investigate adsorption under conditions where electrostatics can be expected to dominate the interactions. Of specific focus in this work is the response of the adsorption to the addition of simple salt (i.e., a process where electrostatics is gradually screened out). Theoretical predictions from a recently developed correlation-corrected classical density functional theory for polyelectrolytes are evaluated by direct quantitative comparisons with corresponding experimental data, as obtained by ellipsometry measurements. We find that, at low concentrations of simple salt, the adsorption increases with ionic strength, reaching a maximum at intermediate levels (about 200 mM). The adsorption then drops but retains a finite level even at very high salt concentrations, indicating the presence of nonelectrostatic contributions to the adsorption. In the theoretical treatment, the strength of this relatively modest but otherwise largely unknown nonelectrostatic surface affinity was estimated by matching predicted and experimental slopes of adsorption curves at high ionic strength. Given these estimates for the nonelectrostatic part, experimental adsorption data are essentially captured with quantitative accuracy by the classical density functional theory

Comparative properties of the pulp and paper obtained from kraft-ethanol and kraft-ethylene glycol processes

The Study investigates the effects of ethanol or ethylene glycol addition, during, conventional kraft cooking, oil the properties of pulp and paper sheets. After optimization of the kraft pulping conditions according to the ratio of chemicals, cooking temperature and time, with Pinus nigra subsp. pallasiana as a raw material, ethanol or ethylene glycol, in concentrations of 10%, 20%, 30% and 40%, was added to the kraft cooking liquor. The experiments were repeated with anthraquinone as a catalyst. The pulp yields were not significantly changed when the delignification ratio was increased by adding ethanol to the conventional kraft cooking. Addition of ethylene glycol to the conventional kraft cooking liquor had a positive impact on the physical and mechanical properties of the paper sheets. On the other hand, addition of anthraquinone to the kraft-solvent cooking media had no effect on the pulp and paper properties