Adsorption of cationic amylopectin on microcrystalline cellulose.

The effects of electrolyte concentration and pH on the adsorption of cationic amylopectin on microcrystalline cellulose were investigated. The adsorbed amount in the pseudo-plateau of the isotherm showed a maximum as a function of the electrolyte concentration. We compared the data with a recent theory on polyelectrolyte adsorption. The increase in the adsorbed amount with pH was strongly correlated with the increase in surface charge, indicating the central role of electrostatic attraction between adsorbate and substrate. However, the maximum in the adsorption results from two additional effects: (i) a non-electrostatic attraction between polymer and surface and (ii) specific adsorption of counter-ions. The specificity of the latter adsorption increases in the order Cs > K ≈ Na > Li