INTERACTIONS BETWEEN MICA SURFACES IN THE PRESENCE OF CARBOHYDRATES

The forces acting between muscovite mica surfaces across solutions con taining either uncharged carbohydrates (cyclodextrin and sucrose) or a weakly charged hemicellulose (xylan) were measured using a surface fo rce apparatus, Both the uncharged carbohydrates and xylan adsorb onto the mica basal plane, The adsorption of the uncharged carbohydrates re sults in a decrease in the long-range electrostatic double-layer force , thereby indicating a reduction in surface charge density. At a low i onic strength (1 x 10(-3) M KBr) the adsorption of xylan is very limit ed, and the resulting adsorbed layer has a thickness similar to that o bserved for cyclodextrin and sucrose, When the ionic strength of the s olution is increased, a stow buildup of the adsorbed xylan layer takes place. The functional form of the interactions between these thicker layers is consistent with the forces expected for anchored polymer bru shes in a good solvent. (C) 1995 Academic Press, Inc.