THE ADSORPTION OF A POLYSACCHARIDE AT THE TALC AQUEOUS-SOLUTION INTERFACE

An investigation of the mechanism of adsorption of guar, a natural non ionic polysaccharide, at the talc-aqueous solution interface has been performed. Hydrophobic interactions were found to dominate the adsorpt ion process, leading to adsorption of the guar onto hydrophobic sites, i.e. the talc ''face''. Hydrogen bonding made only a small contributi on to the adsorption, whilst chemical interactions were completely abs ent. In the case of ionically modified guars, the electrostatic contri bution to the overall thermodynamics of adsorption was weak. Both unmo dified and modified guars were found to adsorb in a very flat conforma tion with in er,cess of 75% of the constituent segments present in the form of ''trains'' at the talc-aqueous solution interface. Determinat ions of adsorbed layer thickness, calculated from microelectrophoresis measurements, supported this finding. The mannose backbone of the gua r chain adsorbed to the talc surface, leaving the pendant galactose gr oups protruding into the bulk solution. (C) 1998 Elsevier Science B.V. All rights reserved.