ADSORPTION OF POLY(METHACRYLIC ACID) AND ITS EFFECT ON THE STABILITY AND ELECTROSURFACE PROPERTIES OF GRAPHITE DISPERSIONS - 1 - THE EFFECTOF MOLECULAR-MASS

The adsorption of poly(methacrylic acid) (PMA) of various molecular ma sses (M = 1.0 x 10(4), 2.8 x 10(4), and 6.6 x 10(4)) on graphite from aqueous solutions and its effect on the stability, electrokinetic pote ntial (zeta), and specific conductivity of graphite dispersions at pH 4.2 +/- 0.3 and the constant concentration of the background electroly te (C-KCl = 5 x 10(-3) mol/dm(3)) were studied. Adsorption of PMA on g raphite increased with molecular mass. The close relation between the structure of the polymer adsorption layer at different coverages and t he variation of the stability and zeta-potential of the dispersions wa s revealed. In the PMA concentration range studied, two regions corres ponding to weak and strong stabilization of the dispersions were discl osed, The appearance of these regions is attributed to the effect of t he electrostatic and sterical factors of colloidal stabilization. The dependences of the dispersion stability on PMA concentration and molec ular mass were interpreted based on the identification of the adsorpti on mechanism and conformational changes of macromolecules in a solutio n and in the adsorbed state. The dispersing and stabilizing effect of PMA was confirmed by the calculations of the van der Waals attraction energy between the graphite particles covered with the polymer adsorpt ion layers.