ADSORPTION OF POLY(METHACRYLIC ACID) AND ITS EFFECT ON THE STABILITY AND ELECTROSURFACE PROPERTIES OF GRAPHITE DISPERSIONS - 3 - THE EFFECTOF PH OF A MEDIUM
Vn. Moraru et al., ADSORPTION OF POLY(METHACRYLIC ACID) AND ITS EFFECT ON THE STABILITY AND ELECTROSURFACE PROPERTIES OF GRAPHITE DISPERSIONS - 3 - THE EFFECTOF PH OF A MEDIUM, Colloid journal of the Russian Academy of Sciences, 60(4), 1998, pp. 484-489
The effect of pH on the adsorption of poly(methacrylic acid) (PMA) fro
m aqueous solutions on graphite at constant ionic strength of a backgr
ound electrolyte (5 x 10(-3) mol/dm(3) KCl) and on the character of th
e changes of the surface charge, stability, and the zeta-potential of
polymer-containing graphite dispersions was studied. The nonmonotonic
character of PMA adsorption in the pH range varying from 1 to 5 is att
ributed to the change in the value and the sign of the adsorbent and a
dsorbate charge. As the pH value increases above 5.0 (IEP), the PMA ad
sorption on graphite decreases down to zero due to an increase in the
similar negative charge of the surface and macromolecules, as well as
the prevalence of Coulombic forces of repulsion over the forces of the
adsorbate-adsorbent specific interaction. Based on the combined analy
sis of the pH dependences of adsorption and the conformational state o
f the PMA macromolecules as well as the pattern of the variation of su
rface charge and the zeta-potential of graphite at various pH values,
the structure of polymer adsorption layer on graphite was determined,
which is consistent with the extreme pattern of the dependence of the
stability of polymer-containing dispersions on pH of a medium. There i
s no simple correlation between the value of PMA adsorption, stability
, and the zeta-potential of graphite dispersions. The data obtained in
dicate the key contribution the macromolecule conformations and electr
ostatic interactions make towards the stabilization of the systems stu
died. The stabilization is attributed to the complex combination of el
ectrostatic and sterical mechanisms of colloidal protection.