Colloidal stability of chitosan-modified poly(methyl methacrylate) latex particles

Experiments of coagulation kinetics were used to study the influence of the electrolyte concentration on the colloidal stability of cationic poly(meth yl methacrylate) latex particles with various degrees of chitosan modificat ion. For the chitosan-free latex products prepared by various levels of 2,2 ' azobis(2-amidinopropane) dihydrochloride (V-50) at constant pH, the criti cal coagulation concentration (ccc) increases with increasing V-50 concentr ation, due to the enhanced particle surface charge density. On the other ha nd, the chitosan-modified latex products at constant pH do not exhibit very different values of ccc. This result is attributed to the counterbalance b etween two opposite effects related to the grafted chitosan, that is, the i ncreased particle surface charge density and the enhanced shift of the part icle's shear plane toward the aqueous phase with the chitosan content. The ccc of the latex products with various degrees of chitosan modification dec reases significantly when the pH increases from 3 to 7. This is because the degree of ionization of the surface amino groups (the particle surface cha rge density) decreases with increasing pH. As a result, the stability of th e colloidal system decreases significantly with increasing pH. The apparent Hamaker constant and diffuse potential were obtained from the coagulation kinetics data. These two parameters along with the zeta potential and parti cle size data for the latex samples taken immediately after the end of the coagulation experiments were also used to study the effect of ionic strengt h on the colloidal stability of the latex particles.