title: Colloidal stability of aqueous polymeric dispersions: effect of pH and salt concentration.
abstract: Aqueous film coatings often contain some electrolytes, organic acids, and pigments to give functions of sustained release, time-controlled release, or protection against light. Additions of some electrolytes or organic acids into latex dispersion for an aqueous film coating affect its colloidal stability. We characterized the aqueous polymeric latexes used in the pharmaceutical industry by measuring zeta potential and particle size, and evaluated this colloidal stability using DLVO theory. Three polymethacrylate-based aqueous polymeric latexes, Eudragit L30D-55, Eudragit RS30D and Eudragit NE30D, having anionic, cationic, and neutral polymer, respectively, were used in this study. The Hamaker constant of the polymethacrylate-based latex was determined to be 6.35 x 10(-21) J, and the total potential energy of the latex dispersion was calculated. The total potential energy of interaction between pairs of latex particles changes by altering the salt concentration and pH. The experimental results of stability in the anionic and the cationic latex dispersions can be explained by the total interaction energies. However, the stabilization of the neutral latex did not match the calculated result. The steric interaction produced by the surfactant likely resulted in the stable dispersion of this latex.
authors.affiliation: Pharmaceutical Research Center, Kyowa Hakko Kogyo Co. Ltd., 1188 Shimotogari, Nagaizumi-cho, Sunto-gun, Shizuoka 411-8731, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Yasuki
authors.initials: Y
authors.lastname: Katoh
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohshima
mesh_terms: D000465:Algorithms; D003102:Colloids / Q000737:chemistry*; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D011109:Polymethacrylic Acids / Q000737:chemistry*; D012212:Rheology; D012492:Salts / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D003102:Colloids; D011108:Polymers; D011109:Polymethacrylic Acids; D012492:Salts; C038300:methylmethacrylate-methacrylic acid copolymer