Electrokinetic Properties and Colloidal Stability of Cationic Amino-ContainingN-Isopropylacrylamide−Styrene Copolymer Particles Bearing Different Shell Structures

The electrokinetic properties and colloidal stability behavior of styrene/ N -isopropylacrylamide and styrene/ N -isopropylacrylamide- co -aminoethyl methacrylate core−shell latexes were investigated. The electrophoretic mobility was first measured as a function of pH, temperature, and ionic strength. On the basis of the results obtained for the electrokinetic measurement, a charge distribution model (volume charge distribution) was proposed to help the suggested interpretation. By use of Eversole and Bordman's equation, the shear plane positions were estimated as a function of ionic strength and good correlation was found between the calculated values and the values obtained from the quasi-elastic light scattering measurement. The colloidal stability of those core−shell latexes was examined above and below the low critical solution temperature (LCST) (∼32 °C). Below the LCST, stabilization was mainly attributed to the combination of both electrostatic and steric stability. Whereas, above the LCST, only the electrostatic stability was the driving parameter. In addition, an apparent Hamaker constant of the core−shell latex was experimentally determined above the LCST.