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

Abstract

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.

Thermosensitive core-shell particles as model systems for studying the flow behavior of concentrated colloidal dispersions

“…This effect has been already observed in previous studies of similar particles, 14 for systems synthesized with a cationic initiator 13,16,17 or for PNIPAM microgels. 6 This is due to the residual charges originating from the synthesis of these particles and has been attributed to the remaining initiator fragments.…”

“…It becomes possible to monitor not only the process of flocculation upon raising the temperature but also the process of dissociation of the particles when the temperature is lowered again as already pointed out for PNIPAM microgels 6 and for PS/PNIPAM core-shell. 16,17 Figure 3 demonstrates that this breakup of the coagulated particles can be seen indeed. Here the hydrodynamic radius is measured by the Zetasizer that allows us to change the temperature of the suspension quickly enough.…”

“…Two types of particles can be prepared: either the particles consist totally of a PNIPAM network [5][6][7][8][9][10][11][12] or the PNIPAM-network is polymerized onto a solid core. [14][15][16][17][18][19] A great number of possible applications have been discussed for these systems that include widely separate fields as, e.g., protein adsorption. 20,21 They have also been recently used as a template for the reduction of metal nanoparticles [22][23][24] for applications in catalysis.…”

“…6 This is due to the residual charges originating from the synthesis of these particles and has been attributed to the remaining initiator fragments. 6,14,16,17 The charges of the core particles will be preserved when polymerizing the shell onto these cores and lead to the observed electrophoretic mobility. They are very important for the synthesis of the particles.…”

Hofmeister Effects on Poly(NIPAM) Microgel Particles: Macroscopic Evidence of Ion Adsorption and Changes in Water Structure

“…[23] Both aspects can be readily regulated thanks to the versatility of the thermally sensitive microgels based on polyA C H T U N G T R E N N U N G (NIPAM) formulations. These systems enable us to control the sign of charge of the particles by using different ionic initiators and co-monomers during polymerization, [26,27] and the hydrophilic/ hydrophobic character of the polymer just by varying temperature. In this work, a cationic and an anionic polyA C H T U N G T R E N N U N G (NIPAM) microgel have been employed to investigate in parallel the effect of electrolytes acting either as co-ions or counterions.…”