Cationic amino-containing N -isopropyl- acrylamide-styrene copolymer particles: 2-surface and colloidal characteristics

Abstract

In a previous paper [1], the synthesis of various polystyrenepoly[NIPAM] core-shell latexes bearing cationic amidino and/or amino charges has been described. Several colloidal properties of these cationic latexes have been characterized such as: particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich layer in the shell, it was found that temperature played a significant role on all these properties, a LCST around 33°C being exhibited. In addition, ionic strength was also found to affect the colloidal behavior of these latexes, the largest effect being observed with latexes having both amidino and amino surface charges. The critical coagulation concentrations (CCC) of the various latexes above and below the LCST were determined, highlighting the contribution of electrostatic and steric repulsive forces to the stability of these particles.

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.…”

“…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.…”

“…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.…”

Preparation and Characterization of Micrometer-Sized Poly(N-isopropylacrylamide) Hydrogel Particles

“…1,2 PNIPAM particles also show the dramatic change of their colloidal properties such as hydrophobicity, 3 particle size, 4 electrophoretic mobility, 5,6 colloidal stability, 7,8 rheology 9,10 etc. in response to temperature changes across the LCST.…”