Preparation and characterization of polyelectrolyte coated particles.

摘要

There is a growing interest in polyelectrolyte stabilized dispersions in aqueous environments because of their technological applications and their similarity to many biological systems. It is important to have control over the stability of these particles and to understand how the properties of these systems, such as the charged layer thickness and electrostatic potential distribution, can be probed using scattering and electrokinetic techniques. Ultimately, these properties determine the bulk characteristics of a dispersion.; Model colloidal particles with polyelectrolyte layers were prepared in an aqueous environment and studied using light scattering and electrokinetic techniques. The systems consisted of monodisperse latex particles with adsorbed, fully charged poly(methacrylic acid) bound to the latex particles by a polystyrene anchor block in addition to micelles formed by polystyrene-b-poly(methacrylic acid) copolymers. The properties of these particles were manipulated by changing either the quantity of added electrolyte or the concentration of fixed charge in the polyelectrolyte layer. Light scattering and electrokinetic measurements were interpreted using the known properties of the particles.; We were able to quantitatively predict the changes in the size of thin polyelectrolyte layers as a function of ionic strength. Since polymers provide a steric barrier to prevent flocculation, understanding how the size of a polyelectrolyte layer changes under differing conditions has a direct impact on colloidal stability. We also found that the electrophoresic mobilities of the bare and polyelectrolyte coated latex particles are similar, so electrophoresis may not be an ideal technique for probing the charged layer. Additionally, extant theories for the mobility of charged, porous particles failed to capture the observed behavior of our model systems, suggesting that these theories do not include all relevant phenomena. However the dielectric responses of a polyelectrolyte coated particles with differing amounts of charge and bare latex particles are dramatically different. The dielectric spectra of polyelectrolyte coated particles exhibited relaxations associated with the various dimensions characteristic of the charged, porous particles. Additionally, the high frequency conductivity of self-assembled polyelectrolyte micelles reflected the charge carried by the micelles. The high frequency conductivity of a suspension was the most straight forward method to measure the charge on a charged, porous particle. Dielectric spectroscopy is a powerful tool capable of probing the structure and charge of polyelectrolyte layers.