M. J. García-Salinas

Electrophoretic mobility and swelling behaviour of 2-acrylamido-2-methylpropane sulphonic acid /poly(N-isopropylacrylamide) microgel particles(N-isopropylacrylamide) microgel particles

A microgel system has been characterized by measuring the size (by photon correlation spectroscopy) and the electrophoretic mobility in different conditions. The microgel particles are poly(N-iso-propylacrylamide) cross-linked with N,N’-methylene bisacrylamide, and the anionic charge of this system is increased by copolymerization with 2-acrylamido-2-methylpropane sulphonic acid. Both the electrophoretic mobility and the hydrodynamic diameter of the particles were measured as a function of pH and electrolyte concentration. Although a weak charge was detected by titration, no trend was observed for the size or mobility against pH variations. In order to apply Ohshi-ma’s electrophoretic theories for soft particles to fit the mobility data, the swelling behaviour of the particles was taken into account.

Influence of counterion type and diffusion on the primary electroviscous effect

Abstract A review of our latest results on the primary electroviscous effect is presented here. The aim is to incorporate several electrokinetic topics (electrophoretic mobility, zeta potential, primary electroviscous coefficient, counterion diffusion, etc.) into the discussion. In this way, a deeper knowledge of some phenomena involved in electrokinetics can be achieved by relating ideas and contributions from different scopes. First, some previous results are revised and commented. Then, several interesting findings regarding counterion diffusion and type are reported, including theoretical predictions and experimental data when possible. Colloidal suspensions of polystyrene latex have been used as the experimental system, which has been characterized electrokinetically, making electrophoresis, size and viscosity measurements. Zeta potential has been obtained by different conversion theories and used for the theoretical calculations of the primary electroviscous effect using Booths and Watterson–Whites theories. A good agreement is generally obtained between experiment and theory. Reduction of counterion diffusion has been considered as a possible explanation for the theoretical underestimation of the primary electroviscous effect. It has been shown that the inclusion of the real diffusion coefficients of the ionic species present in the double layer, instead of the ones at infinite dilution, improves the agreement. In order to study the influence of the type of electrolyte ions composing the double layer, four electrolytes have been used. Electrophoretic mobility against electrolyte concentration has been measured and zeta potentials have been calculated. Then, viscosity measurements have been carried out to find the primary electroviscous effect, which displays, within the concentration range studied, similar values for the different electrolytes.

Zeta potential study of a polystyrene latex with variable surface charge : influence on the electroviscous coefficient

Electrophoretic mobilities of a carboxyl polystyrene latex have been measured against electrolyte (NaCl) concentration for different pH values. The aim of this study is to know how the changes in the surface charge density affect the electrokinetic behaviour of this latex and, particularly, the presence and position of the maximum in the mobility versus electrolyte concentration curves. Mobilities become greater with increasing surface charge and the maximum mobility becomes greater and is reached at higher electrolyte concentration. This behaviour is discussed by analysing the classical explanations (hairy layer, coion adsorption, surface conductivity) proposed. Zeta potentials have also been calculated using different mobility—zeta potential conversion theories and the results have been compared. These mobility-zeta potential conversion theories have also been tested with an experimental study that is different from the usual electrokinetic techniques: the primary electroviscous effect.

Empirical multiresolution models applicable to gray-level image processing☆

Abstract This paper deals with empirical multiresolution linear models intended for image processing. Such models contain information about gray-level composition of regions in the image. First, a general method for building these models from samples of selected images is described. Then, a measure of their quality, based on the Jensen-Shannon divergence, is introduced. This divergence is also used as a distance measure for classifying images. Applications in non-linear image filtering are provided, giving better result than classical median filtering.