RESUMO
The elastic properties of fcc crystals consisting of charge stabilized colloidal particles are determined from real space imaging experiments using confocal microscopy. The normal modes and the force constants of the crystal are obtained from the fluctuations of the particles around their lattice sites using the equipartition theorem. We show that the Cauchy relation is not fulfilled and that only noncentral many-body forces can account for the elastic properties.
Assuntos
Coloides/química , Modelos Químicos , Cristalização , Elasticidade , Polimetil Metacrilato/químicaRESUMO
We solve the nonlinear Poisson-Boltzmann equation around a charged colloidal sphere in an electrolyte that is confined in a cell. The colloid has an eccentric position inside the confining sphere. This models the situation in a highly concentrated charge-stabilized colloidal suspension, where a single colloid simultaneously interacts with the whole cage of neighboring colloids. We calculate the ion density profiles, the free energy, and the osmotic pressure as a function of the shifting position. We express the total force acting on the particle as a sum of pair contributions and compare the resulting pair interaction potential law with the standard Derjaguin-Landau-Verwey-Overbeck expression.
RESUMO
This article discusses the charging behavior of particles in a colloidal suspension allowing for a simple model reaction at the surface of the colloidal particles that regulates the total number Z(f) of free counterions. This number is to be distinguished from an effective number of charges Z* calculated in the Wigner-Seitz cell model to determine the interaction between the colloidal particles. We discuss the problem in terms of the full free energy of the system. The number of free counterions Z(f) as a function of the structural charge of the colloid is derived from the minimum of this free energy. Our results are compared with experimental data. Copyright 1999 Academic Press.
