Equilibrio de osmossedimentação sob-gravidade : polidispersões aquosas de prata

AUTOR(ES)
DATA DE PUBLICAÇÃO

1983

RESUMO

This thesis shows results obtained from theoretical and experimental work on osmosedimentation of silver sols under gravity. The osmosedimentation velocity is shown to be strongly dependent on sol concentration and cell geometry. The results show the existence of a osmosedimentation equilibrium state. In this state, the particle distribution along the cells, in the gravitational field, is the same as that expected for the components of ordinary solutions in (normal) sedimentation equilibrium. For the silver sols studied, the values of w =(5000±900) Kg mol,z = (6000±1080) Kg mol, BSD =(3,87±0,34) L mol Kg and BLS=(2,10±0,34) L mol Kg are obtained from the extrapolation of the measured concentration gradients (in cells 15 cm height, at 300 K) to infinite dilution. Also, the complete concentration/ height data for infinite dilution is determined from the experimental results. The values obtained for w, z and the extrapolated concentration/height data are in fair agreement with those calculated from electron microscopy measurements of particle size. Analytical expressions for DG, DH, DS, Dmi, DI and D in the sedimentation process are given. Numerical calculations are performed for special cases. The measured values of BSD and BLS are discussed, and a simple method for the calculation of the molecular weight distribution from the extrapolated concentration/height data is proposed. The usefulness of the osmosedimentation technique, as applied to the fractionation and concentration of colloidal dispersions, is discussed, as well as scaling-up prospects for this method.

ASSUNTO(S)

coloide quimica de superficie termodinamica

ACESSO AO ARTIGO

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