Cinetica de coagulação de latex de poliestireno

AUTOR(ES)
DATA DE PUBLICAÇÃO

1990

RESUMO

Polystyrene latex coagulation (by NaCl) was followed by density gradient centrifugation and light scattering measurements. Coagulation products obtained at various NaCl and latex concentrations and temperatures were determined; from these data, coagulation rate constants were calculated. Experimental rate constants at [NaCl] = 0.50 mol dm and T = 25 and 45°C agree with the values predicted by von Smoluchowski´s theory (corrected by viscous interactions) and with other experimental data. Under milder conditions ([NaCl] = 0.30 mol dm and T = 10°C) the experimental rate constants are less than the theoretical ones and under more drastic conditions ([NaCl] = 1.0 mol dm and T = 60°C) the experimental constants agree with the incorrected theoretical prediction. Latex aggregation above the critical coagulation concentration (ccc) can be reverted by transferring the coagulated latex to a medium of lower ionic strength. Heterocoagulation of two PS latices (Fnom = 0.109 and 0.460 mm) was observed, under conditions of rapid coagulation for the smaller one, only. Latex aggregation below ccc was also observed, but this is quite slow; it proceeds faster at the earlier stages and slows down, to reach a steady state. Second-order rate constants are latex concentration-dependent, when the coagulation is performed at NaCl 0.30 M; higher constants are obtained at lower latex particle concentrations.Full aggregate species distribution curves were obtained, as a function of coagulation time; the sizes of the largest aggregates formed in each case were determined. Aggregate friction and diffusion coefficients were also determined. These were explained by a modification of Reynolds and Goodwin spherical aggregates model. The combination of techniques used in this work proved to be powerful, although simple to perform. It can yield the concentrations of the various intervening aggregate species, coagulation rate constants, sedimentation, friction and diffusion coefficients, Hamaker constant estimates and stability ratios.

ASSUNTO(S)

coagulação coloides (quimica)

ACESSO AO ARTIGO

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