Low angle light scattering technique for the study of coagulation

Abstract

A new low angle light scattering technique for the measurement of absolute coagulation rate constants of monodisperse spherical sols has been developed. Measurements have been made on a series of polystyrene latices under both rapid and slow coagulation conditions. The results were compared with calculated values which incorporate (i) a hydrodynamic correction due to Spielman and Honig et al., (ii) an estimate of the electrostatic repulsion between the particles based on constant potential calculations and electrophoretic measurements and (iii) an estimate of the van der Waals attraction based on the Hamaker theory. From the rapid rate measurements (accurate to within & 13 %) the value of the Hamaker constant is expected to lie within the range, 3 x J. The slow coagulation results suggest that the van der Waals attraction is salt dependent: in 0.2 M NaCl the measured Hamaker constant is -4x lo-" J which is the value expected from the classical Hamaker theory, in 0.09 M NaCl agreement between theory and experiment requires this value to have increased to 1.1 x lo-'' J. These findings are in qualitative agreement with the recent theoretical predictions of Parsegian and Ninham which are based on the macroscopic Lifshitz theory of van der Waals interactions. to 1.6 x

Colloid Stability of Clays Using Photon Correlation Spectroscopy

“…Recently, Novich (1983) related clay colloid stability to the geotechnical properties of waste clay tailings and showed a parallel relationship between slurry yield strength and the engineering properties of the slurry and soil. Coagulation rates for colloids have been measured in the past 50 years by direct methods, such as direct counting in the ultramicroscope (Overbeck, 1952) or in the Coulter counter (Mathews and Rhodes, 1970) in which sample disturbance and aging give highly variable results, and by indirect methods such as total-intensity light scattering (Lips and Willis, 1973;Bleier and Matijevi6, 1976;Sasaki et aL, 1980) and turbidimetry (Reerink and Overbeek, 1954;Weise and Healy, 1975), in which particle morphology and size have strong effects.…”

Rapid coagulation of polystyrene latex in a stopped-flow spectrophotometer

“…The rate of rapid coagulation of lyophobic colloids has been measured in the past fifty years with various methods, such as direct counting in the ultramicroscope (la, 2, 3) or in the Coulter Counter (4,5), light scattering (6,7), and turbidimetry (2,8). During coagulation many processes occur; they can be described in general as the combination of an aggregate of m monomers with an aggregate of n monomers to form one of m + r~ monomers.…”

Contrasting Roles Of Natural Organic Matter On Colloidal Stabilization And Flocculation In Freshwaters

“…Indeed, under conditions for which the energy barrier for aggregation lies at subnanometer distances, there appear to be significant discrepancies between theory and experimentally measured coagulation rates (e.g. (Lips and Willis 1973;Behrens and Borkovec 2000)). In the following sections, the solvation and the hydrophilic effects are examined in greater detail.…”