Size distribution of aggregates in flocculating dispersions

• Published in: Journal of colloid and interface science 1987-06, Vol.117 (2), p.406-414
• Main Authors: Cahill, J., Cummins, P.G., Staples, E.J., Thompson, L.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(87)90400-0

Experiments which involve the diffusion-controlled flocculation of polymer latex dispersions into potential energy minima of various depths are discussed. In earlier work involving deep minima we used a model in which the kernel of the Smoluchowski expression D ij R ij is modified by an aggregate size ( N)-dependent term ( N i −α + N j −α)( N i β + N j β). Here we extend our data to longer reaction times, comparing and contrasting our findings with those of P. Meakin, Z. Chen, and J. M. Deutch ( J. Chem. Phys. 82, 3786 (1985)). It is concluded that using this kernel the best-fit value of the exponent α varies between 0.1 for small aggregates and Meakin's value of 0.55 for larger aggregates, while the value of β remains at a constant value consistent with fractal dimensions throughout. The interpretation and implications of the low value of α for small aggregates is discussed. Where the depth of the potential energy minimum is reduced by surfactant addition or by formation of an electrostatic secondary minimum, deviations from the Smoluchowski distribution occur at a much lower level of aggregation than that for strong aggregation. Moreover the deviations are more pronounced in that a much wider aggregate distribution is observed.