Characterising latex particles and fractal aggregates using image analysis

Abstract

The fractal nature of latex particles and their aggregates was characterised by image analysis in terms of fractal dimensions. The one- and two-dimensional fractal dimensions, D1 and D2, were estimated for polystyrene latex aggregates formed by flocculation in citric acid/phosphate buffer solutions. The dimensional analysis method was used, which is based on power law correlations between aggregate perimeter, projected area and maximum length. These aggregate characteristics were measured by image analysis. A two-slopes method using cumulative size distributions of aggregate length and solid volume has been developed to determine the three-dimensional fractal dimension (D3) for the latex aggregates. The fractal dimensions D1, D2 and D3 measured for single latex particles in distilled water agreed well with D1 = 1, D2 = 2 and D3 = 3 expected for Euclidean spherical objects. For the aggregates, the fractal dimension D2 of about 1.67 ± 0.04 (±standard deviation) was comparable to the fractal dimension D3 of approximately 1.72 ± 0.13 (±standard deviation), taking the standard deviations into account. The measured three-dimensional fractal dimension for latex aggregates is within the fractal dimension range 1.6–2.2 expected for aggregates formed through a cluster-cluster mechanism, and is close to the D3 value of about 1.8 indicated for cluster formation via diffusion-limited colloidal aggregation.