A turbidity study of particle interaction in latex suspensions

Abstract

A turbidimetric analysis of particle interaction in latex suspensions is given. The turbidity measured at different wavelengths λ can be rendered by the product of an integrated form factorQ(λ²) and a suitably defined integrated structure factorZ(λ²,c). This factorization rests on the expansion of the form factor of the particlesP(q) and the structure factorS(q) [q=(4π/λ)sin(θ/2); θ: scattering angle] of the system in even powers ofq. The accuracy of this approximation has been shown by calculating the turbidity for a system of hard spheres in terms of the Percus-Yevick structure factor by numerical integration. Also, the effect of polydispersity has been taken into account within the frame of Percus-Yevick-Vrij theory for non-uniform hard spheres. It is shown that the influence of small polydispersity (standard deviation below 8%) is within experimental uncertainty. The method is applied to precise UV-spectra (400≤λ≤800 nm) obtained from a polystyrene latex with a diameter of 77.4 nm. The integrated structure factorZ(λ²,c) obtained experimentally can be interpreted in terms of an effective diameter of interaction giving a measure for the strength of electrostatic interaction.