A TURBIDITY STUDY OF PARTICLE INTERACTION IN LATEX SUSPENSIONS

A turbidimetric analysis of particle interaction in latex suspensions is given. The turbidity measured at different wavelengths lambda can be rendered by the product of an integrated form factor Q(lambda2) and a suitably defined integrated structure factor Z(lambda2, c). This factorization rests on the expansion of the form factor of the particles P(q) and the structure factor S(q) [q = (4pi/lambda)sin(theta/2); theta: scattering angle] of the system in even powers of q. 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 less-than-or-equal-to lambda less-than-or-equal-to 800 nm) obtained from a polystyrene latex with a diameter of 77.4 nm. The integrated structure factor Z(lambda2, C) obtained experimentally can be interpreted in terms of an effective diameter of interaction giving a measure for the strength of electrostatic interaction.