PRECISE ANALYSIS OF THE TURBIDITY SPECTRA OF A CONCENTRATED LATEX

A precise analysis of turbidity spectra of a concentrated polystyrene latex (number-average diameter of particles: 68 nm) for a range of wavelength between 400 and 1100 nm is given. By suitable definition, the measured turbidity of the nonuniform system as function of lambda (lambda is the wavelength in the medium) is factored into a ''measured'' integrated form factor Q(M)(lambda(2)) and a ''measured'' integrated structure factor Z(M)(lambda(2),c) (c is the weight concentration). The normalized scattering cross sections Q(M)(lambda(2)) evaluated from the experimental specific turbidities extrapolated to vanishing concentration are in full agreement with the theoretical results provided by the Mie theory. The turbidities measured at finite concentrations (up to 8.2 wt %) yield the function Z(M)(lambda(2),c) which furnishes the structure factor S(q) [q = (4 pi/lambda) sin(theta/2); theta: is the scattering angle] in the region of low scattering angles. In particular, it can be demonstrated that S(0) as well as alpha, the first coefficient of the expansion of S(q) in terms of even powers of q, can be obtained with good accuracy without the need of assuming a specific model of particle interaction.