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 wav elength between 400 and 1100 nm is given. By suitable definition, the measured turbidity of the nonuniform system as function of lambda (lam bda is the wavelength in the medium) is factored into a ''measured'' i ntegrated form factor Q(M)(lambda(2)) and a ''measured'' integrated st ructure factor Z(M)(lambda(2),c) (c is the weight concentration). The normalized scattering cross sections Q(M)(lambda(2)) evaluated from th e experimental specific turbidities extrapolated to vanishing concentr ation are in full agreement with the theoretical results provided by t he Mie theory. The turbidities measured at finite concentrations (up t o 8.2 wt %) yield the function Z(M)(lambda(2),c) which furnishes the s tructure factor S(q) [q = (4 pi/lambda) sin(theta/2); theta: is the sc attering angle] in the region of low scattering angles. In particular, it can be demonstrated that S(0) as well as alpha, the first coeffici ent of the expansion of S(q) in terms of even powers of q, can be obta ined with good accuracy without the need of assuming a specific model of particle interaction.