PARTICLE-SIZE DISTRIBUTION BY ZERO-ANGLE DEPOLARIZED LIGHT-SCATTERING

Zero-angle depolarized dynamic light-scattering methods for particle size determinations are demonstrated by a study on aqueous colloidal suspensions of titanium dioxide. Previous results on a poly(tetrafluoroethylene) latex suspension are also briefly recounted and updated to include reanalysis by an additional independent Laplace inversion method, Provencher's CONTIN. Both of these colloidal suspensions depolarize light strongly, and the result is homodyne correlation functions with signal-to-noise ratios comparable to those of typical finite-angle quasi-elastic light-scattering measurements. Size distributions may be obtained by Laplace inversion of the correlation functions, with excellent agreement among the various Laplace inversion algorithms. Resolution is greatly improved compared to conventional quasi-elastic light-scattering measurements, because rotational motions, which are more sensitive to size than translational motions, are detected at zero angle. The size distribution from zero-angle depolarized light scattering agrees very well with that from electron microscopy in the case of the poly(tetrafluoroethylene) latex. There is reasonable agreement in the case of TiO2, but significant differences do exist. It is not yet possible to determine which technique is more accurate in this case.