文档介绍：Polymer Analysis by Thermal-Diffusion
Forced Rayleigh Scattering
W. Köhler 1, R. Schäfer 2, 3
1 Physikalisches Institut, Universität Bayreuth, D-95440 Bayreuth, Germany
e-mail: werner.******@uni-
2 Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55021 Mainz, Germany
3 Present address: IBM, Hechtsheimer Strasse 2, D-55131 Mainz, Germany
e-mail: ******@de.
The holographic grating technique of thermal-diffusion forced Rayleigh scattering (TD-
FRS) is used for the study of Fickian and thermal diffusion in simple liquids and polymer
solutions. All three diffusion coefficients Dth, D, DT and the Soret coefficient ST can be ob-
tained from a single experiment. Due to the short diffusion length of the order of a few µm,
the whole system is very stable against perturbations like convection. TDFRS and photon
correlation spectroscopy (PCS) pared in detail. In case of polydisperse solutes, TD-
FRS does not suffer from the high scattering power of ponents, which dominate
the PCS correlation function. Quantities of interest for polymer analysis are distribution
functions and averages of diffusion coefficients and molar masses. The weight distribution
of the hydrodynamic radius follows directly from the heterodyne diffraction efficiency,
without the need to resort to scaling relations. Pseudostochastic binary sequences with a
broad power spectrum allow for the direct measurement of the linear response function, to
which the individual molar masses contribute strictly concentration proportional, with a
high spectral power density. Certain diffusive modes can be suppressed or enhanced by
random binary sequences with colored power spectra, which are tailored to the specific ex-
perimental problem.
Keywords. Diffuson, thermal diffusion, forced Rayleigh scattering, polymer solutions, poly-
dispersity, pseudostochastic noise
List of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1 Introduction . . . .