Light scattering correlation length

The rod length and diameter can also be inferred from d5mamic depolarized Rayleigh scattering. The translahonal and rotational diffusion coefficients can be determined. The depolarized light-scattering correlation function can be expressed as ... 

Measurements of static light or neutron scattering and of the turbidity of liquid mixtures provide information on the osmotic compressibility x and the correlation length of the critical fluctuations and, thus, on the exponents y and v. Owing to the exponent equality y = v(2 — ti) a 2v, data about y and v are essentially equivalent. In the classical case, y = 2v holds exactly. Dynamic light scattering yields the time correlation function of the concentration fluctuations which decays as exp(—Dk t), where k is the wave vector and D is the diffusion coefficient. Kawasaki s theory [103] then allows us to extract the correlation length, and hence the exponent v. 

Fig. 5. Correlation length, scaled on Rt, as a function of reduced concentration X c/c as measured through static light-scattering by Wiltzius et al. (1983). Symbols denote various molecular weight polystyrenes in toluene and methyl ethyl ketone at 25°C.

Since we are dealing with motions of the order of one bond length or more in a dense medium, inertial effects can be neglected, and the dynamics on that scale only involve correlation functions over r and Uj. Different spectroscopic techniques may probe different C F. For instance. Neutron or polarized light scattering probe translation C F, (acting only or r) such as the well known Van Hove C F ... 

The Kerr constant around cf> v0.1 becomes very large for ATB microemulsions and the decay curve becomes exponential.The measured decay time t is in fairly good agreement with the lifetime tg of a critical density fluctuation of size . is the correlation length of the density fluctuations previously measured in ATB microemulsion by light scattering and 3... 

As above, the interfacial and bulk properties have been studied by light scattering (17). All the results that we obtained are in fairly good agreement with the renormalization group theory of critical phenomena and the experimental variations of the interfacial tensions and correlation lengths are given in table III. 

Maeda and Saito (1973) have calculated the spectrum of light scattered from optically anisotropic rigid rods whose length is >q J. This calculation is even more complex than that for the integrated intensity (zero-time scattered-field correlation function) for the same model given in Appendix 8.B, and will, therefore, not be given here. The interested reader should consult the article by Maeda and Saito. 

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