Light scattering in gels

The morphology of gels, which are a framework of macromolecular branches filled with IjMVVL, leads to specific properties of structural fluctuations causing scattering of light and other kinds of radiation. 

motion equation of gel (as an elastic motion) (Equation 22.1 in Landau and Lifshitz, 1987) comprises an additional term owing to the friction forces ari.sing when liquid moves over the elements of a polymer framework (Tanaka et al., 1973) 

This motion equation of an elastic medium is, in fact, the Newton second law. Its left-hand side is the product of the acceleration of a network unit cube by its mass (( is the network density). The right-hand side contains the sum of the forces acting on a unit cube. The first summand of the force corresponds to Equation 3 while the second one represents the friction force and is written like the Stokes formula Fjr = —6nRt]u. 

Special analysis shows the modes in I able 3.3 to have significantly different relaxation periods which enables them to be distinguished. 

Phase equilibrium in crossliaked polymer -h LMWL system 

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E. Geissler, and A. M. Hecht, Dynamic light scattering from gels in a poor solvent, J. Physique (Paris) 39(9), 955-960 (1978). 

Dilute solution light scattering and gel permeation chromatographic studies (performed in 1-chloronaphthalene at 220°C), and the inherent viscosity (performed in 1-chloronaphthalene at 206°C) is 0.16. The polymer is as polymerized, just before the curing step... 

Information about the molecular weight distributions for D light scattering in solution. When D> the number of cross-links is determined from e.g. the sol/gel fraction, swelling or elastic moduli. 

We remark incidentally that the scattered light intensity in gels must be lower than that in solutions with other conditions being equal, as the development of polymer concentration fluctuations is restricted by the presence of crosslinks. So, gels may well be very transparent if, of course, the number of crosslinks does not exceed the threshold of i -induced microphcisc separation. 

Doth static and dynamic light scattering in homogeneous molecular gel are due lo the modes of structural fluctuations depending on the gel elasticity moduli. 

When the probe polymer is larger than the network size, the Stokes-Einstein (S-B) type diffusion as shown in Eq. (7) becomes difficult and the polymer diffuses by reptation. In this case, the diffusion coefficient can be expressed by Eq. (8). Pajevic et al. [3] measured the diffusion coefficient D of polyst) ne (PS), which is included in the gel as a probe molecule, by using dynamic light scattering. The gel used was poly(methyl methacrylate) gel, which is composed of 12.5% (v/v) polymer and is swollen by toluene. The results are shown in Fig. 14 [3] where is the diffusion coefficient of PS at each molecular weight (Mf) in toluene and... 

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