Light scattering polymer chain

Light scattering teclmiques play an important role in polymer characterization. In very dilute solution, where tire polymer chains are isolated from one anotlier, tire inverse of tire scattering function S (q) can be expressed in tire limit of vanishing scattering vector > 0 as 1121... 

Figure 10.10 Interference of light rays scattered by segments j and k in a polymer chain. Destructive interference increases with increasing 6.

Theta temperature is one of the most important thermodynamic parameters of polymer solutions. At theta temperature, the long-range interactions vanish, segmental interactions become more effective and the polymer chains assume their unperturbed dimensions. It can be determined by light scattering and osmotic pressure measurements. These techniques are based on the fact that the second virial coefficient, A2, becomes zero at the theta conditions. 

Fig. 44.—Interference of light scattered by different parts of a polymer chain comparable in dimension with the wavelength.

Fig. 46.—Dissymmetry ratio for light scattered at 45° and 135° as a function of -x/r /X for random coil polymer chains. ...

Branching in the polymer chain affects the relationship between retention and molecular weight.83 Universal calibration has been used with some success in branched polymers, but there are also pitfalls. Viscosimetry84-91 and other instrumental methods have proved to be useful. A computer simulation of the effects of branching on hydrodynamic volume and the detailed effects observable in GPC is available in the literature.92 93 In copolymer analysis, retention may be different for block and random copolymers, so universal calibration may be difficult. However, a UV-VIS detector, followed by a low-angle light-scattering (LALLS) detector and a differential... 

Also, a good correlation between Mw (light scattering) and intrinsic viscosity is observed for [Ph(Me)PN]n over the molecular weight range of the samples studied. Thus, the Mark-Houwink relationship, [rj] = K(AOa, yields values of K = 1.44x1 o 4 (with [rj] in dL/g) and a = 0.66. These data again indicate a well solvated, extended-chain structure of the polymer in THF. 

Like Raman scattering, fluorescence spectroscopy involves a two-photon process so that it can be used to determine the second and the fourth rank order parameters. In this technique, a chromophore, either covalently linked to the polymer chain or a probe incorporated at small concentrations, absorbs incident light and emits fluorescence. If the incident electric field is linearly polarized in the e direction and the fluorescent light is collected through an analyzer in the es direction, the fluorescence intensity is given by... 

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