Gyration, light scattering measurement

In this study, g" was determined by using the above equation. The radii of gyration of stars and similar linear polymers [68] were obtained from light scattering measurements. The g" values were calculated as 0.36 and 0.40, respectively. 

Chapter C deals with molecular dimensions of interrupted helices. Typical theories for mean-square radius of gyration and mean-square end-to-end distance are reviewed. Important predictions from theory are compared with the results of recent light-scattering measurements. Complications attendant upon the analysis of light-scattering data for polypeptides in the helix-coil transition region are discussed. 

The radii of gyration of amylose and cellulose are calculated by a method of Lifson for different glucose conformations. It is found that the radii of gyration differ widely and it can be determinated clearly by means of viscosity and light-scattering measurements which kind of glucose conformation is present in the polysaccharides. The effects of twisting upon the linear molecule is discussed. 

The situation becomes more complex if light scattering measurements are made at larger angles where there is intraparticle interference in the scattered light. The angular variation of intensity is related to the radius of gyration RG of the polymer. 

The exponent v characterizes the swelling of a long polymer chain in very dilute solutions. In theory, it could be measured in several ways. However, can we trust results obtained by the simplest technique which consists in measuring the intrinsic viscosity These measurements produce values for the exponent v which are always lower than those obtained by light scattering measurements of the radius of gyration. It was necessary to explain this discrepancy in order to make a proper comparison between experimental and theoretical values of the exponent v. 

Light scattering measurements can also be used to determine the molecular weight (M2) of solute molecules as well as interactional (second and third virial coefficients) and structural parameters (radius of gyration) [60, 61]. The reader is referred to Chapter 18 for more information on light scattering methods. The dependence of A2 and Rj) on M have been the subject of many research studies in polymer solution thermodynamics [29, 62]. Many other experimental techniques can been used to determine these and other related parameters [28, 35, 63]. 

With light scattering measurement of the radius of gyration (see Eq. (3.6)), direct comparisons of g values can be made. In solvents, the experimental g values generally agree with calculations, with some exceptions (Small, 1975). 

Equation (A4-21) allows the theoretically important end-to-end chain distance to be calculated from the experimentally accessible (e.g., by light scattering measurements) radius of gyration. This calculation remains valid for the linear valence angle chain and the linear valence angle chain with hindered rotation, but is not valid for polymers in good solvents. 

The radius of gyration of a polymer in solution can be determined from light-scattering measurements. 

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