Molecular dimensions, direct determination

From specimens cut in the x-z and y-z shearing planes, mean square chain dimensions similar to Rg j and Rg q can also be determined in the principal shear directions x, y and z. Typical isointensity patterns in the three shearing planes are shown in Fig. 28 for sample B. It can be seen that the shape of these curves in the x-z and y-z planes is nearly elliptical like in the x-y plane. However, due to the symmetry of the shear flow, the z direction is a principal direction for molecular orientation at all scales and the major and minor axes of the isointensity curves are indeed found to be parallel to the x,z and y,z directions. Therefore, the analysis of the scattering data in the x-z and y-z planes has been carried out by fixing the direction of the axes of the ellipse (to 0° and 90°) in the least-squares fit program. The major and minor axes of these ellipses then define the scattering vectors q, q and q in the principal shear directions and allow us to calculate the mean square chain dimensions Rg, Rg y and Rg 2-... 

The advance of synthetic techniques in the last decade made possible the synthesis of model branched polymers of known and controlled structure and, equally important, relatively homogeneous in molecular weight and structure (204, 221, 228). Investigations (101, 136, 141, 196) (Fig. 9) of a variety of branched polymers of different branched chain configurations but of the same chemical stmctiure and total molecular weight permits direct determination of the effect of coil dimensions and configurations on rj. 

VII. Enthalpic and Entropic Contributions to Rubber Elasticity Force-Temperature Relations Vtn. Direct Determination of Molecular Dimensions IX. Single-Molecule Elasticity References... 

The bond distances in crystals with rock salt, fluorite, diamond, sphalerite, or wurtzite stmctures could be determined with great accuracy because they could be calculated directly from the unit cell dimensions. The determination of bond distances in molecular compounds in general requires the determination of the coordinates of the individual atoms within the unit cell. In the early 1930s, such studies were time consuming and difficult, and the resulting bond distances were... 

The factors that control separation and dispersion are quite different. The relative separation of two solutes is solely dependent on the nature and magnitude of the Interactions between each solute and the two phases. Thus, the relative movement of each solute band would appear to be Independent of column dimensions or particle geometry and be determined only by the choice of the stationary phase and the mobile phase. However, there is a caveat to this statement. It assumes that any exclusion properties of the stationary phase are not included in the term particle geometry. The pore size of the packing material can control retention directly and exclusively, as in exclusion chromatography or, indirectly, by controlling the access of the solute to the stationary phase in normal and reverse phase chromatography. As all stationary phases based on silica gel exhibit some exclusion properties, the ideal situation where the selective retention of two solutes is solely controlled by phase interactions is rarely met in practice. If the molecular size of the solutes differ, then the exclusion properties of the silica gel will always play some part in solute retention. 

Chain-type in crystals of linear polymers. In drawn fibres of these substances the molecules are approximately parallel to the fibre axis, and the unit cell dimension along the fibre axis is also the identity-period of the molecule itself. The fact that it is possible so simply to determine intra-molecular distances has far-reaching consequences. The magnitude of this identity-period may lead directly to a knowledge of... 

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