Rotatory diffusion constant

The orientational mechanism of EB in solutions of r id-chain polymers and the possibility of determining rotatory diffusion constants of their molecules from dispersion curves may be utilized for the characterization of equilibrium conformational properties of their drains. The theory of rotational friction of kinetically rigid molecules developed by Hearst makii% use of the statistics of worm-like chains can be employed for this purposes. The results of this theory for the two limiting cases of molecular conformation refering to the slightly bent rod and the worm-like coil are expressed by Eqs. (27) and (28) (Sect. 2.3). 

J. Riseman and J. G. Kirkwood, The intrinsic viscosity, translational and rotatory diffusion constants of rod-like molecules in solution, J. Chem. Phys., 18 (1950) 512-516. 

In terms of the average torque the rotatory diffusion constant D, is given by... 

From diffusion measurements it is known that the translatory mobility of solvent molecules in polymers changes abruptly at the glass temperature. Below T0 the diffusion constants are of the order of 10-12 to 10 14sq. cm. /sec., above Tg of the order of 10 4 to 10 8sq. cm./sec. (13). We have found that even below the glass temperature, plasticizer molecules may perform rather rapid motions, preferably rotatory motion. If the plasticizer has long aliphatic side chains, as with phthalates, rotating motions in the side chains should also result in a narrow... 

As the particles arc subject to rotatory BROWNian motion, the collision diameters will be of the order of the largest diameter of the particles. The diffusion constant, however, depends on a sort of mean diameter of the particle which, in the case of rods, may be considerably smaller than the length of the rod. Consequently anisodimcnsional particles have a relatively large collision diameter combined with a relatively large diffusion constant which results in a high probability of collision. 

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