The hydrodynamic scaling model for polymer self-diffusion

Abstract

5029 t 0 I Aj I I I I I" I rrFigure 4.Profile of the potential energy as a function of radial coordinate for TEMPOCA anion (left) and TEMPOCA acid (right). These potential profiles are drawn only on a qualitative basis. Solid curves are for larger micelles and dotted curves are for smaller micelles. Because this molecule does not dissolve in the solvent (isooctane), the potential is very high outside of the micelle. Minima occur at the center of water pool ( r = 0) and also at the interface between the water pool and the surfactant layer (represented qualitatively as a potential well). translational motion) for A-in the core of water pool decreases drastically because it is roughly proportional to the volume of core water. On the other hand, that of A H trapped at the interface as Figure 31V may not decrease so sharply and is essentially proportional to the surface area of the water pool. (3) A part of the apparent enthalpy change of 3.2 kcal/mol may be assigned to the potential difference between A H at the interface and Ain the core of the water pool. These may be the mechanism for the increase of A H type at high temperatures and low water contents. FEATURE ARTICLEFrom the above discussion, we can depict the potential curves schematically for A H and A-solubilized in the reversed micelle as shown in the left and the right diagrams of Figure 4, respectively. The solid curve is for a larger micelle, and the dotted one is for a smaller micelle. For both A-and AH, there are potential minima at both the center of the water pool and the interface between the water pool and the apolar layer of the reversed micelle. Because A-is mainly located in the water pool, the potential at the interface for A-is considerably higher than that at the center of the pool. On the other hand, the stable form of A H of Figure 31V corresponds to the potential well. The minimum at the center of the pool becomes deeper with increasing the diameter of water pool, since the dielectric constant becomes larger with the diameter.2Considering the phenomenon from a microscopic point of view, we can regard the phenomenon as switching of the system, the reversed micelle dissolving one amphiphilic carboxylic acid in the water pool, to the acidic form ( Figure 3IV) from the basic form ( Figure 31) by a single proton perception. It is interesting to point out that physiologists suggest carboxyl groups as the specific receptor sites for the taste response to salts and acids.22The hydrodynamic scaling model for polymer dynamics is described. Phenomenological results on probe diffusion in polymer solutions, on polymer and protein self-diffusion coefficients, and on related macromolecule transport properties (viscosity, sedimentation) are considered. A universal scaling equation is obtained for the concentration and molecular weight dependences of these transport coefficients. Implications are noted for the nature of polymer dynamics. Experimentally, polymer solutions are fundamentally unlike gels, even on short time scales. A physical model for transp...

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