Polymers transport properties

The hydrodynamic radius reflects the effect of coil size on polymer transport properties and can be determined from the sedimentation or diffusion coefficients at infinite dilution from the relation Rh = kBT/6itri5D (D = translational diffusion coefficient extrapolated to zero concentration, kB = Boltzmann constant, T = absolute temperature and r s = solvent viscosity). 

The dynamical properties of polymer molecules in solution have been investigated using MPC dynamics [75-77]. Polymer transport properties are strongly influenced by hydrodynamic interactions. These effects manifest themselves in both the center-of-mass diffusion coefficients and the dynamic structure factors of polymer molecules in solution. For example, if hydrodynamic interactions are neglected, the diffusion coefficient scales with the number of monomers as D Dq /Nb, where Do is the diffusion coefficient of a polymer bead and N), is the number of beads in the polymer. If hydrodynamic interactions are included, the diffusion coefficient adopts a Stokes-Einstein formD kltT/cnr NlJ2, where c is a factor that depends on the polymer chain model. This scaling has been confirmed in MPC simulations of the polymer dynamics [75]. 

An example of an enantiomerically pure polymer is also shown [11]. Aoki et al. showed that films of a polyacetylene substituted with a (-)-p-pinene derivative formed an effective membrane for chromatographic resolutions of racemic mixtures. ( )-2-Butanol was resolved to 29.8% eje. and unsaturated polymers for both liquid-phase and gas-phase separation applications (8, 9, 79]. It has been suggested that the rigidity and irregularity of the highly substituted polyacetylene chain, combined with the presence of aliphatic substituents which reduce interchain interactions, are important for the polymers transport properties [10]. 

Transport properties determine a polymer s ability to move through some medium or to have some penetrant medium move between its constituent segments. This definition encompasses processes with diverse driving forces such as concentration and pressure gradients, and even electrical or temperature gradients capable of motivating one component relative to another. This article emphasizes polymer transport properties under conditions of low to intermediate penetrant concentration, where extraordinary differences can exist between the diffiisivities of penetrants having relatively small differences in molecular size or shape. 

In a polymer melt, polymer transport properties follow scaling laws in M. A reasonable inference for a boundary between solutions and the melt is that there is a transition from a stretched-exponential to a power-law molecular weight dependence at some elevated (c, M). A transition having the correct form is seen in measurements by Nemoto, et who measured the molecular weight dependence of Ds at a few fixed concentrations and a very large range (43.9 5 < 5480... 

G. D. J. Phillies and P. C. Kirkitelos. Higher-order hydrodynamic interactions in the calculation of polymer transport properties. /. Polymer Sci. B Polymer Physics, 31 (1993), 1785-1797. 

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