Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Dielectric relaxation and chain dimensions

This chapter considers only solutions of polymers that have type-A dipoles. A polymer with a center of symmetry cannot have a type-A dipole. Polyethers (-CHR-CH2-0-) are an obvious general class of polymer lacking central symmetry. This symmetry constraint excludes large numbers of homopolymers and A-B block copolymers from further consideration. A polymer with an A-B-C oriented repeat unit satisfies the symmetry condition. [Pg.134]

A brief description of relationships between dielectric spectroscopy and molecular motions follows from the reviews by Adachi, et al.(2) and Watanabe(3). The [Pg.134]

Here p,(t) is the dipole moment of monomer unit i of molecule a, dependent on t because p, reflects the current orientation of its monomer, the sum is over all N monomers in the polymer, and 9i = reflects whether the monomer was inserted into the polymer in a head-to-tail or a tail-to-head orientation. [Pg.135]

The total dipole moment due to all type-A dipoles in a solution is [Pg.135]

Dielectric relaxation is sensitive to the time correlation function of the collective variable P(t) that is the total dipole moment, just as quasielastic light scattering is sensitive to the time correlation function of the collective variable YTj= exp(iq r (t)) that is the spatial Fourier component of the concentration. [Pg.135]


So far we have not been able to treat chains with bond correlations in more than one dimension. The introduction of more detailed or realistic models of local conformational processes, such as those of Reneker34 or of Schatzki,35 has, therefore, not been feasible. We may remark that the theory of dielectric relaxation by Work and Fujita,36 which applies Glauber s methods25 to delayed (dynamic) correlations between chain dipoles, is also in essence a one-dimensional affair. [Pg.318]

At elevated polymer concentrations, many quantities, e.g., t] and D, cease to be useful for determining chain dimensions, because they are perturbed by interchain interactions. In contrast, dielectric relaxation, static light scattering, and elastic neutron scattering all continue to determine chain dimensions in appropriately-chosen nondilute ternary solutions. Dielectric relaxation measurements were described above. We now turn first to the older static light scattering studies and then to more recent applications of elastic neutron scattering. [Pg.146]

So far we have not precisely defined the term protein . For the statistical thermodynamic treatment we differentiate between protein and bulk buffer. In a thermodynamic sense the term protein or protein system is meant to refer to the polypeptide chain plus the hydration shell. The hydration shell is considered to have physical properties different from those of the bulk buffer . The term bulk buffer refers to those parts of the protein solution that have the same physical properties as the pure buffer without protein chains. The dimensions of the hydration shell are generally assumed to be in the order of one monolayer [50]. Recently the hydration shell of RNase was estimated by dielectric relaxation studies. It was found that the amount of water accounting for hydration effects was smaller than the number of water molecules calculated for full monolayer coverage of the surface [51]. [Pg.81]


See other pages where Dielectric relaxation and chain dimensions is mentioned: [Pg.134]    [Pg.136]    [Pg.138]    [Pg.140]    [Pg.142]    [Pg.144]    [Pg.146]    [Pg.148]    [Pg.150]    [Pg.152]    [Pg.154]    [Pg.156]    [Pg.158]    [Pg.160]    [Pg.162]    [Pg.164]    [Pg.166]    [Pg.168]    [Pg.170]    [Pg.466]    [Pg.134]    [Pg.136]    [Pg.138]    [Pg.140]    [Pg.142]    [Pg.144]    [Pg.146]    [Pg.148]    [Pg.150]    [Pg.152]    [Pg.154]    [Pg.156]    [Pg.158]    [Pg.160]    [Pg.162]    [Pg.164]    [Pg.166]    [Pg.168]    [Pg.170]    [Pg.466]    [Pg.360]    [Pg.360]    [Pg.164]    [Pg.44]    [Pg.44]    [Pg.84]    [Pg.196]    [Pg.303]    [Pg.335]    [Pg.74]    [Pg.298]   


SEARCH



Chain dimensions

Chain relaxation

Dielectric relaxation

© 2024 chempedia.info