Quasielastic scattering by dilute polymer solutions

Akcasu, Ziya; Gurol, H.

doi:10.1002/pol.1976.180140101

Cited by 118 publications

(10 citation statements)

References 8 publications

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“…Here, by the term “universal” we mean that the plot of η 0 Ω( k )/ k B Tk 3 against 〈 S 2 〉 1/2 k , especially its height in an intermediate range of k , is independent of the polymer−solvent system, where η 0 is the solvent viscosity, k B the Boltzmann constant, T the absolute temperature, and 〈 S 2 〉 the mean-square radius of gyration. This is just the prediction by the Gaussian chain theory. − Very recently, however, it has been shown on the basis of the helical wormlike (HW) chain model that the above plot may depend on the kind of polymer even for large molecular weights . The purpose of the present paper is to examine experimentally whether this is the case or not.…”

Section: Introductionmentioning

confidence: 79%

Dynamic Structure Factor of Polystyrene and Poly(methyl methacrylate) in ϑ Solvents

1998

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The dynamic structure factor and its first cumulant Ω(k) as functions of the magnitude k of the scattering vector were determined from dynamic light scattering (DLS) measurements for two atactic polystyrene samples having the weight-average molecular weights M w ) 6.40 × 10 6 and 8.04 × 10 6 in cyclohexane at 34.5°C (Θ) and for two atactic poly(methyl methacrylate) samples having Mw ) 4.82 × 10 6 and 1.31 × 10 7 in acetonitrile at 44.0°C (Θ). The translational diffusion coefficient and the mean-square radius of gyration 〈S 2 〉 were also determined from DLS and static light scattering measurements, respectively, for all the samples except for the a-PS sample with the smaller Mw. It is found that even in such a range of large Mw, the "universal" behavior cannot be realized; i.e., the plot of η0Ω(k)/kBTk 3 against 〈S 2 〉 1/2 k depends on the kind of polymer in the k 3 -region, where η0 is the solvent viscosity, kB the Boltzmann constant, and T the absolute temperature. This result is consistent with the theoretical prediction on the basis of the helical wormlike (HW) chain model, although the HW theory cannot quantitatively explain the experimental data for the individual polymer.

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Section: Introductionmentioning

confidence: 79%

Dynamic Structure Factor of Polystyrene and Poly(methyl methacrylate) in ϑ Solvents

1998

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“…Dilute Solutions: Asymptotic Behavior. The observed angular dependence is a clear indication for internal segmental motions. ,,, It is instructive to plot double logarithmically D app (q)/D z against qR g and to have a closer look at the asymptotic behavior. − ,, Both variables in such a plot are dimensionless and are scaled quantities. Therefore, a certain universality can be expected.…”

Section: Resultsmentioning

confidence: 99%

“…These internal modes of motion are superimposed upon the translational motion of the center of mass. The correct translational diffusion coefficient is now obtained only after extrapolating the data of Γ /q 2 to zero scattering angle, , where Γ is the first cumulant of the field time correlation function (TCF), g 1 (q,t) , obtained by dynamic LS. The data of Γ /q 2 are angular dependent when objects with internal flexibility are studied and increase with the scattering angle.…”

Section: Introductionmentioning

confidence: 99%

Starch Fractions as Examples for Nonrandomly Branched Macromolecules. 4. Angular Dependence in Dynamic Light Scattering

Galinsky

Burchard

1997

Macromolecules

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The angular dependence of dynamic light scattering from five degraded potato starch samples was studied. The study allowed the determination of internal modes of motion in branched structures that resemble hyperbranched polymers. The properties of the investigated starches are dominated by the large size of the amylopectin. Measurements were made at infinite dilution (c = 0) and at concentrations c > c* where c* is the overlap concentration. The time correlation function (TCF) at low concentration was analyzed by its first cumulant at low values of qR g and in the asymptotic region of qR g > 2. The first cumulant Γ describes the initial decay of the TCF, g 1 (q,t). A double logarithmic plot of Γ/q 2 ≡ D app (q) against qR g gave a curve that lies between those for hard spheres and flexible coils. In contrast to linear chains, it showed an asymptotic slope of 0.80−0.85 instead of the theoretically expected slope of 1.00. The reduced first cumulant Γ*(q) ≡ (Γ/q 3 )(η0/kT) did not approach a constant plateau at large q but decayed continuously below the experimentally observed plateau value for linear chains. The reason for this behavior is seen in the high branching density and a loss of internal flexibility. In a second part, the angular dependence of the first cumulant in the semidilute regime, up to c/c* = 5, was measured. The data from the different concentrations could be condensed to one common master curve when an empirical scaling parameter was used. A plot of the TCF's from the various concentrations as a function of Γ(q,c,)t resulted in q-independent shape functions g 1 (Γt), which gradually changed from Zimm to Rouse behavior when the concentration was increased beyond the overlap concentration c*. This change is interpreted as a result of hydrodynamic screening.

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“…B3 in Montgomery and Berne (37), restricted to a single rigid body, and insert it into Eq. 17 of Akcasu and Gurol (38), with the density r(R N ) ¼ S j b j exp(iQR j ) (Eq. 8) to yield the expression for D 0 (Q).)…”

Section: Diffusional Dynamicsmentioning

confidence: 99%

Large Domain Fluctuations on 50-ns Timescale Enable Catalytic Activity in Phosphoglycerate Kinase

Inoue

Biehl

Rosenkranz

et al. 2010

Biophysical Journal

108

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Large-scale domain motions of enzymes are often essential for their biological function. Phosphoglycerate kinase has a wide open domain structure with a hinge near the active center between the two domains. Applying neutron spin echo spectroscopy and small-angle neutron scattering we have investigated the internal domain dynamics. Structural analysis reveals that the holoprotein in solution seems to be more compact compared to the crystal structure but would not allow the functionally important phosphoryl transfer between the substrates if the protein were static. Brownian large-scale domain fluctuation dynamics on a timescale of 50 ns was revealed by neutron spin echo spectroscopy. The dynamics observed was compared to the displacement patterns of low-frequency normal modes. The displacements along the normal-mode coordinates describe our experimental results reasonably well. In particular, the domain movements facilitate a close encounter of the key residues in the active center to build the active configuration. The observed dynamics shows that the protein has the flexibility to allow fluctuations and displacements that seem to enable the function of the protein. Moreover, the presence of the substrates increases the rigidity, which is deduced from a faster dynamics with smaller amplitude.

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Quasielastic scattering by dilute polymer solutions

Cited by 118 publications

References 8 publications

Dynamic Structure Factor of Polystyrene and Poly(methyl methacrylate) in ϑ Solvents

Dynamic Structure Factor of Polystyrene and Poly(methyl methacrylate) in ϑ Solvents

Starch Fractions as Examples for Nonrandomly Branched Macromolecules. 4. Angular Dependence in Dynamic Light Scattering

Large Domain Fluctuations on 50-ns Timescale Enable Catalytic Activity in Phosphoglycerate Kinase

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