Polystyrene density fluctuation

Figure 4.11 X-Ray scattering data obtained with atactic polystyrene at temperatures above and below the glass transition temperature, showing how the intensity I(q), arising mostly from density fluctuations, depends on q as q approaches zero. (From Roe and Curro.19)...

The crosses in Fig. 10 display the SAXS-intensity due to the capillary filled with water as compared to the smeared intensity of the polystyrene latex [81] measured at a volume fraction of 18% (open circles) [73]. It is easy to see that at small scattering angles the intensity measured from the latex is partially due to the effect of the sample holder used for the measurement of the latex. The other important contribution is given by the intensity due to the density fluctuation of water (cf. below). Both contributions can be removed according to [82] ... 

Fig. 13. Removal of the contribution caused by density fluctuations of the solid polystyrene [85, S6].Empty circles Desmeared scattering intensity the marked range shows the q-range used for the fit of filled circles scattering intensity after subtraction of...

Roe, R. J., and Curro, J. J., Small angle x-ray scattering smdy of density fluctuation in polystyrene annealed below the glass transition temperature. Macromolecules, 16, 428-434 (1983). 

Figure 1. Segmental density fluctuation of alternating lamellae of pure polystyrene-b-polyisoprene-b-polystyrene block copolymer. The density (referenced to each pure segment composition) varies between 0 and 1 for each domain phase and in the interphase region which has finite thickness, d. The periodic pattern distance of the lamellae structure is denoted by D.

FIG. 63 The dependence of the relative variance of particle density fluctuations = Np) — Np) / Np) on particle coverage 0. The points denote the experimental results obtained for polystyrene latex particles on mica under the diffusion-controlled transport for/ = 10 M [182] the inverted triangles show the RSA simulation results the continuous line represents the analytical results stemming from the SPT theory for equilihrium system Eq. (236). 

As long as the concentration of the small molecule is low (<5%), the scattered intensity due to concentration fluctuations will be negligible relative to the density or anisotropy fluctuations. In polystyrene, the HV spectrum will not have any contribution due to concentration fluctuations, but in principle there could be a contribution due to the diluent anisotropy. The average relaxation time will be determined by the longest time processes and thus should reflect only the polymer fluctuations. The data were collected near the end of the thermal polymerization of styrene. Average relaxation times were determined as a function of elapsed time during the final stages of the reaction... 

Such phase-separated polymer mixtures serve as an excellent model system where molecular-level interactions between components are small. The system studied here is a film made of an immiscible binary mixture of atactic polystyrene and low-density polyethylene [2], The dynamic IR measurement was carried out as before by mechanically stimulating the system at room temperature with a 23-Hz dynamic tensile strain with an amplitude of 0.r/>. The time-dependent fluctuations of IR absorbance induced by the strain were recorded at a spectral resolution of 4 cm. ... 

T. Koch, G. Strobl, and B. Stuehn. Light-scattering smdy of fluctuations in concentration, density, and local anisotropy in polystyrene-dioxane mixtures. Macromolecules, 25(1992), 6255-6261. 

Borsali, et al. applied NSE to a polystyrene perdeuteropolystyrene block copolymer and to a mixture of polystyrene and perdeuteropolystyrene copoly-mers(85). By using a benzene perdeuterobenzene contrast-matching solvent, it was possible to arrange matters so that fluctuations in the number density of the block copolymer scattered no neutrons. Under these conditions, NSE spectra revealed a single mode for the block copolymer with relaxation rate linear in q and a nonzero intercept as 0. NSE spectra of the homopolymers instead revealed a mode with relaxation rate linear in and a zero intercept as 0. This result is very close to the predictions of Pecora(l-3) as confirmed with light scattering by Han and Akcasu(l 1) and Ellis, et a/.(14), but here the incident neutron waves had X = 8.5A, and the observed time range was 0.3-17 ns. 

C. Konak and W. Brown. Coupling of density to concentration fluctuations in concentrated solutions of polystyrene in toluene. J. Chem. Phys., 98 (1993), 9014-9017. 

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