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Concentration fluctuations in a binary glass former investigated by x-ray photon correlation spectroscopy
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Image of FIG. 1.
FIG. 1.

2D-plot of detected intensity with covered primary beam (left) and shells of same magnitude of the scattering vector (right).

Image of FIG. 2.
FIG. 2.

DSC measurement with heating rate of 30 K/min for sample 40%M-THF/oligo-MMA. The pure component s are 91 K for M-THF (Ref. 46) and 340 K for the oligomeric MMA. Dashed auxiliary lines as a guide for the eyes and the first derivative (right axis) of the DSC-curve are given for clarity.

Image of FIG. 3.
FIG. 3.

Dielectric loss of 40%M-THF/oligo-MMA. Solid lines are fits using a generalized gamma distribution as described in the text. The dc-conductivity was included in the fit of the -relaxation (left axis) as it is shown for two temperatures together with the raw data. For the dashed lines and all other fits the dc-conductivity was subtracted from the data. For low temperatures ( and , right axis) the -process of M-THF is included in the fit. Inset: The relaxation strength for the -process was determined independently for high (solid symbols) and fixed on a Curie–Weiss law for low temperatures (open circles).

Image of FIG. 4.
FIG. 4.

Combined wide and small-angle scan for the mixture 40%M-THF/oligo-MMA (open squares and circles). Inset: for comparison in the wide angle range, the respective pure components (down-triangles: oligo-MMA and up-triangles: M-THF) are shown. Open diamonds represent a weighted superposition of the pure components to demonstrate the influence of CFs at lower . Solid and dashed lines show the global fit and its decomposition according to Eq. (4).

Image of FIG. 5.
FIG. 5.

XPCS correlation functions for sample 40%M-THF/oligo-MMA at 260 K for different scattering vectors . Lines are KWW-fits with Eq. (6), errors of fit parameters are normally . The data are normalized to fit amplitude . KWW line shape exponents and averaged relaxation times are characteristic of diffusive behavior with a distribution of diffusivities (see also Fig. 6).

Image of FIG. 6.
FIG. 6.

KWW line shape exponent (top) and averaged relaxation time (bottom) plotted vs scattering vector in a logarithmic and double-logarithmic representation, respectively. The symbols denote different temperatures. The straight lines represent the limits of (diffusive) and (ballistic), respectively. The connective lines in the upper plot are guides to the eyes.

Image of FIG. 7.
FIG. 7.

XPCS correlation functions for sample 40%M-THF/oligo-MMA at fixed scattering vector for different temperatures, given in the plot. Lines are KWW-fits, errors of fit parameters are normally . The data are normalized to fit amplitude . The trend to larger KWW line shape exponents with decreasing temperature is clearly seen by the increasing steepness of the curves (see also Fig. 6).

Image of FIG. 8.
FIG. 8.

Relaxation times for the two glass-processes and obtained by DS and for the CFs (XPCS-data taken at a representative -value of ) in an Arrhenius representation. Lines correspond to Vogel–Fulcher–Tammann and Arrhenius fits, respectively. The -relaxation time corresponding to the glass transition detected by DSC is calculated following Eq. (1). Open triangles denote points, where the dielectric relaxation strength was extrapolated according to a Curie–Weiss law (cf. inset Fig. 3).

Image of FIG. 9.
FIG. 9.

The temporal variance of the intensity autocorrelation function of 40%M-THF/oligo-MMA at different scattering vectors (bottom) and different temperatures (top). is normalized by the squared amplitude of the corresponding decay in . The peaked shape indicates dynamic heterogeneity.


Generic image for table
Table I.

Some relevant physical properties and constants of oligo-MMA and M-THF under normal conditions.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Concentration fluctuations in a binary glass former investigated by x-ray photon correlation spectroscopy