Concentration fluctuations in a binary glass former investigated by x-ray photon correlation spectroscopy

Abstract

We investigate structure and dynamics of concentration fluctuations in the binary glass former methyl-tetrahydrofuran and oligomeric methyl metacrylate by photon correlation spectroscopy with partially coherent x-rays from a synchrotron source. Although the system is macroscopically well miscible and optically clear in the full temperature range, calorimetric and dielectric measurements reveal two distinct glass transition temperatures. The relaxation of long range concentration fluctuations turns out to be diffusive and exponential only well above the upper glass transition temperature. As the characteristic time tau(cf) for concentration fluctuations shows a much weaker temperature dependence than the alpha-relaxation both traces finally intersect upon lowering the temperature. Thus, close to T(g), the concentration fluctuations show pronounced features of out-of-equilibrium dynamics such as compressed relaxation functions and a crossover to a ballistic wave vector dependence of tau(cf), like previously observed in various soft matter systems. Moreover, the analysis of time-resolved correlation functions reveals that the relaxation of concentration fluctuations around T(g) involves pronounced dynamic heterogeneities.

Characterization of Low-Frequency Noise in Etched GaAs Nanowire Field-Effect Transistors Having SiNxGate Insulator

“…27) We used this function because of the analogue in the mathematical expression of the spectrum and also since its time-domain form as a function of A F was analyzed using a stretched and compressed exponential function. 27,28) Evaluated time constant is summarized in Fig. 6.…”

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“…This ballistic relaxation occurs at all volume fractions studied here for both bare and silanized particles This non-diffusive scaling phenomenon has been widely reported for jammed soft systems and glassy liquids. [22][23][24][25][26][27][48][49][50][51][52][53][54] It has also been seen specifically in silica-PEG systems. 19 The characteristic relaxation time Γ at q* is plotted as a function of volume fraction ϕ c for both the bare and silanized systems in Fig 10. It can be seen that there is a decrease in Γ with volume fraction for the bare particles.…”