Signature of a Type-A Glass Transition and Intrinsic Confinement Effects in a Binary Glass-Forming System

Abstract

We study dynamically highly asymmetric binary mixtures comprised of small methyl tetrahydrofuran (MTHF) molecules and polystyrene. Combined use of dielectric spectroscopy, 2H nuclear magnetic resonance, incoherent quasielastic neutron scattering, and depolarized dynamic light scattering allows us to selectively probe the dynamics of the components in a broad dynamic range. It turns out that the mixtures exhibit two glass transitions in a wide concentration range although being fully miscible on a macroscopic scale. In between both glass transition temperatures, the dynamics of the small molecules show strong confinement effects, e.g., a crossover from Vogel-Fulcher to Arrhenius behavior of the time constants. Moreover, the dynamical behavior of small molecules close to the slow matrix is consistent with mode coupling theory predictions for a type-A glass transition, which was expected from recent theoretical and simulation studies in comparable systems.

Sucrose diffusion in aqueous solution

“…Similar effects have also been observed for binary colloidal suspensions 51 , 53 and for binary mixtures of glass-forming liquids and oligomers or polymers. 54 , 55 …”

Dynamics of tetrahydrofuran as minority component in a mixture with poly(2-(dimethylamino)ethyl methacrylate): A neutron scattering and dielectric spectroscopy investigation

“…In polymer blends, [1][2][3][4][5] mixtures of oligomers and lowmolecular weight systems 6,7 and also in mixtures of polymers and low-molecular weight systems, [8][9][10] it has been shown the existence of two different glass transitions associated to the freezing of the α-relaxation corresponding to each of the components in the system. A particularly interesting situation has been identified for these mixtures when the neat a) Electronic mail: sckgorag@ehu.es components present a large difference in their glass-transition temperatures.…”

“…Interestingly, a Vogel-Fulcher to Arrhenius crossover has also been recently reported for methyl-tetrahydrofuran (MTHF) as minority component in mixtures with polystyrene. 7 The question whether this is a general phenomenon or under which circumstances it appears is still open.…”

Structure and component dynamics in binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with water and tetrahydrofuran: A diffraction, calorimetric, and dielectric spectroscopy study

“…Such kind of behavior has recently been reported for methyl-THF in polystyrene. 51 To detect this effect, other kind of measurements selective for the THF component dynamics and extending the dynamic range would be required, like, e.g., QENS. With the results at hand, what we can firmly state is the absence of crossover for THF dynamics in the dynamic window explored in this work.…”