From the Dynamically Nanostructured Liquid to the Glassy State: A Phenomenological Approach

E-print/Working paper (2008)

Based on experimental evidences we present a phenomenological description of the thermal glass transition as a dynamical phase transition. Different susceptibilities calculated on the basis of this ... [more ▼]

Based on experimental evidences we present a phenomenological description of the thermal glass transition as a dynamical phase transition. Different susceptibilities calculated on the basis of this description are in good qualitative agreement with experimental data. As an essential feature this novel view of the glass transition reflects the kinetic as well as the transition aspect of the thermal glass transition. [less ▲]

Organization versus frustration: low temperature transitions in a gelatine-based gel

in New Journal of Physics (2008), 10

A commercial physical gel composed of gelatine, water and glycerol shows a sol–gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not ... [more ▼]

A commercial physical gel composed of gelatine, water and glycerol shows a sol–gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not observable in the longitudinal acoustic mode measured at hypersonic frequencies with Brillouin spectroscopy. Depending on the thermal treatment of the investigated material during the sol–gel transition and within the gel state, Brillouin spectroscopy reflects tremendously different hypersonic dynamics. These distinct dynamics are responsible for the formation of different glassy states at low temperatures including that of a glass-ceramic. The large variety of super-cooled and glassy states is attributed to distinct distributions of the gel's constituents within the samples. Surprisingly, the same gel state can be produced either by annealing the gel over months or by the non-equilibrium effect of thermo-diffusion (Soret effect) in the course of some minutes. [less ▲]

About the nature of the structural glass transtion: an experimental approach

in Henkel, M.; Pleimling, M.; Sanctuary, Roland (Eds.) Aging of the Glass Transition (2007)

The nature of the glassy state and of the glass transition of structural glasses is still a matter of debate. This debate stems predominantly from the kinetic features of the thermal glass transition ... [more ▼]

The nature of the glassy state and of the glass transition of structural glasses is still a matter of debate. This debate stems predominantly from the kinetic features of the thermal glass transition. However the glass transition has at least two faces: the kinetic one which becomes apparent in the regime of low relaxation frequencies and a static one observed in static or frequency-clamped linear and non-linear susceptibilities. New results concerning the so-called ?-relaxation process show that the historical view of an unavoidable cross-over of this relaxation time with the experimental time scale is probably wrong and support instead the existence of an intrinsic glass transition. In order to prove this, three different experimental strategies have been applied: studying the glass transition at extremely long time scales, the investigation of properties which are not sensitive to the kinetics of the glass transition and studying glass transitions which do not depend at all on a forced external time scale. [less ▲]

Complex specific heat capacity of two nanocomposite systems

in Thermochimica Acta (2006), 445(2), 111-115

Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The ... [more ▼]

Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The properties of nanocomposites may vary between those of a simple mixture of independent components and those of a system, where specific interfacial interactions between the constituting parts lead to ‘new’ properties. Depending on the type of the nanoparticles filled into the matrix, the resulting properties might be closer to one or to the other extreme. We used temperature modulated differential scanning calorimetry (TMDSC) to investigate a matrix of the oligomer diglycidyl ether of bisphenol A (DGEBA) filled either with SiO2- or Al2O3-nanoparticles. The dependence of the complex specific heat capacity () on the concentration of nanoparticles shows a clear difference between the two systems as far as the glass transition of the oligomer is concerned. The SiO2 composite seems to behave more like a simple mixture, whereas the Al2O3 composite shows ‘new’ properties. [less ▲]

Comment on "thermal glass transition beyond the vogel-fulcher-tammann behavior for glass forming diglycidylether of bisphenol A".

in Physical Review Letters (2005), 94(12), 129603-129604

Mechanical Interphases in Epoxies as seen by Nondestructive High-Performance Brillouin Microscopy

in Adhesion - Current Research and Application (2005)

Cauchy-like relation between elastic constants in amorphous materials.

in Physical Review. B, Condensed Matter and Materials Physics (2002), 66(1), 012206-012210

It is well known that in addition to the longitudinal modulus, viscoelastic liquids show a shear stiffness at sufficiently high probe frequencies due to structural relaxations. For probe frequencies that ... [more ▼]

It is well known that in addition to the longitudinal modulus, viscoelastic liquids show a shear stiffness at sufficiently high probe frequencies due to structural relaxations. For probe frequencies that are large compared to the structural relaxation frequency, the measured elastic longitudinal and shear moduli become so-called clamped properties (c11∞ and c44∞, respectively). During freezing or polymerization of amorphous liquids, these clamped moduli behave in a strongly nonlinear fashion as a function of temperature or polymerization time. Based on Brillouin spectroscopy data we will show that there exists a linear relation between c11∞ and c44∞ over a large temperature or polymerization time range. Surprisingly, the parameters of this linear relation between the elastic moduli vary only little for different materials. Implications for the nonlinear elastic behavior at the glass transition will be discussed on the basis of mode Grüneisen parameters. [less ▲]

Freezing of Nano-Scaled Fractal Molecules: Dendrimers

in Ferroelectrics (2001), 259(1-4), 27-36

Within this paper we present mono-disperse dendrimers as a new class of ideal canonical glass formers where the frustration mechanism originates from the self similar intramolecular order. Because of ... [more ▼]

Within this paper we present mono-disperse dendrimers as a new class of ideal canonical glass formers where the frustration mechanism originates from the self similar intramolecular order. Because of their fractal intramolecular structure these dendrimers are hardly able to build up a three dimensional translation symmetry necessary to form the crystalline state. Instead they show an unconventional dynamic and static freezing behavior at rather low temperatures. Based on temperature modulated differential scanning calorimetry (TMDSC) and Brillouin spectroscopy (BS) we give further evidences for the existence of an ideal primary glass transition with a thermal glass transition temperature which increases with the generation index of the fractal molecule. However, the primary glass transitions of higher generations do not completely erase the memory of the fractal intramolecular mobility but allow the survival of dynamic processes significant for the freezing of the constituting molecular unit. [less ▲]

Surface Induced Order in Organic and Anorganic Materials on Nano-Structured Poly-tetrafluoroethylene.

in Proceedings of Frontiers in Science and Technology, Advanced Physics Studies Press (2000),7th FSRC FERROELECTRICS-2000 (2000)

Existence of An Intrinsic Glass Transition In A Silicon Rubber: Hypersonic Versus Calorimetric Properties

in Physical Review. B, Condensed Matter and Materials Physics (1999), 60(14), 10037-10041

Time-domain temperature-modulated differential scanning calorimetry and high-performance Brillouin spectroscopy have been used as experimental techniques in order to investigate the effect of the thermal ... [more ▼]

Time-domain temperature-modulated differential scanning calorimetry and high-performance Brillouin spectroscopy have been used as experimental techniques in order to investigate the effect of the thermal glass transition on the specific heat as well as on the acoustic properties, quantities which are intimately related by thermodynamics, but measured at completely different frequencies. Using a siloxane as a model substance, we demonstrate the efficiency of hypersonic relaxations until thermal freezing of the material. Introducing the optoacoustic dispersion function as a sensitive measure for structural relaxations, we show that the high-frequency α relaxations are truncated by the thermal glass transition instead of dying out at much higher temperatures. Moreover, the extrapolated static compliance of the rubbery state goes to zero close to but below the thermal glass transition temperature Tg, indicating the existence of an acoustic instability which is reminiscent of the so-called Kauzmann paradox. [less ▲]