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 ▲]

Temperature modulated Differential Scanning Calorimetry: The Dynamic Aspect of the Specific Heat Capacity and its Relation to Entropy Production

in Beiträge zur Experimentalphysik, Didaktik und computergestützten Physik (2007)

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 ▲]

A Reply to the Comment by A. Rivera et al.

in Physical Review Letters (2005), 94

Different glassy states, as indicated by a violation of the generalized Cauchy relation.

in New Journal of Physics (2003), 5(80), 1-11

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus can be measured in addition to the longitudinal modulus already well above the thermal glass ... [more ▼]

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus can be measured in addition to the longitudinal modulus already well above the thermal glass transition. On slow cooling of the liquid through the thermal glass transition temperature Tg, both moduli show a kink-like behaviour and the function follows a generalized Cauchy relation (gCR) defined by the linear relation , which completely hides the glass transition. In this work we show experimentally that on fast cooling this linear transformation becomes violated within the glassy state, but that thermal ageing drives the elastic coefficients towards the gCR, i.e. towards a unique glassy state. [less ▲]

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 ▲]

Elastic properties of single-crystalline and consolidated nano-structured yttrium oxide at room temperature.

in Journal of Physics : Condensed Matter (2000), 12(25), 5403-5409

High resolution Brillouin spectroscopy was used to characterize the elastic stiffness properties of consolidated nano-crystalline yttrium oxide as well as of the related single-crystalline state. Defect ... [more ▼]

High resolution Brillouin spectroscopy was used to characterize the elastic stiffness properties of consolidated nano-crystalline yttrium oxide as well as of the related single-crystalline state. Defect enriched grain boundaries are discussed as sources for the extremely soft elastic properties of the nano-crystalline state. [less ▲]

On the Influence of Nano-Scaling on the Glass Transition of Molecular Liquids

in Nanostructured Materials (1999), 12(1), 519-522

The nature of the glass transition is still a matter of debate. We used temperature modulated DSC (TMDSC) and Brillouin spectroscopy ( BS ) to investigate the freezing behaviour of canonical glasses ... [more ▼]

The nature of the glass transition is still a matter of debate. We used temperature modulated DSC (TMDSC) and Brillouin spectroscopy ( BS ) to investigate the freezing behaviour of canonical glasses ( salol and di-n-butyl-phtalate (DBP)) confined to controlled pore glasses (CPG) with pore diameters between 2.5 and 20 nm. The temperature behaviour of the heat capacity of the composite system deviates from the bulk fluid properties and we interpret the remaining kink-like anomaly at Tg as a static glass transition. In smaller pores Tg is only slightly shifted to lower temperatures. This operative Tg is in good agreement with sound velocity data showing a sharp kink at Tg. The working hypothesis of the existence of a static glass transition is supported by the fact that the -relaxation process disappears with decreasing pore diameter. [less ▲]