Intermittent cluster dynamics and temporal fractional diffusion in a bulk metallic glass.

Glassy solids evolve towards lower-energy structural states by physical aging. This can be characterized by structural relaxation times, the assessment of which is essential for understanding the glass' time-dependent property changes. Conducted over short times, a continuous increase of relaxation times with time is seen, suggesting a time-dependent dissipative transport mechanism.

Entering a New Dimension in Powder Processing for Advanced Ceramics Shaping.

Filigree structures can be manufactured via two-photon polymerization (2PP) operating in the regime of nonlinear light absorption. For the first time, it is possible to apply this technique to the powder processing of ceramic structures with a feature size in the range of the critical defect sizes responsible for brittle fracture and, thus, affecting fracture toughness of high-performance ceramics. In this way, tailoring of advanced properties can be achieved already in the shaping process.

Predicting nonlinear physical aging of glasses from equilibrium relaxation via the material time.

The noncrystalline glassy state of matter plays a role in virtually all fields of materials science and offers complementary properties to those of the crystalline counterpart. The caveat of the glassy state is that it is out of equilibrium and therefore exhibits physical aging, i.e.

Time-scale ordering in hydrogen- and van der Waals-bonded liquids.

The time scales of structural relaxation are investigated on the basis of five different response functions for 1,2, 6-hexanetriol, a hydrogen-bonded liquid with a minor secondary contribution, and 2,6,10,15,19,23-hexamethyl-tetracosane (squalane), a van der Waals-bonded liquid with a prominent secondary relaxation process. Time scales of structural relaxation are derived as inverse peak frequencies for each investigated response function. For 1,2,6-hexanetriol, the ratios of the time scales are temperature-independent, while a decoupling of time scales is observed for squalane in accordance with the literature.

Polyamorphism in vapor-deposited 2-methyltetrahydrofuran: A broadband dielectric relaxation study.

Depositing a simple organic molecular glass-former 2-methyltetrahydrofuran (MTHF) onto an interdigitated electrode device via physical vapor deposition gives rise to an unexpected variety of states, as revealed by dielectric spectroscopy. Different preparation parameters, such as deposition temperature, deposition rate, and annealing conditions, lead, on the one hand, to an ultrastable glass and, on the other hand, to a continuum of newfound further states. Deposition below the glass transition temperature of MTHF leads to loss profiles with shape parameters and peak frequencies that differ from those of the known bulk MTHF.

Mechanical and dielectric response within and beyond the linear regime.

In this work a comparison of dielectric and mechanical data is presented based on experiments within the linear response limit and beyond that limit. The linear dynamic and shear-mechanical response is discussed in terms of the molecular supercooled liquid tetramethyl-tetraphenyl-trisiloxane. As the dynamics measured by the two methods depict the same temperature-dependence, the underlying cause for the observed responses is assumed to be identical for both methods, namely structural relaxation.

Dielectric properties of vapor-deposited propylbenzenes.

Dielectric susceptibility data of vapor-deposited films of iso-propylbenzene (IPB) and n-propylbenzene (NPB) have been recorded across a wide range of deposition temperatures, T, mostly below the glass transition temperature, T. The results for the real and imaginary components of dielectric susceptibility are compared with recently published results for 2-methyltetrahydrofuran (MTHF). Common to all three systems are the following: (i) increased kinetic stability seen as higher onset temperature for the transformation to the liquid state for T ≈ 0.

Ultrastable and polyamorphic states of vapor-deposited 2-methyltetrahydrofuran.

This work reports results gained from dielectric spectroscopy on the organic molecular glass-former 2-methyltetrahydrofuran (MTHF), which was deposited onto an interdigitated electrode device by physical vapor deposition. By a suitable selection of preparation parameters (deposition temperature, deposition rate, and annealing conditions), various states of MTHF could be created: ultrastable glass, a liquid state with unusual dielectric properties, or the ordinary liquid state as obtained by supercooling. Observations on kinetic stability as well as on the suppression of dielectric loss in the ultrastable state resemble previous findings for other molecular glass-formers.

Rate exchange rather than relaxation controls structural recovery.

We observe structural recovery after an electric field step by probing the dielectric loss profile near its maximum, which displays a field-induced shift towards lower frequencies. These dynamics display time aging-time superposition (TaTS) for the majority of relaxation modes, thus implying homogeneous recovery dynamics. Although assumed by generally accepted models, the same modes can not be responsible for structural relaxation and for structural recovery, as the former is heterogeneous and the latter is homogeneous regarding the nature of the dynamics.

Emergent interparticle interactions in thermal amorphous solids.

Amorphous media at finite temperatures, be them liquids, colloids, or glasses, are made of interacting particles that move chaotically due to thermal energy, continuously colliding and scattering off each other. When the average configuration in these systems relaxes only at long times, one can introduce effective interactions that keep the mean positions in mechanical equilibrium. We introduce a framework to determine the effective force laws that define an effective Hessian that can be employed to discuss stability properties and the density of states of the amorphous system.

Surfactant adsorption kinetics in microfluidics.

Emulsions are metastable dispersions. Their lifetimes are directly related to the dynamics of surfactants. We design a microfluidic method to measure the kinetics of adsorption of surfactants to the droplet interface, a key process involved in foaming, emulsification, and droplet coarsening.

Controlling molecular transport in minimal emulsions.

Emulsions are metastable dispersions in which molecular transport is a major mechanism driving the system towards its state of minimal energy. Determining the underlying mechanisms of molecular transport between droplets is challenging due to the complexity of a typical emulsion system. Here we introduce the concept of 'minimal emulsions', which are controlled emulsions produced using microfluidic tools, simplifying an emulsion down to its minimal set of relevant parameters.

Structural recovery in plastic crystals by time-resolved non-linear dielectric spectroscopy.

The dielectric relaxation of several different plastic crystals has been examined at high amplitudes of the ac electric fields, with the aim of exploring possible differences with respect to supercooled liquids. In all cases, the steady state high field loss spectrum appears to be widened, compared with its low field limit counterpart, whereas peak position and peak amplitude remain almost unchanged. This field induced change in the loss profile is explained on the basis of two distinct effects: an increased relaxation time due to reduced configurational entropy at high fields which affects the low frequency part of the spectrum, and accelerated dynamics at frequencies above the loss peak position resulting from the added energy that the sample absorbs from the external electric field.

The homogeneous ice nucleation rate of water droplets produced in a microfluidic device and the role of temperature uncertainty.

Ice nucleation was investigated experimentally in water droplets with diameters between 53 and 96 micrometres. The droplets were produced in a microfluidic device in which a flow of methyl-cyclohexane and water was combined at the T-junction of micro-channels yielding inverse (water-in-oil) emulsions consisting of water droplets with small standard deviations. In cryo-microscopic experiments we confirmed that upon cooling of such emulsion samples ice nucleation in individual droplets occurred independently of each other as required for the investigation of a stochastic process.