114 research outputs found
The relationship between fragility, configurational entropy and the potential energy landscape of glass forming liquids
Glass is a microscopically disordered, solid form of matter that results when
a fluid is cooled or compressed in such a fashion that it does not crystallise.
Almost all types of materials are capable of glass formation -- polymers, metal
alloys, and molten salts, to name a few. Given such diversity, organising
principles which systematise data concerning glass formation are invaluable.
One such principle is the classification of glass formers according to their
fragility\cite{fragility}. Fragility measures the rapidity with which a
liquid's properties such as viscosity change as the glassy state is approached.
Although the relationship between features of the energy landscape of a glass
former, its configurational entropy and fragility have been analysed previously
(e. g.,\cite{speedyfr}), an understanding of the origins of fragility in these
features is far from being well established. Results for a model liquid, whose
fragility depends on its bulk density, are presented in this letter. Analysis
of the relationship between fragility and quantitative measures of the energy
landscape (the complicated dependence of energy on configuration) reveal that
the fragility depends on changes in the vibrational properties of individual
energy basins, in addition to the total number of such basins present, and
their spread in energy. A thermodynamic expression for fragility is derived,
which is in quantitative agreement with {\it kinetic} fragilities obtained from
the liquid's diffusivity.Comment: 8 pages, 3 figure
Some remarks on the low-energy excitations in glasses: interpretation of Boson peak data
Composites prepared from the waterborne polyurethane cationomers-modified graphene. Part II. Electrical properties of the polyurethane films
Lakes beneath the ice sheet: The occurrence, analysis, and future exploration of Lake Vostok and other Antarctic subglacial lakes
Airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of Antarctica. The largest, Lake Vostok, is more than 250 km in length and 1 km deep. Subglacial lakes occur because the ice base is kept warm by geothermal heating, and generated meltwater collects in topographic hollows. For lake water to be in equilibrium with the ice sheet, its roof must slope ten times more than the ice sheet surface. This slope causes differential temperatures and melting/freezing rates across the lake ceiling, which excites water circulation. The exploration of subglacial lakes has two goals: to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors. The technological developments required for in situ measurements mean, however, that direct studies of subglacial lakes may take several years to happen
Through vial impedance spectroscopy (TVIS): A novel approach to process understanding for freeze-drying cycle development
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Through vial impedance spectroscopy (TVIS) provides a new process analytical technology for monitoring a development scale lyophilization process, which exploits the changes in the bulk electrical properties that occur on freezing and subsequent drying of a drug solution. Unlike the majority of uses of impedance spectroscopy, for freeze-drying process development, the electrodes do not contact the product but are attached to the outside of the glass vial which is used to contain the product to provide a non-sample-invasive monitoring technology. Impedance spectra (in frequency range 10 Hz to 1 MHz) are generated throughout the drying cycle by a specially designed impedance spectrometer based on a 1 GΩ trans-impedance amplifier and then displayed in terms of complex capacitance. Typical capacitance spectra have one or two peaks in the imaginary capacitance (i.e., the dielectric loss) and the same number of steps in the real part capacitance (i.e., the dielectric permittivity). This chapter explores the underlying mechanisms that are responsible for these dielectric processes, i.e., the Maxwell-Wagner (space charge) polarization of the glass wall of the vial through the contents of the vial when in the liquid state, and the dielectric relaxation of ice when in the frozen state. In future work, it will be demonstrated how to measure product temperature and drying rates within single vials and multiple (clusters) of vials, from which other critical process parameters, such as heat transfer coefficient and dry layer resistance, may be determined
Development of a Simple Dielectric Analysis Module for Online Cure Monitoring of a Commercial Epoxy Resin Formulation
Detection of dengue viruses using reverse transcription-loop-mediated isothermal amplification
Molecular kinetics in amorphous solids
This essay is based on a lecture presented on the occasion of the award of Le Prix Aniuta Winter-Klein by l’Académie des Sciences, on 4 June, 1992 at the Institut National des Sciences Appliquées, Villeurbanne, France. It describes the various aspects of molecular motions in amorphous solids and their consequences for the thermodynamic, mechanical and electrical properties of such solids. After discussing the nature of disorder, a central theme, namely that the properties of an amorphous solid are determined by the presence of spatially random regions of frozen-in density fluctuations in its molecular or atomic structure, has been developed. Localized diffusion involving both phonon-assisted tunneling, and thermal activation, in these regions contribute to the thermodynamic and kinetic behaviours of a solid and liquid. The number of such regions, or the extent of heterogeneity in an amorphous structure, determines the temperature and time-dependence of the properties of an amorphous solid
Response to the comment on ‘Time-dependent paths, fictive temperatures and residual entropy of glass’
Amorphization of ice by collapse under pressure, vibrational properties, and ultraviscous water at 1 GPa
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