Search results for "Supercooling"
showing 10 items of 127 documents
GFP-mut2 Proteins in Trehalose-Water Matrixes: Spatially Heterogeneous Protein-Water-Sugar Structures
2007
We report investigations on the properties of nanoenvironments around single-GFP-mut2 proteins in trehalose-water matrixes. Single-GFPmut2 molecules embedded in thin trehalose-water films were characterized in terms of their fluorescence brightness, bleaching dynamics, excited state lifetime, and fluorescence polarization. For each property, sets of approximately 100-150 single molecules have been investigated as a function of trehalose content and hydration. Three distinct and interconverting families of proteins have been found which differ widely in terms of bleaching dynamics, brightness, and fluorescence polarization, whose relative populations sizably depend on sample hydration. The r…
The Ultimate Fate of Supercooled Liquids
2010
In recent years it has become widely accepted that a dynamical length scale {\xi}_{\alpha} plays an important role in supercooled liquids near the glass transition. We examine the implications of the interplay between the growing {\xi}_{\alpha} and the size of the crystal nucleus, {\xi}_M, which shrinks on cooling. We argue that at low temperatures where {\xi}_{\alpha} > {\xi}_M a new crystallization mechanism emerges enabling rapid development of a large scale web of sparsely connected crystallinity. Though we predict this web percolates the system at too low a temperature to be easily seen in the laboratory, there are noticeable residual effects near the glass transition that can account …
Nanoscale heterogeneity if glass-forming liquids: experimental advances
1998
Abstract Recent evidence indicates that in supercooled liquids the cooperativity of molecular motion extends over certain temporal and spatial ranges. A key advance is the experimental and theoretical exploration of higher-order correlation functions that can track the molecular coordinates for more than just two points in time or space. Uncontested experimental determinations of the heterogeneity length scale at the glass transition remain a major goal.
Growing length scales in a supercooled liquid close to an interface
2002
We present the results of molecular dynamics computer simulations of a simple glass former close to an interface between the liquid and the frozen amorphous phase of the same material. By investigating F_s(q,z,t), the incoherent intermediate scattering function for particles that have a distance z from the wall, we show that the relaxation dynamics of the particles close to the wall is much slower than the one for particles far away from the wall. For small z the typical relaxation time for F_s(q,z,t) increases like exp(Delta/(z-z_p)), where Delta and z_p are constants. We use the location of the crossover from this law to the bulk behavior to define a first length scale tilde{z}. A differe…
Static Properties of a Simulated Supercooled Polymer Melt: Structure Factors, Monomer Distributions Relative to the Center of Mass, and Triple Correl…
2004
We analyze structural and conformational properties in a simulated bead-spring model of a non-entangled, supercooled polymer melt. We explore the statics of the model via various structure factors, involving not only the monomers, but also the center of mass (CM). We find that the conformation of the chains and the CM-CM structure factor, which is well described by a recently proposed approximation [Krakoviack et al., Europhys. Lett. 58, 53 (2002)], remain essentially unchanged on cooling toward the critical glass transition temperature of mode-coupling theory. Spatial correlations between monomers on different chains, however, depend on temperature, albeit smoothly. This implies that the g…
Ion transport in the fragile glass former3KNO3-2Ca(NO3)2
1996
The molten salt ${3\mathrm{K}\mathrm{N}\mathrm{O}}_{3}$-2Ca(${\mathrm{NO}}_{3}$${)}_{2}$ has been studied in the frequency range 5 mHz40 GHz and for temperatures 10 KT500 K using impedance spectroscopy. It is found that in the microwave regime the dynamic conductivity traces the primary response. In the radio- and audio-frequency ranges the mobile ion relaxation becomes increasingly decoupled and the time scale and stretching of the response as determined from electrical modulus spectra differ from those obtained by spectroscopies probing the structural response. For T\ensuremath{\gtrsim}360 K minima are detected in the dielectric loss that make possible a comparison with recent mode-coupli…
Shape-persistent V-shaped mesogens—formation of nematic phases with biaxial order
2006
A homologous series of shape-persistent V-shaped molecules has been designed to form the biaxial nematic phase. Phenyleneethynylene moieties are attached to a bent fluorenone unit to create an apex angle of about 90°, which is determined from the single crystal structure. Two mesogens, one symmetric and another unsymmetric, have been synthesized by attaching a cyano group to one or both of the peripheral phenyl units, respectively. These groups introduce local dipoles essential for the formation of the nematic phases. The tendency to form a crystalline phase is reduced by laterally substituted hexyloxy chains which allow the nematic phase to be supercooled to a glassy state. Two of the thre…
Dynamics of nanoparticles in a supercooled liquid
2008
The dynamic properties of nanoparticles suspended in a supercooled glass forming liquid are studied by x-ray photon correlation spectroscopy. While at high temperatures the particles undergo Brownian motion the measurements closer to the glass transition indicate hyperdiffusive behavior. In this state the dynamics is independent of the local structural arrangement of nanoparticles, suggesting a cooperative behavior governed by the near-vitreous solvent.
Secondary relaxation in the glass-transition regime of ortho-terphenyl observed by incoherent neutron scattering.
1992
We report on incoherent-neutron-scattering measurements in the supercooled regime of the van der Waals liquid ortho-terphenyl. A secondary localized relaxational process on the picosecond time scale is found. In accordance with mode-coupling theories of the glass transition, the relaxational dynamics around a critical temperature ${\mathit{T}}_{\mathit{c}}$ decomposes into two time regimes.
Localized Motion in Supercooled Glycerol as Measured by 2 H-NMR Spin-Lattice Relaxation and Incoherent Neutron Scattering
1991
Selectively deuterated glycerol has been subjected to 2H-NMR spin-lattice relaxation and quasi-elastic neutron scattering experiments. The measurements yield relaxation rates and a non-Gaussian Q-dependence of the Debye-Waller factor which are different for the two hydrogen sites. The data analysis shows that below the onset of the glass transition α-process the hydrogens perform a local motion (≈ 10-12 s) in addition to what is expected from harmonic phonons. The resulting mean-square displacements are highly temperature dependent but are significantly smaller than those found in van der Waals glasses. Amplitudes and activation energies of the carbon-bonded and oxygen-bonded hydrogens are …