Search results for "Glass transition"

Statics and Dynamics of a Glassy Crystal: A NMR- and Neutron Scattering Investigation of (NaCl) 0.35 (NaCN) 0.65

1987

The statics and the dynamics of the glass transition in (NaCl)0.35(NaCN)0.65 have been investigated by inelastic neutron scattering and are directly compared to NMR results. Insight into the relaxation dynamics is gained via the temperature dependence of the transverse acoustic phonon modes and via the spin relaxation time T1. The statics of the system is reflected by the growth of a central peak and by the distribution of electric-field gradients. Both quantities are directly related to the glass order parameter. The temperature dependence of the order parameter provides experimental evidence that in NaCl:NaCN mixed crystals the glass transition is dominated by random fields rather than by…

2015

In many technical applications, but also in natural processes like ice nucleation in clouds, crystallization proceeds in the presence of stresses and flows, hence the importance to understand the crystallization mechanism in simple situations. We employ molecular dynamics simulations to study the crystallization kinetics of a nearly hard sphere liquid that is weakly sheared. We demonstrate that shear flow both enhances and suppresses the crystallization kinetics of hard spheres. The effect of shear depends on the quiescent mechanism: suppression in the activated regime and enhancement in the diffusion-limited regime for small strain rates. At higher strain rates crystallization again become…

Nondiverging vortex pinning barriers at low current densities across the putative elastic vortex-glass–vortex-liquid transition inYBa2Cu3O7−δfilms

2001

A detailed analysis of the electric field--current density $(E\ensuremath{-}J)$ characteristics of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films across the putative thermally induced elastic vortex-glass--vortex-liquid transition predicted by the $E(J)$ curve scaling reveals that the expected increase of the collective pinning barriers with decreasing J is cut off in the low-$J$ region, signaling a dissipation process which involves the plastic deformation of the vortex system. The temperature and magnetic field dependence of the pinning barriers at low J does not change across the scaling-predicted glass transition line. For the investigated m…

Quantification of low levels of amorphous content in sucrose by hyperDSC.

2005

A method was developed for the quantification of low levels of amorphous content in sucrose with hyperDSC. The method was based on the fact that the change of specific heat at the glass transition is linearly proportional to the amorphous content. It was found out that as annealing time increased, the glass transition temperature moved to a higher temperature and the change of specific heat increased. DeltaC(p) for annealed totally amorphous sucrose was 0.761+/-0.012 Jg(-1) degrees C(-1). Synthetic mixtures with various proportions of crystalline and amorphous sucrose were prepared. The following linear regression between DeltaC(p) and amorphous content was obtained: DeltaC(p)=0.0075x - 0.0…

The molecular dynamics of thermoreversible networks as studied by broadband dielectric spectroscopy

1995

Polybutadienes modified by a small number of 4-phenyl-1,2,4-triazoline-3,5-dione form thermoreversible networks via hydrogen bonding between the polar stickers. The molecular dynamics of systems with different contents of polar stickers are investigated by broadband dielectric spectroscopy in the frequency regime of 10−1–109 Hz. Unmodified polybutadiene shows two relaxation processes, the α-relaxation which is correlated to the dynamic glass transition of the polybutadiene, and a β-relaxation corresponding to a local relaxation of polybutadiene segments. In the polar functionalized systems, besides these two relaxations, an additional relaxation process (called α*) is observed, which occurs…

Effective hydrostatic limits of pressure media for high‐pressure crystallographic studies

2007

The behavior of a number of commonly used pressure media, including nitrogen, argon, 2-propanol, a 4:1 methanol–ethanol mixture, glycerol and various grades of silicone oil, has been examined by measuring the X-ray diffraction maxima from quartz single crystals loaded in a diamond-anvil cell with each of these pressure media in turn. In all cases, the onset of non-hydrostatic stresses within the medium is detectable as the broadening of the rocking curves of X-ray diffraction peaks from the single crystals. The onset of broadening of the rocking curves of quartz is detected at ∼9.8 GPa in a 4:1 mixture of methanol and ethanol and at ∼4.2 GPa in 2-propanol, essentially at the same pressures …

Shear moduli of two dimensional binary glasses

2012

The shear moduli of two-component glasses in two dimensions are studied within mode coupling theory. Varying the concentration, strong mixing effects are observed along the glass transition lines for two interaction potentials. Nonoverlapping disks with size ratios between 0.3 and 0.9, and point particles interacting with (magnetic) dipoles of strength ratio between 0.1 and 0.6 are considered. Equilibrium structure factors (partially obtained from Monte Carlo simulations) and glass form factors, and perturbative calculations show that a softening of the elastic shear constant of glass upon adding another component arises from a dilution effect of the majority component. For very disparate m…

Triphenylmethyl and triphenylsilyl based molecular glasses for photonic applications

2015

Triphenylmethyl and triphenylsilyl structural fragments can be used to obtain glass forming, solution processable materials from polar chromophore molecules. Large number of compounds has been synthesized taking advantage of this approach, making it possible to identify some structure-property relations. Regarding the non-linear optical (NLO) properties of the given materials it is evident that triphenylmethyl groups help shielding unwanted NLO efficiency limiting dipolar interactions between polar chromophores in solid films. Chromophore stacking is still observed for compounds with large dipole momentum values. The glass transition temperatures of the compounds increase with the molecular…

Predictability of drug encapsulation and release from propylene carbonate/PLGA microparticles.

2020

Abstract Key parameters for microparticle-based parenteral depot formulation development are entrapment efficiency and sustained drug release, which both depend on the intermolecular affinity of the components. Here, partial solubility parameters were evaluated as descriptors for 21 drug substances and 3 polymers in propylene carbonate (PC). Out of these 21 drug substances, eight BCS class II substances (celecoxib, clotrimazole, erythromycin, ibuprofen, indomethacin, itraconazole, lopinavir and ritonavir) were encapsulated using PLGA (Poly(DL-lactide-co-glycolide)) as polymer matrix and PC as a polar aprotic solvent in order to assign microparticle properties to potential affinity-related i…

Thermal and optical properties of red luminescent glass forming symmetric and non symmetric styryl-4H-pyran-4-ylidene fragment containing derivatives

2012

Abstract Dyes with amorphous structure deposited from organic solvents and having good fluorescence properties show potential for photonic device applications. Organic glass-forming symmetric and non symmetric styryl- derivatives of 2(2,6-substituted-4H-pyran-4-ylidene)-malononitrile (it has backbone of known laser dye 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran), 2(2,6-substituted-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione and 2(2,6-substituted-4H-pyran-4-ylidene)-pyrimidine-2,4,6(1H,3H,5H)-trione were synthesized and investigated. Glass transition temperatures higher than 110 °C were achieved. The absorption bands in dichloromethane solution cover the spectral regi…