ترغب بنشر مسار تعليمي؟ اضغط هنا

Kinetic stability and energetics of simulated glasses created by constant pressure cooling

126   0   0.0 ( 0 )
 نشر من قبل Grzegorz Szamel
 تاريخ النشر 2016
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We use computer simulations to study the cooling rate dependence of the stability and energetics of model glasses created at constant pressure conditions and compare the results with glasses formed at constant volume conditions. To examine the stability, we determine the time it takes for a glass cooled and reheated at constant pressure to transform back into a liquid, $t_{mathrm{trans}}$, and calculate the stability ratio $S = t_{mathrm{trans}}/tau_alpha$, where $tau_alpha$ is the equilibrium relaxation time of the liquid. We find that, for slow enough cooling rates, cooling and reheating at constant pressure results in a larger stability ratio $S$ than for cooling and reheating at constant volume. We also compare the energetics of glasses obtained by cooling while maintaining constant pressure with those of glasses created by cooling from the same state point while maintaining constant volume. We find that cooling at constant pressure results in glasses with lower average potential energy and average inherent structure energy. We note that in model simulations of the vapor deposition process glasses are created under constant pressure conditions, and thus they should be compared to glasses obtained by constant pressure cooling.

قيم البحث

اقرأ أيضاً

Recently, ultrastable glasses have been created through vapor deposition. Subsequently, computer simulation algorithms have been proposed that mimic the vapor deposition process and result in simulated glasses with increased stability. In addition, r andom pinning has been used to generate very stable glassy configurations without the need for lengthy annealing or special algorithms inspired by vapor deposition. Kinetic and mechanical stability of experimental ultrastable glasses is compared to those of experimental glasses formed by cooling. We provide the basis for a similar comparison for simulated stable glasses: we analyze the kinetic and mechanical stability of simulated glasses formed by cooling at a constant rate by examining the transformation time to a liquid upon rapid re-heating, the inherent structure energies, and the shear modulus. The kinetic and structural stability increases slowly with decreasing cooling rate. The methods outlined here can be used to assess kinetic and mechanical stability of simulated glasses generated by using specialized algorithms.
The time evolution of the pore size distributions and mechanical properties of amorphous solids at constant pressure is studied using molecular dynamics simulations. The porous glasses were initially prepared at constant volume conditions via a rapid thermal quench from the liquid state to the glassy region and allowing for simultaneous phase separation and material solidification. We found that at constant pressure and low temperature, the porous network becomes more compact and the glassy systems relocate to progressively lower levels of the potential energy. Although the elastic modulus and the average glass density both increase with the waiting time, their dependence is described by the power-law function with the same exponent. Moreover, the results of numerical simulations demonstrated that under tensile loading at constant pressure, low-density porous samples become significantly deformed and break up into separate domains at high strain, while dense glasses form a nearly homogeneous solid material.
Unlike crystals, glasses age or devitrify over time to lower their free energy, reflecting their intrinsically non-equilibrium nature. This lack of stability is a serious issue in many industrial applications. Here, we show by numerical simulations t hat devitrification and ageing of quasi hard-sphere glasses are prevented by suppressing volume-fraction inhomogeneities in the spatial arrangement of the particles. A glass of monodisperse quasi hard-sphere particles, known to devitrify and age with `avalanche-like intermittent dynamics, is subjected to small iterative adjustments to particle sizes to make the local volume fractions spatially uniform. We find that this almost entirely prevents structural relaxation and devitrification even in the presence of crystallites. The homogenisation of local volume fractions leads to a dramatic change in the local mechanical environment of each particle, with a clear homogenisation in the number of load-bearing nearest neighbours each particle has. This indicates that we may stabilise glasses by making them more `mechanically homogeneous. Our finding provides a physical principle for glass stabilisation and opens a novel route to the formation of mechanically stabilised glasses.
We report on the results of a molecular dynamics simulation study of binodal glassy systems, formed in the process of isochoric rapid quenching from a high-temperature fluid phase. The transition to vitreous state occurs due to concurrent spinodal de composition and solidification of the matter. The study is focused on topographies of the porous solid structures and their dependence on temperature and average density. To quantify the pore-size distributions, we put forth a scaling relation that provides a robust data collapse in systems with high porosity. We also find that the local density of glassy phases is broadly distributed, and, with increasing average glass density, a distinct peak in the local density distribution is displaced toward higher values.
We demonstrate passive feedback cooling of a mechanical resonator based on radiation pressure forces and assisted by photothermal forces in a high-finesse optical cavity. The resonator is a free-standing high-reflectance micro-mirror (of mass m=400ng and mechanical quality factor Q=10^4) that is used as back-mirror in a detuned Fabry-Perot cavity of optical finesse F=500. We observe an increased damping in the dynamics of the mechanical oscillator by a factor of 30 and a corresponding cooling of the oscillator modes below 10 K starting from room temperature. This effect is an important ingredient for recently proposed schemes to prepare quantum entanglement of macroscopic mechanical oscillators.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا