arXiv subjects

Marta Gonzalez-Silveira

Publications and source records attributed to Marta Gonzalez-Silveira.

3 recordsLinked to original sources

arXiv2023

Real-time microscopic view of the relaxation of a glass

The understanding of glassy dynamics above the devitrification temperature of a glass remains poorly understood. Here, we use real-time AFM imaging to build a spatio-temporal map of the relaxation dynamics of a highly stable glass into its supercooled liquid. This new methodology enables a direct visualization of the progression of the liquid phase and clarifies and quantifies the presence of localized fast mobility regions separated by giant length scales. Our data permit to establish a clear correlation between dynamic length and time scales in glasses. This approach may also be applicable to unveil the microscopic structure and dynamics of other glass forming systems with much shorter length and time scales, including liquid-cooled glasses.

physics.app-ph↗

arXiv2023

Experimental evidence of a crossover between cooperative relaxation and liquid growth dynamics

In stark contrast with the conventional understanding of the glass transition, where the transition from glass to liquid appears as a dynamic process where atoms/molecules cooperatively relax into the equilibrium phase, we experimentally show that the nature of the glass transition depends at a given temperature on the ratio between the relaxation time of the glass, τ_glass, taken as its transformation time, and the alpha relaxation time, τ_α. Although the relaxation of liquid-cooled glasses is not totally synchronous, due to the existence of a distribution of relaxation times, there has been no clear observation of phase separation. However, at temperatures at which τ_glass/τ_α is large, high mobility regions nucleate into the liquid phase that subsequently grow by dynamic facilitation before, or while, cooperative glass relaxation sets into play. On the contrary, at temperatures associated to smaller τ_glass/τ_α the glass transition proceeds by cooperative relaxation dynamics all across the material. This behavior is independent of the experimental procedure or protocol to produce the glass.

cond-mat.dis-nn↗

arXiv2017

Evidence of thermal transport anisotropy in stable glasses of vapour deposited organic molecules

Vapour-deposited organic glasses are currently in use in many optoelectronic devices. Their operation temperature is limited by the glass transition temperature of the organic layers and thermal management strategies become increasingly important to improve the lifetime of the device. Here we report the unusual finding that molecular orientation heavily influences heat flow propagation in glassy films of small molecule organic semiconductors. The thermal conductivity of vapour-deposited thin-film semiconductor glasses is anisotropic and controlled by the deposition temperature. We compare our data with extensive molecular dynamics simulations to disentangle the role of density and molecular orientation on heat propagation. Simulations do support the view that thermal transport along the backbone of the organic molecule is strongly preferred with respect to the perpendicular direction. This is due to the anisotropy of the molecular interaction strength that limit the transport of atomic vibrations. This approach could be used in future developments to implement small molecule glassy films in thermoelectric or other organic electronic devices.

cond-mat.mtrl-sci↗