scholarly journals Structure and glass transition of amorphous materials composed of titanium-oxo oligomers chemically modified with benzoylacetone

RSC Advances ◽  
2020 ◽  
Vol 10 (27) ◽  
pp. 15665-15669
Author(s):  
Shinya Oda ◽  
Shinji Kohara ◽  
Ryo Tsutsui ◽  
Mamoru Kasasaku ◽  
Hiromitsu Kozuka
Keyword(s):  
Glass Transition ◽  
Amorphous Materials ◽  
Chemically Modified

Titanium-n-butoxide was hydrolyzed in the presence of benzoylacetone, and the resulting solution was concentrated and dried at 120 or 140 °C to obtain transparent amorphous materials.

On relaxation nature of glass transition in amorphous materials

2017 ◽  
Vol 523 ◽  
pp. 96-113 ◽  
Author(s):  
Damba S. Sanditov ◽  
Michael I. Ojovan
Keyword(s):  
Glass Transition ◽  
Amorphous Materials ◽  
Relaxation Nature

scholarly journals X-ray reflectivity study of the glass transition temperature of thin films

2014 ◽  
Vol 70 (a1) ◽  
pp. C885-C885
Author(s):  
Krassimir Stoev ◽  
Kenji Sakurai
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Amorphous Materials ◽  
Bulk Material ◽  
Grazing Incidence ◽  
X Ray ◽  
Surface And Interface

The glass transition takes place in amorphous materials (like polymers) during heating or cooling, and can be described as reversible transition from a hard and brittle state into a rubber-like state. Although physical properties of the material change significantly during the glass transition, this is not a phase transition of the material. The temperature at which the transition between the glassy and rubbery state occurs is called the glass transition temperature, and this temperature is always lower than the melting temperature. Thermodynamically, the glass transition is associated with transfer of heat between the system and its surrounding and with an abrupt volume change. Previously it was shown that the glass transition temperature of nano-films is different from that of bulk materials [1], which signifies the importance of determining this parameter for such systems. In the current work, we use quick X-ray reflectivity (qXRR) measurements to determine the glass transition temperature of polyvinyl acetate (PVAc). PVAc is rubbery synthetic polymer with the formula (C4H6O2), a density of 1.18 g/cm3, and a glass transition temperature for bulk material of 30oC [2]. Regular X-ray reflectivity measurements are based on θ/2θ scans at grazing incidence and typically require 0.5-1.5 h for a single scan. The qXRR technique is based on simultaneous measurement of the whole angular x-ray reflectivity profile and is suitable for in-situ measurement without moving the sample and/or the x-ray optics. Thus, the qXRR technique allows for very fast measurement of the x-ray reflectivity curves (duration of each scan is typically 0.1–20 sec [3]), which permits studying the time evolution of chemical, thermal, and mechanical changes at the surface and interface of different materials. X-ray reflectivity measurements give information about both density and thickness of thin films, and are suitable for studying glass transition phenomena. Nano-thickness PVAc layers on a Si substrate were examined with the qXRR technique, with x-ray reflectivity scans (each 10-seconds in duration) being recorded while temperature was changed from 20 to 50oC (total of 331 scans over 7 hours and 46 minutes). In the current paper, the experimental setup, the data-processing, and the analysis of the results from the qXRR measurements will be presented.

scholarly journals Emergent solidity of amorphous materials as a consequence of mechanical self-organisation

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Hua Tong ◽  
Shiladitya Sengupta ◽  
Hajime Tanaka
Keyword(s):  
Glass Transition ◽  
Long Range ◽  
Amorphous Materials ◽  
Energy Landscape ◽  
Amorphous Solids ◽  
Zero Temperature ◽  
Nonlocal Correlation ◽  
Potential Energy Landscape ◽  
Stress Transmission ◽  
Self Organisation

Abstract Amorphous solids have peculiar properties distinct from crystals. One of the most fundamental mysteries is the emergence of solidity in such nonequilibrium, disordered state without the protection by long-range translational order. A jammed system at zero temperature, although marginally stable, has solidity stemming from the space-spanning force network, which gives rise to the long-range stress correlation. Here, we show that such nonlocal correlation already appears at the nonequilibrium glass transition upon cooling. This is surprising since we also find that the system suffers from giant anharmonic fluctuations originated from the fractal-like potential energy landscape. We reveal that it is the percolation of the force-bearing network that allows long-range stress transmission even under such circumstance. Thus, the emergent solidity of amorphous materials is a consequence of nontrivial self-organisation of the disordered mechanical architecture. Our findings point to the significance of understanding amorphous solids and nonequilibrium glass transition from a mechanical perspective.

On Fluidization of Borosilicate Glasses in Intense Radiation Fields

2009 ◽  
Author(s):  
Michael Ojovan ◽  
Guenter Mo¨bus ◽  
Jim Tsai ◽  
Stuart Cook ◽  
Guang Yang
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Viscous Flow ◽  
Electron Irradiation ◽  
Amorphous Materials ◽  
Flow Behaviour ◽  
High Electron ◽  
Borosilicate Glasses ◽  
Glassy Materials

The viscosity is rate-limiting for many processes in glassy materials such as homogenisation and crystallisation. Changes in the viscous flow behaviour in conditions of long-term irradiation are of particular interest for glassy materials used in nuclear installations as well as for nuclear waste immobilising glasses. We analyse the viscous flow behaviour of oxide amorphous materials in conditions of electron-irradiation using the congruent bond lattice model of oxide materials accounting for the flow-mediating role of broken bonds termed configurons. An explicit equation of viscosity was obtained which is in agreement with experimental data for non-irradiated glasses and shows for irradiated glasses, first, a significant decrease of viscosity, and, second, a stepwise reduction of the activation energy of flow. An equation for glass-transition temperature was derived which shows that irradiated glasses have lower glass transition temperatures. Intensive electron irradiation of glasses causes their fluidisation due to non-thermal bond breaking and can occur below the glass transition temperature. Due to surface tension forces fluidisation of glasses at enough high electron flux densities can result in modification of nano-size volumes and particles such as those experimentally observed under TEM electron beams.

scholarly journals Structure and Glass Transition Temperature of Amorphous Dispersions of Model Pharmaceuticals with Nucleobases from Molecular Dynamics

Pharmaceutics ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1253
Author(s):  
Ctirad Červinka ◽  
Michal Fulem
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Amorphous Materials ◽  
Computational Study ◽  
Pharmaceutical Ingredients ◽  
Quantitative Accuracy ◽  
Racemic Ibuprofen ◽  
Dynamics Simulations

Glass transition temperature (Tg) is an important material property, which predetermines the kinetic stability of amorphous solids. In the context of active pharmaceutical ingredients (API), there is motivation to maximize their Tg by forming amorphous mixtures with other chemicals, labeled excipients. Molecular dynamics simulations are a natural computational tool to investigate the relationships between structure, dynamics, and cohesion of amorphous materials with an all-atom resolution. This work presents a computational study, addressing primarily the predictions of the glass transition temperatures of four selected API (carbamazepine, racemic ibuprofen, indomethacin, and naproxen) with two nucleobases (adenine and cytosine). Since the classical non-polarizable simulations fail to reach the quantitative accuracy of the predicted Tg, analyses of internal dynamics, hydrogen bonding, and cohesive forces in bulk phases of pure API and their mixtures with the nucleobases are performed to interpret the predicted trends. This manuscript reveals the method for a systematic search of beneficial pairs of API and excipients (with maximum Tg when mixed). Monitoring of transport and cohesive properties of API–excipients systems via molecular simulation will enable the design of such API formulations more efficiently in the future.

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