Possible Causes of the Change of Dynamics in Glass-Forming Materials Subjected to Reduced Dimension

1996 ◽  
Vol 455 ◽  
Author(s):  
K. L. Ngai ◽  
A. K. Rizos
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Bulk Material ◽  
Three Dimensions ◽  
Radius Of Gyration ◽  
Length Scale ◽  
Glass Forming ◽  
Reduced Dimension

ABSTRACTThere is currently many ongoing investigations of the change in the glass transition temperature when a material is reduced in dimension from the normal bulk state. The reduction in dimension can be accomplished by casting the material as thin films with or without a substrate or putting it in nanometer size pores. In this work, we explore possible causes of the change in dynamics of the bulk material when the glass-former is subjected to such modifications. The existence of a growing cooperative length scale L(T) with decreasing temperature in bulk fragile glass-forming liquids reaching the size of approximately 1.5–2.0 nm at the glass transition temperature is the basis of our consideration. When the reduced dimension is comparable to L(Tg), cooperative dynamics within a lengthscale equal to L(Tg) can no longer be maintained in all three dimensions throughout the sample. The imposed reduction of the cooperative length scale speeds up the dynamics and causes a reduction of the glass transition temperature. For polymeric glass-formers particularly at higher molecular weights, reduction of one dimension in thin films engenders orientation of the polymer chains when their radius of gyration becomes comparable to the film thickness. The latter is known to cause also a reduction of the glass transition temeperature.

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 Physical Aging Behavior of a Glassy Polyether

Polymers ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 954
Author(s):  
Xavier Monnier ◽  
Sara Marina ◽  
Xabier Lopez de Pariza ◽  
Haritz Sardón ◽  
Jaime Martin ◽  
...  
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Physical Aging ◽  
Glassy State ◽  
Aging Behavior ◽  
Scanning Calorimetry ◽  
Narrow Temperature Range ◽  
Glass Forming ◽  
Fast Scanning Calorimetry

The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the α relaxation does not hold true when aging is carried out deep in the glassy state.

Impact of Surface-Modified Nanoparticles on Glass Transition Temperature and Elastic Modulus of Polymer Thin Films

2007 ◽  
Vol 40 (22) ◽  
pp. 7755-7757 ◽  
Author(s):  
Jong-Young Lee ◽  
Kristin E. Su ◽  
Edwin P. Chan ◽  
Qingling Zhang ◽  
Todd Emrick ◽  
...  
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Elastic Modulus ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Polymer Thin Films ◽  
Surface Modified ◽  
Surface Modified Nanoparticles

Variations in the glass transition temperature of polyester with special architectures confined in thin films

Polymer ◽  
2010 ◽  
Vol 51 (1) ◽  
pp. 129-135 ◽  
Author(s):  
M. Erber ◽  
A. Khalyavina ◽  
K.-J. Eichhorn ◽  
B.I. Voit
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature

scholarly journals Long-Term Physical (In)Stability of Spray-Dried Amorphous Drugs: Relationship with Glass-Forming Ability and Physicochemical Properties

Pharmaceutics ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 425 ◽  
Author(s):  
Edueng ◽  
Bergström ◽  
Gråsjö ◽  
Mahlin
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Physicochemical Properties ◽  
Physical Stability ◽  
Glass Forming Ability ◽  
Melt Quenching ◽  
Glass Forming ◽  
Spray Dried

This study shows the importance of the chosen method for assessing the glass-forming ability (GFA) and glass stability (GS) of a drug compound. Traditionally, GFA and GS are established using in situ melt-quenching in a differential scanning calorimeter. In this study, we included 26 structurally diverse glass-forming drugs (i) to compare the GFA class when the model drugs were produced by spray-drying with that when melt-quenching was used, (ii) to investigate the long-term physical stability of the resulting amorphous solids, and (iii) to investigate the relationship between physicochemical properties and the GFA of spray-dried solids and their long-term physical stability. The spray-dried solids were exposed to dry (<5% RH) and humid (75% RH) conditions for six months at 25 °C. The crystallization of the spray-dried solids under these conditions was monitored using a combination of solid-state characterization techniques including differential scanning calorimetry, Raman spectroscopy, and powder X-ray diffraction. The GFA/GS class assignment for 85% of the model compounds was method-dependent, with significant differences between spray-drying and melt-quenching methods. The long-term physical stability under dry condition of the compounds was predictable from GFA/GS classification and glass transition and crystallization temperatures. However, the stability upon storage at 75% RH could not be predicted from the same data. There was no strong correlation between the physicochemical properties explored and the GFA class or long-term physical stability. However, there was a slight tendency for compounds with a relatively larger molecular weight, higher glass transition temperature, higher crystallization temperature, higher melting point and higher reduced glass transition temperature to have better GFA and better physical stability. In contrast, a high heat of fusion and entropy of fusion seemed to have a negative impact on the GFA and physical stability of our dataset.

scholarly journals Influence of grafting on the glass transition temperature of PS thin films

2017 ◽  
Vol 40 (1) ◽  
Author(s):  
Marceau Hénot ◽  
Alexis Chennevière ◽  
Eric Drockenmuller ◽  
Kenneth Shull ◽  
Liliane Léger ◽  
...  
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature

Glass Transition Temperature in Confined Polymers

2006 ◽  
Vol 977 ◽  
Author(s):  
Rahmi Ozisik ◽  
Tong Liu ◽  
Richard W. Siegel
Keyword(s):  
Thin Films ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Nearest Neighbor ◽  
Scanning Calorimetry ◽  
Thin Film Thickness ◽  
Confined Polymers ◽  
Microscope Images ◽  
Scanning Electron

AbstractGlass transition temperature of polyetherimide (PEI) thin films and nanoporous PEI samples was investigated using differential scanning calorimetry. In both of these systems, the glass transition temperature decreased with respect to the bulk value. In the nanoporous system, scanning electron microscope images were used to characterize pore size distribution, and Monte Carlo simulations were performed to calculate the nearest neighbor pore-to-pore distances. Pore-to-pore distances and thin film thickness values were used to establish a quantitative analogy between thin films and nanoporous system.

Conformational analysis and molecular dynamics of glass-forming aromatic thiacrown ethers

2020 ◽  
Vol 22 (32) ◽  
pp. 17948-17959
Author(s):  
Hubert Hellwig ◽  
Andrzej Nowok ◽  
Jan Grzegorz Małecki ◽  
Piotr Kuś ◽  
Agnieszka Jędrzejowska ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Glass Transition ◽  
Transition Temperature ◽  
Dielectric Properties ◽  
Glass Transition Temperature ◽  
Conformational Analysis ◽  
Ring Type ◽  
Glass Forming ◽  
Thiacrown Ethers

The dielectric properties, glass transition temperature and molecular dynamics of thiacrown ethers are strongly dependent on the thiacrown ring type.

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