A Coupled Thermodynamic Model for Transport Properties of Thin Films during Physical Aging

A coupled diffusion model based on continuum thermodynamics is developed to quantitatively describe the transport properties of glassy thin films during physical aging. The coupled field equations are then embodied and applied to simulate the transport behaviors of O2 and CO2 within aging polymeric membranes to validate the model and demonstrate the coupling phenomenon, respectively. It is found that due to the introduction of the concentration gradient, the proposed direct calculating method on permeability can produce relatively better consistency with the experimental results for various film thicknesses. In addition, by assuming that the free volume induced by lattice contraction is renewed upon CO2 exposure, the experimental permeability of O2 within Matrimid® thin film after short-time exposure to CO2 is well reproduced in this work. Remarkably, with the help of the validated straightforward permeability calculation method and free volume recovery mechanism, the permeability behavior of CO2 is also well elucidated, with the results implying that the transport process of CO2 and the variation of free volume are strongly coupled.

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Mathematical Modeling of Thickness Dependent Physical Aging in Polymeric Membranes

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.701.275 ◽

2016 ◽

Vol 701 ◽

pp. 275-280 ◽

Cited By ~ 3

Author(s):

Serene Sow Mun Lock ◽

Kok Keong Lau ◽

Irene Sow Mei Lock ◽

Azmi Mohd Shariff ◽

Yin Fong Yeong ◽

...

Keyword(s):

Free Volume ◽

Physical Aging ◽

Small Deviation ◽

Dual Mode ◽

Lattice Contraction ◽

Volume Relaxation ◽

Implementation Challenges ◽

Wide Range ◽

Dimensional Finite Element ◽

Complex Differential Equations

The drawback of membrane process that reduces its competitive edge with the conventional separation technologies is ascribed to its decline separative performance over time due to the aging nature of polymeric material. The most widely accepted mechanism that has been thought of governing the volume relaxation process over the course of aging is the dual mode mechanism, whereby it is comprised of two components. The first is the “Lattice contraction” mechanism that describes the uniform collapse of free volume throughout the unrelaxed polymer matrix. The second is the “Diffusion of free volume” mechanism from the interior to the surface of the glassy polymer. Albeit acknowledgement of the dual mode mechanism as the contributing factor, previous aging model renders high implementation challenges to characterize the complicated nature of aging evolution, which requires adaptation of high end computational tools to solve the relatively complex differential equations. In this work, the dual mode mechanism governing the physical aging process has been modelled employing a simple one dimensional finite element numerical solution whereby the film has been divided into many finite slices with equal thickness along the depth of the membrane. The applicability of the mathematical model has been validated with experimental aging data, whereby a small deviation is observed between the two over a wide range of film thicknesses and reasonable intuitive explanation pertaining to the parameters is obtained.

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Gas permeation in thin films of “high free-volume” glassy perfluoropolymers: Part I. Physical aging

Polymer ◽

10.1016/j.polymer.2014.09.022 ◽

2014 ◽

Vol 55 (22) ◽

pp. 5788-5800 ◽

Cited By ~ 63

Author(s):

Rajkiran R. Tiwari ◽

Zachary P. Smith ◽

Haiqing Lin ◽

B.D. Freeman ◽

D.R. Paul

Keyword(s):

Thin Films ◽

Free Volume ◽

Physical Aging ◽

Gas Permeation

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Stoichiometry control and electronic and transport properties of pyrochlore Bi2Ir2O7 thin films

Physical Review Materials ◽

10.1103/physrevmaterials.2.114206 ◽

2018 ◽

Vol 2 (11) ◽

Cited By ~ 5

Author(s):

W. C. Yang ◽

Y. T. Xie ◽

X. Sun ◽

X. H. Zhang ◽

K. Park ◽

...

Keyword(s):

Thin Films ◽

Transport Properties ◽

Stoichiometry Control

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Fabrication, micro-structure characteristics and transport properties of co-evaporated thin films of Bi2Te3 on AlN coated stainless steel foils

Scientific Reports ◽

10.1038/s41598-021-83476-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Aziz Ahmed ◽

Seungwoo Han

Keyword(s):

Thin Film ◽

Crystal Structure ◽

Thin Films ◽

Stainless Steel ◽

Substrate Temperature ◽

Transport Properties ◽

Structural Defects ◽

Film Composition ◽

High Substrate ◽

Foil Substrate

AbstractN-type bismuth telluride (Bi2Te3) thin films were prepared on an aluminum nitride (AlN)-coated stainless steel foil substrate to obtain optimal thermoelectric performance. The thermal co-evaporation method was adopted so that we could vary the thin film composition, enabling us to investigate the relationship between the film composition, microstructure, crystal preferred orientation and thermoelectric properties. The influence of the substrate temperature was also investigated by synthesizing two sets of thin film samples; in one set the substrate was kept at room temperature (RT) while in the other set the substrate was maintained at a high temperature, of 300 °C, during deposition. The samples deposited at RT were amorphous in the as-deposited state and therefore were annealed at 280 °C to promote crystallization and phase development. The electrical resistivity and Seebeck coefficient were measured and the results were interpreted. Both the transport properties and crystal structure were observed to be strongly affected by non-stoichiometry and the choice of substrate temperature. We observed columnar microstructures with hexagonal grains and a multi-oriented crystal structure for the thin films deposited at high substrate temperatures, whereas highly (00 l) textured thin films with columns consisting of in-plane layers were fabricated from the stoichiometric annealed thin film samples originally synthesized at RT. Special emphasis was placed on examining the nature of tellurium (Te) atom based structural defects and their influence on thin film properties. We report maximum power factor (PF) of 1.35 mW/m K2 for near-stoichiometric film deposited at high substrate temperature, which was the highest among all studied cases.

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