Molecular Structure Dependence of Out-of-Plane Thermal Diffusivities in Polyimide Films: A Key Parameter for Estimating Thermal Conductivity of Polymers

2010 ◽  
Vol 43 (18) ◽  
pp. 7583-7593 ◽  
Author(s):  
Daisuke Yorifuji ◽  
Shinji Ando
Keyword(s):  
Molecular Structure ◽  
Thermal Conductivity ◽  
Polyimide Films ◽  
Structure Dependence ◽  
Out Of Plane ◽  
Thermal Diffusivities ◽  
Key Parameter

Waxd Study of Low TCE Polyimide Films Formed from Polyamic Acid Blends and Copolymers.

1992 ◽  
Vol 264 ◽  
Author(s):  
Thomas L. Nunes ◽  
Krishna G. Sachdev
Keyword(s):  
Molecular Structure ◽  
Tensile Strength ◽  
Crystallinity Index ◽  
Moisture Uptake ◽  
Chain Segment ◽  
Polyimide Films ◽  
Flexible Chain ◽  
Polyamic Acid ◽  
Out Of Plane ◽  
Molecular Anisotropy

AbstractLow TCE polyimides, typically BPDA-PDA and related materials are well known for their special properties which include low in-plane TCE, up to 3X higher elastic modulus and ultimate tensile strength, and lower moisture uptake relative to the commonly known flexible chain polyimides [1]. These differences are due to the rod-like orientation and highly organized molecular structure of the polyimides that are derived from linear-planar precursors resulting in more anisotropic properties such as the X-Y vs Z-direction TCE [2], and optical as well as dielectric properties.In the present study, we have measured the WAXD patterns of polyimide films formed from BPDA-PDA and BTDA-PDA polyamic acid mixtures and BPDA-BTDA-PDA random copolyamic acids. In order to examine the effect of a highly flexible chain segment on the molecular anisotropy of rod-like polyimides, preliminary WAXD patterns were recorded for films of BPDA-BDAF and a BPDA-PDA-BDAF copolyimide.An in-plane and an out-of-plane crystallinity index, measures of molecular order within the polyimide films studied were estimated from the WAXD patterns. The data are correlated with the various blends and copolymer compositions and discussed in terms of structural implications.

Thermal Conductivity Reduction in Few-Layer Graphene

2011 ◽  
Author(s):  
Dhruv Singh ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Thermal Conductivity ◽  
Weak Coupling ◽  
Phonon Scattering ◽  
Single Layer ◽  
Acoustic Mode ◽  
Single Layer Graphene ◽  
Boltzmann Transport ◽  
Layer Graphene ◽  
Out Of Plane ◽  
Few Layer Graphene

Using the linearized Boltzmann transport equation and perturbation theory, we analyze the reduction in the intrinsic thermal conductivity of few-layer graphene sheets accounting for all possible three-phonon scattering events. Even with weak coupling between layers, a significant reduction in the thermal conductivity of the out-of-plane acoustic modes is apparent. The main effect of this weak coupling is to open many new three-phonon scattering channels that are otherwise absent in graphene. The highly restrictive selection rule that leads to a high thermal conductivity of ZA phonons in single-layer graphene is only weakly broken with the addition of multiple layers, and ZA phonons still dominate thermal conductivity. We also find that the decrease in thermal conductivity is mainly caused by decreased contributions of the higher-order overtones of the fundamental out-of-plane acoustic mode. Moreover, the extent of reduction is largest when going from single to bilayer graphene and saturates for four layers. The results compare remarkably well over the entire temperature range with measurements of of graphene and graphite.

Orientation Specific Thermal Properties of Polyimide Film

2000 ◽  
Vol 123 (3) ◽  
pp. 273-277 ◽  
Author(s):  
Robert J. Samuels ◽  
Nancy E. Mathis
Keyword(s):  
Thermal Conductivity ◽  
Heat Dissipation ◽  
Polyimide Film ◽  
New Materials ◽  
Polyimide Films ◽  
Nondestructive Technique ◽  
Theoretical Understanding ◽  
First Time ◽  
The Relationship ◽  
Transfer Mechanisms

The present study examines the relationship between thermal conductivity and planarity in polyimide films. The samples tested were specially prepared to range in orientation from three dimensionally random to highly planar. The molecular structure and orientation of the polyimide film have been characterized by polarizing microscope techniques, while the thermal conductivity measurements were done using a new rapid nondestructive technique. This correlation represents the first time thermal conductivity has been measured by modified hot wire techniques and related to the internal structure of polyimide. This work contributes to a deeper theoretical understanding of thermal conductivity and heat transfer mechanisms as they relate to orientation. Thermal conductivity evaluation could provide a new tool in the arsenal of structural characterization techniques. This relationship between thermal conductivity and orientation is key for applications of directional heat dissipation in the passive layers of chip assemblies. Such a correlation has potential to speed the development cycles of new materials during formulation as well as assure properties during production.

scholarly journals Thermal transport properties of decagonal quasicrystals and their approximants

2013 ◽  
Vol 1517 ◽  
Author(s):  
Petar Popčević ◽  
Ante Bilušić ◽  
Kristijan Velebit ◽  
Ana Smontara
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
Transport Properties ◽  
Heat Transport ◽  
Thermal Transport ◽  
Strong Relationship ◽  
Decagonal Quasicrystal ◽  
Decagonal Quasicrystals ◽  
Plane Anisotropy ◽  
Out Of Plane

ABSTRACTTransport properties (thermal conductivity, electrical resistivity and thermopower) of decagonal quasicrystal d-AlCoNi, and approximant phases Y-AlCoNi, o-Al13Co4, m-Al13Fe4, m-Al13(Fe,Ni)4 and T-AlMnFe have been reviewed. Among all presented alloys the stacking direction (periodic for decagonal quasicrystals) is the most conductive one for the charge and heat transport, and the in/out-of-plane anisotropy is much larger than the in-plane anisotropy. There is a strong relationship between periodicity length along stacking direction and anisotropy of transport properties in both quasicrystals and their approximants suggesting a decrease of the anisotropy with increasing number of stacking layers.

Thermal Diffusivity of Copper/Linear-low-density Polyethylene Composites

2017 ◽  
Vol 25 (6) ◽  
pp. 447-452
Author(s):  
James K. Carson ◽  
Mohamed Alsowailem
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
High Density Polyethylene ◽  
Relative Increase ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Linear Low Density Polyethylene ◽  
Capacity Data ◽  
Thermal Diffusivities ◽  
Polyethylene Composites

The thermal diffusivities of copper/linear-low-density polyethylene (Cu/LLDPE) composites were measured relative to the thermal diffusivity of pure LLDPE. The relative thermal diffusivities were similar to those obtained for copper/high-density polyethylene composites, but were noticeably different from estimated values derived from thermal conductivity, density and specific heat capacity data for Cu/LLDPE from the literature. The thermal diffusivity of the composite material initially decreased below that of the pure polymer with the addition of a small amount of copper, before increasing above it as more was added. There would appear to be marginal or no benefit from adding less than about 15 to 20% metal by volume to a polymer, since the relative increase in thermal diffusivity only becomes significant for greater volumes.

scholarly journals Phonon hydrodynamics and ultrahigh–room-temperature thermal conductivity in thin graphite

Science ◽  
2020 ◽  
Vol 367 (6475) ◽  
pp. 309-312 ◽  
Author(s):  
Yo Machida ◽  
Nayuta Matsumoto ◽  
Takayuki Isono ◽  
Kamran Behnia
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Wide Temperature Range ◽  
Room Temperature ◽  
Phonon Dispersion ◽  
High Conductivity ◽  
Temperature Range ◽  
A Value ◽  
Out Of Plane ◽  
Intimate Link

Allotropes of carbon, such as diamond and graphene, are among the best conductors of heat. We monitored the evolution of thermal conductivity in thin graphite as a function of temperature and thickness and found an intimate link between high conductivity, thickness, and phonon hydrodynamics. The room-temperature in-plane thermal conductivity of 8.5-micrometer-thick graphite was 4300 watts per meter-kelvin—a value well above that for diamond and slightly larger than in isotopically purified graphene. Warming enhances thermal diffusivity across a wide temperature range, supporting partially hydrodynamic phonon flow. The enhancement of thermal conductivity that we observed with decreasing thickness points to a correlation between the out-of-plane momentum of phonons and the fraction of momentum-relaxing collisions. We argue that this is due to the extreme phonon dispersion anisotropy in graphite.

Increasing Efficiencies of Thermoelectric Devices Through Angular Interface Geometries

2009 ◽  
Author(s):  
D. P. Sellan ◽  
C. H. Amon
Keyword(s):  
Thermal Conductivity ◽  
Figure Of Merit ◽  
Equation Model ◽  
Boltzmann Transport ◽  
Thermoelectric Efficiency ◽  
Thermoelectric Figure ◽  
Subsequent Increase ◽  
Acoustic Mismatch ◽  
Out Of Plane ◽  
Plane Direction

The phonon Boltzmann transport equation model is used to evaluate the reduction of out-of-plane thermal conductivity and subsequent increase in thermoelectric figure of merit when an angular interface is patterned between a germanium thin-film and silicon substrate. According to the acoustic mismatch model, the angular structure reduces the out-of-plane thermal conductivity by spatially redistributing phonons traveling in the out-of-plane direction. Simulation results demonstrate a 43% reduction in out-of-plane thermal conductivity when operating in the fully ballistic regime. This decrease in phononic thermal conductivity would result in an increase of intrinsic thermoelectric efficiency by a factor of 1.75.

Thermal Property Measurement of Thin Aluminum Oxide Layers for Giant Magnetoresistive (GMR) Head Applications

2003 ◽  
Author(s):  
Bahareh Behkam ◽  
Yizhang Yang ◽  
Mehdi Asheghi
Keyword(s):  
Thermal Conductivity ◽  
Areal Density ◽  
Dielectric Constants ◽  
Recording Head ◽  
Magnetic Disks ◽  
Low Dielectric ◽  
Plane Normal ◽  
Thin Aluminum ◽  
Out Of Plane ◽  
Property Measurement

In recent years, the magnetic recording storage industry has developed a growing interest in increasing recording density of the magnetic disks. Since dimensions of the recording head read transducer have been scaled down to increase areal density, all other parameters being equal, the energy required to cause damage by an ElectroStatic Discharge (ESD) event is reduced substantially. The reduction of insulator thickness between the leads and shields, to increase linear density, further lowers the threshold for ESD breakdown voltage. This problem will become increasingly acute with use of a large number of new and exotic passivation materials having low dielectric constants and thermal conductivities. The present work characterizes the thermal transport properties of Al2O3 Gap layer, which are essential to address the ESD failure in GMR head. This study provides data for out-of-plane (normal) thermal conductivity of thin Al2O3 layers. Thermal conductivity data is obtained using steady-state Joule heating and electrical-resistance thermometry technique.

Thermal Performance Enhancement of Glass Interposer

2015 ◽  
Author(s):  
Sangbeom Cho ◽  
Yogendra K. Joshi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Performance ◽  
Lower Cost ◽  
Performance Enhancement ◽  
Vapor Chamber ◽  
Low Loss ◽  
Packaging Technology ◽  
High Electrical Resistivity ◽  
Fundamental Limitations ◽  
Out Of Plane

As demands on performance for mobile electronics continue to increase, traditional packaging technology is facing its limit in number of input/outputs (I/Os) and thermal challenges. Glass interposers offer many advantages over previous packaging technology for mobile electronics, including ultra-high electrical resistivity, low loss, and lower cost at processed interposer levels. However, it has two fundamental limitations; brittleness and relatively low thermal conductivity (∼1 W/mK), compared to Si (∼150 W/mK). This paper presents a study on thermal performance enhancement of glass interposer based on thermal modeling, and compares it with silicon interposer. The model captures in-plane and out-of-plane thermal performance enhancement with copper structures incorporated in the interposer. To further study the effect of advanced cooling schemes on interposer technology, an integrated vapor chamber design is evaluated through computational modeling.

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