Electrohydrodynamic Flow in Thick Liquid Crystal Cells

1989 ◽  
Vol 177 ◽  
Author(s):  
David H. Van Winkle ◽  
Jit Gurung ◽  
Rand Biggers
Keyword(s):  
Thermal Conductivity ◽  
Liquid Crystal ◽  
Thermal Transport ◽  
Room Temperature ◽  
Liquid Crystal Cell ◽  
Optical Observations ◽  
Constant Voltage ◽  
Maximum Enhancement ◽  
Flowing Liquid ◽  
Crystal Cells

ABSTRACTThe thermal transport across a thick (0.66 cm) liquid crystal cell has been measured versus applied ac voltage and frequency. These measurements are correlated with the optically observed onset of flow and turbulence in cells as identical as practicable to those used for the thermal transport measurements. In addition, the measurements are compared with reported observations in thin cells. The thermal transport across the liquid crystal is characterized by an effective thermal conductivity Kf. It was found that Kf increases with increasing frequency, at constant voltage, to a maximum enhancement at about 40 Hz at room temperature. Optical observations on thick cells indicate that dynamic columnar domains of flowing liquid crystal are the primary mode of heat transport, as determined by correlating the structure and characteristic lifetime of such domains as a function of voltage and frequency. Optical observations at low voltages suggest that Williams Domains do not exist in these thick cells, and that all observed responses are functions of electric field strength, not applied voltage (as in thin Williams Domain cells).

Thermal Transport in Few-Quintuple Bi2Te3 Thin Films and Nanoribbons

2011 ◽  
Author(s):  
Bo Qiu ◽  
Xiulin Ruan
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Temperature Dependence ◽  
Thermal Transport ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Boundary Scattering ◽  
Nanoporous Films

In this work, thermal conductivity of perfect and nanoporous few-quintuple Bi2Te3 thin films as well as nanoribbons with perfect and zig-zag edges is investigated using molecular dynamics (MD) simulations with Green-Kubo method. We find minimum thermal conductivity of perfect Bi2Te3 thin films with three quintuple layers (QLs) at room temperature, and we believe it originates from the interplay between inter-quintuple coupling and phonon boundary scattering. Nanoporous films and nanoribbons are studied for additional phonon scattering channels in suppressing thermal conductivity. With 5% porosity in Bi2Te3 thin films, the thermal conductivity is found to decrease by a factor of 4–6, depending on temperature, comparing to perfect single QL. For nanoribbons, width and edge shape are found to strongly affect the temperature dependence as well as values of thermal conductivity.

Thermometry and Thermal Transport in Micro/Nanoscale Solid-State Devices and Structures

2001 ◽  
Vol 124 (2) ◽  
pp. 223-241 ◽  
Author(s):  
David G. Cahill ◽  
Kenneth Goodson ◽  
Arunava Majumdar
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Single Crystal ◽  
Time Resolution ◽  
Thermal Transport ◽  
Room Temperature ◽  
Lateral Resolution ◽  
Small Range ◽  
Single Crystal Films ◽  
Crystal Films

We review recent advances in experimental methods for high spatial-resolution and high time-resolution thermometry, and the application of these and related methods for measurements of thermal transport in low-dimensional structures. Scanning thermal microscopy (SThM) achieves lateral resolutions of 50 nm and a measurement bandwidth of 100 kHz; SThM has been used to characterize differences in energy dissipation in single-wall and multi-wall carbon nanotubes. Picosecond thermoreflectance enables ultrahigh time-resolution in thermal diffusion experiments and characterization of heat flow across interfaces between materials; the thermal conductance G of interfaces between dissimilar materials spans a relatively small range, 20<G<200 MW m−2K−1 near room temperature. Scanning thermoreflectance microscopy provides nanosecond time resolution and submicron lateral resolution needed for studies of heat transfer in microelectronic, optoelectronic and micromechanical systems. A fully-micromachined solid immersion lens has been demonstrated and achieves thermal-radiation imaging with lateral resolution at far below the diffraction limit, <2 μm. Microfabricated metal bridges using electrical resistance thermometry and joule heating give precise data for thermal conductivity of single crystal films, multilayer thin films, epitaxial superlattices, polycrystalline films, and interlayer dielectrics. The room temperature thermal conductivity of single crystal films of Si is strongly reduced for layer thickness below 100 nm. The through-thickness thermal conductivity of Si-Ge and GaAs-AlAs superlattices has recently been shown to be smaller than the conductivity of the corresponding alloy. The 3ω method has been recently extended to measurements of anisotropic conduction in polyimide and superlattices. Data for carbon nanotubes measured using micromachined and suspended heaters and thermometers indicate a conductivity near room temperature greater than diamond.

Thermal Conductivity of α-Tetragonal Boron Nanoribbons

2009 ◽  
Author(s):  
Scott W. Waltermire ◽  
Juekuan Yang ◽  
Deyu Li ◽  
Terry T. Xu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Room Temperature ◽  
High Hardness ◽  
Mean Free Path ◽  
Good Oxidation Resistance ◽  
Elemental Boron ◽  
Past Half Century ◽  
Materials Research ◽  
Low Dimensional

Elemental boron has many interesting properties, such as high melting point, low density, high hardness, high Young’s modulus, good oxidation resistance, resulting from its complex crystalline structure from its electron-deficient nature. Boron forms complex crystalline structures according to the various arrangements of B12 icosahedra in the lattice, such as α (B12)- and β (B105)-rhombohedral and α (B50)- and β (B196)-tetragonal boron polymorphs, among others. Even though considerable materials research has been conducted over the past half century on boron and boron-based compounds, investigating their unique structures and corresponding properties, our understanding of this complex class of materials is still poor, compared to some other well-studied materials with much simpler structures such as silicon. Thermal transport studies through bulk boron have been performed mainly on β-rhombohedral and amorphous boron, because of the difficulty to grow high quality bulk α-rhombohedral boron samples [1–3]. Some efforts have been made to measure B12As2, B12P2, AlB12 samples that have an α-rhombohedral form [2,3]. There is almost no information available on α-tetragonal boron. However, Slack predicted the thermal conductivity of α-boron should be ∼200 W/m-K at room temperature, which is 1/2 that of copper. Large phonon mean free path has been predicted for α-boron (from ∼200 nm at room temperature to 6 nm at the Debye temperature), which could lead to interesting thermal transport properties for low dimensional boron structures.

Structures and alignment of anisotropic liquid crystal particles in a liquid crystal cell

RSC Advances ◽  
2014 ◽  
Vol 4 (76) ◽  
pp. 40617-40625 ◽  
Author(s):  
Jong-Hyun Lee ◽  
Tahseen Kamal ◽  
Stephan V. Roth ◽  
Peng Zhang ◽  
Soo-Young Park
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Room Temperature ◽  
Liquid Crystal Cell ◽  
Crystal Cell ◽  
Anisotropic Liquid

Anisotropic porous liquid crystal (LC) particles with ∼60 μm diameters were prepared using microfluidics and directional UV photopolymerization of 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene/4-cyano-4′-pentylbiphenyl (RM257/5CB) mixtures at room temperature in the presence of a magnetic field.

Unusual thermal transport behavior in self-assembled fullerene nanorods

RSC Advances ◽  
2016 ◽  
Vol 6 (72) ◽  
pp. 67509-67513 ◽  
Author(s):  
Hao Tang ◽  
Kunpeng Dou ◽  
Yucheng Xiong ◽  
Feng Wang ◽  
Yang Zhao ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Room Temperature ◽  
Transport Behavior ◽  
Self Assembled

Ultralow thermal conductivity (less than 0.06 W m−1 K−1) is observed for self-assembled C60 nanorods at room temperature.

A Convenient and Reliable Method of Manufacturing Inclined Bulk Graphite for Measuring Thermal Conductivity With TDTR

2019 ◽  
Author(s):  
Yu Zhao ◽  
Hongyang Yu ◽  
Jingjie Sha ◽  
Yunfei Chen
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Room Temperature ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Layered Materials ◽  
Bulk Graphite ◽  
Intrinsic Mechanism ◽  
New Perspective ◽  
The Time Domain

Abstract In this work, in order to study the thermal transport along arbitrary direction in bulk graphite, we develop a simple and convenient method to manufacture inclined bulk graphite applying Focused Ion beam (FIB). Then, we measure the thermal conductivity of inclined bulk graphite with the time-domain thermoreflectance (TDTR) technique and the measured results show that our processing method is reliable. Based on the TDTR measurement of inclined bulk graphite with a tilt angle of 90°, the in-plane thermal conductivity is on the order of 2030 Wm−1 K−1 and the cross-plane thermal conductivity is on the order of 5.5 Wm−1 K−1 at room temperature, which is close to the previously reported results. Our processing and measurement methods provide a new perspective on the study of the intrinsic mechanism of anisotropic thermal transport in anisotropic layered materials.

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