Thermal Crystal Research Articles

Induced Smectic A Phase through Intermolecular Hydrogen Bonding: Part XVIII: Influence of p-n-Alkyl Benzoic Acids on Thermal and Phase Behavior οf Hydrogen-Bonded Liquid Crystals

Induced Smectic A Phase through Intermolecular Hydrogen Bonding: Part XVIII: Influence of p-n-Alkyl Benzoic Acids on Thermal and Phase Behavior οf Hydrogen-Bonded Liquid Crystals

Contributions on Thermal Behaviour and Crystal Chemistry of Anhydrous Phosphates. XXXXI [1]. Refinement of the Superstructure of FeTi4(PO4)6 – An Example of a Highly Ordered Member of the NASICON Structure Family

AbstractSingle crystals of NASICON type phosphates Mn1.65TiIII/IV4(PO4)6 (black), FeTi4(PO4)6 (orange‐red) and CoTi4(PO4)6 (lavender colour) were grown by chemical vapour transport. The crystal structures of Mn1.65Ti4(PO4)6 and FeTi4(PO4)6 were refined from single crystal data. For the first time a superstructure for a NASICON type phosphate of general formula AIIBIV4(PO4)6 is observed and successfully refined (FeTi4(PO4)6 [data for Mn1.65Ti4(PO4)6 in brackets] rhombohedral, R32 [R3], Z = 6 (3), a = 8.5164(8) [8.5575(17)]Å, c = 41.852(6) [20.898(5)]Å, R1 = 0.053 [0.025], wR2 = 0.136 [0.061], 2598 [1261] independent reflections, 109 [59] variables). For FeTi4(PO4)6 a structure with a highly ordered cation distribution among the octahedral voids and crystal chemical reasonable interatomic distances (2.18 ≤ d(FeII‐O) ≤ 2.20) results. SXRD investigations on CoTi4(PO4)6 reveal also the presence of a superstructure along the NASICON c‐axis (c′= 5cNASICON). A new description of the NASICON structure based on group‐subgroup considerations shows its close relationship to the NiAs structure (3 x NiAs ⇒ 3 x AX ⇒ AB2(XO4)3 ⇒ □AB4(XO4)6).

Beiträge zum thermischen Verhalten und zur Kristallchemie wasserfreier Phosphate. XXXIX

AbstractContributions on the Thermal Behaviour and Crystal Chemistry of Anhydrous Phosphates. XXXIX, Syntheses, Crystal Structures and Structural Systematics of Quaternary Vanadium(IV) Oxidephosphates MIIV2O2(PO4)2 (MII: Co, Ni, Cu)By vapour‐phase assisted solid state reactions single‐crystals of the oxidephosphates α‐CoV2O2(PO4)2 (green), β‐NiV2O2(PO4)2 (yellow), and CuV2O2(PO4)2 (brown) suitable for structural investigations were grown (α‐CoV2O2(PO4)2: P21/c, Z = 2, a = 6.310(1), b = 7.275(1), c = 7.441(2) Å, β = 90.30(2)°, R1 = 0.044, wR2 = 0.083, 1515 independent reflections, 71 variables; β‐NiV2O2(PO4)2: P21/c, Z = 2, a = 7.4013, b = 7.2595, c = 7.4230Å, β = 121.56°, R1 = 0.037, wR2 = 0.084, 1117 independent reflections, 61 variables; CuV2O2(PO4)2: Pbca, Z = 8, a = 7.352(1), b = 12.652(1), c = 14.504(2) Å, R1 = 0.048, wR2 = 0.067, 2886 independent reflections, 136 variables). β‐CoV2O2(PO4)2 and α‐NiV2O2(PO4)2 were obtained as powders only. The α‐forms belong to the α‐Fe2O(PO4) structure family, while the β‐forms are isotypic to NiTi2O2(PO4)2 (Lipscombite/Lazulite structure family). The oxidephosphate structures are characterized by three‐dimensional networks of [PO4] tetrahedra and [MV2O12] groups formed by face‐sharing of [MIIO6] and [VIVO6] octahedra.

Synthesis and characterization of PEO–PCL–PEO triblock copolymers: Effects of the PCL chain length on the physical property of W 1/O/W 2 multiple emulsions

A series of poly(ethylene glycol)- block-poly( ɛ-caprolactone)- block-poly(ethylene glycol) (PEO–PCL–PEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of ɛ-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties of water-in-oil-in-water (W 1/O/W 2) multiple emulsions containing a model reagent, ascorbic acid-2-glucoside (AA2G). In the synthesis, the [CL]/[EO] was varied from 0.11 to 0.31. The molecular weights and compositions of PEO–PCL–PEO were determined by GPC and 1H NMR analyses. Thermal behavior and crystal formation were studied by DSC, XRD, FT-IR, and polarized optical microscopy (POM). Aggregate behavior of PEO–PCL–PEO was confirmed by DLS, UV, and 1H NMR. Morphology and relative stiffness of the W 1/O/W 2 multiple emulsions in the presence of PEO–PCL–PEO were studied by confocal laser scanning microscopy (CLSM) and rheometer. Variation in the [CL]/[EO] significantly affects the crystalline temperature and spherulite morphology of PEO–PCL–PEO. As the [CL]/[EO] increases, the CMCs of PEO–PCL–PEO decreases and the slope of aggregate size reduction against the copolymer concentration becomes steeper except for the lowest [CL]/[EO] value of PEO–PCL–PEO (i.e., P-222). P-222 significantly increases the viscosity of continuous (W 2) phase, which implies the copolymer would exist in the W 2 phase. On the other hand, the triblock copolymers with relatively high [CL]/[EO] ratios mainly contribute to the size reduction of multiple emulsions and the formation of a firm wall structure. The particle size of the multiple emulsion decreases and the elastic modulus increased as [CL]/[EO] increases, confirmed by microscopic and rheometric analyses.

Synthesis, characterisation and liquid crystal properties of 2,5‐bis[5‐alkyl(alkoxy)phenyl‐1,3,4‐oxadiazole]bromobenzenes

A series of new thermal bilateral liquid crystal compounds with the phenylenebis‐1,3,4‐oxadiazole structure was synthesised. The molecular structures of the oxadiazole compounds were confirmed by FT‐IR and 1H NMR spectroscopy, elemental analysis and mass spectrometry. Thermogravimetric analysis indicates that the compounds in an atmosphere of nitrogen have good thermal stability. Measurements using differential scanning calorimetry, polarising optical microscopy and temperature‐dependent wide‐angle X‐ray diffraction indicated that the liquid crystalline properties are related to the length of the end groups. When the end group was tert‐butyl or alkoxy with four and six carbons, the compounds exhibit no liquid crystal phase. However, compounds with end groups containing more than eight carbons show significant bidirectional thermally‐induced liquid crystal properties and the structure of the liquid crystal phase is the lamellar smectic A phase. All the compounds exhibit blue fluorescence.

Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor—Part II: Heat Transfer Results

Measurements using a novel heat flux sensor were performed in an internal ribbed channel representing the internal cooling passages of a gas turbine blade. These measurements allowed for the characterization of heat transfer turbulence levels and unsteadiness not previously available for internal cooling channels. In the study of heat transfer, often the fluctuations can be equally as important as the mean values for understanding the heat loads in a system. In this study, comparisons are made between the time-averaged values obtained using this sensor and detailed surface measurements using the transient thermal liquid crystal technique. The time-averaged heat flux sensor and transient TLC results showed very good agreement, validating both methods. Time-resolved measurements were also corroborated with hot film measurements at the wall at the location of the sensor to better clarify the influence of unsteadiness in the velocity field at the wall on fluctuations in the heat flux. These measurements resulted in turbulence intensities of the velocity and heat flux of 20%. The velocity and heat flux integral length scales were about 60% and 35% of the channel width, respectively, resulting in a turbulent Prandtl number of 1.7 at the wall.

Low temperature nuclear orientation observations of severe neutron activation damage in ( 160 Tb)TbNiAl 4

An unusually large attenuation (approximately 500%) in the low temperature nuclear orientation directional gamma anisotropy from unannealed thermal neutron irradiated single crystal (160Tb)TbNiAl4 has been observed in the region of saturation of the second order nuclear orientation coefficient, B2. It is suggested that the form of the remanent neutron activation recoil damage in unannealed (160Tb)TbNiAl4 is fundamentally electric quadrupolar in origin, as opposed to magnetic dipolar.

Thermography and Thermometry in the Assessment of Diabetic Neuropathic Foot: A Case for Furthering the Role of Thermal Techniques

There are currently 3 established techniques employed routinely to determine the risk of foot ulceration in the patient with diabetes mellitus. These are the assessment of circulation, neuropathy, and foot pressure. These assessments are widely used clinically as well as in the research domain with an aim to prevent the onset of foot ulceration. Routine neuropathic evaluation includes the assessment of sensory loss in the plantar skin of the foot using both the Semmes Weinstein monofilament and the biothesiometer. Thermological measurements of the foot to assess responses to thermal stimuli and cutaneous thermal discrimination threshold are relatively uncommon. Indeed, there remains uncertainty regarding the importance of thermal changes in the development of foot ulcers. Applications of thermography and thermometry in lower extremity wounds, vascular complications, and neuropathic complications have progressed as a result of improved imaging software and transducer technology. However, the uncertainty associated with the specific thermal modality, the costs, and processing times render its adaptation to the clinic. Therefore, wider adoption of thermological measurements has been limited. This article reviews thermal measurement techniques specific to diabetic foot such as electrical contact thermometry, cutaneous thermal discrimination thresholds, infrared thermography, and liquid crystal thermography.

Thermal effect of microbubbles in the focused ultrasound field

High-intensity focused ultrasound (HIFU) has been developed for the treatment of tumor, and additionally the medical applications with microbubbles such as ultrasound imaging have attracted much attention. In the field of the bubble dynamics, it is known that the microbubble is an energy converter of ultrasound mechanical energy to heat when subjected to an acoustic field. The goal is the tissue heating enhanced by microbubbles. In this study, the relationship between the heating effect and the behavior of microbubbles is analyzed. The temperature rise was measured by a thermocouple and a thermal liquid crystal sheet, and the bubble behavior was simultaneously observed with a camera. The ultrasound frequency is 2.2 MHz and the intensity is 100–2000 W/cm2. The temperature rise became larger as the number density of microbubbles (Levovist) around the focal region increased. As the number density became too large, the conversion efficiency from ultrasound energy to heat became smaller because the shielding effect of ultrasound by the existence of too many bubbles became larger. From these results, it is indicated that it is important to choose the optimal conditions of microbubbles and ultrasound in order to control the heat deposition from microbubbles.

Precise Determination of Thermal Expansion Coefficients Observed in 4H-SiC Single Crystals

The coefficient of thermal expansion (CTE) of SiC single crystals is important, in particular, for both designing device assembly and controlling stress distributions in heteroepitaxial thin film structures grown onto SiC substrates. We have performed very precise measurements of the CTEs for SiC single crystals comprising of single 4H polytype PVT-grown in NIPPON Steel Corporation for a temperature range from 123 K to 473 K using a laser interferometry method. This method allows us to directly measure the temperature dependent variation in thermal expansion of the crystal volume with much higher accuracy, and enables us to straightforwardly obtain practical information of CTE data. Furthermore in order to discuss the CTE behavior for a wider temperature range the CTEs at higher temperatures up to 1573 K have been also measured using dilatometer method. The CTE obtained for a nitrogen-doped 4H-SiC single crystal increases continuously from 0.8 ppm/K to 3.1 ppm/K for temperatures of 273 K and 423 K respectively, and further increases to 5.4 ppm/K at 1273 K. We conclude from our data that the CTE variations are likely to be almost independent of the crystal axis directions of SiC from 123 K up to 1573 K.

Anisotropic thermal expansion and magnetostriction ofYNi2B2C single crystals

We present results of anisotropic thermal expansion and low temperature magnetostriction measurementson YNi2B2C single crystals grown by high temperature flux and floating zone techniques. Quantumoscillations of magnetostriction were observed at low temperatures for starting at fields significantly belowHc2 (H<0.7Hc2). Large irreversible, longitudinal magnetostriction was seen in both in-plane and along thec axis directions of the applied magnetic field in the mixedsuperconducting state. Anisotropic uniaxial pressure dependences ofTc were evaluated using results of zero field, thermal expansion measurements.

High diffraction efficiency, broadband, diffraction crystals for use in crystal diffraction lenses

A major goal of the MAX program is to detect and measure gamma rays produced following the nuclear reactions that take place in a supernova explosion. To detect a reasonable number of supernovae, sensitivities of the order of a few times 10-7 γ cm-2sec-1 are needed — much better than possible with current instruments. The approach in the MAX program is to use a crystal diffraction lens to collect photons over a large area and concentrate them on a small well-shielded detector, greatly improving the signal to noise ratio. The crystals need to have both high diffraction efficiency and a relatively broad energy bandwidth. With mosaic crystals there is a trade-off between bandwidth and diffraction efficiency — one can have either high efficiency or large bandwidth, but not both without losing too much intensity through atomic absorption. A recent breakthrough in our understanding of crystal diffraction for high-energy gamma rays has made it possible to develop crystals that have both high diffraction efficiency and a relatively broad energy bandwidth. These crystals have near perfect crystal structure, but the crystalline planes are slightly curved. Such curved planes can be obtained in 3 different ways, by using mixed crystals with a composition gradient, by applying a thermal gradient, and by mechanically bending a near perfect crystal. A series of experiments have been performed on all three types of crystals using high-energy x-ray beams from the Advanced Photon Source at the Argonne National Laboratory. Experiments performed at 3 energies, 93 keV, 123 keV and 153 keV, with both the thermal gradient Si crystals and with the mechanically bent Si crystals, demonstrated that one can achieve diffraction efficiencies approaching 100% with moderate energy bandwidths (ΔE/E=1.4%) and low atomic absorption (transmission = 0.65), in excellent agreement with theory. The use of this type of diffraction crystal is expected to increase the sensitivity of gamma ray telescopes by a factor of 5 over that possible with normal mosaic crystals.

Synthesis, characterization and liquid crystal‐aligning properties of new poly{3‐[4‐(n‐alkyloxy)phenyloxy]pyromellitimide}s

AbstractFour new polypyromellitimides (MCm‐PPIs and MCm‐OPIs, m = 6, 8) that are singly substituted with a flexible n‐alkyloxy side branch at the pyromellitimide ring were prepared by the two‐step polycondensation of 3‐[4‐(n‐alkyloxy)phenyloxy]pyromellitic dianhydrides (MCm‐PMDAs, m = 6, 8) with p‐phenylenediamine (PDA) and 4,4′‐oxydianiline (ODA), respectively. The dianhydride monomers were synthesized from durene via several reaction steps. Inherent viscosities of the precursor poly(amic acid)s ranged from 0.57 to 1.58 dl/g. After chemical structures of the polyimides had been characterized, their thermal properties, crystalline structures, and liquid crystal (LC) aligning abilities on their rubbed thin films were determined and discussed in comparison to the polypyromellitimides that are doubly substituted at the pyromellitimide ring with the same side branches. For all polymers thermogravimetric analysis (TGA) programs showed a typical two‐step degradation behavior with onset temperatures in the 430–455°C range. In X‐ray scattering studies all the samples were found to be amorphous, but the presence of a loosely developed layer structure could be confirmed, in which two main chains gather together to form a double‐strand backbone layer and n‐alkyl branches fill the space between the layers. On the rubbed surfaces of the polyimide thin films LCs uniformly aligned parallel to the rubbing direction with the pre‐tilt angles 5–7° in MCm‐OPIs and 18–32° in MCm‐PPIs. Copyright © 2006 John Wiley &amp; Sons, Ltd.

10303 集束超音波音場における微小気泡を含む媒質内の温度分布(流体(1))

HIFU (High Intensity Focused Ultrasound) treatment combined with microbubbles as a heat transducer has currently been investigated. It has been indicated that microbubbles have a potential to enhance the heat deposition around the focal region of ultrasound. In order to realize this method, it is needed that the coagulation region in the tissue which contains microbubbles is well-controlled. In this study, the temperature distribution in the medium with microbubbles is analyzed in detail. This time, a thermal liquid crystal (TLC) sheet is used for the measurement of temperature distribution in a polyacrylamide gel. In the case of no bubbles, the shape of the high temperature region was ellipse. In the case of some bubbles, the shape grew more complicated and its area became larger. The microbubbles radiate heat energy around them, and the attenuation effect of ultrasound becomes larger. In the case of too many bubbles, the temperature at the geometric focus didn't become so high. The bubbles shield the most of ultrasound energy. It is very important to choose the optimal conditions of microbubble-enhanced HIFU treatment, considering these phenomena.

Spectroscopic, thermal and X-ray crystal structure studies of some bis-(pyrazine-2-carboxylato) nickel(II) complexes

Three nickel(II) complexes [Ni(PC)2(H2O)2], 1, [Ni(PC)2(TU)2], 2 and [Ni(PC)2(ABI)2]· 2(H2O), 3, PC = pyrazine-2-carboxylate, TU = thiourea and ABI = 2-aminobenzimidazole, were synthesized and characterized by elemental analysis, IR spectroscopy and thermal analysis. The complexes were also investigated by single crystal X-ray diffraction analysis. Structures of the monomeric complexes showed nickel(II) chelated to two PC ions from an oxygen atom of carboxylate ion and the adjacent hetero nitrogen atom. The three complexes were crystallized in a monoclinic system with P2 1 /c space group for 1, while 2 and 3 had C2/c space groups. The structure of 1 showed two coordinated water molecules occupying the trans positions of a slightly elongated octahedron. The structure of 2 consisted of two PC ions and two thiourea molecules in trans positions. The structure of 3 was different and showed a highly distorted octahedron with two ABI molecules chelated to the nickel ion in cis positions through their hetero nitrogen atoms. Two water molecules of crystallisation were shown in the structure of 3.

Growth of Relaxor Ferroelectric Single Crystals PbZn1/3Nb2/3O3 (PZN) by High Temperature Solution Growth

The effects of Lead oxide (as solvent) content in the perovskite phase formation in spontaneous growth of PZN single crystal have been studied. In spite of adopting columbite route, 50 wt% of solvent leads to the growth of undesirable pyrochlore phase. With the increase of solvent content, the probability of formation of perovskite phase was found to increase. Growth run performed with PZN/PbO weight ratio 35:65 resulted the growth of crystals with > 98% perovskite phase present in it. With the help of oscillating thermal profile PZN single crystal was grown of the size 10× 10× 8 mm 3 .

Contributions on Thermal Behaviour and Crystal Chemistry of Anhydrous Phosphates. XXXIV [1] Oxygen Equilibrium Pressures in Ternary Systems M / P / O (M = Co, Ni) and Heats of Formation of Anhydrous Cobalt(II) and Nickel(II) Phosphates

AbstractOxygen equilibrium pressures have been measured in the temperature range 800 °C to 1000 °C by coulometric/potentiometric techniques for several equilibrium regions in the ternary systems M / P / O (M = Co, Ni). In both systems oxygen coexistence pressures of three‐phase equilibrium solids phosphide/phosphate are about 3 to 5 orders of magnitude smaller than p(O2) above the corresponding Ms / MOs system.Heats of formation ΔfH°298 and standard entropies S°298 for the phosphates have been obtained from 2nd and 3rd law evaluation of the temperature dependence of the oxygen coexistence pressures. Thermodynamic data from literature for the phosphides of cobalt and nickel and estimated heat capacities for the anhydrous phosphates Co3(PO4)2, Co2P2O7, Ni3(PO4)2, Ni2P2O7 and Ni2P4O12 were used for these calculations. Thus obtained enthalpies and entropies are compared to results from thermodynamic modelling of observed solid phase equilibria in the ternary systems M / P / O (M = Co, Ni).

Multi-dimensional heat flux reconstruction using narrow-band thermochromic liquid crystal thermography*

An inverse algorithm is developed to reconstruct multi-dimensional surface heat flux using transient surface temperature measurements provided by narrow-band thermal liquid crystals (TLC) or phase-change material (PCM). In this thermographic technique, the information provided is the time it took a certain location to reach the characteristic temperature of the TLC or PCM. A quadratic functional to be minimized is formulated. The Levenberg-Marquardt method and genetic algorithms are used to minimize the functional. It is shown that GA's can be used successfully to retrieve surface heat flux distributions with significant error in input times to arrival at the TLC or PCM critical temperature.

Specific heat capacity and thermal conductivity ofNdGaO3 and LaAlO3 single crystals at low temperatures

For single-crystalline samples of NdGaO3 and LaAlO3 thespecific heat capacity cp(T) (temperature ranges 2.24-100 K and4.35-350 K, respectively) and the thermal conductivity κ(T)(15-300 K) are determined. From an analysis of the specific heat capacityof NdGaO3 the crystalline electric field contribution and thehigh-temperature tail from the magnetic ordering are extracted. Thethermodynamic standard values for enthalpy and entropy at 298.15 K arecalculated: H° = 18.40(18) kJ mol-1, S° = 121.0(1.2) J mol-1 K-1 (NdGaO3); H° = 14.57(22) kJ mol-1, S° = 86.6(1.3) J mol-1 K-1(LaAlO3). Significant contributions to the entropy from the magneticordering of the Nd3+ ions are included in the calculation. A recentlypublished value of the standard entropy for the related NdAlO3 isre-evaluated (S° = 105.1(3) J mol-1 K-1) in this context.The thermal conductivity of NdGaO3 at low temperatures is limited byspin-wave scattering, while that of LaAlO3 in the same temperaturerange is lessened by the short phonon mean free path, which is due to thepresence of twin domains.

Novel polypyromellitimides and their liquid crystal aligning properties

Various aromatic poly{3,6-bis[(4-n-alkyloxy)phenyloxy]-pyromellitimide}s {poly(Ar-C m -PMDA)s, m = 1, 4, 8, 12] were prepared in film form by routine two-step condensation of 3,6-bis[(4-n-alkyloxy)phenyloxy]pyromellitic dianhydrides (C m -PMDAs) with various aromatic diamines. After characterization of their chemical structures their solution, thermal and liquid crystal (LC)-aligning properties in terms of pretilt angle at various rubbing densities were measured and discussed with respect to their backbone structures. All polyimide films showed excellent thermal stability and homogeneous LC alignment, but the poly(p-phenylene-C 12 -PMDA) exhibited completely homeotropic alignment while the pretilt angle values of poly(p-phenylene-C 8 .-PMDA) varied with varying rubbing density.