An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

The phenomenon whereby sudden changes in helicoidal pitch occur in thin chiral nematic devices with strong surface anchoring has been studied experimentally. This has been done with the aim of examining the underlying process in the context of existing theory. Thin devices (∼2.5 µm thick) containing two commercially available chiral nematic liquid crystals were employed in the study. The samples were chosen for their dependence of pitch on temperature; one exhibits a very slow increase in pitch with increasing temperature (95.6% of the Merck material BL131 in BL130), while the second shows the more common rapid reduction in pitch with increasing temperature (the Merck mixture TM1001). High resolution reflection spectra were obtained for the devices and a numerical fitting algorithm, based on the Berreman 4×4 matrix technique, provided accurate information on changes in the pitch, refractive indices, device thickness and changes in the surface director across the pitch jump region. We demonstrate that changes in refractive index and device thickness are negligible in analysis of the reflection spectra across the pitch jumps. We further show that the pitch changes discontinuously at the pitch jump, with no variation in its value as the process occurs. We find evidence that the surface directors also change by less than 10° during this process in a manner analogous to coiling or uncoiling a constrained spring. This mechanism differs somewhat from others proposed in the literature.     

聚合物电致发光二极管热特性研究

采用ANSYS有限元分析软件中热分析结构单元,对聚合物电致发光二极管(PLED)在光强为1000cd/m2时的热特性进行模拟,获得其温度场、热流分布及温度梯度的分布图,从仿真结果知PLED器件的最高温度为45.968℃,处于PFO-BT发光层,最低温度为45.95℃,处于石英玻璃基底末端.计算得出聚合物发光器件总热阻为1305℃/W,聚合物发光层至石英玻璃基底末端热阻为1℃/W.通过改变PLED器件输入功率、基底材料以及基底厚度3个参数,分别模拟得出其对PLED器件热特性的影响,仿真结果表明器件最高温度TH与输入功率P显现良好的线性关系;不同基底材料对器件温度影响小,负极端为器件主要散热通径;当基底厚度不断增加时,PLED器件最高温度随着增加,而最低温度不断减少,器件总热阻基本不变,发光层至石英基底末端热阻线性增大.     

Characterization of the local temperature in space and time around a developing Drosophila embryo in a microfluidic device

This paper characterizes a microfluidic platform that differentially controls the temperature of each half of a living Drosophila melanogaster fruitfly embryo in space and time (E. M. Lucchetta, J. H. Lee, L. A. Fu, N. H. Patel and R. F. Ismagilov, Nature, 2005, 434, 1134-1138). This platform relies on laminar flow of two streams of liquid with different temperature, and on rapid prototyping in polydimethylsiloxane (PDMS). Here, we characterized fluid flow and heat transport in this platform both experimentally and by numerical simulation, and estimated the temperature distribution around and within the embryo by numerical simulation, to identify the conditions for creating a sharper temperature difference (temperature step) over the embryo. Embryos were removed from the device and immunostained histochemically for detection of Paired protein. Biochemical processes are sensitive to small differences in environmental temperature. The microfluidic platform characterized here could prove useful in understanding dynamics of biochemical networks as they respond to changes in temperature.     

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarising optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system. On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single-handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 μm to 15 μm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/μm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail.     

Determination of pressure in the extradendritic liquid area during solidification

Complex-shaped lamellar graphite iron castings are susceptible to casting defects related to the volume change during solidification. The formations of these recurring defects are caused by the flow of the liquid in the intradendritic area, between the austenite dendrite arms, and in the extradendritic area between the austenite grains. The conditions for the liquid flow, in turn, are determined by the solidification behavior. The present study suggests a new measurement method and a novel calculation algorithm to determine the pressure of the extradendritic liquid during solidification. The method involves a spherical sample suspended in a measurement device, where the temperature and the volume changes are measured during solidification. The calculation algorithm is based on the numerical interpretation of the Clausius–Clapeyron equation where the temperature variation, the volume change and the released latent heat are processed to determine the local pressure of the extradendritic liquid area during solidification.

     

Temperature‐Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix

Temperature‐responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor–acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color‐tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.     

固相微萃取在水样污染物检测中的应用

固相微萃取是一种具有高灵敏度、回收率和重复性等优点的前处理技术,广泛应用于水中痕量污染物的处理,本文从固相微萃取装置、基本原理及其在水样污染物检测的中应用展开介绍,并以固相微萃取作为主题检索词,利用ISI Web of Knowledge中Web of Science引文数据库,对1998年到2012年间的相关文献进行计量分析。结果表明,固相微萃取主要应用于水样前处理,杀虫剂是主要的富集对象,气相、液相色谱以及质谱是常使用的检测器。     

Thermostating in capillary electrophoresis

Summary The use of high voltages across a electrophoresis capillary will increase the temperature of the buffer due to Joule heating. As a result temperature control in CE is rather important since variations in the buffer temperature will result in changes in the pH of the buffer, peak shape, migration time, reproducibility, efficiency, 3-D structure of macromolecular analytes, etc. Six different thermostating systems have been evaluated: (i) natural convection, (ii) fan, (iii) home-made and (iv and v) two commercially available high-speed air and a (vi) liquid thermostated device. In all cases the temperature of the buffer in the capillary is calculated according to the temperature-conductivity relationship. For this purpose two parameters are introduced describing temperature control: the temperature onset (δT) and the temperature rise factor (α). From these results, it can be concluded that high speed air thermostating can be as efficient as liquid thermostating.     

含[BMIM]Cl-ZnCl2和非质子溶剂的凝胶聚合物电解质的合成

以烯类单体MA、MMA、HEMA为基质,通过原位聚合,合成了同时含离子液体[BMIM]Cl-ZnCl2和非质子溶剂的一系列新型凝胶聚合物电解质,用FTIR、AC、TG等方法对其结构和性能进行了表征。研究表明,聚合物电解质具有复合物结构;[BMIM]Cl-ZnCl2和非质子溶剂PC﹑DMC的加入使聚合物电解质的室温离子电导率大大增加,达2.83×10⁻³ S/cm,且与温度的关系符合VTF方程;聚合物电解质的热分解温度大于275 ℃,显示出良好的热稳定性。     

Fast switching and luminance-controlled fringe-field switching liquid crystal device for vehicle display

ABSTRACT

Liquid crystal displays (LCDs) for vehicle displays should exhibit a fast response time in wide temperature range and wide-viewing angle in horizontal and downward directions without grey-scale inversion but limited brightness in the upward direction because the display images can be reproduced in the front window glass of a vehicle, affecting driver’s front visibility. Currently, fringe-field switching (FFS) liquid crystal device is widely commercialised for high resolution and wide-viewing-angle LCD; however, it needs to improve response times and limit the display brightness in the upward direction. As a solution, we propose a homogeneously aligned liquid crystal device in which liquid crystal director does tilt as well as twist deformation in a confined area by both vertical- and fringe-electric fields, exhibiting about two times faster decay response time than that of conventional FFS mode with suppressed luminance in the upward direction. The proposed liquid crystal device can be applied to LCDs for vehicle displays.     

Theoretical investigation of low liquid load and low temperature operation in gas chromatography

The change in resolution resulting from the simultaneous reduction of liquid load and temperature is theoretically treated. The effects of decreases in load and temperature are formulated in terms of a standard reduction (in which the zone to gas velocity ratio is constant) plus any small changes in temperature required to match the observed changes in zone velocity. Taking the standard reduction as the norm. it is found that both the thcrmodynamic (relative peak clution times) and rate (peak spreading) effects favor the liquid load and temperature decreases. This is discussed specifically in relationship to diatomaccous earth and glass beads as the solid support and also to capillary columns.     

Kinetics of poly(ethylene terephthalate) glycolysis by diethylene glycol. I. Evolution of liquid and solid phases

The kinetics of uncatalysed glycolysis, at 220 °C, of poly(ethylene terephthalate) (PET) by diethylene glycol (DEG) in high excess has been studied. An experimental device allowing good separation, at reaction temperature, of the solid and liquid phases was set up.The results suggest that PET is initially depolymerized in the slightly swollen solid phase, by glycolysis of the amorphous interlamellar chains. This mechanism continues until a solid phase of highly crystallized polyester is obtained.The internal tensions engendered by this chemical modification cause cracks, delamination and mechanical disintegration of the polymer. The transfer towards the liquid phase is then strongly accelerated and the solvolysis of the depolymerization products continues in the liquid phase, up to equilibrium.     

Device for filling of small diameter capillaries with stationary phase solutions in liquefied gases

This paper describes a high pressure device for filling small diameter capillaries with stationary phase solutions is described. A liquid is forced into the capillary column with the help of high pressure syringe whose needle (provided with a side opening) is tightened in a PTFE seal. The device allows use of liquefied gas as solvent. A detailed procedure is given for filling the capillary with stationary phase solution. The performance of the device was evaluated by filling 12 m × 15 μm i. d. glass capillary with 6.5 % (w/v) SE-54.     

分子间作用力对咪唑盐介晶相性质的影响

通过对咪唑环1位(N1)取代烷基、3位(N3)取代基及阴离子的修饰合成了一系列具有近晶A (SmA)相的咪唑类离子液晶. 利用差示扫描量热法、单晶衍射、小角度X射线衍射等手段研究了咪唑盐的介晶相温度范围、介晶态的结构, 并测量了部分咪唑盐的各向异性导电率. 结果表明, 咪唑环N1取代烷基、N3取代基及咪唑盐的阴离子会改变分子间范德华力和氢键, 从而对咪唑盐的介晶相性质产生影响. 此外, 当乙烯基引入到咪唑环N3位置时, 咪唑盐相邻的层结构之间形成π-π堆积作用, 不仅有利于介晶态的形成, 同时使氟硼酸类离子液晶具有最大的层间距和最小的各向异性导电率. 这一结果表明, 调控离子液晶的性质时必须综合考虑各种分子间作用力的影响.     

Electroclinic behaviour of polymer doped low molar mass ferroelectric liquid crystals

Recently there has been much interest in the electroclinic effect due to its potential application in high speed optical modulators and grey scale displays. In present materials, however, the electroclinic effect is very dependent on temperature and falls off rapidly with increasing temperature. This limits the useful device operating range. In this paper the electroclinic behaviour of new, side chain polymer doped, low molar mass ferroelectic liquid crystal mixtures is reported. By measuring the rate of change of the electroclinic coefficient with temperature it is shown that the temperature range over which the electroclinic effect exists increases with polymer concentration. Data are also presented on electroclinic response times.     

Temperature selectivity in reversed-phase high performance liquid chromatography

Column temperature plays two important roles in reversed-phase high-performance liquid chromatography (RP-HPLC): control of retention (k) and control of selectivity (a). While changes in retention as a function of temperature are ubiquitous, selectivity changes for any given solute pair are more pronounced for ionized samples and samples with more polar substituents. With many samples, column temperature can be selected in a manner that optimizes resolution. The selectivity effects observed for temperature changes in RP-HPLC generally are complementary to those observed for mobile phase strength changes, so it is often possible to improve resolution by simultaneous optimization of temperature and mobile phase percent organic or gradient steepness. Computer simulation is a powerful tool for such optimization experiments. This paper reviews the influence of temperature on chromatographic selectivity for RP-HPLC.     

New possibility for an organic semiconductor: a smectic liquid crystalline semiconductor having a long conjugated core and two long alkyl chains

We report a new possibility for liquid crystalline organic semiconductors. These materials exhibit smectic liquid crystalline phases, in which the molecules assume a smectic molecular order by self‐assembly. Because of the strong dispersion force among long alkyl chains, on cooling, smectic molecular order was retained at room temperature. A charge transport ability was also retained. The conductivity of a device having smectic liquid crystalline order is about 5×10⁷ that of a device with no smectic order. The current?–?voltage characteristic of the device has a very sharp increase at low threshold voltage (5?V). A high carrier mobility of 1.8×10^‐2 was observed in the smectic phase of one of the compounds studied (e).     

New possibility for an organic semiconductor: a smectic liquid crystalline semiconductor having a long conjugated core and two long alkyl chains

We report a new possibility for liquid crystalline organic semiconductors. These materials exhibit smectic liquid crystalline phases, in which the molecules assume a smectic molecular order by self-assembly. Because of the strong dispersion force among long alkyl chains, on cooling, smectic molecular order was retained at room temperature. A charge transport ability was also retained. The conductivity of a device having smectic liquid crystalline order is about 5×10⁷ that of a device with no smectic order. The current - voltage characteristic of the device has a very sharp increase at low threshold voltage (5 V). A high carrier mobility of 1.8×10^-2 was observed in the smectic phase of one of the compounds studied (e).     

Nanocomposites Based on Antiferroelectric Liquid Crystal (S)-MHPOBC Doping with Au Nanoparticles

Modification of the physical properties of the (S)-MHPOBC antiferroelectric liquid crystal (AFLC) by doping with low concentrations of gold nanoparticles is presented for the first time. We used several complementary experimental methods to determine the effect of Au nanoparticles on AFLC in the metal–organic composites. It was found that the dopant inhibits the matrix crystallization process and modifies the phase transitions temperatures and switching time, as well as increases the helical pitch and spontaneous polarization, while the tilt angle slightly changes. We also showed that both the LC matrix and Au nanoparticles show strong fluorescence in the green light range, and the contact angle depends on the temperature and dopant concentration.     

Development of a DSC method for determination of certain technological parameters of margarine and mixed-fat spread

Nutritional-physiological research of near past decades had established the real nutritional value of fats and oils. In the former theory the nutritional value of fats and oils is influenced mainly by the rate of saturated/unsaturated fats. It was ruled out, and positive, inert or risk physiological effect of every single fatty acid had been established. The health-care effect of omega-3 fatty acid mainly by the favourable (<3:1) rate of omega-6/omega-3 was established, as inert was concerned the saturated C₁₆ fatty acid and the maximal amount of trans-fatty acids carrying health risk in fats was legally regulated in some countries. These nutritional-physiological requirements were mainly fulfilled by margarine producers and the elementary fats were selected in such a way that they should meet these requirements. Our method helps to the producers to quickly determine the amount of the liquid and solid fat at certain temperature and/or to adjust the technological temperature parameters. The main steps of our method are: a./ determination of cooling rate (K min^–1) of the crystallizer device; b./ determination of the rate of liquid/solid fat at 10°C temperature. This value is used for the determination of the rate of fats and oils as a function of technology and required consistency firmness (spread ability); c./ determination of the temperature from the cooling curve where the crystallization of most part of the fat has finished. This value is used for the determination of outlet temperature parameter of product coming out from the crystallizer device for margarines or mixed-fat spreads with water-in-oil system.