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131.
We investigate the properties of the nematic mixture BL037 with terahertz time domain spectroscopy. Both, the refractive indices and absorption coefficients for extraordinary and ordinary polarization are extracted from the measured data. Besides the frequency dependence of the material parameters we also study their temperature dependence and compare the results to the properties of the pure liquid crystals. We find that the mixture exhibits the largest terahertz birefringence reported so far for liquid crystals. Thus, BL037 is an ideal candidate for THz devices. 相似文献
132.
利用激光诱导击穿光谱技术对CuSO4溶液中的Cu元素浓度进行实验测量。利用配置的七种浓度的CuSO4溶液,采用统计探索性数据分析方法给出了Cu元素定标曲线,其拟合度系数R2大于0.98,激光诱导击穿光谱的平均相对偏差值为6.9%,Cu元素的平均最小检测限为12ppm。利用去一交互检验方法采用分析谱线CuⅠ324.75nm和CuⅠ327.40nm对应的七种溶液的平均测量相对误差分别为6.52%和5.86%。当Cu元素浓度在10ppm时实验相对误差较大,其值为10.3%,而浓度达到2 000ppm时相对误差值减小,仅为1.1%,说明LIBS技术在溶液较低元素浓度检测方面的准确度有待提高。研究结果表明激光诱导击穿光谱技术在环境水污染重金属元素检测方面具有潜在的应用前景。 相似文献
133.
The depolarisation ratio for the Raman-active phenyl stretching mode has been measured over the whole of the mesophase range,
and the orientational order parameters deduced, in the uniaxial nematic liquid crystal octylcyanobiphenyl (8CB). Linearly
polarised light was incident normally on a homogeneously aligned sample and a χ2 minimisation routine performed on the 360° depolarisation ratio profile. The order parameters 〈P
200〉 and 〈P
400〉 , together with the differential polarisability ratio, r , are used as fitting parameters and measured as a function of temperature. Interestingly, we show that the value for r , conventionally measured in the isotropic phase and assumed to remain constant, has a clear temperature dependence, ranging
from -0.032±0.008 in the isotropic phase through to -0.245±0.015 at the nematic-to-smectic A phase transition. The measured
order parameters 〈P
200〉 and 〈P
400〉 varied from 0.35- 0.55±0.02 and 0.180- 0.245±0.02 , respectively, across the 8 ° C wide nematic phase range. The values of both 〈P
200〉 and 〈P
400〉 are in excellent agreement with theory, but it is noteworthy that 〈P
400〉 shows a much better quantitative match than has been reported in previous work. Crucially the temperature dependence of
r is shown to be a contributing factor in the low 〈P
400〉 values that have been conventionally reported from Raman scattering measurements. The potential for fitting the entire angular
depolarisation ratio distribution in liquid crystalline systems that are described by more order parameters, specifically
biaxial materials, is discussed. 相似文献
134.
Oettel M Domínguez A Tasinkevych M Dietrich S 《The European physical journal. E, Soft matter》2009,28(2):99-111
The elastic and capillary interactions between a pair of colloidal particles trapped on top of a nematic film are studied
theoretically for large separations d. The elastic interaction is repulsive and of quadrupolar type, varying as d-5. For macroscopically thick films, the capillary interaction is likewise repulsive and proportional to d-5 as a consequence of mechanical isolation of the system comprised of the colloids and the interface. A finite film thickness
introduces a nonvanishing force on the system (exerted by the substrate supporting the film) leading to logarithmically varying
capillary attractions. However, their strength turns out to be too small to be of importance for the recently observed pattern
formation of colloidal droplets on nematic films. 相似文献
135.
Chenghang Wang 《Applied Surface Science》2006,253(4):2282-2288
In this paper, thin films of titanium oxide imprinted with O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrobenyl) methinephosphonate (Phi-NO2) were prepared via liquid phase deposition (LPD) method on a glassy carbon electrode. The imprinted molecular in the films was removed by treatment with immersion in CH2Cl2. X-ray diffraction (XRD) and electrochemical methods were introduced to show the evidence of the molecular imprinting phenomenon. It was also found that the recognition ability of the sensor depended on the substituents associated with tridimensional structures of the nitro-compounds. Under the optimized condition, the sensor showed better sensitivity, selectivity and reproducibility to the imprinted molecule and the linear relationship between the current and the concentration of analyte in the range of 0.1-50 μM was obtained. LPD proved to be a powerful method for imprinting titanium oxide thin sense films. 相似文献
136.
YU Jie ZHU Shu-wen LU Quan-fang ZHANG Zhi-chao ZHANG Xiao-min WANG Xing YANG Wu 《光谱学与光谱分析》2018,38(11):3550-3557
由于重金属毒性大,且在环境、动物和人体器官中易积聚,因而在矿石开采、冶炼和加工之前,监测其中的微量重金属显得尤为重要。著名的原子光谱仪器,如原子荧光光谱(AFS)、原子吸收光谱(AAS)、电感耦合等离子体(ICP)等已广泛用于各种样品中元素的检测,但它们体积大、能耗高、价格昂贵、气体消耗大,这些缺点严重阻碍了野外现场的连续监测。为了满足分析仪器的微型化趋势,1993年Cserfalvi开发了一种电解液阴极放电原子发射光谱(ELCAD-AES)技术并将其用于分析检测中。该装置中,待测溶液以8~10 mL·min-1的流速从细管顶端溢出,然后沿管壁流入装满电解液的35 mL储液池中,以溢出溶液的液面作为放电阴极,在和流动液体电极相距2~4 mm处放一金属W(Ti)棒为阳极,细管浸入电解液并尖端向上弯曲超出储液池液面1~3 mm,细管顶端溢出的液体流入储液池并通过其中的碳棒与电源负极相连,从而构建放电系统。从那时起,为了提高激发效率和放电稳定性,人们对ELCAD进行了大量改进。基于ELCAD的特点,通过改进放电装置,建立了一种新的液相阴极辉光放电(LCGD)分析系统。该系统中,放电在直径0.5 mm的铂针阳极和内径1 mm的毛细管顶端溢出的溶液阴极之间的间隙中产生。毛细管上端和铂丝之间的间隙为2 mm,毛细管插入石墨管且露出石墨管的距离为2.5 mm。样品溶液以4.5 mL·min-1从毛细管顶端溢出流经石墨管上的凹槽,石墨管和电源负极连接。与ELCAD相比,LCGD的优点在于:Pt针做阳极,可形成尖端放电,从而降低能耗(<60 W),提高激发效率;蠕动泵管上打结,可降低泵的脉动性,提高放电的稳定性;石墨管链接电源负极,删除ELCAD中的储液池,使样品消耗更少。为了评估方法的分析性能,用LCGD测定了HNO3-HCl消化的精铜矿样品中的铅和锌。系统研究了放电稳定性以及放电电压、溶液流速、支持电解质和溶液pH对发射强度的影响,并将LCGD与其他ELCAD的分析性能进行比较。此外,用ICP对LCGD的测试结果进行验证,t检验分析两种结果的差异性。结果表明,当电压从620升高到680 V,发射强度逐渐增大,这是因为电压升高,激发能量增大,单位体积内激发的金属原子增多,激发效率提高。考虑到放电稳定性,选择650 V为最佳放电电压。当流速从2.5增加到4.5 mL·min-1时,发射强度增加,这是由于流速增加导致进入放电区的样品量增加,发射强度增强;流速高于4.5 mL·min-1后,发射强度有下降的趋势,这是由于水荷载的增加引起放电区能量密度降低以及过量水加热消耗了用于激发样品的能量,导致激发能量降低。因此,选择最佳流速为4.5 mL·min-1。pH=1的HNO3具有较高的激发强度,因而选择pH=1为最佳pH。最佳条件下,Pb和Zn的检出限分别为0.38和0.59 mg·L-1,相对标准偏差分别为0.9%和1.2%,功率低于60 W。实验中的检出限与其他类似方法所测结果有一定差距,这可能与所选谱仪有关。固定激发波长下研究发现,放电过程有较好的稳定性。矿石样品中Pb和Zn的回收率在87.6%~107.4%,LCGD测试结果与ICP基本一致,两种方法基本无显著性差异。与ICP相比,LCGD具有低能耗、高激发效率、小型便携等优点。随着进一步改进,有望开发出可用于实时、在线检测金属元素的微型化仪器。 相似文献
137.
Dielectric properties of a nematic liquid crystal (NLC) mixture ZhK-1282 were investigated in the frequency range of 102–106Hz and a temperature range of ?20 to 80?°С. On the basis of the Debye’s relaxation polarization model dielectric spectra of temperature dependence of the orientational relaxation time τ and the dielectric strength δe were numerically approximated at the parallel orientation of a molecular director relative to alternating electric field. Influence of ester components in the mixture plays crucial role in relaxation processes at low temperature and external field frequency. The activation energy of the relaxation process of a rotation of molecules around their short axis was measured in a temperature interval of ?20 to ?+15?°С in which the dispersion of a longitudinal component of the dielectric constant takes place. The energy of potential barrier for polar molecules rotation in the mesophase was calculated. The value of the transition entropy from the nematic to isotropic phase was obtained from this calculation. The values of the coefficient of molecular friction and rotational diffusion were obtained by different methods. The experimental data obtained are in a satisfactory agreement with the existing theoretical models. 相似文献
138.
Liquid crystal lens with focus movable in focal plane 总被引:1,自引:0,他引:1
A liquid crystal lens with focus movable in the focal plane is reported. There are three electrodes in the cell. One electrode with a hole in the center is divided into four subelectrodes. The potential of each subelectrode is adjusted to produce a desired asymmetrical phase transformation resulting in off-axis movement of the focus. The potential of another electrode is adjusted to maintain the focus in the focal plane. Movements of the focus in three directions in the focal plane are demonstrated experimentally, and off-axis movement as large as approximately 800 μm is realized. 相似文献
139.
提出了利用数字全息干涉术可视化观测液相扩散过程.实验中,采用马赫-曾德干涉仪光路记录乙醇与水之间两相扩散过程的多幅数字全息图;再通过数值再现不同扩散状态的波前相位分布,获得液体中的摩尔浓度分布;最后,根据菲克定律获得两相流扩散系数.结果表明:利用数字全息干涉术可实现对液相扩散传质过程的快速、实时及高精度测量;该方法还具有可实现远程监控、拥有大量微观数据的优点;此外,采用文中全息干涉光路结合波分与角分复用技术可实现多相流扩散系数的测量,为获得溶液中非线性变化特征参量提供了有效技术手段. 相似文献
140.