Internal electrolyte temperatures for polymer and fused-silica capillaries used in capillary electrophoresis

Polymers are important as materials for manufacturing microfluidic devices for electrodriven separations, in which Joule heating is an unavoidable phenomenon. Heating effects were investigated in polymer capillaries using a CE setup. This study is the first step toward the longer-term objective of the study of heating effects occurring in polymeric microfluidic devices. The thermal conductivity of polymers is much smaller than that of fused silica (FS), resulting in less efficient dissipation of heat in polymeric capillaries. This study used conductance measurements as a temperature probe to determine the mean electrolyte temperatures in CE capillaries of different materials. Values for mean electrolyte temperatures in capillaries made of New Generation FluoroPolymer (NGFP), poly-(methylmethacrylate) (PMMA), and poly(ether ether ketone) (PEEK) capillaries were compared with those obtained for FS capillaries. Extrapolation of plots of conductance versus power per unit length (P/L) to zero power was used to obtain conductance values free of Joule heating effects. The ratio of the measured conductance values at different power levels to the conductance at zero power was used to determine the mean temperature of the electrolyte. For each type of capillary material, it was found that the average increase in the mean temperature of the electrolyte (DeltaT(Mean)) was directly proportional to P/L and inversely proportional to the thermal conductivity (lambda) of the capillary material. At 7.5 W/m, values for DeltaT(Mean) for NGFP, PMMA, and PEEK were determined to be 36.6, 33.8, and 30.7 degrees C, respectively. Under identical conditions, DeltaT(Mean) for FS capillaries was 20.4 degrees C.     

Doping of fullerite with molecular oxygen at low temperature and pressure

Two methods are described for doping of fullerite C₆₀ with molecular oxygen at a pressure of ∼104 Pa and at temperature 20–30 °C. It was found by mass spectrometry using oxygen ¹⁸O as dopant that a portion of molecular oxygen absorbed by the pre-decontaminated fullerite (first method) is removed as CO and CO₂ at the heating temperature ≤200 °C. Doping during fullerite precipitation from the liquid phase (second method) makes it possible to prepare samples with the oxygen content ≥1.2 at.%. The fullerite doped with oxygen to this level is diamagnetic. The paramagnetic properties of an O₂ molecule disappear when O₂ is incorporated into the fullerene lattice. This is interpreted on the basis of quantum chemical calculations as a sequence of equilibrium formation of the adduct C₆₀O₂. Calculations showed that the subsequent chemical transformation of C₆₀O₂ resulting in the O-O bond cleavage is energetically favorable, enabling prerequisites for the formation of products of incomplete (CO) and deep (CO₂) oxidation of fullerene under mild conditions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 662–671, April, 2006     

CaWO4荧光体的微波热法合成和光致发光

本文报道微波热法合成 Ca WO4荧光体 ,X射线粉末衍射分析确证为四方晶系 ,Ca WO4:Pb0 .0 1 荧光体最大激发波长 λex=2 66.0 nm,最大发射波长 λem=450 .0 nm,在 2 54nm激发下 ,色坐标 x=0 .1 66,y=0 .1 2 4 ,与市售同类荧光体比较 ,相对发光亮度 86% ,荧光体中心粒径 D50 为9.1 8μm,体积比表面 SV 为 81 93 1 / cm。     

Coherent scattering of microwaves by plasma density fluctuations. Application: Observation of lower hybrid waves in wega

The scattering of 2 mm radiation by the density fluctuation associated with lower hybrid waves is used to localize the injected waves within a cross-section of the plasma. A translating antenna setup scores a region extending from the center of the plasma to the boundary with two fixed scattering angles. The measured amplitudes allow one to determine the local value of certain spectral components of n_" in the plasma.     

高交联大孔苯乙烯-二乙烯苯共聚物的微波加热磺化

研究了高交联大孔苯乙烯-二乙烯苯共聚物(60％DVB)在微波加热条件下发生的磺化反应．采用高功率问歇加热的方式，考察了不同的加热方法、溶胀荆、反应物的配比对磺化反应的影响，并与低交联大孔苯乙烯-二乙烯苯共聚物(8％DVB)的磺化反应作了比较．     

微波加热法测定粮食中的水分

采用微波加热法测定粮食中的水分，测定条件是：微波功率700w、加热时间8min。测定结果的标准偏差为0．023％～0．047％(n=5)。该方法操作简便，分析时间短，分析结果准确、可靠。     

A NOVEL APPROACH TO RHEOLOGICAL CHARACTERIZATION FOR THE GELATION IN POLYMER CRYSTALLIZATION

The isothermal crystallizations of three kinds of commercial isotactic polypropylene have been studied by DSC and rheometric experiments, in a range of temperatures where the rate of crystallization is moderate. As the crystallization proceeds, volume contraction induces tensile force upon the parallel plates. The tensile force relaxed quickly in liquid states,but after a critical amount of the relative crystallinity, it starts to accumulate in the static test, that is, with the motionless parallel plates. A new method to determine the liquid-solid transition by the static tensile force is proposed and compared with two dynamic methods of detecting liquid-solid transition, that is, the power-law modulus theory and the yield modulus model. The tensile force method predicted considerably earlier transition than the dynamic methods, and the corresponding DSC data indicate relative crystallinity of larger than 0.2 at the transition times. The limitation of dynamic methods and other possible errors have been analyzed. While the dynamic methods are suitable for slow crystallization, the tensile force method is more appropriate for the crystallization of moderate rates. Moreover, it has the advantage of almost not disturbing the crystallizing materials before the transition.     

2，2，3-三甲基丁烷(C7H16)晶体的成核动力学

High temperature solid phase I of 2,2,3-trimethylbutane(C7H16)(TMB) was investigated by X-ray powder diffraction. The electron diffraction technique for observing the kinetics of phase transitions in the condensed matter has been applied to study the freezing of TMB clusters with diameter of~13nm. Cluster beams were generated from the supersonically expanded TMB vapor with mole fraction of 0.01 in neon carrier gas. The freezing evolution was monitored by electron diffraction in interval of 7-9 μs. Clusters with an average size of ~5,500 molecules were observed to freeze into the solid phase I at a nucleation rate of 3.5 × 1028 m-3•s- 1 at the freezing temperature of clusters, ～170K. The estimated growth rate of postcritical nuclei indicates that the observed nucleation in the present experiment corresponds to mononuclear freezing of the clusters into single crystals of solid phase I.     

Plasma homo- and copolymerizations of tetrafluoroethylene and chlorotrifluoroethylene

The plasma homo- and copolymerizations of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE) in a capacitively coupled tubular reactor (TR) with external electrodes were studied by means of microgravimetry and FT-IR and XPS analyses. The deposition rates for CTFE/TFE plasma copolymers, as well as the ratios of IR absorbances at 1180 and 1225 cm⁻¹, and the XPS-derived Cl/C and F/C ratios, varied regularly with mol % CTFE in the feed, all of which results were dependent upon the rf power at which the plasma copolymerizations were conducted. The deposition rates for the plasma homopolymers of TFE (PPTFE) and CTFE (PPTCFE) depended markedly on rf power (W) and monomer molar flow rate (F). The F/C ratio for PPTFE was nearly independent of the composite parameter,W/FM (whereM is the monomer molecular weight), while for PPCTFE, the F/C ratio decreased significantly and the Cl/C ratio increased slightly with increase inW/FM. The percentage of carbon as CF₃ was 20–24% in PPTFE and 7–14% in PPCTFE. Plots of deposition rate versusW/FM for PPTFE and PPCTFE obtained in a TR differed considerably from corresponding plots in the literature for the same homopolymers prepared in a glass-cross or bell-jar reactor.     

Selective synthesis of fluorinated carbohydrates using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine

Deoxyfluorination of a hydroxy group in carbohydrates was carried out using N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine. A primary hydroxy group in carbohydrates was effectively converted to the corresponding fluoride under microwave irradiation or at 100 °C. Deoxyfluorination of hydroxy groups at the anomeric position proceeded at below room temperature, and glycosyl fluorides could be obtained in good yields. The reaction chemoselectively proceeded, and various protecting groups of carbohydrates can survive under the reaction conditions.