The application of dielectric analysis to drying latex films

Measurements of real and imaginary capacitance (C andC) have been made during the drying of a film-forming latex. In one experiment dielectric measurements at frequencies between 1 Hz and 100 kHz were made simultaneously with gravimetric measurements on a microbalance. It was found that both the rate of water evaporation and the a.c. conductance decrease sharply at high polymer volume fraction. These results are discussed qualitatively in terms of a model for the film-forming process. In another experimentC andC were recorded at 10 Hz along with automatic measurements of the build-up of the scratch resistance of the film. It was found that the mechanical response to film-formation appears significantly earlier than the dielectric response. This is also discussed qualitatively in terms of the model.The authors would like to thank Dr. I. Abrahams, Dr. S. Bell, and Dr. M. Reading for useful discussions regarding this work and M. Bahra for his help with the TFA measurements.     

Value function and optimality conditions for semilinear control problems

This paper is concerned with optimal control problems of Mayer and Bolza type for systems governed by a semilinear state equationx(t)=Ax(t) + f(t, x(t), u(t)), u(t) U, whereA is the infinitesimal generator of a strongly continuous semigroup in a Banach spaceX. We prove necessary and sufficient conditions for optimality and then use these conditions to investigate properties of the value function related to superdifferentials. Conversely, we use the value function to obtain criteria for optimality and feedback systems.Work (partially) supported by the Research Project Equazioni di evoluzione e applicazioni fisicomatematiche (M.U.R.S.T.-Italy).     

XPS定量分析及其在CdTe（Ⅲ）面识别化学物种中的应用

我们用谱仪能量传输函数修正的相对原子灵敏度因子获得了ＸＰＳ定量数据。通过将定量结果与结合能的化学位移相结合的方法，分析了ＣｄＴｅ表面的两个氧化过程，结果表明，机械抛光样品表面的构成是：６６％ＣｄＴｅ，２８．９％的Ｃｄ（ＯＨ）２和５．１％ＴｅＯｘ（Ｘ＞２），而经化学抛光的表面构成是∶８４．４％的ＴｄＴｅＯ４和１５．６％ＴｅＯｘ（Ｘ＞１）。     

Ionic conductivity of poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium)] salts with univalent counter-ions in aqueous solutions

In order to determine the counter-anion effect on conductivity of poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium)] backbone in aqueous solutions, a set of three polyelectrolytes with three different counter-ions: poly[N-(3,6,9-trioxadecyl)-4-vinylpyridinium]bromide P4VP164Br and its chlorate and tosylate derivatives P4VP164ClO₄ and P4VP164Ts respectively, were prepared by spontaneous polymerization of 4-vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on each pyridinic moiety on the backbone. The conductivities of cationic polyelectrolyte aqueous solution were determined in the concentration range from 10⁻⁴ to 10⁻² M at 25 °C. The variation of the conductivity versus concentration of the investigated system exhibits a typical polyelectrolyte behavior. The polycation mobility was found to be dependent on the counter-anion nature. Thus, the polyelectrolyte conductivity increases with the ion size. This shows that big ions are weakly or not associated to the backbone.In order to confirm this steric hindrance, we have considered the conductivities of these three anions Br⁻, ClO₄⁻ and Ts⁻ in their sodium salts, both alone and in the presence of 3,6,9-trioxadecanol (PEO164) free chains. In the two cases, the conductivities decrease in the order Λ_Br>Λ_ClO4>Λ_Ts.These results suggest that counter-ion mobility is mainly influenced by steric effect PEO164 grafted chains.Values of the conductivity predicted from Manning rod-like polyelectrolyte model were compared with our experimental results.     

Two new standard reference materials for the determination of drugs of abuse in human hair

Two new standard reference materials (SRM) for drugs of abuse in human hair have been developed. SRM 2379 consists of hair spiked with cocaine, benzoylecgonine, cocaethylene, phencyclidine, amphetamine, and methamphetamine. SRM 2380 consists of hair spiked with codeine, morphine, monoacetylmorphine, and tetrahydrocannabinol (THC). The SRMs were prepared by soaking the hair in a solution of the target analytes in water-dimethylsulfoxide. The concentration of each analyte was determined using two methods, one based upon gas chromatography/mass spectrometry (GC/MS) and one based upon liquid chromatography/mass spectrometry (LC/MS). Both methods used 0.1 M HCl for extraction of all the analytes from the hair, except for THC, which was extracted with 1 M NaOH. For isolation of the analytes from the extracts, the GC/MS-based methods used different clean-up procedures from those used for the LC/MS-based methods. The results from the two methods were in good agreement with mean differences for the analytes ranging from 4% to 16%. These materials will enable laboratories performing analyses of hair for drugs of abuse to test the accuracy of their methods.     

1,6-六亚甲基二异氰酸酯自聚产物的结构表征

用IR与NMR表征了用醋酸钾为催化剂时 1,6 六亚甲基二异氰酸酯 (HDI)自聚产物的结构 .结果表明 ,自聚主产物是三聚体异氰脲酸酯 ,主要含有三聚体异氰脲基、异氰酸根 ,同时含有由杂质带来的微量氨基甲酸酯、脲基甲酸酯基、取代脲基、缩二脲基 .一维核磁谱及二维化学位移相关谱分辨出 7种羰基 ,一种NCO基 ,确定了氮上 8种不同取代结构的分子链连接情况 .通过建立理论模型 ,定量地描述了自聚产物的结构 .     

Structure and microporous formation of cellulose/silk fibroin blend membranes: Part II. Effect of post-treatment by alkali

Blend membranes (RCF1) were prepared from mixture solution of cellulose and silk fibroin (SF) in cuoxam by coagulating with acetone–acetic acid (4:1 by volume). The blend membranes were subjected to post-treatment with 10% NaOH aqueous solution, and their structure and properties were characterized by FT-IR, X-ray diffraction, DSC, SEM and DMTA. In previous work, cellulose/SF blend membranes (RCF2) prepared by coagulating with 10% NaOH aqueous solution formed a microporous structure, in which the SF as a pore former was almost completely removed from the membrane. However, when the blend membranes RCF1 were immersed in 10% NaOH aqueous solution for post-treatment, a strong hydrogen bonding between cellulose and SF inhibited the removal of SF. Although alkali is a good solvent for SF, the blend membranes RCF1 such obtained from cellulose and SF were alkali resistant. The crystallinity and the mean pore size of the blend membranes slightly decreased with increasing post-treatment time. This work provided a cellulose/silk blend membrane, which can be used under alkaline medium.     

Determination of trace metals in industrial boron carbide by solid sampling optical emission spectrometry. Optimization of DC arc excitation (current, atmosphere and chemical modifier)

Graphite arc emission spectrometry has become possible as a result of the invention of novel types of optical spectrometers with Echelle-optics and semiconductor array detectors, and by the application of electronically controlled, high current arc generators. An optimization of the excitation parameters to boron carbide analysis is reported here, measuring background corrected line intensities that were integrated for the time of total evaporation of 5 mg boron carbide sample with or without added chemical modifiers. The following set of experimental conditions were compared with respect of analytical sensitivity and precision: (A) no modifier, Ar + O₂ (20%), 16 A; (B) sample + graphite powder (1 + 1), Ar + O₂ (20%), 16 A; (C) sample + CaF₂ (1 + 1), Ar, 25 A; (D) sample + CaF₂ + graphite powder (1 + 1 + 1), Ar, 25 A. The graphite powder modifier resulted in improved precision in general, and the CaF₂ was effective as a plasma ionization buffer and fluorinating agent. The best compromise was found under conditions B, when oxygen was present in the discharge atmosphere. This is likely due to the stepwise conversion of the boron carbide matrix to the more volatile boron oxide. Under conditions B, detection limits in the ranges of 0.3–9 μg g⁻¹ for Al, Ca, Cr, Cu, Fe, Mg, Mn and Si and that of 18–38 μg g⁻¹ for Ti, W, and Zr were attained. Average RSDs of 10.2 and 9.7% were found, respectively, without and with internal referencing to boron.     

Determination of methylmercury fluxes across the air–water and air–soil interfaces by gas chromatography with electron capture detection

A method for the determination of methylmercury (MeHg) fluxes across the air–water and air–soil interfaces was developed using an in situ chamber. The MeHg in the air coming out of the chamber was captured by a column containing sulfhydryl cotton fiber adsorbent. MeHg was then desorbed from the column by using 2 mol L^–1 HCl. The MeHg in the effluent was extracted with benzene, and determined by gas chromatography with electron capture detection. Finally, the MeHg flux was calculated using the chamber. The method was applied to simulated experiments, and the results showed that the MeHg fluxes in the air–water system were higher than those in the air–soil–water system. The method was also successfully applied to the field measurements of an environment polluted by a chemical factory, and the results showed that the MeHg fluxes across the air–soil and air–water interfaces were 0.21–3.09 and 0.14–0.79 ng m^–2 h^–1, respectively. The method will be a useful tool in the environmental study of MeHg.     

Online preconcentration system for determining ultratrace amounts of Cd in vegetal samples using thermospray flame furnace atomic absorption spectrometry

A system has been developed for online preconcentration and determination of Cd using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). It is based on the solid-phase extraction of Cd in an Amberlite XAD-2 minicolumn loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM), and the metal ion is eluted with 1 mol L⁻¹ hydrochloridric acid, followed by its determination. The online system allows determining Cd with a detection limit of 8.0 ng L⁻¹ and a quantification limit of 25.0 ng L⁻¹. The precision (repeatability), calculated as the relative standard deviation (% RSD) in sample solutions containing 0.5 and 3.0 μg L⁻¹ of Cd, was 6.1 and 4.5%, respectively. The preconcentration factor obtained was 24. The system’s accuracy was confirmed by analyzing the following certified reference materials (CRMs): Rice flour NIES 10b, Apple leaves NIST 1515 and Orchard leaves NBS 1571. This procedure was applied to the determination of Cd in cabbage and powdered guarana samples.