恒电流暂态法研究镁在非水体系的电沉积

恒电流暂态法做为研究金属电沉积的有效工具广泛被采用。传统的恒电流暂态法需要用示波器及照相装置,操作较繁。本文利用Model-273恒电势仪和Apple-Ⅱ微机联用完成了恒电流暂态实验,利用该装置可使操作全部自动化,数据的采集、贮存、打印以及超电势与时间之间关系图的绘制全部由计算机完成,不仅操作简便,且精度高。在验证该装置可靠的基础上,本文用其测定了镁在二甲基甲酰胺中电沉积的动力学参数。不仅加深了对镁     

添加Ag或Ag,Ni的V2O5表面氧性质及催化性能研究

用ＴＰＤ－ＭＳ及甲苯选择氧化活性测定等方法研究了Ｖ２Ｏ５和添加Ａｇ或Ａｇ，Ｎｉ的３种样品的表面氧和晶格氧的热脱附性能及催化活性。结果表明，在Ｖ２Ｏ５中加入Ｎｇ或Ａｇ，Ｎｉ后，样品表面上的Ｏ＾－和Ｏ＾２－氧物种的脱附活化能明显降低。添加Ａｇ，Ｎｉ样品表面氧的脱附活化能最低，而苯甲醛生成的选择性最高，在Ｖ２Ｏ５和含有Ａｇ，Ｎｉ的样品中，温度为９６８和７３４℃时，均依次出现以晶格氧（Ｏ＾２－）脱附为主的     

Brillouin scattering study of a polymer hydrogel

Brillouin light-scattering measurements of H₂O imbibed in hydrogels of poly(2-hydroxyethyl methacrylate) of two cross-linking densities have been made at 294 K. Increase in the amount of water imbibed in 19-30 Å size pores of the cross-linked network causes the velocity of sound to decrease monotonically from a value, which differs for the two pure polymers, to a limiting value for pure water. The absorption coefficient reaches a maximum at about 30% water content and then decreases toward that for pure water. The velocity and absorption coefficient of both pure polymer and hydrogel containing 32% water were measured from 110 to 300 K. The former decreases and the latter increases with increasing temperature, and both show a change in the slope at about 160 K for the hydrogel, which agrees with the calorimetric glass transition temperature of the hydrogel. The effect of the water on the velocity and absorption coefficient of the polymer increases with temperature. © 1992 John Wiley & Sons, Inc.     

Association of hydrophobic counterions in aqueous solution of poly(allylammonium) chloride: Comparison between p-n-propylbenzenesulfonate and p-iso-propylbenzenesulfonate ions

The hydrophobic association behavior of p-propylbenzenesulfonate ions (n-PBS^? and iso-PBS^?) around poly(allylammonium) cation (PAAH⁺ was studied by absorption and ¹H nuclear magnetic resonance (NMR) spectroscopy. In the presence of PAAH⁺Cl^?, the broadening (hypochromism) of absorption band of PBS^? were observed. In addition, all ¹H NMR signals of PBS^? exhibited up-field shift which resulted from the intermolecular ring current shift. These results indicate the hydrophobic association of negative PBS^? around PAAH⁺. The hydrophobic association arises from the accumulation of counterions around the polyion, and is stabilized by the hydrophobic interaction between propyl groups and the stacking interaction between benzene rings. The association of iso-PBS^? ions is rather weaker than that of n-PBS^?, suggesting that the steric hindrance of isopropyl groups prevents an effective association of hydrophobic counterions. Furthermore, through viscosity and Cl^? activity measurements, it was found that the binding of associated PBS^?,s to PAAH⁺ causes the change of its surroundings to hydrophobic character and its conformation. © 1994 John Wiley & Sons, Inc.     

Ternary complexes of substituted catechols and catecholamines

Stability constants of the ternary complexes [CuAL] whereA = 5-Nitro-1,10-phenanthroline, bis(2-pyridyl) ketone (DPK) orbis(2-pyridyl)amine (DPA) andL is the dianion of catechol, tiron, protocatechic acid, pyrogallol, 1,8-dihydroxynaphthalene, catecholaldehyde, 2,3-dihydroxynaphthalene, dopamine or adrenaline have been determined by potentiometric titration in dioxane water (1:1 v/v) medium using a SCOGS computer programme. The observed trend of stability is explained on the basis of the nature of substitution over the ligands, chelate ring size and also the composition of mixed solvent in case of DPK. Structural changes in DPK have also been discussed as a function of pH, composition of medium and coordinating mode of the secondary ligand in the ternary complexes.     

Plasticization of a poly(ethyl acrylate) ionomer by an alkyl aniline

The plasticization by 4-decylaniline (4DA) of a microphase-separated poly(ethyl acrylate) ionomer containing sodium carboxylate groups is examined. Dynamic mechanical thermal analysis, supplemented by differential scanning calorimetry, shows that the matrix and cluster glass transitions (T_g's) in the ionomer are both depressed by ca. 1°C/wt % 4DA; this, in turn, is similar to the T_g depression in the blend of the parent poly(ethyl acrylate) (PEA) with 4DA. There is no evidence of 4DA crystallinity in the blend. Small-angle x-ray scattering (SAXS) measurements show that the ionomer peak increases in intensity and decreases in scattering angle with increasing concentration of 4DA in the blend; the corresponding Bragg spacing, initially at 2.3 nm, increases by ca. 0.04 nm/wt % 4DA. These results, supported by preliminary spectroscopic measurements, are attributed to hydrogen bonding interactions between the amine groups of 4DA and the ester groups in PEA and the ionomer, rendering the blend miscible. It is argued that the uniform distribution of 4DA throughout the material plasticizes both phases of the ionomer by adding free volume; this also accounts for the increase in the characteristic spacing detected by SAXS.     

涡旋辅助分散液液微萃取-悬浮固化/高效液相色谱法测定水样中7种萘二酚

建立了水样中7种萘二酚的涡旋辅助分散液液微萃取-悬浮固化/高效液相色谱(VA-DLLME-SFO/HPLC)测定方法。以乙醚-十二醇为二元微萃取剂,通过涡旋分散方式协同萃取水样中的目标化合物,采用C18色谱柱分离,HPLC测定。优化了萃取剂及用量、萃取时间、氯化钠用量等条件。最佳萃取条件为：萃取剂为100μL乙醚和50μL十二醇,氯化钠用量为0.2g/mL,涡旋萃取3min。在优化条件下,7种萘二酚在一定质量浓度范围内线性关系良好,相关系数均大于0.997,方法检出限(S/N=3)为1.7~6.0μg/L;3个加标水平下的平均回收率为82.1%~106.0%,日内相对标准偏差(RSD,n=5)为1.2%~4.1%;中间添加水平的日间RSD(n=5)为2.5%~5.7%。该方法前处理简单,涡旋分散大大提高了物质传质速率,增大了萃取效率,缩短了萃取时间,是一种适用于水样中萘二酚类物质富集检测的绿色方法。     

Synthesis,spectroscopic and structural characterization of diphenyltin(IV) complexes of acetone Schiff bases of S-alkyldithiocarbazates

New diphenyltin(IV) complexes of empirical formula, [Sn(C₆H₅)₂(NS)Cl] (NS = anionic forms of the acetone Schiff bases of S-methyl or S-benzyldithiocarbazate) have been prepared and characterized by IR, NMR and Mössbauer spectroscopic techniques. The crystal and molecular structures of the acetone Schiff bases of S-methyldithiocarbazate (Hacsme) and S-benzyldithiocarbazate (Hacsbz) and their tin(IV) complexes have been determined by X-ray diffraction. In the solid state, both the Schiff bases exist in their thioketo tautomeric forms with the azomethine nitrogen atom trans to the thione sulfur atom but in the tin(IV) complexes they are present in their deprotonated ene-thiolate forms being coordinated to the tin atom as bidentate chelating agents via the azomethine nitrogen and thiolate sulfur atoms. The tin atom adopts a five-coordinate, approximately trigonal bipyramidal geometry, with the thiolate sulfur atom of the Schiff base and the two phenyl groups occupying the equatorial positions. The azomethine nitrogen atom and the chlorine ligand occupy axial positions. The distortion from a regular trigonal bipyramidal or a square-pyramidal geometry is attributed to the restricted bite sizes of the five-membered chelate rings.     

Chemical Reconstruction of Pt-Rh(100) Alloy and Pt/Rh(100), Rh/Pt(100) Bimetallic Surfaces

When Cu(110), Ni(l 10), Ag(110) surfaces are exposed to O₂ at room temperature, one dimensional metal-oxygen strings grow in the < 001 > direction of the (110) surfaces. A similar phenomenon occurs in the adsorption of H₂ on Ni( 110) surface at room temperature, where the one dimensional strings grow along the < 110 > direction. These phenomena are undoubtedly different from the adsorption induced reconstruction but are explained by the chemical reconstruction involving the formation of quasi-compounds and their self-ordering on the metal surfaces. The chemical reconstruction is indispensablly important to understand the structure and catalysis of alloy and bimetallic surfaces. Pt_0.25Rh_0.75(100) alloy surface being active for the reaction of NO with H₂ is an interesting example. When the Pt-Rh(100) alloy surface is exposed to NO or O₂ at arround 500 K, a p(3 × 1) ordered Rh-O over-layer is obtained on a Pt-enriched 2nd layer by the chemical reconstruction. Ordering of Rh-0 in the p(3 × 1) structure on the Pt(100) surface was reproduced by heating a Rh/Pt(100) bimetallic surface in O₂, and the chemical reconstruction making the p(3 × 1) Rh-O overlayer on a Pt enriched 2nd layer was also proved by heating a Pt/Rh(100) bimetallic surface in O₂ or NO. The activation mechanism of the Pt-Rh alloy and the Pt/Rh bimetallic surfaces by the chemical reconstruction was evidently shown by using a Pt deposited Rh(100), Pt/Rh(100), surface. That is, the Pt/Rh(100) is not so active for the reaction of NO with H₂, but the reconstructed p(3 × 1)Rh-O/Pt-layer/Rh(100) surface is very active for the reaction. Therefore, it was concluded that the chemical reconstruction of the Pt-Rh catalyst makes the active surface which is composed of Rh-O and a Pt layer.     

Dynamic light scattering from bulk poly(n-hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n-hexylmethacrylate) PHMA (M_w = 1.6·10⁵, T_g = ?5°C) have been studied in the temperature range of ?2–25°C. The experimental time correlation functions over the time range 10^?6?10² s were represented by the Kohlrausch-Williams-Watts (KWW) function exp{?(t/τ)^β} with a virtually temperature-independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass-rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass-rubber or α-relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10^?6 s near T_g. © 1992 John Wiley & Sons, Inc.