结晶PET驻极体的分子运动与陷阱性质

半晶性的聚对苯二甲酸乙二醇酯(PET)存在不同尺寸运动单元的多重形式的分子运动,而且PET等高聚物前结构欠序、晶界和杂质等缺陷还使电子价带与导带间的禁带中出现局域能级(陷阱),并成为捕获载流子的中心,从而影响载流子的输运性质。分子运动和陷阱     

Role of Hydrodynamic Conditions in the Distribution of Anodic Dissolution Rates in Cavity Etching Regions during Electrochemical Micromachining of Partially Insulated Surfaces

Experimental study of the distribution of local rates of electrochemical micromachining in the presence of photoresist masks in various hydrodynamic conditions (macroscopically nonuniform rotating disk electrode, sprayer flow, an electrode placed into a cell with chaotic bulk electrolyte mixing) shows that the maximum etching localization is achieved at the control of the dissolution rate by the mass transport rate (at achieving the anodic limiting current). The localization enhancement as compared to the primary current distribution takes place in the case of a turbulent flow at hydrodynamic conditions where the removal of dissolution products from the undercutting region is hindered. These conditions (electrochemical reaction limited by the ion mass transport rate, high resistance to the mass transport in the undercutting region) are necessary for the localization enhancement using a pulsed anodic–cathodic treatment.     

Ferric borate formation in aqueous solution

Potentiometric analyses indicate that previous investigations have overestimated the stability of ferric borate complexes. The FeB(OH) ₄ ²⁺ formation constant result obtained in the present work is_Bβ ₁ ^* = [FeB(OH) ₄ ²⁺ ][H⁺][Fe³⁺]^-1[B(OH)₃]^-1 = (5.4±0.3) x 10^-3 at 25.0°C and 0.7 molal ionic strength. Our result indicates that solution concentrations of FeOH²⁺ and FeB(OH) ₄ ²⁺ are approximately equal in aqueous solution for boric acid concentrations on the order of 0.3 molal. Fe(B(OH)₄) ₂ ⁺ is a minor species in solution compared to FeB(OH)₄ ²⁺ for conditions such that [B(OH)₃][H⁺]^-1≤ 350, and ferric borate complexation is insignificant in solutions such as seawater where [B(OH)₃] ≤ 4× 10^-4 molal.     

Synthesis and conformational analysis of naphth[1′,2′:5,6][1,3]oxazino[3,2-c][1,3]benzoxazine and naphth[1′,2′:5,6][1,3]oxazino[3,4-c][1,3]benzoxazine derivatives

A new functional group, the hydroxy group, was inserted into a Betti base by reaction with salicylaldehyde, and the naphthoxazine derivatives thus obtained were converted by ring-closure reactions with formaldehyde, acetaldehyde, propionaldehyde or phosgene to the corresponding naphth[1′2′:5,6][1,3]oxazino[3,2-c][1,3]benzoxazine derivatives. Further, the conformational analysis of these polycyclic compounds by NMR spectroscopy and an accompanying molecular modelling are reported; especially, both quantitative anisotropic ring current effects of the aromatic moieties in these compounds and steric substituent effects were employed to determine the stereochemistry of the naphthoxazinobenzoxazine derivatives.     

Potentiometric Membrane Sensor for Determination of Saccharin

A potentiometric poly(vinyl chloride) membrane sensor for determination of saccharin is described. It is based on the use of Aliquat 336S-saccharinateion-pair as an electroactive material in plasticized PVC membranes with o-nitrophenyloctylether or dioctylphthalate. The sensor is conditioned for at least two days in 0.1 mol L⁻¹ sodium saccharinate before use. It exhibits fast, stable and Nernstian response for saccharinate ions over the concentration range of 1.0 × 10⁻¹–5.0 × 10⁻⁵ mol L⁻¹ and pH range of 4.5–11. The sensor is used for determination of saccharin in some dosage forms. Results with an average recovery of 101% and a mean standard deviation of 0.2% are obtained which is compared favourably with data obtained using the British pharmacopoeia method. The sensor shows reasonable selectivity towards saccharin in presence of many anions and natural sweeteners.     

Resolving the copper interference effect on the stripping chronopotentiometric response of lead(II) obtained at bismuth film screen-printed electrode

As copper(II) is a common ion in a variety of analytical samples, its effect on the stripping response of lead(II) at bismuth film screen-printed carbon electrode (BFSPCE) was investigated. The study was conducted using a screen-printed three-electrode system (working, counter and reference electrodes), with the carbon-working electrode plated in situ with bismuth film. Copper present at significant concentration level in samples was found to affect the sensitivity of the electrode by reducing the constant current stripping chronopotentiometric (CCSCP) response of lead(II). Recovery of the lead stripping response at the BFSPCE in the presence of copper was obtained when 0.1 mM ferricyanide was added to the test solution. The ferricyanide added circumvents the detrimental effect of copper(II) by selectively masking the copper ions by forming a complex. The analytical utility of the procedure is illustrated by the stripping chronopotentiometric determinations of lead(II) in soil extracts.     

Competitive potentiometric determination of binding constants between α-cyclodextrin and 1-alkanols

The binding constants of 1-alkanols with α-cyclodextrin (α-CD) were determined by indirect competitive potentiometry, although potentiometry is usually inapplicable to nonionic compounds. This novel method utilizes competitive binding of 1-alkanol and octyltrimethylammonium bromide (OTAB) to α-CD in aqueous media, where the concentration of free OTAB depending on the competitive binding is monitored with an OTAB-selective electrode. Therefore, the concentration of 1-alkanol is indirectly estimated from the observed electromotive force. The binding constants of 1-propapnol, 1-butanol, 1-hexanol, and 1-octanol with α-CD, obtained by this method, are close to the literature values. The implications and limitations of this indirect competitive potentiometry were discussed.     

吲哚-3-乙酸与部分过渡金属离子M(Ⅱ)二元配合物的pH电位法研究

在25℃,I=0.10 mol/L KNO3的实验条件下,用pH电位法测定了吲哚-3-乙酸(IAA)在甲醇-水混合溶剂中的质子化常数,讨论了有机溶剂对质子化常数的影响,结果表明在实验范围内溶剂甲醇含量对质子化常数的影响呈线性关系.确定了二元体系M(Ⅱ)-IAA(M=Fe、Co、Ni、Cu、Zn和Cd)在甲醇含量为50%(V/V)的混合溶剂中主要存在的配合物物种,并测定了配合物的稳定常数.实验数据的处理运用计算机程序Hyperquad、Glee和Hyss完成.     

Differences in the electrorheological response of a particle suspension under direct current and alternating current electric fields

We have observed an unusual reduction of shear stress with increasing shear rate under direct current electric fields, for an electrorheological fluid composed of sulfonated poly(styrene-co-divinylbenzene) particles dispersed in silicone oil. At all shear rates, the shear stress under the electric field is larger than that in the absence of the field, indicating that there is still some field-induced agglomeration of the particles. In contrast, the behavior under alternating current electric fields is the Bingham-fluid-type response commonly observed with electrorheological fluids. It is suggested that the conventional dipole–dipole interaction approach based on simplified microstructural models would be unable to explain these phenomena. Received: 27 November 2000 Accepted: 22 May 2001     

TS和PTS单晶体的热刺激电流

测定了双(对甲基磺酸)2,4-己二炔-1,6-二醇酯(TS)及其不同聚合程度TS-PTS混合体和完全聚合的聚合物PTS在100-300K温度范围内的热刺激电流。在沿分子堆砌方向上(对PTS则是大分子链方向)上观察到了它们的热刺激电流,并在相应于它们相变152K和192K处呈现热刺激电流峰。研究了聚合程度对相变的影响,绘制了TS-PTS体系的相图。对另三个热刺激电流峰的归属作了定性解释。