Thermodynamics of mixtures of hexane and heptane isomers with normal and branched hexadecane

Molar excess mixing enthalpies h ^E , Gibbs free energies g ^E and hence entropies s ^E have been obtained using calorimetry and the vapor sorption method at 25°C for hexane isomers+2,2,4,4,6,8,8-heptamethylnonane, a highly branched C ₁₆ . The h ^E and g ^E are negative while Ts ^E are positive, but small. The values are explained by the Prigogine-Flory theory through negative free volume contributions to h ^E and Ts ^E , counterbalanced in the case of Ts ^E by the positive combinatiorial Ts ^E for mixing molecules of different size. No contribution is seen from the interaction between methyl and methylene groups. The excess quantities are also obtained for hexane and heptane isomers mixed with n-hexadecane. Values of h ^E and Ts ^E are now strongly positive, while those of g ^E are only slightly less negative. The interpretation requires two recently advanced contributions in addition to those of the Prigogine-Flory theory: 1) a decrease of order when correlations of orientations between n-C ₁₆ molecules in the pure liquid are replaced in the solution by weaker correlations whose strengths depend on the shapes of the lower alkane isomers. For lower alkane isomers of the same shape, but highly sterically hindered, h ^E and Ts ^E are small, manifesting, 2) a negative contribution, ascribed to a rotational ordering of n-C ₁₆ segments on the sterically-hindered molecule. Enthalpy-entropy compensation is observed for these new contributions, arising from their rapid fall-off with increase of temperature.     

Kinetics of thermal decomposition of alkaline phosphates

Summary The thermal behavior of KH₂PO₄, NaH₂PO₄ and Na₂HPO₄ under non-isothermal conditions using TG method with different heating rates was studied. The values of the reaction rate were processed by means of Friedmans differential-isoconversional method. A dependence of the activation energy vs. conversion was observed. Therefore a procedure based on the compensation effect (suggested by Budrugeac and Segal) was applied. A less speculative data processing protocol was offered by the non-parametric kinetics method suggested by Serra, Nomen and Sempere. Three steps were observed by non-isothermal heating: a dehydration, a dimerization and a polycondensation. The differences in the intimate reaction mechanism are determined by the initial number of water molecules.     

Dielectric behaviour of a side-chain-bearing liquid-crystalline polysiloxane

The relaxation of electric field-induced polar orientation in a side-chain-bearing liquid-crystalline polysiloxane was measured by means of thermally stimulated depolarization currents. Different relaxation mechanisms were identified and characterized: the glass transition cooperative relaxation exhibits compensation behaviour. On the other hand, lowerT _g and upperT _g discharges were observed and their molecular nature is discussed.     

光度分析中协同系数补偿方法的研究──三次标准加入法同时测定钼、钨和钛

本文在两次标准加入法[1]的基础上，提出了三组份同时测定的三次标准加入法，并应用于钼、钨和钛的流动注射同时测定。测定条件：［水杨基荧光酮（SAF）］＝1．25　×10-4mol／L，［溴化＋六烷基三甲基铵（CTMAB）」＝2．5×10－3mol／L，pH1．35，25℃，采样、进样时间分别为10s和18s，进样频率128次／h。为消除组份间协同作用引起的吸光度加合性的偏离，定义了三组份协同系数。将其引入三组份同时测定方法，补偿了吸光度对线性的偏离。补偿后钼、钨和钛的测定范围分别为0．05～0．35，0．25～1．00，0．025～0．30mg／L。测定了钢样及模拟样品中钼、钨和钛含量，结果较好。     

Compensation effect in the electrical conduction process in a series of pyrenyl polyenes

The semiconductive properties of a series of pyrenyl polyenes of the type R-(CH=CH)_n-R, are studied as a function of the adsorption of different amount of a vapour. With regard to the compensation temperature (T ₀) the compounds are divided into two groups. For compounds which have odd number of double bonds,T ₀ is infinite and in compounds having even number double bonds,T ₀ is finite.T ₀ for II₂ is higher while that of II₄ is lower than the experimental temperature. DifferentT ₀ for the compounds having odd or even number of double bonds suggests a physical basis for the compensation rule, which we believe, is related to the molecular and crystalline structure of the compounds     

Solubility Enhancement of Low Soluble Biologically Active Compounds by β-Cyclodextrin and Dimethyl-β-cyclodextrin

The solubility enhancement of triflumizole by complexation with -cyclodextrin and with dimethyl--cyclodextrin is compared with respect to the different physico-chemical properties of the host molecules. Although the inclusion reaction constants are rather similar for both complexation reactions, a completely different temperature dependence of the host-guest interaction is observed, which indicates a change of the reaction mechanisms. Moreover, the influence of ethanol as cosolvent is studied.     

Thermal Degradation of Polychloroprene Rubber Under Isothermal and Non-Isothermal Conditions

The results of a kinetic investigation of the non-isothermal degradation and the isothermal degradation of the residual deformation under constant deflection for polychloroprene rubber are presented. A relationship was derived between the degree of non-isothermal conversion and the value of the investigated mechanical property. This revised version was published online in July 2006 with corrections to the Cover Date.     

A vibrationally compensated far infrared laser interferometer for plasma density measurements

A modulated far-infrared laser interferometer which is presently operating on the PDX experiment at Princeton is described. The interferometer geometry permits the characterization of inside D, outside D as well as circular discharges. To achieve this versatility, a titanium corner cube reflector, mounted inside the PDX vacuum vessel is used in conjunction with a second visible wavelength interferometer for vibration corrections. In addition, the use of room temperature quasi-optical Schottky diodes in the far-infrared interferometer is reported. The minimum detectable line average density of the system is 5×10¹¹ cm^–3.     

Different Views on the Stability of Protein Conformations and Hydrophobic Effects

Apparently contradictory statements about the thermodynamics of aqueous protein solutions and of hydrophobic effect are quoted and discussed. Some credibility is found in the divergent points of view and it is pointed out that they focus attention on different aspects of the complicated conditions in aqueous solutions, some of which are more important than others for the stability of protein conformations.The importance of characteristics of solvent water is emphasized, in particular (1) the strong mutual cohesion of water molecules, and (2) structural changes of water induced by (nonpolar) solute molecules. It is stressed that consideration of only one of these effects and an inexpedient choice of standard states are origins of confusion in the literature about aqueous systems. A simple approach to hydrophobic effects considering both of the above mentioned effects, is proposed.     

数字喷墨印刷关键技术及其实现

经过20多年的完善与发展，喷墨技术已经成为大幅面广告印刷行业的主要印刷技术。随着图书按需印刷需求的快速扩张以及国家环保政策的迅速落地，喷墨印刷技术作为一项高效环保的数字化印刷技术，得到越来越高的关注，业内普遍认为喷墨印刷技术将是数字化印刷的必然发展趋势。然而与已经成熟的多Pass喷墨印刷设备不同，单Pass喷墨印刷设备在数据带宽、数据在线重构、高精度同步控制、喷嘴在线补偿等方面有着极高的技术要求。本文首先简要介绍了喷墨技术，然后针对单Pass喷墨印刷设备需要解决的技术问题提出了相应的解决方案。依据本文技术设计的单Pass书刊喷墨印刷机已经投放市场，并且获得了用户的普遍认可。