Thermoreversible gelation of polyacrylonitrile/dimethylformamide-solution

The thermoreversible gelation of semi-diluted atactic polyacrylnitrile (PAN)/dimethylformamide (DMF)-solutions has been studied. The structural features of PAN/DMF-gels, formed by supercooling have been investigated by DSC-, x-ray- and swelling measurements. A new structural model has been introduced to describe the morphology of the junction zones of PAN/DMF-gels and to also explain the gelation behavior of PAN/DMF-solutions as the structural features of PAN/DMF-gels. The junction zones of a PAN/DMF-gel have been defined as ordered junction zones.A gelation enthalpy of about H=–6 kJ/mol supports the idea that an ordered junction zone is formed by intermolecularly neighboring stereoregular parts of atactic PAN chains due to a nucleation process in the solution. It can be defined as a strongly distributed fringed micelle.     

Effect of ageing atmospheres on the changes in surface free energies of oxygen plasma-treated polyethylene films

The changes in the surface properties of oxygen plasma-treated polyethylene films during ageing in various atmospheres (water, dry nitrogen gas, and hexane) were studied from the viewpoint of the interaction of the surface functional groups formed on the films and the ageing media. The XPS (x-ray photoelectron spectroscopy) and the SSIMS (static secondary ion mass spectrometry) spectra indicated the formation of polar groups containing oxygen such as C=O on the film surface. The changes in the critical surface tension (_C) of the film with ageing time were largely affected by the ageing atmospheres: the _C value of the film aged in water increased, and those of the films aged in nitrogen gas and hexane decreased with an increase in ageing time. These different tendencies among the ageing media could be understood reasonably with examining the surface free energy ratios (the total energy, _S ^tot , the dispersion force component, _S ^d / _S ^tot , the polar component, _S ^p / _S ^tot , the hydrogen bonding component, _S ^h / _S ^tot ) of the films. The ageing in water of which _L is large gave the films with higher _S ^p / _S ^tot values, suggeting that the overturn and/or the orientation of the polar groups toward the water phase occurred so as to minimize the discrepancy of the surface free energy between the polymer surface and water. On the other hand, the ageing in nitrogen gas and hexane media of which _L are small gave the films with lower _S ^p / _S ^tot and _S ^h / _S ^tot values, suggesting the overturn and/or the orientation of the polar groups into the bulk polymer.     

Fluid multiphase equilibria and critical phenomena in binary and ternary mixtures of carbon dioxide, certain n-alkanols and tetradecane

Experimental results of fluid multiphase equilibria occurring in ternary mixtures of near-critical carbon dioxide, certain n-alkanols and tetradecane are presented. The following n-alkanols were used in this investigation: decanol, octanol, heptanol, hexanol and pentanol. In the ternary systems with decanol, octanol or heptanol a closed loop liquid-vapor two-phase region in the three-phase surface liquid-liquid-vapor was found. As far as the ternary system with decanol is concerned, this phenomenon is in agreement with an earlier and unexpected finding of Patton et al. (1993). In addition, it was also found in this study that the phase diagrams of the ternary mixtures with hexanol or pentanol as the n-alkanol show further complications.     

乙二醇对烷基三甲基溴化铵胶团化行为的影响

利用电导法研究了烷基三甲基溴化铵表面活性剂(CnTAB,n=12,14,16),即十二烷基三甲基溴化铵(DTAB),十四烷基三甲基溴化铵(TTAB)和十六烷基三甲基溴化铵(CTAB),在混合极性溶剂乙二醇/水(体积分数0～40%)中的胶团化行为。考察了温度对胶团形成的影响,应用相分离模型估算了三个表面活性剂的胶团热力学参数。结果表明临界胶团浓度(cmc)和反离子解离度(α)都随乙二醇组分的增加而增大。在乙二醇/水混合溶剂中胶团形成的标准吉布斯自由能相差很小,混合焓都是负值,而混合熵都为正值,说明焓-熵补偿效应在胶团形成中起主导作用。     

超临界水的分子动力学模拟

采用分子动力学(MD)模拟的方法对超临界条件下水的结构及扩散性质进行了研究.模拟结果表明超临界条件下水分子之间的氢键作用明显减弱,分子极性大大降低.扩散性质与常温下相比,其大小约上升了两个数量级.     

Intrachain and Interchain Interactions in Polystyrene: Dilute and Semidilutc Solutions

Thestudiesofpolymersolutionpropertiesfromdilatetoconcentratedsolutionbyfluorescencetechniquehaveattractedmoreattentionsinrecentdecadesl'2.InordertoinvestigateintrachainandinterchainilltCractionsindilutesolutionregion,pyrenewasusedaslabelsattachedtopolystyrene,whichwasintenselyfluorescentwithalongfluorescentlifetime3.Inthepresentwork,thepolystyreneattachedwithpyrenylgroupshadanunfavourablestrUcturetothenearestneighborexcimerformationwiththepyrenylgroupsseparatedbymorethanthreeatomsalongthechain…     

Partitioning behaviour of organic compounds between ionic liquids and supercritical fluids

Applications and prospects of two-phase, tuneable solvent systems composed of ionic liquids (ILs) and supercritical fluids with an emphasis on supercritical carbon dioxide (scCO(2)) are reviewed. The IL-scCO(2) biphasic systems have increasingly been used in diverse fields of chemistry and technology, and some examples of these applications are mentioned here. Rational design of such applications can obviously benefit from pertinent data on phase equilibria including the partition coefficients of the prospective products and reactants between the two phases. Therefore, a reliable technique to measure the limiting partition coefficients would be of value. Here, the pros and cons of supercritical fluid chromatography in this respect are discussed. An overview of methods for predictive thermodynamic modelling of binary (IL-scCO(2)) and ternary (solute-IL-scCO(2)) systems is also included.     

Analysis of critical points on the potential energy surface

A simple classification scheme is proposed for critical points, based only on rankr and signatures of the (n,n)-matrixG of harmonic force constants. The determination ofr ands, e.g. by the well-known factorizationG=L ^T gL (L: triangular matrix,g: diagonal matrix), has several theoretical as well as practical (computational) advantages over the inspection of eigenvalues ofG, so far used in quantum chemistry. The eigenvalues are sufficient butnot necessary for a classification whereas rank and signature are the only necessary and sufficient prerequisites for solving the task. For the purpose of presenting a working example, by calculating only a 2×2 torque constant matrix, it is shown that the coplanar ethylbenzene is unstable in the CNDO/2 picture.     

Thermodynamic properties of aqueous organic mixtures near the critical demixing: Cases of 2,6-dimethylpyridine and of 2-isobutoxyethanol

Phase diagrams, volumes and heat capacities of aqueous mixtures of 2,6-dimethylpyridine (2,6-L) and 2-isobutoxyethanol (iBE) and activities of 2,6-L in aqueous mixtures were measured in the monophasic region near the lower critical solution temperature (LCST). With 2,6-L some measurement were also made just above the LCST. From the temperature dependence of these data, partial molar relative enthalpies (2,6-L), expansibilities and the temperature derivative of heat capacities were calculated and show that iBE undergoes a microphase transition at low concentration which is not related to the phase separation. On the other hand, the properties of 2,6-L in the water-rich region at temperatures well below the LCST indicates that this solute has only a slight tendency to associate. The heat capacities of 2,6-L show an important increase near the LCST. Such changes are not observed for iBE and other alkoxyethanols and amines since these systems already exist in the form of microphases; the partial molar properties of iBE near the LCST are nearly equal to the molar values of the pure liquid, and the changes in thermodynamic properties corresponding to the macroscopic phase transition, are therefore too small to be measured by the present techniques.