Surface Energy and Wettability of Plasma-treated Polyacrylonitrile Fibers

Polyacrylonitrile fibers were treated with a nitrogen glow-discharge plasma. The surfaces of untreated and treated fibers were examined with contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Surface energy calculations of the fibers were carried out from contact angle measurements using the relationships developed by Fowkes. It is found that plasma treatment causes a reduction in water contact angle on the fiber surfaces. The dispersion component of surface energy changes slightly, while the polar component is increased significantly from 14.6 mN/m to 58.7 mN/m and the total surface energy increase is 139%. The increase of surface energy is mainly caused by the introduction of hydrophilic groups on the fiber surfaces after plasma treatment.     

Statistical Thermodynamics of a Dipole Hard Sphere Liquid. Hindered Rotation Model

Approximate analytical expressions are obtained using the hindered molecular rotation model to describe the thermodynamic properties of a model polar liquid of dipolar hard spheres; the results are in good agreement with the available computer simulation data. A polar liquid is represented as a macromolecular knot of particles bonded by dipole forces. The resulting formulas correspond to the first and second neighbor interaction approximation. The formulas may be applied to classical one-dimensional systems described by the Ising or Heisenberg Hamiltonians.     

Excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane)

The excess properties of the mixture bis(2-dichloroethyl)ether (chlorex) + 2,2,4-trimethylpentane (isooctane), i.e. excess volumev ^E, excess enthalpyh ^E, excessGibbs energyg ^E and excess heat capacityc _p ^E are reported. The excess volume is small, negative on the chlorex side and positive on the isooctane side. The excess enthalpy at 293.15 K is 1 913 J mol^–1 for equimolar composition, the excessGibbs energy amounts to 1 367 J mol^–1 under the same conditions. The system undergoes phase separation below 290.47 K. Due to the nearness of the critical point,c _p ^E exhibits a strong maximum at the critical composition (x _isooctane=0.508), though the basic part ofc _p ^E is negative. Discussion focusses on the effects of polarity of chlorex as mixing partner, on near-critical properties, and on mixing rules of avan der Waals-type equation of state.Dedicated to Prof. Dr.K. Komarek on the occasion of his 60th birthday.     

Stiefel-Whitney classes and the conormal cycle of a singular variety

A geometric construction of Sullivan's Stiefel-Whitney homology classes of a real analytic variety is given by means of the conormal cycle of an embedding of in a smooth variety. We prove that the Stiefel-Whitney classes define additive natural transformations from certain constructible functions to homology. We also show that, for a complex analytic variety, these classes are the mod 2 reductions of the Chern-MacPherson classes.

     

m-Systems and Partial m-Systemsof Polar Spaces

LetP be a finite classical polar space of rankr, withr 2. A partialm-systemM ofP, with 0 m r - 1, is any set (₁), ₂,..., _k ofk ( 0) totally singularm-spaces ofP such that no maximal totally singular space containing _i has a point in common with (_{1 2} ... _k) — _i,i = 1, 2,...,k. In a previous paper an upper bound for ¦M¦ was obtained (Theorem 1). If ¦M¦ = , thenM is called anm-system ofP. Form = 0 them-systems are the ovoids ofP; form =r - 1 them-systems are the spreads ofP. In this paper we improve in many cases the upper bound for the number of elements of a partialm-system, thus proving the nonexistence of several classes ofm-systems.Dedicated to Hanfried Lenz on the occasion of his 80th birthday     

Thermochemical conversion of cellulose in polar solvent (sulfolane) into levoglucosan and other low molecular-weight substances

Pyrolysis of cellulose in sulfolane, an aprotic polar solvent, was conducted at the temperature between 200 and 330 °C. Sulfolane was used as a good solvent for levoglucosan, the major anhydromonosaccharide formed from cellulose pyrolysis, for prevention of the polymerization reaction. Cellulose was observed completely decomposed into soluble products in sulfolane within 3, 10, 60 and 480 min at 330, 280, 240 and 200 °C, respectively. The soluble products had molecular weights less than 500 after acetylation (GPC analysis) and similar product composition to that from cellulose pyrolysis under nitrogen (levoglucosan, levoglucosenone, furfural and 5-hydroxymethylfurfural by HPLC analysis). Pyrolysis of cellulose in polar solvent, which can solubilize anhydromonosaccharides, is proposed as a method for selective formation of levoglucosan and other low molecular-weight (MW) substances. As well, the cellulose pyrolysis in sulfolane did not suffer from carbonization reactions (microscopic and IR spectroscopic analysis) as did cellulose pyrolysis under nitrogen or in dioctyl phthalate (a poor solvent for levoglucosan) which gave brown/black solids. The residues obtained from the pyrolysis in sulfolane were colorless and gave similar IR spectra to that of the original cellulose. Based on these results, a ‘surface-peeling mechanism’ is proposed, and the role of the solvent in the mechanism is discussed.     

Excess molar heat capacities and excess molar volumes of some mixtures of propylene carbonate with aromatic hydrocarbons

Excess molar volumes V ^E and excess molar heat capacities C _P ^E at constant pressure have been measured, at 25°C, as a function of composition for the four binary liquid mixtures propylene carbonate (4-methyl-1,3-dioxolan-2-one, C₄H₆O₃; PC) + benzene (C₆H₆;B), + toluene (C₆H₅CH₃;T), + ethylbenzene (C₆H₅C₂H₅;EB), and + p-xylene (p-C₆H₄(CH₃)₂;p-X) using a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. All the excess volumes are negative and noticeably skewed towards the hydrocarbon side: V ^E (cm³-mol^–1) at the minimum ranges from about –0.31 at x₁=0.43 for {x₁C₄H₆O₃+x₂p-C₆H₄(CH₃)₂}, to –0.45 at x₁=0.40 for {x₁C₄H₆O₃+x₂C₆H₅CH₃}. For the systems (PC+T), (PC+EB) and (PC+p-X) the C _P ^E s are all positive and even more skewed. For instance, for (PC+T) the maximum is at x _1,max =0.31 with C _P,max ^E =1.91 J-K^–1-mol^–1. Most interestingly, C _P ^E of {x₁C₄H₆O₃+x₂C₆H₆} exhibits two maxima near the ends of the composition range and a minimum at x _1,min =0.71 with C _P,min ^E =–0.23 J-K^–1-mol^–1. For this type of mixture, it is the first reported case of an M-shaped composition dependence of the excess molar heat capacity at constant pressure.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Lipids of Ricinus communis Seeds

Lipids of Kazachok castor seeds were studied. The compositions of neutral lipids of the benzine extract and of the fatty acids of neutral and polar lipids were found. The principal acids were palmitic, oleic, linoleic, and 12-hydroxyoctadec-9-enoic.     

La3ScBi5的合成与晶体结构

在氩气保护下，将金属单质置于钽管中进行高温固相反应得到了一个新的三元极性金属间化合物,La₃ScBi₅。通过X-射线单晶衍射确定了它的晶体结构。La₃ScBi₅晶体属六方晶系，空间群为P6₃/mcm(No.193)，晶胞参数为：a=b=0.975 73(5) nm，c=0.655 92(6) nm，V=0.543 41(9) nm³，Z=2。La₃ScBi₅属反式Hf₅Sn₃Cu结构类型，其结构特征为Bi的一维直线链和由ScBi₆八面体之间通过共面形成的{ScBi₃}链。能带计算表明La₃ScBi₅呈金属导电性。