Squeezing Molecularly Thin Alkane Lubrication Films: Layering Transitions and Wear

The properties of alkane lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and the elastic properties of the solid surfaces. We consider linear alkane molecules of different chain lengths, C₃H₈, C₄H₁₀, C₈H₁₈, C₉H₂₀, C₁₀H₂₂, C₁₂H₂₆, and C₁₄H₃₀ confined between smooth gold surfaces. We observe well-defined molecular layers develop in the lubricant film when the width of the film is of the order of a few atomic diameters. An external squeezing-pressure induces discontinuous changes in the number n of lubricant layers. We find that with increasing alkane chain length, the transition from n to n - 1 layers occurs at higher pressure, as expected based on the increasing wettability with increasing chain length. We obtain good correlation between our theoretical results and wear experiments.     

Transfer, Perception, and Activity of Male Pheromone of Acrolepiopsis assectella with Special Reference to Conspecific Male Sexual Inhibition

In the leek moth, Acrolepiopsis assectella, the male, stimulated by a calling female, produces a sexual pheromone that is active on the female. The male-produced pheromone blend contains eight alkanes previously isolated from the male hair-pencils. We used EAG techniques to study the effect of the pheromone on females reared on leek or on artificial diet and on males reared on leek. The optimal stimulation duration appeared to be 1.6 sec exposure to the pheromone or components. The concentrations tested on the antenna were of the order of 10¹² molecules/cm³. The hair-pencil extract tested was of an estimated concentration of around 10⁹ molecules/cm³. The antennal responses are expressed relative to responses to a standard, amyl acetate, but also as an absolute value. Generally, females reared on artificial diet and males reared on leek responded better than females reared on leek. Of the alkanes tested, those present in hair-pencils gave higher responses, with hexadecane always giving the strongest response. A possible inhibiting activity of male leek moth pheromone on the sexual behavior of conspecific males was investigated. The behavior of sexually stimulated males was observed in the presence of other males, hair-pencil extracts, and different compounds either pure or in a mixture. The experiments established that in this species, male pheromone inhibits wing fluttering duration of conspecific males. This inhibition was obtained not only with fluttering males as a source of pheromone but also with all the alkanes tested. The inhibition was due to hair-pencil chemicals, particularly if these were perceived by olfaction plus contact. Wing fluttering increased the inhibitory activity of male-derived alkanes.     

受激布里渊散射的新介质

为了寻找性能良好的受激布里渊散射(SBS)介质,根据SBS对介质的要求,试验了几种全卤代烃新介质。测定或计算了增益系数、声子寿命和吸收系数等参数。四氯乙烯(C2Cl4)具有良好的SBS特性,其增益系数为9.0cm·GW-1,声子寿命为0.59ns,吸收系数为0.003cm-1。分析和讨论了介质化学结构对SBS特性的影响。     

Inter- and intradiffusion in liquid mixtures of methane andn-decane

The interdiffusion coefficient,D ₁₂, has been measured by Mach-Zehnder interferometry for liquid mixtures of methane andn-decane at 303 K. The mole fraction of methane was from 0.11 to 0.96 and the pressure was from 30 to 60 MPa. This includes measurements in the critical region, the critical locus being approached from supercritical pressures to within 0.4 MPa. The accuracy inD ₁₂ is estimated to be from 3 to 10%, depending on the composition. Our data are compared with the Sigmund correlation, which is widely used to estimate diffusion coefficients in hydrocarbons at high pressures. The deviation between estimate and measurement is one order of magnitude for some of the states. We have also compared with a more recent correlation used by Erkey, but this one is not found to be applicable to the compositions studied in the present work. Our data were related to recently measured intradiffusion coefficients,D ₁ andD ₂, at the same state points. On this basis, we have evaluated different mixing rules for obtaining the interdiffusion coefficient from intradiffusion coefficients, both close to and away from the critical region. It is found that the so-called Darken and Adamson relations have the right qualitative behavior.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Viscosity of biniary mixtures. III. Tri-n-butylamine with alkanes and monoalkylamines at 303.15 and 313.15 K

Viscosities of seven binary systems of n-propylamine, n-butylamine, n-hexylamine, n-octylamine, n-hexane, n-octane, and isoctane (2,2,4-trimethylpentane) with tributylamine have been measured at 303.15 and 313.15 K with an Ubbelohde suspended-level viscometer. Based on Eyring's theory, values of excess Gibbs energy of activation G ^*E of viscous flow have been calculated. Deviations of viscosities from linear dependence on the mole fraction and values of G ^*E are attributed to the H-bonding and to the size of alkylamine and alkane molecules. The free volume theory of Prigogine-Flory-Patterson in combination with work by Bloomfield-Dewan has been used to estimate the excess viscosity ln and the terms corresponding to enthalpy, entropy, and free volume contributions for the present binary mixtures.     

Estimation of the critical constants of long-chain normal alkanes

Correlations between the critical constants of normal alkanes and the number of carbon atoms in a molecule have been considered. In an approximation of a self-consistent field for a polymeric fluid, an equation of state of the van der Waals type has been written, and the dependences of the critical constants of chain molecules on the number of mers have been obtained. It has been found that for an infinitely long alkyl chain, the limiting values of the critical temperature, the critical pressure, and the critical density are equal to, respectively, 1135 K, 0 M Pa, and 0 kg · m^–3. A method of pulse heating of a wire probe immersed in the substance under investigation has been used to measure the dependence of the temperature of the attainable superheatT ^* of low-density polyethylene on the pressure p and the duration of heating pulset ^*. Extrapolation has been used to obtain an estimation of the attainable-superheat temperature of polyethyleneT ^*(p=0,t ^*=0)= 1175 K, which can be treated as the critical temperature of polyethylene.     

The solubility of HCFC22, CFC114 and HFC152A in n-hexadecane

The solubilities of chlorodifluoromethane (HCFC22), 1, 2-dichlorotetrafluoroethane (CFC114) and 1,1-difluoroethane (HFC 152a) in n-hexadecane have been measured at temperatures between 303. 15 and 343. IS K and Henry's constants have been derived. The measurements were made with two different methods, a GLC method and an isochoric method. In general the results of the methods differ less than their combined margin of error, which is estimated to be less than 5% for the GLC method and less than 2% for the isochoric method.     

Allelochemical inhibition of recruitment in a sedimentary assemblage

Chemical signals affect recruitment of organisms in many habitats. Most of the described biogenic chemical moieties in marine environments elicit specific positive responses, for example, of predators to prey or of conspecific larvae to suitable habitats. However, organisms also release noxious chemicals that may elicit negative responses from neighboring members of the assemblage. Herein we measured the effect on recruitment of the release of such compounds (halogenated aromatics) into sediments. The common, sediment-dwelling, terebellid polychaeteThelepus crispus contains brominated aromatic metabolites and contaminates the sediments surrounding its tube with these compounds. Sediments so contaminated are actively rejected by recruitingNereis vexillosa (Nereidae: Polychaeta). Interestingly, many of these noxious biogenic compounds have low solubility in water and, therefore, potentially long residence times in sedimentary environments. The negative response of larvae to sediment contaminated with them is a novel, potentially common, and very important mechanism in which sediment-dwelling organisms release haloaromatic compounds and thus impose a recruitment filter on their community.     

纤维状BPO4/SiO2催化剂的制备及其丙烷氧化脱氢性能

通过静电纺丝法制备了一种高温焙烧后具有纤维状结构的磷酸硼/二氧化硅（BPO₄/SiO₂）催化剂,并考察了BPO₄负载量和焙烧温度对该催化剂的结构和催化丙烷氧化脱氢性能的影响。研究发现焙烧过程使纤维直径减小。随着BPO₄负载量的增加,丙烷氧化脱氢活性增高。当BPO₄负载量为7%（质量分数）,焙烧温度为600℃时,BPO₄/SiO₂催化剂具有最佳的催化性能;在反应温度为480℃下,丙烷转化率和丙烯产率分别达到17.0%和13.0%,且催化剂稳定性良好。当焙烧温度较低时（550℃）,催化剂中的有机物分子未被除尽,导致烯烃的选择性偏低;当焙烧温度较高时（700℃）,SiO₂结构收缩紧密,抑制了活性相的暴露。由于纤维结构可暴露更多活性位点,该催化剂较相同条件下粉末状BPO₄催化剂有着更高的催化活性。     

烷烃异构铂催化剂及其在燃油制取中的研究现状

铂催化剂具有优异的催化活性和异构选择性,综述了其在汽油、润滑油和柴油、以及生物燃油等领域的研究进展。铂催化剂中铂负载量、金属助剂和载体改性等对轻质烷烃异构化、提高汽油辛烷值有影响;载体的产物择形性能对润滑油、柴油的铂催化剂性能有影响;生物燃料用催化剂需具备加氢脱氧和异构化的能力,分子筛载体的酸性、酸量和孔道尺寸对性能影响很大。基于文献分析,提出了各类烷烃异构化铂催化剂的研发方向。