Molecular weight dependence of phase Behavior of PEO/P(EO-b-DMS) blends: Application of Sanchez-Lacombe lattice fluid theory

Molecular weight dependence of phase separation behavior of the Poly (ethylene oxide) (PEO)/Poly(ethylene oxide-block-dimethylsiloxane) (P(EO-b-DMS)) blends was investigated by both experimental and theoretical methods. The cloud point curves of PEO/P(EO-b-DMS) blends were obtained by turbidity method. Based on Sanchez-Lacombe lattice fluid theory (SLLFT), the adjustable parameter, epsilon*(12)/k (quantifying the interaction energy between different components), was evaluated by fitting the experimental data in phase diagrams. To calculate the spinodals, binodals, and the volume changes of mixing for these blends, three modified combining rules of the scaling parameters for the block copolymer were introduced.

Calculating the equation of state parameters and predicting the spinodal curve of isotactic polypropylene/poly(ethylene-co-octene) blend by molecular dynamics simulations combined with Sanchez-Lacombe lattice fluid theory

Molecular dynamics simulations are adopted to calculate the equation of state characteristic parameters P*, rho*, and T* of isotactic polypropylene (iPP) and poly(ethylene-co-octene) (PEOC), which can be further used in the Sanchez-Lacombe lattice fluid theory (SLLFT) to describe the respective physical properties. The calculated T* is a function of the temperature, which was also found in the literature. To solve this problem, we propose a Boltzmann fitting of the data and obtain T* at the high-temperature limit. With these characteristic parameters, the pressure-volume-temperature (PVT) data of iPP and PEOC are predicted by the SLLFT equation of state. To justify the correctness of our results, we also obtain the PVT data for iPP and PEOC by experiments. Good agreement is found between the two sets of data. By integrating the Euler-Lagrange equation and the Cahn-Hilliard relation, we predict the density profiles and the surface tensions for iPP and PEOC, respectively. Furthermore, a recursive method is proposed to obtain the characteristic interaction energy parameter between iPP and PEOC. This method, which does not require fitting to the experimental phase equilibrium data, suggests an alternative way to predict the phase diagrams that are not easily obtained in experiments.

Pressure effects on the thermodynamics of trans-decahydronaphthalene/polystyrene polymer solutions: Application of the Sanchez-Lacombe lattice fluid theory

The cloud-point temperatures (T-cl's) of trans-decahydronaphthalene(TD)/polystyrene (PS, (M) over bar (w) = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1-16degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol.-% polymer). The system phase separates upon cooling and T-cl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of polymer solutions under different pressures were observed for different compositions, which demonstrated that pressure has a greater effect on the TD/PS solutions when far from the critical point as opposed to near the critical point. The Sanchez-Lacombe lattice fluid theory (SLLFT) was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified PS scaling parameters can describe the thermodynamics of the TD/PS system well. Moreover the SLLFT describes the experimental results well.

Theoretical estimation of thermodynamic properties of the system PS/PPO on the basis of modified combining rule of Sanchez-Lacombe lattice fluid model

The three scaling parameters described in Sanchez-Lacombe lattice fluid theory (SLLFT), T*, P* and rho* of pure polystyrene (PS), pure poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their mixtures are obtained by fitting corresponding experimental pressure volume-temperature data with equation-of-state of SLLFT. A modified combining rule in SLLFT used to match the volume per mer, v* of the PS/PPO mixtures was advanced and the enthalpy of mixing and Flory-Huggins (FH) interaction parameter were calculated using the new rule. It is found that the difference between the new rule and the old one presented by Sanchez and Lacombe is quite small in the calculation of the enthalpy of mixing and FH interaction parameter and the effect of volume-combining rule on the calculation of thermodynamic properties is much smaller than that of energy-combining rule. But the relative value of interaction parameter changes much due to the new volume-based combining rule. This effect can affect the position of phase diagram very much, which is reported elsewhere [Macromolecules 34 (2001) 6291]

Thermodynamics of blends of PEO with PVAc: application of the Sanchez-Lacombe lattice-fluid theory

Sanchez-Lacombe (SL) lattice-fluid theory was used to predict the miscibility of the PEO/PVAc blending system. Integral interaction parameters, g of this polymer pair were calculated by using SL theory. And the effect of the temperature, composition of blends and molecular weight of PVAc on the extent of their miscibility has been discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.

Thermodynamics of PMMA/SAN blends: Application of the Sanchez-Lacombe lattice fluid theory

Polymer blends of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) with an acrylonitrile content of about 30 wt % were prepared by means of solution-casting and characterized by virtue of pressure-volume-temperature (PVT) dilatometry. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of the mixing, the volume change of the mixing, and the combinatorial and vacancy entropies of the mixing for the PMMA/SAN system. A new volume-combining rule was used to evaluate the close-packed volume per mer, upsilon*, of the PMMA/SAN blends. The calculated results showed that the new and the original volume-combining rules had a slight influence on the FH interaction parameter, the enthalpy of the mixing, and the combinatorial entropy of the mixing. Moreover, the spinodals and the binodals calculated with the SL theory by means of the new volume-combining rule could coincide with the measured data for the PMMA/SAN system with a lower critical solution temperature, whereas those obtained by means of the original one could not.

Phase-separation behavior of the system PES/phenoxy: An application of the Sanchez-Lacombe lattice fluid theory

Cloud-point curves reported for the system polyethersulfone (PES)/phenoxy were calculated by means of the Sanchez-Lacombe (SL) lattice fluid theory. The one adjustable parameter epsilon(12)*/k (quantifying the interaction energy between mers of the different components) can be evaluated by comparison of the theoretical and experimental phase diagrams. The Flory-Huggins (FH) interaction parameters are computed based on the evaluated epsilon(12)*/k and are approximately a linear function of volume fraction and of inverse temperature. The calculated enthalpies of mixing of PES/phenoxy blends for different compositions are consistent with the experimental values obtained previously by Singh and Walsh [1].

Application of the Sanchez-Lacombe lattice fluid theory to the system pvme/ps and model calculations

Cloud point curves reported in the literature for five representatives of the system poly(vinyl methyl ether)/polystyrene were evaluated theoretically by means of the Sanchez-Lacombe lattice fluid theory. The measured phase separation behavior can be described within experimental error using only one adjustable parameter (quantifying the interaction between the unlike mers). The Flory-Huggins interaction parameters calculated from this theoretical description depend in good approximation linearly on composition (volume fractions) and on the inverse temperature. An evaluation of these data yields a maximum heat effect which is almost one order of magnitude less (ca. -0.25 J/cm(3)) than obtained via Hess's cycle (dissolution of the components and of the blend) from calorimetric measurements. Model calculations on the basis of the present theory demonstrate that the critical points shift to a different extent upon a certain relative change in the molar mass of the blend components. The sensitivity of the calculated phase diagrams against changes in the scaling parameter decreases in the following order: interaction energies between unlike mers, differences in the scaling temperatures, pressures and densities.

Game Vertebrate Densities in Hunted and Nonhunted Forest Sites in Manu National Park, Peru

Manu National Park of southern Peru is one of the most renowned protected areas in the world, yet large-bodied vertebrate surveys conducted to date have been restricted to Cocha Cashu Biological Station, a research station covering <0.06 percent of the 1.7Mha park. Manu Park is occupied by >460 settled Matsigenka Amerindians, 300-400 isolated Matsigenka, and several, little-known groups of isolated hunter-gatherers, yet the impact of these native Amazonians on game vertebrate populations within the park remains poorly understood. On the basis of 1495 km of standardized line-transect censuses, we present density and biomass estimates for 23 mammal, bird, and reptile species for seven lowland and upland forest sites in Manu Park, including Cocha Cashu. We compare these estimates between hunted and nonhunted sites within Manu Park, and with other Neotropical forest sites. Manu Park safeguards some of the most species-rich and highest biomass assemblages of arboreal and terrestrial mammals ever recorded in Neotropical forests, most likely because of its direct Andean influence and high levels of soil fertility. Relative to Barro Colorado Island, seed predators and arboreal folivores in Manu are rare, and generalist frugivores specializing on mature fruit pulp are abundant. The impact of such a qualitative shift in the vertebrate community on the dynamics of plant regeneration, and therefore, on our understanding of tropical plant ecology, must be profound. Despite a number of external threats, Manu Park continues to serve as a baseline against which other Neotropical forests can be gauged.

Efficient synthesis and utilization of phenyl-substituted heteroaromatic carboxylic acids as aryl diketo acid isosteres in the design of novel HIV-1 integrase inhibitors

Three new types of aryl diketo acid (ADK) isosteres were designed by conversion of the biologically labile 1,3-diketo unit into heteroaromatic motif such as isoxazole, isothiazole, or 1H-pyrazole to improve the physicochemical property of ADK-based HIV-1

聚合物共混物的相容性及热力学研究

近二十年来，共混已经成为简便而有效地制备新的具有各种附加性能的高分子材料的一种重要方法。共混物间的相容性及相容的程度往往决定其最终性质，因此，高聚物共混物的相容性和相行为成为高聚物共混热力学研究的热点。我们选取了二乙酸纤维素(CDA)／聚乙烯基砒烙烷酮(PVP)、聚氧化乙烯(PEO)／聚醋酸乙烯酯(PVAc)和聚氧化乙烯(PEO)／聚甲基丙烯酸甲酯(PMMA)三个共混体系作为研究对象，用溶液法、量热法和红外光谱等实验手段研究了三个体系的相容性及相容程度，用现代热力学理论预测了它们的相容性及相行为。CDA/PVP共混体系 1．用DSC和DMA测定了不同组成的CDA/PVP共混物的玻璃化转变温度，所有组成的共混物均只有一个介于两个纯组分玻璃化转变温度之间的T_g，且不同组成共混物的玻璃化转变温度高于用Fox方程计算得到的玻璃化转变温度，说明该体系是相容性共混体系，且两组分间存在特殊相互作用。2．用奥氏粘度计和乌氏粘度计分别测定的不同组成共混物的绝对粘度和稀溶液特性粘数，都远远大于按相应比例的CDA和PVP计算的相关粘度和特性粘数的数学平均值，这应该归结为两组分间的特殊相互作用使共混溶液中线团的尺寸变大，导致粘度增大。3．共混物的红外光谱谱图显示PVP的加入使CDA的羟基吸收峰向低频率方向移动，同时，随CDA含量的增加，PVP的羰基吸收峰也向低频率方向移动，说明CDA与PVP分子间形成了氢键，使官能团的电子云密度降低，吸收峰频率降低。4．溶液量热法得到的不同组成共混物的混合热焓均为负值，直接证明该共混体系是热力学相容体系，而且随CDA含量的增加，混合热焓的绝对值也增大，表明体系的相容程度与共混组成有关。PEO/PVAc共混体系 1．用乌氏粘度计测定了不同组成不同分子量的PEO/PVAc共混物的稀溶液特性粘数，计算出表征分子间相互作用的参数，△b。发现随PVAc分子量的增加，体系的相容性降低，体系的相容程度还与共混组成及溶液浓度有关。2．用DSC方法首次得到不同分子量的PEO/PVAc共混体系的“云点”和混合热焓。随着PVAc分子量的增加，“云点”曲线向低温方向移动。不同组成共混物的混合热焓值都小于零，直接证明该体系是热力学相容体系。溶液量热法得到的混合热焓值也都为负，与DSC方法得到的结果一致。3．PEO与PVAc间只存在弱相互作用，所以，选择Hamada等人改进的Flory状态方程理论对PEO/PVAc共混体系的相容性和相行为进行预测。利用溶液量热法的混合热焓值，得到该体系的Flory相互作用参数与温度和共混组成的关系，结果表明该体系是相容性共混体系，而且应该存在LCST相行为，体系的相容程度随PEO含量的增加而降低。4．Sanchez-Lacombe(SL)格子流体理论也适用于PEO/PVAc共混体系，通过PVAc分子量与相互作用能的定量关系建立了该共混物的热力学参数的预测体系。将SL理论拟合出的spinodal曲线和binodal曲线组成的相图与DSC法得到的相图（用“云点”表示）对比，发现二者完全相符。随PVAc分子量的增加，binodal曲线向低温方向移动，临界点向富含PEO的方向移动。混合热焓的实验值也与理论值相符。Flory相互作用参数随温度和共混组成的变化与Hamada等人改进的Flory状态方程理论预测的结果一致。PEO/PMMA共混体系 1．用乌氏粘度计测定了不同组成、不同分子量的PEO/PMMA共混物的稀溶液特性粘数，计算出表征分子间相互作用的参数，Δb。发现PEO与分子量最小的PMMA共混的体系是相容性共混体系，与分子量最大的PMMA共混的是不相容性共混体系，说明随PMMA分子量的增加，体系的相容性降低。2．溶液量热法得到PEO/PMMA = 50/50（重量比）的共混物的混合热焓为负值，表明该体系是热力学相容体系。DSC法得到的不同组成共混物的混合热焓值也都为负，与溶液量热法结论一致。3．Hamada等人改进的Flory状态方程理论也适用于PEO/PMMA体系，因为PEO与PMMA之间不存在特殊相互作用。用溶液量热法得到的混合热焓值，计算出该体系的Flory相互作用参数与温度的关系，结果表明该体系是相容性共混体系，而且应该存在LCST相行为。

System size dependence of associated yields in hadron-triggered jets STAR Collaboration

We present results on the system size dependence of high transverse momentum di-hadron correlations at root s(NN) = 200 GeV as measured by STAR at RHIC. Measurements in d + Au, Cu + Cu and Au + Au collisions reveal similar jet-like near-side correlation yields (correlations at small angular separation Delta phi similar to 0, Delta eta similar to 0) for all systems and centralities. Previous measurements have shown Chat the away-side (Delta phi similar to pi) yield is suppressed in heavy-ion collisions. We present measurements of the away-side Suppression as a function of transverse momentum and centrality in Cu + Cu and Au + Au collisions. The suppression is found to be similar in Cu + Cu and An + An collisions at a similar number of participants. The results are compared to theoretical calculations based on the patron quenching model and the modified fragmentation model. The observed differences between data and theory indicate that the correlated yields presented here will further constrain dynamic energy loss models and provide information about the dynamic density profile in heavy-ion collisions. (C) 2009 Elsevier B.V. All rights reserved.

Measurement of the Bottom Quark Contribution to Nonphotonic Electron Production in p plus p Collisions at root s=200 GeV

The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at root s = 200 GeV has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of p(T) >= 5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high p(T).

Higher Moments of Net Proton Multiplicity Distributions at RHIC

200 GeV corresponding to baryon chemical potentials (mu(B)) between 200 and 20 MeV. Our measurements of the products kappa sigma(2) and S sigma, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long-range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the root s(NN) dependence of kappa sigma(2). From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for mu(B) below 200 MeV.