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1.
We revisit the Simha-Somcynsky model of polymer fluids with the purpose of developing novel theoretical and computational approaches to simplify and speed up its solution as well as the fitting of experimental data, and decrease its level of mathematical complexity. We report a novel method that allows us to solve one of the two equations of the model exactly, thus putting the level of mathematical difficulty on a par with the one of other models for polymer fluids. Moreover, we describe a computational algorithm capable of fitting all five parameters of the model in an unbiased way. The results obtained reproduce literature results and fit experimental pressure-volume-temperature and solubility parameter data for three polymers very accurately. Moreover, the new techniques allow for the investigation of the model at very low temperatures. Unexpectedly, the model predicts behaviors that could be interpreted as a glass transition, as routinely observed in dilatometry and differential scanning calorimetry, and a glass phase. We compared the predicted and experimental T g’s for cis poly(1,4-butadiene) and found an excellent quantitative agreement.  相似文献   
2.
G. P. Wright  P. Zoller 《高压研究》2013,33(1-6):282-284
Abstract

Results on the temperature- and pressure dependence of the specific volume, thermal expansivity and compressibility of elastomeric compounds are reported.  相似文献   
3.
物理气相输运法(PVT)是实验室最为常见的碳化硅(SiC)大块单晶生长方法.本文在碳化硅晶体生长模型化研究中,针对碳化硅单晶PVT生长过程中的传热传质等现象引入了对流传热中的场协同原理,利用这一原理对生长室内的流场温度场进行了优化,并对改良前后分别进行了数值模拟,研究了该原理对晶体生长的影响.实验室碳化硅单晶的生长成功...  相似文献   
4.
The pressure–volume–temperature behavior of miscible blends of poly(ethylene oxide) (PEO) and poly(methyl acrylate) (PMA) was studied over extended ranges of temperature and pressure. From pressure–volume–temperature data, the reduction parameters for the Flory‐Orwoll‐Vrij equation‐of‐state were determined. It was found that reduction parameters as well as density, thermal expansion coefficient, and isothermal compressibility vary with composition in a nonlinear manner. The surface tension of the blends in the molten state was measured over the whole composition range using the sessile drop method. The surface tension was found to display negative deviation from additivity pointing toward a remarkable surface excess of PMA. Moreover, surface tension displays a minimum in the range of low PEO content at weight fraction of ~0.19. In addition, the temperature coefficient of surface tension shows negative deviation from linearity. It stays constant when PMA is in excess. Results are discussed in terms of equation‐of‐state thermodynamics. The minimum of surface tension can be well explained by weak self‐association of PEO in the bulk. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1893–1900, 2010  相似文献   
5.
A mathematical framework for applying a density-and-temperature-dependent volume translation in a thermodynamically consistent manner was developed. Volumetric equations of state (EOS)s that incorporate this translation procedure can be used to generate derived properties, such as fugacity and enthalpy departure, that are based on isothermal departure or residuals from ideal gas state conditions. This kind of translation serves to improve the original EOS and not simply act as a correlation for molar volumes. A density-and-temperature-modified translation of this type was applied to the Soave–Redlich–Kwong EOS and was shown to possess accuracy for saturation pressure predictions equivalent to the untranslated EOS, as well as greatly improved density predictions compared to what is available when using only constant valued translation. The EOS translated in this manner retains many of the important features of the untranslated EOS, such as explicit calculation of volume roots, while having the representation capabilities of substantially more complicated models, such as the extended virial equation of Benedict, Webb, Rubin, and Starling.  相似文献   
6.
本文依据对应态原理,提出新定义的对比压缩因子Zr=(1-Z)/(1-ZC)的无量纲交换式和对饱和温度的对比温度Tsr=T/Ts式,并根据两种流体工质对比压力Pr1=Pr2,对比温度Tsr1=Tsr2相等时,Zr1=Zr2相等的原则,导出了从一种已知PVT关系的物质推算它种物质的PVT值的通用方法。用本方法以水为标准物质推算了R12、R131、R134a、C2H4等几种物质在过热气体区、超临界区和液体区比容,计算值与文献实验值的平均偏差小于2,最大偏差小于4%。  相似文献   
7.
The anisotropy of the thermal expansion of polyimide films was investigated . Out-of-plane or thickness direction coefficients of linear thermal expansion (CTE) were calculated from the difference between the coefficient of volumetric expansion (CVE) and the sum of the in-plane or film direction coefficients of linear thermal expansion for commercial and spin-coated PMDA//ODA and BPDA//PPD films and spin coated BTDA//ODA/MPD films. The CVEs were obtained from a pressure-volume-temperature (PVT) technique based on Bridgeman bellows. The CVE was shown to be essentially constant, independent of molecular orientation and thickness. A decrease in the in-plane CTEs therefore occurs at the expense of an increase in the out-of-plane CTE. In all cases the calculated out-of-plane CTE was higher than the measured in-plane CTE. The ratio of the out-of-plane CTE to the in-plane CTE was 1.2, 3.8, and 49.3 for the spin-coated BTDA//ODA/MPD, PMDA//ODA, and BPDA//PPD films, respectively. © 1994 John Wiley & Sons, Inc.  相似文献   
8.
This article reports on an experimental investigation of the equation of state and the transition behavior of main-chain thermotropic liquid crystalline polymers over a wide temperature range, and at pressures to 200 MPa. The materials studied were a series of azomethine ether polymers. A varying number n (= 4, 7, 8, 9, 10 and 11) of methylene spacer units in the backbone provided systematic variation of the structure. Experimental techniques used included high-pressure dilatometry (PVT measurements) to 200 MPa, high-pressure differential thermal analysis, also to 200 MPa, and conventional (atmospheric-pressure) differential scanning calorimetry (DSC). The equation of state of the materials can be well represented by the Tait equation in distinct regions, separated by a glass transition, Tg(P), a first-order transition to a nematic state, Tk-n(P), and a first-order transition to an isotropic melt state Tc(P). The atmospheric pressure values of Tk-n and Tc decreased with increasing number of spacer units and showed a clear odd-even effect. Tg and Tk-n both increased with pressure. The pressure dependence of Tc could not be observed due to the onset of degradation in the same temperature region. On isobaric cooling at 3°C/min, the crystallization from the nematic state occurred a few tens of degrees below Tk-n. This supercooling was independent of pressure for some materials, while for others it increased with increasing pressure. The values of the enthalpy and entropy associated with the first-order transition into the nematic state were lower than those of typical isotropic polymers at their melting transitions. The transition enthalpy did not have any systematic variation with increasing number of spacer units. Values of the transition enthalpy calculated from the Ciapeyron equation did not always agree with the values measured by DSC. This may be due to the two-phase nature of the low-temperature state. At the transition to the isotropic state, the transition enthalpy at P = 0 decreased with n and showed an odd-even effect. © 1994 John Wiley & Sons, Inc.  相似文献   
9.
The scaling law for relaxation times, recently proposed by Casalini and Roland, is utilized in the framework of KAHR (Kovacs, Aklonis, Hutchinson, and Ramos) phenomenological theory. With this approach it is shown that the pressure, volume, and temperature (PVT) data obtained on Poly(methyl-methacrylate) (PMMA) can be reliably predicted, in the region of the alpha-relaxation, by using only two fitting parameters, namely: the relaxation time in the reference state, τg, and the fractional exponent, β, that describes the dispersion of the alpha-relaxation.  相似文献   
10.
借助专业晶体生长模拟软件FEMAG和自主开发的对流、传质、过饱和度及生长速率预测等有限元模块研究了物理气相传输法(PVT)同质外延生长氮化铝(AlN)单晶工艺时的初始传热及传质过程,并分析了不同形状籽晶台对生长室内的温度场、流场、过饱和度及生长速率的影响。温度场模拟结果表明籽晶台侧部角度改变可影响籽晶表面轴向及径向温度梯度,流场及传质模拟表明籽晶台侧部角度变化对籽晶台周边的传质有巨大影响。传质及过饱和度模拟结果表明,当籽晶台侧部角度为130°时,籽晶表面温度梯度较小且可以完全抑制籽晶台侧部多晶沉积,有利于通过同质外延工艺生长出无寄生、无裂纹的高质量氮化铝单晶锭。  相似文献   
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