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21.
The aim of this article is to examine the limits of applicability of the Simha‐Somcynsky (S‐S) equation of state (EOS) by comparing the pressure‐volume‐temperature (PVT) data and the derivatives (compressibility, κ, and thermal expansion coefficient, α) of anionic linear polystyrene (PS) with poly(benzyl ether) dendrimers (PBED). Fitting the PVT of PBED data to the S‐S EOS was similarly satisfactory as that of PS and the computed Lennard‐Jones (L‐J) interaction parameters showed similar errors of ca. 1%. Next, the experimental derivatives, α and κ of PS and PBED were compared with these functions computed from the S‐S EOS—good agreement was obtained for α at ambient pressure, P, indicating validity of the S‐S theory at least up to the first derivative. While the predicted κ = κ(P) dependence for PS and a linear PBED homologue was correct, for dendrimers the compressibility was higher at low pressure and it was lower at high P than theory predicts. Also the extracted values of the L‐J repulsion volume, v*, between a segment pair was smaller than expected. The specific architecture of dendrimer molecules is responsible for this behavior, since their 3D configuration is significantly different from the S‐S model with uniform segmental density and oxygen bonds in the main and side chains add flexibility. © 2009 NRC Canada. J Polym Sci Part B: Polym Phys 48: 322–332, 2010 相似文献
22.
R. Pantani F. De Santis A. Sorrentino F. De Maio G. Titomanlio 《Polymer Degradation and Stability》2010,95(7):1148-1478
Poly(lactic acid) (PLA) is an emerging material mainly because it can be synthesized from renewable resources and is thus environmentally and ecologically safe. The mechanical properties, above all the thermal resistance of PLA are determined by the crystalline content: the heat deflection temperature of crystalline PLA can reach 100 °C, whereas amorphous PLA loses mechanical properties at temperatures slightly higher than 60 °C. However, PLA has a low crystallization rate, so that after processing it remains mostly amorphous. This characteristic heavily limits the use of PLA for commercial applications. Many studies have been recently published on the crystallization kinetics of PLA. The effect of processing on this feature is however often neglected. In this work, the significance of processing on the crystallization kinetics of a commercial PLA was investigated. Two processing methods were explored: extrusion and injection moulding. The obtained materials, and the starting pellets of virgin polymer, were analyzed by calorimetry in order to obtain the crystallization kinetics. Two protocols were adopted to determine the crystallization rates during cooling from the melt or heating from the solid. The parameters of a kinetic equation were determined for all the materials and protocols adopted and it was thus possible to describe the evolution of crystallinity during heating and during cooling. 相似文献
23.
Seyyed Mostafa Hoseini 《Physics and Chemistry of Liquids》2017,55(5):559-569
Knowledge of the volumetric or pressure–volume–temperature (PVT) profile of molten polymers is important for both engineering and polymer physics. Ihm–Song–Mason (ISM) equation of state (EOS) has been employed to predict the volumetric properties of 12 molten polymers. The significance of the present paper is three temperature-dependent parameters of the ISM EOS to be determined using corresponding states correlations based on the molecular scaling constants, dispersive energy parameters between segments/monomers (ε) and segment diameter (σ) rather than bulk properties, e.g. the liquid density and temperature both at normal boiling point. The ability of the ISM EOS has been evaluated by comparing the results with 1390 literature datapoints for the specific volumes over the temperature range from 293 to 603.5 K and pressure range from 0.1 to 200 MPa. The average absolute deviation (AAD) of the calculated specific volumes from literature data was found to be 0.52%. The isothermal compressibility coefficients, κT values of molten polymers have also been predicted using the ISM EOS. From 684 datapoints examined, the AAD of estimated κT was equal to 7.55%. Our calculations on the volumetric and thermodynamic properties of studied polymers reproduce the literature data with reasonably good accuracy. 相似文献
24.
We have performed and analyzed extensive pressure-volume-temperature (PVT) measurements on uncrosslinked polybutadiene and polyisoprene elastomers from ambient temperature to about 200°C and 200 MPa. In the polybutadiene series, 1,2 content varied from 8 to 87%, the remainder being similar amounts of cis-1,4 and trans-1,4. In the polyisoprene series the 3,4 content varied from 8 to 64%, the trans-1,4 content was 12–16%, and the remainder was cis-1,4, with < 4% 1,2 content. We report parameters describing the experimental data in terms of the empirical Tait equation, the cell model, the Simha-Som-cynsky equation, the Sanchez-Lacombe, and the Flory-Orwoll-Vrij models. In general the parameters show systematic changes with the microstructure content. The agreement between theory and experiment is excellent for the Tait equation, and also for the Simha-Somcynsky model and the cell model. The maximum deviation between theory and experiment was less than 0.004 cm3/g for the Simha-Somcynsky theory, and less than 0.005 cm3/g for the cell model. Average absolute deviations are three to four times less. For the Sanchez-Lacombe and the Flory-Orwoll-Vrij models, the maximum deviations are 5–8 times as large, and very systematic. Parameter derived from the Simha-Somcynsky theory are discussed with respect to the microstructure, and with respect to the glass transition of these two series of materials. © 1993 John Wiley & Sons, Inc. 相似文献
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The Esmaeilzadeh–Roshanfekr (ER) equation of state (EOS) is used to predict the PVT properties of gas condensate reservoir fluids. Three gas condensate fluid samples taken from three wells in a real field in Iran, referred here as SA1, SA4 and SA8, as well as five samples from literature have been used to check the validity of the ER EOS in calculating the PVT properties of gas condensate mixtures. Some experiments such as constant composition expansion (CCE), constant volume depletion (CVD) and dew point pressures are carried out on these samples. In order to have an unbiased comparison between the ER and the Peng–Robinson (PR) equation of state, van der Waals mixing rules are used without using any adjustable parameters (kij = 0). Also, no pure component parameters are adjusted. The critical properties and acentric factor for plus-fraction are estimated by the Kesler–Lee, Pedersen et al. and Riazi–Daubert characterization methods. The results of dew point pressure calculations show that the ER EOS has smaller error than the PR EOS. For some mixtures, relative volume, gas compressibility factor and condensate drop-out in CVD and CCE test were also predicted. Comparison results between experimental and calculated data indicate that the ER EOS has smaller error than the PR EOS. The total average absolute deviation was found to be 0.82% and 2.97% for calculating gas compressibility factor and gas specific gravity in CVD test. Also, the total average absolute deviation was found to be 2.06% and 3.42% for calculating gas compressibility factor and relative volume in CCE test. 相似文献
27.
Dalmazzone D. Kharrat M. Lachet V. Fouconnier B. Clausse D. 《Journal of Thermal Analysis and Calorimetry》2002,70(2):493-505
The dissociation of gas and model hydrates was studied using a classical thermodynamic method and a calorimetric method, in
various aqueous media including pure water, high concentration calcium chloride solutions and water-in-oil emulsions. Methane
hydrate dissociation temperatures vs. pressure curves were determined using pressure vs. temperature measurements in a constant
volume cell (PVT), and high pressure differential scanning calorimetry (DSC), at 5 to 10 MPa gas pressure and at temperatures
ranging from -10 to +12°C. PVT and DSC results are in good agreement, and concordant with data available in literature. From
a thermodynamic point of view, there are no measurable differences between bulk solutions and emulsions. From a kinetic point
of view, due to the considerable surface of interface between the two phases, emulsions allow the formation of much greater
amounts of hydrate than solutions, without any agitation. Model hydrate of trichlorofluoromethane was studied in 9 to 27 mass%
calcium chloride solutions in emulsion in oil, using DSC under atmospheric pressure, at temperatures ranging from -20 to +5°C.
A diagram of dissociation temperature vs. salt concentration is proposed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
28.
The aim of this work is to develop spherically symmetric effective potentials allowing bulk thermodynamic properties and surface tension of molecular fluids to be predicted semiempirically by the use of statistical mechanical methods. Application is made to the straight chain alkane fluids from methane to decane. An effective Lennard-Jones potential is generated with temperature-dependent parameters fitted to the critical temperature and pressure and to Pitzer's acentric factor. Insertion of this potential into the generalised van der Waals (GvdW) density functional theory yields bulk properties in good agreement with experiments. The surface tension is overestimated for the longer alkane chains. In order to account for the surface tension, an independently adjustable attractive range of interaction is required and obtained through the use of square-well potentials chosen so as to leave the bulk thermodynamics unaltered while the attractive range is fitted to the surface tension at a single temperature. The GvdW theory, which includes binding energy, entropic and profile shape contributions, then generates surface tension estimates that are of good accuracy over the full range of available experimental data. It appears that, given a sufficiently flexible form, effective potentials combined with simple statistical mechanical theory can reproduce both bulk and non-uniform fluid data of great variety in an insighful and practically useful way. 相似文献
29.
Measurement of pressure coefficient of melt viscosity: drag flow versus capillary flow 总被引:1,自引:1,他引:0
The pressure coefficient of viscosity of poly(α-methylstyrene-co-acrylonitrile) was measured using a high-pressure sliding plate rheometer (HPSPR) and two types of capillary
rheometer: a piston-driven device with a throttle at the exit [piston capillary rheometer with throttle (PCRWT)] operated
at a fixed flow rate, and a counter-pressure nitrogen capillary rheometer (CPNCR) operated at a fixed pressure drop. In the
HPSPR, the pressure, shear rate, density, and viscosity are all uniform throughout the sample, while the analysis of capillary
data is complicated by the axial pressure gradient and the radial shear rate gradient. The polymer was found to be piezorheologically
simple, and the HPSPR data indicated that the pressure coefficient of viscosity β ≡ dln(a
P)/dP decreased slightly with increasing pressure at high pressure. While β from PCRWT data from different laboratories and instruments agreed fairly well, the β values were on average about 2/3 of that from the HPSPR. The CPNCR yields β about 18% lower than that of the HPSPR. 相似文献
30.