Effective potential approach to bulk thermodynamic properties and surface tension of molecular fluids I. Single component n-alkane systems

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.     

Glycopolymers resultant from ethylene-vinyl alcohol copolymers: Degradation and rheological behavior in bulk

The physical properties of glycopolymers based on d-(+)-glucosamine, d-(+)-galactosamine and d-(+)-mannosamine derivatives and obtained from two ethylene-vinyl alcohol, EVOH, copolymers with different vinyl alcohol compositions have been analyzed. The thermal degradation of these glycopolymers is almost independent of the type and amount of saccharide incorporated but slightly dependent on the initial EVOH copolymer composition. The glycopolymers derivate from the EVOH copolymer with lower ethylene content present two relaxation processes, while those derivatives from the EVOH copolymer with lower vinyl alcohol composition essentially show three relaxations processes. In both sets of glycopolymers, the relaxation process associated with the cooperative motions that take place at the glass transition is located at analogous temperatures to those previously determined by differential scanning calorimetry, both results being rather consistent.     

Synthesis and characterization of random or gradient butadiene-p-methylstyrene copolymers via anionic polymerization

Copolymers of 1,3-butadiene and p-methylstyrene （p-MS） were synthesized via anionic polymerization. A benzophenone-potassium complex was added to tune the reactivity ratio of the two monomers, leading to random and gradient composition alonglthe copolymer chain. The overall composition and microstructure could be controlled and well characterized by GPC and H-NMR. The p-MS was distributed from gradient to random with increasing the content of the benzophenone-potassium complex, and the 1,2-microstrucmre in the polybutadiene sequence increased at the same time. The hydrogenation of the copolymer of 1,3-butadiene and p-MS resulted in the corresponding saturated copolymer with well- defined structure and narrow molecular weight distribution.     

高温熔体表面张力测量方法的进展

高温熔体表面现象在冶金、化工、熔盐和材料科学等领域十分普遍。测量高温熔体表面张力有着重要的意义。本文评述了高温熔体表面张力的测量原理和方法。并简述了当前关于高温熔体表面现象以及相关的微重力科学的研究进展。     

Characterization of extruded ethylene-vinyl alcohol copolymer based barrier blends with interest in food packaging applications

Based on previous work a number of optimum extruded blends with high contents of a high barrier ethylene-vinyl alcohol copolymer were selected and characterized in terms of phase morphology, water sorption and barrier properties. Blend components were an ethylene vinyl-alcohol copolymer (EVOH with 32 mol% ethylene), an amorphous polyamide (aPA) and a nylon-containing ionomer. A fine two phase structure was found for these blends in all cases. However, Raman spectroscopy results indicated a poor interface interaction between the blend components in the case of the EVOH/aPA blends. Higher interface interaction had been previously found in the dry EVOH/ionomer blends. Equilibrium moisture solubility and diffusion were found to be higher than expected from simple additivity. However, the oxygen transmission rate was found to be clearly lower than expected from the rule of mixtures, particularly under dry conditions, fitting closely a simple Maxwell model.     

Impact of carbon dioxide on the surface tension of 1-hexanol aqueous solutions

Effects of carbon dioxide presence on the surface tension and adsorption kinetics of 1-hexanol solutions were investigated. Experiments were performed at a range of carbon dioxide vapor pressures and varying concentrations of 1-hexanol aqueous solution. Both dynamic and steady-state surface tensions of 1-hexanol aqueous solution were found to decrease with carbon dioxide pressure, and a linear relationship was observed between the steady-state surface tension and carbon dioxide pressure. To explain the experiments, adsorption and desorption of the two species (1-hexanol and carbon dioxide) from two sides of the vapor-liquid interface were considered. A modified Langmuir isotherm, the modified Langmuir equation of state and the modified kinetic transfer equation were developed. The resulting steady-state and dynamic surface tension data were modeled using the modified Langmuir equation of state and the modified kinetic transfer equation, respectively. Equilibrium constants and adsorption rate constants of 1-hexanol and carbon dioxide were evaluated through a minimization procedure for CO₂ pressures ranging from 0 to 690 kPa. From the steady-state modeling, the equilibrium parameters for 1-hexanol and carbon dioxide adsorption from vapor phase and liquid phase were found unchanged at different pressures of carbon dioxide. From the dynamic modeling, the adsorption rate constants for 1-hexanol and carbon dioxide from vapor phase and liquid phase were found to decrease with carbon dioxide pressure. Some fluctuations in the fitting parameters of the dynamic modeling (adsorption rate constants) were observed. These fluctuations may be due to experimental errors, or more likely the limitations of the model used. A major limitation of the model is related to large differences in adsorption/desorption between initial and final stages of the process, and a single set of property parameters cannot describe both initial and final states of the system. Variations may occur depending on which set of data, of initial or final states, is used in the model predictions over the entire time range.     

Effects of injection angle on the measurement of surface tension coefficient by drop weight method

The drop weight method for surface tension measurement is based on the weight of drops detached from a nozzle. The original idea was based on a postulate introduced by Tate (On the Magnitude of a Drop of Liquid Formed Under Different Circumstances, Philos. Mag. 27, 176–180, 1864), assuming that the weights of an ideal pendant drop and a detached ideal drop are identical, and that this weight is equal to the surface force that holds a drop attached to the nozzle. To consider the real volume of a drop that detaches from a nozzle, the method required a correction factor. Harkins and Brown suggested such correction factors for vertical injection from a nozzle. In this study, a correction factor for injection at different angles is presented and some of the hydrodynamic effects on surface tension measurement based on the drop weight method are studied. In addition, a model is introduced for the detachment time of drops in directions other than the vertical direction     

Density and surface tension of pure ionic liquid 1-butyl-3-methyl-imidazolium l-lactate and its binary mixture with alcohol and water

The density and surface tension of the pure ionic liquid 1-butyl-3-methyl-imidazolium l-lactate were measured from T (293.15 to 343.15) K. The coefficient of thermal expansion, molecular volume, standard entropy, lattice energy, surface entropy, surface enthalpy, and enthalpy of vaporization were calculated from the experimental values. Density and surface tension were also determined for binary mixtures of {1-butyl-3-methyl-imidazolium l-lactate + water/alcohol (methanol, ethanol, and 1-butanol)} systems over the whole composition range from T (298.15 to 318.15) K at atmospheric pressure. The partial molar volume, excess partial molar volume and apparent molar volume of the component IL and alcohol/water in the binary mixtures were discussed as well as limiting properties at infinite dilution and the thermal expansion coefficients of the four binary mixtures. The surface properties of the four binary mixtures were also discussed.     

Study of polymer-surfactant interactions via surface tension measurements

Interactions between a polymer and a surfactant were studied via surface tension measurements. Poly(ethylene glycol) and sodium dodecyl sulfate were used as a polymer and a surfactant, respectively. The addition of polymer affected the CMC value of the surfactant. The interpretations of the data and theoretical plots of polymer-surfactant interactions are discussed using a theoretical model. Received: 28 September 2000 Accepted: 3 October 2000     

Rapid synthesis of biodegradable poly(epsilon-caprolactone-co-p-dioxanone) random copolymers under microwave irradiation

<正>Biodegradable poly(epsilon-caprolactone-co-p-dioxanone)(PCDO) random copolymers have been synthesized by ring-opening polymerization of epsilon-caprolactone(CL) and p-dioxanone(PDO) under microwave irradiation.The effects of irradiation time and different CL/PDO molar feed ratios on the microwave-assisted ring-opening polymerization(MROP) of PCDO have been discussed.The resultant products were characterized by ~1H NMR,GPC and DSC.It was found that the polymerization was completed within 20 min at 140℃.In the presence of different CL/PDO molar feed ratios,the conversions of both monomers were kept relatively constant.DSC sturdy suggested that with increasing the content of PDO in the copolymers,the crystalline degree of the copolymers decreased gradually.It is believed to be a promising biodegradable material.     

Morphological,rheological, crystalline and mechanical properties of ethylene-vinyl acetate copolymer/linear low-density polyethylene/amphiphilic graphene oxide nanocomposites

Chemical modification of graphene oxide has become a popular method for imparting unique properties to extend its application. Here, we show a simple way to synthesize amphiphilic graphene oxide (AGO) by grafting quaternary ammonium salt onto GO sheets. The AGO sheets not only showed high thermal stability and good dispersion in many polar and non-polar solvents in comparison to GO sheets but also the chemical modification maintained the two-dimensional structure. As a result, the AGO sheets improve the interfacial interaction between ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE). Because of the large size of AGO, the location of AGO is very dependent on the mixing strategy. The AGO was dispersed in the EVA phase when AGO was mixed first with EVA and then with LLDPE, whereas it was confined in the LLDPE phase when AGO was mixed first with LLDPE and then with EVA. AGO sheets were found at the interface of LLDPE and EVA when AGO, EVA, and LLDPE were mixed together, suggesting that AGO has a high interfacial interaction with both LLDPE and EVA. These high interfacial interactions lead to high tensile strength, Young's modulus, complex viscosity and crystallization temperature in comparison to the EVA/LLDPE blends without AGO sheets.     

气-液界面上十六烷基溴化吡啶水溶液动态表面张力的研究

滴体积法测定了十六烷基溴化吡啶溶液的动态表面张力。考察了浓度、温度对动态表面张力的影响。讨论了十六烷基溴化吡啶分子在气／液界面上的吸附动力学,发现吸附遵从扩散-动力学控制机理．从表观扩散系数计算了吸附能垒,分析了吸附能垒存在的原因。     

Effect of solution viscosity on dynamic surface tension detection

A dynamic surface tension detector (DSTD) was used to examine the molecular diffusion and surface adsorption characteristics of surface-active analytes as a function of solution viscosity. Dynamic surface tension is determined by measuring the differential pressure across the air/liquid interface of repeatedly growing and detaching drops. Continuous surface tension measurement throughout the entire drop growth is achieved for each eluting drop (at a rate of 30 drops/min for 2 μl drops), providing insight into the kinetic behavior of molecular diffusion and orientation processes at the air/liquid interface. Three-dimensional data are obtained through a calibration procedure previously developed, but extended herein for viscous solutions, with surface tension first converted to surface pressure, which is plotted as a function of elution time axis versus drop time axis. Thus, an analyte that lowers the surface tension results in an increase in surface pressure. The calibration procedure derived for the pressure-based DSTD was successfully extended and implemented in this report to experimentally determine standard surface pressures in solutions of varied viscosity. Analysis of analytes in viscous solution was performed at low analyte concentration, where the observed analyte surface activity indicates that the surface concentration is at or near equilibrium when in a water mobile phase (viscosity of 1.0 Cp). Two surface-active analytes, sodium dodecyl sulfate (SDS) and polyethylene glycol (MW 1470 g/mol, PEG 1470), were analyzed in solutions ranging from 0 to 60% (v/v) glycerol in water, corresponding to a viscosity range of 1.0-15.0 Cp. Finally, the diffusion-limited surface activity of SDS and PEG 1470 were observed in viscous solution, whereby an increase in viscosity resulted in a decreased surface pressure early in drop growth. The dynamic surface pressure results reported for SDS and PEG 1470 are found to correlate with solution viscosity and analyte diffusion coefficient via the Stokes-Einstein equation.     

Phase behavior and surface tensions of amphiphilic fluorinated random copolymer aqueous solutions

Phase behavior and surface tension of aqueous solutions of fluorinated random copolymers [perfluoroalkylacrylate]–[poly(ethyleneoxide)methacrylate], [C_mRf-acrylate]-[EO_n-methacrylate] with fluroalkyl carbon number m = 8, 6, 4, 2 and number of ethyleneoxide unit, n = 9 and 4.5 were investigated as a function of composition and different combinations of m and n. Isotropic solutions are formed at lower temperatures over wide concentration range of copolymer but at higher temperature phase separation occurs. The cloud point of copolymer decreases with decreasing n as well as m, and also with decreasing the number of poly(ethyleneoxide)methacrylate chain per perfluorinatedalkylacrylate chain, suggesting that the copolymers become more hydrophobic on decreasing m and n. Equilibrium and dynamic surface tension measurements show that copolymers become increasingly surface active as m as well as n decrease but the adsorption at the air–water interface is very slow due to bulkiness of the molecules. No clear evidence of the formation of micellar aggregates could be obtained from surface tension–composition curves.     

Correlation between topological features and surface tension of binary liquid mixtures

Summary The excess surface tension of a large number of binary liquid mixtures has been correlated with their topological features quantified in terms of the molecular connectivity indices. The agreement between the calculated and experimental ^E values is reasonably well for all the mixtures. A simple correlation has also been proposed between ^E and molar excess volume (V ^E ) of a binary mixture. The correlation is quite useful in correlating ^E data even for the mixtures where either one or both the components are associated in the pure state and/or there is interaction between them.

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Korrelation zwischen topologischen Gegebenheiten und Oberflächenspannung von binären flüssigen Mischungen

Zusammenfassung Die Exzeß-Oberflächenspannungen einer großen Anzahl von binären flüssigen Mischungen wurden mit der Topologie ihrer Komponenten in Form der molekularen Konnektivitätsindices korreliert. Die Übereinstimmung zwischen den ^E -Werten ist für alle Mischungen relativ gut. Es wurde ebenfalls eine einfache Korrelation zwischen ^E und den molaren Exzeß-Volumina (V ^E ) der binären Mischungen vorgeschlagen. Diese Korrelierung ist nützlich, um die ^E -Werte sogar dann für die Korrelation von Mischungen verwenden zu können, wenn entweder eine oder beide Komponenten im Reinzustand assoziiert sind und/oder eine Wechselwirkung zwischen ihnen besteht.

     

Pressure–volume–temperature data and surface tension of blends of poly(ethylene oxide) and poly(methyl acrylate) in the melt

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     

The influence of soft segment length on the properties of poly(butylene terephthalate-co-succinate)-b-poly(ethylene glycol) segmented random copolymers

Three series of poly(butylene terephthalate-co-succinate)-b-poly(ethylene glycol) segmented random copolymers with starting PEG number-average molecular weight (M_n(PEG)) at 600, 1000 and 2000, respectively, as well as hard segment poly(butylene succinate) (PBS) molar fraction (M_PBS) increasing from 10% to 30% were synthesized through a transesterification/polycondensation process and characterized by means of GPC, NMR, DSC, WAXD and mechanical testing etc. The investigations were mainly focused on the influence of M_n(PEG) on the properties of resulting copolymers bearing two sorts of hard segments. It is revealed that all the samples show a relatively symmetrical GPC curves with the number-average molecular weight more than 4 × 10⁴, while the polydispersity decreases from 1.9 to 1.4 as the increasing M_n(PEG) because of the prolonged time for polycondensation and the faster exclusion of small molecules by-product with the decreased molten viscosity. The sequence distribution analysis shows that the average sequence length of hard segment PBT decreases while that of PBS increases with the increasing M_PBS and are independent of the soft segment length. The approximate unit degree of randomness as well as the soft segment length turns out that the segments take a statistically random distribution along the backbone. Micro-phase separation structure is verified for the appearance of two glass transition temperatures and two melting points, respectively, in DSC thermograms of most samples. The depression of melting points and the reduction of crystallinity of hard segments with increasing M_PBS are related to the crystal lattice transition from α-PBT to PBS and discussed in the viewpoint of cohensive energy. Mechanical testing results demonstrate that the increase of amorphous domains the increase of M_PBS as well as M_n(PEG) will provide high elongation and good flexibility of copolymer chain. The in vitro degradation experiments show that the partial substitution of aromatic segment PBT with aliphatic PBS will substantially accelerate the degradation rate with enhanced safety of degradation by-products and while changing M_n(PEG) broaden the spectrum to tailor the properties.     

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.