3种粘结剂材料的力学性能对比研究

对比研究了F2311、F2314和Estane5703粘结剂的粘弹性能和准静态拉伸、压缩力学性能.利用修正的"朱-王-唐"非线性粘弹性本构关系描述了粘结剂拉伸屈服前的力学响应.结果表明,弹性模量关系为F2314＞F2311＞Estane5703;拉伸断裂强度关系为F2314＞Estane5703＞F2311;拉伸断裂延伸率关系为F2311＞Estane5703＞F2314.总的来说,F2311与Estane5703性能比较接近,而F2314与前两者相差较大.Estane5703具有介于F2311和F2314之间的断裂强度和韧性,是很好的粘结剂.研究结果为PBX炸药配方设计中粘结剂材料的选择提供了重要的依据.     

Equilibrium and nonequilibrium computer simulation studies of polar fluids and nonpolar mixtures

We present a technique for estimating intermolecular potential model parameters for polar compounds. This technique has been used for two polar compounds, hydrogen chloride and ammonia. The potential models are then used to study a wide range of static and dynamic properties using computer simulations. Where possible, results have been compared with experimental data to demonstrate the adequacy of the models. Static properties have been calculated using the methods of Monte Carlo and equilibrium molecular dynamics. The shear viscosity has been obtained using the nonequilibrium molecular dynamics method. Finally, we also report results for a computer simulation study of quadrupolar mixtures. This study investigates the changes in properties caused by a change in the sign of the quadrupole moment of one mixture component.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Computation of interface interactions and mechanical properties of HMX-based PBX with Estane 5703 from atomic simulation

Atomic simulation was applied to investigate the interface interactions and mechanical properties of β-octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX)-based polymer-bonded explosive (PBX) with Estane 5703. The interface structure of HMX (100) crystal surface with Estane 5703 was analyzed using pair correlation function (PCF), and the interfacial binding energies between them were calculated. It is shown that there exist hydrogen bonds and electrostatic interactions on the interface. By calculating and comparing the bonds lengths and distributions for possible initial bonds fractured in detonation, it is known that the interactions do not affect the stability of the PBX. Moreover, the elastic constants for HMX and the HMX-based PBX were computed using static elastic constants analysis method, and the engineering moduli and Poisson ratios were derived by Reuss average. Based on the value of Cauchy pressure, it is indicated that the ductibility of crystalline HMX can be effectively improved by blending the polymer in small amount. The relevancy to shockwave stability for this PBX in detonation was discussed finally.     

Preparation of a polyurethane scaffold for tissue engineering made by a combination of salt leaching and freeze-drying of dioxane

In the past several types of synthetic porous materials have been made as meniscus reconstruction materials. Most of these materials lacked a good combination between suitable mechanical properties and a high interconnectivity. In this work porous scaffolds were made from the polyurethane Estane 5701-F1 by freeze drying of a dioxane and water solution in combination with salt leaching. It was possible to obtain very porous scaffolds with a very high interconnectivity. Porosity, pore size and interconnectivity can be independently adjusted by varying the amount of water, porogen size and the amount of porogen used. The obtained compression moduli of the scaffolds were between 40 kPa and 400 kPa with a variation in porosity between 72 and 87%. These scaffolds are very suitable for the use as meniscus replacement materials.     

Impact compression of alkali metals: Computer-aided simulation

This article describes a method for calculation of the potential of the embedded atom model (EAM), suitable for calculation of the properties of alkali metals in highly compressed states. For the first time, sequential consideration of the thermal energy and thermal pressure of collective electrons has been introduced into the EAM flowchart. The parameters of the EAM potential have been calculated, which make it possible to obtain good agreement in terms of pressure and energy for five alkali metals under impact compression. The properties of the molecular dynamic models of alkali metals at 300 and 0 K are compared with the data of static compression. The agreement between them is sufficient up to pressures of 15–20 GPa, and at higher compression rates divergences become significant. A lack of experimental data makes it impossible to understand whether the reason for these divergences is incomplete adequacy of the EAM potential or systematic errors contained in the experimental data in the range of high pressures. The proposed potentials make it possible to calculate the thermodynamic, structural, and diffusion properties of alkali metals in highly compressed states at temperatures up to 20000–30000 K.     

Rheological characterization of hydroxypropylcellulose gels

The present paper describes the rheological properties of hydroxypropylcellulose (HPC) gels formulated in propylene glycol (PG), water, ethanol, and mixtures of these components. The effects of molecular weight, polymer concentration, and solvent composition on the apparent viscosity and flow characteristics have been studied by continuous shear rheometry. The HPC gels are shear thinning and do not exhibit significant yield or hysteresis in their rheograms. The apparent viscosity increases with increasing molecular weight and concentration of the polymer, as expected. Although not so pronounced at lower concentrations (≤ 1.5%), HPC gels tend to become increasingly non-Newtonian with increasing molecular weight at higher polymer concentrations (3%). A mathematical model has been proposed for the prediction of viscosities of HPC gels. There exists a high degree of dependence on molecular interactions between various solvent molecules in the prediction of mixture viscosities in ternary systems. The effects of solvent composition on the viscoelastic behavior of these gels have also been examined by dynamic mechanical analysis. The HPC gels are highly viscoelastic and exhibit greater degrees of elasticity with increased PG content in ternary solvent mixtures with water and ethanol. The study also suggests that dynamic mechanical analysis could prove to be a useful tool in the determination of zero-shear viscosities, viscosities that are representative of most realistic situations.     

Rheological Characterization of Hydroxypropylcellulose Gels

The present paper describes the rheological properties of hydroxypropylcellulose (HPC) gels formulated in propylene glycol (PG), water, ethanol, and mixtures of these components. The effects of molecular weight, polymer concentration, and solvent composition on the apparent viscosity and flow characteristics have been studied by continuous shear rheometry. The HPC gels are shear thinning and do not exhibit significant yield or hysteresis in their rheograms. The apparent viscosity increases with increasing molecular weight and concentration of the polymer, as expected. Although not so pronounced at lower concentrations (≤ 1.5%), HPC gels tend to become increasingly non-Newtonian with increasing molecular weight at higher polymer concentrations (3%). A mathematical model has been proposed for the prediction of viscosities of HPC gels. There exists a high degree of dependence on molecular interactions between various solvent molecules in the prediction of mixture viscosities in ternary systems. The effects of solvent composition on the viscoelastic behavior of these gels have also been examined by dynamic mechanical analysis. The HPC gels are highly viscoelastic and exhibit greater degrees of elasticity with increased PG content in ternary solvent mixtures with water and ethanol. The study also suggests that dynamic mechanical analysis could prove to be a useful tool in the determination of zero-shear viscosities, viscosities that are representative of most realistic situations.     

A detailed thermal analysis of nanocomposites filled with SiO2, AlN or boehmite at varied contents and a review of selected rules of mixture

In order to investigate and compare the thermal and mechanical properties of nanocomposites filled with various nanoparticles multiple experiments have been carried out. The aim of this study was to enhance the thermal and mechanical properties of epoxy resin for fiber reinforces structures by the addition of nanoparticles. These altered properties were analyzed and reconciled with each other as well as compared to data developed from different rules of mixture. A hot curing epoxy system based on bisphenol-A (DGEBA) has been filled with different contents of silicon dioxide (SiO₂), aluminum nitride (AlN) and boehmite nanoparticles to examine the effects in the material’s thermal and mechanical behavior with variable filler materials and contents compared to the unfilled epoxy. The glass transition temperature fluctuates very little with varied filler content. The coefficient of thermal expansion can be reduced with increasing filler content. This improvement recurs also in thermal conductivity and during dynamic mechanical analysis. Several rules of mixture have been applied to be verified on the basis of varied materials and filler contents. The results did not always match the experiments. The deviations are ascribed to the influence of interphases that build up in the vicinity of the nanoparticles during the process of curing.     

Physical properties of crosslinked hyaluronic acid hydrogels

In order to improve the mechanical properties and control the degradation rate of hyaluronic acid (HA) an investigation of the structural and mechanical properties of the hydrogels crosslinked using divinyl sulfone (DVS), glutaraldehyde (GTA) and freeze-thawing, or autocrosslinking has been carried out. The thermal and mechanical properties of the gels were characterised by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and compression tests. The solution degradation products of each system have been analysed using size exclusion chromatography (SEC) and the Zimm-Stockmayer theory applied. Autocrosslinked gels swell the most quickly, whereas the GTA crosslinked gels swell most slowly. The stability of the autocrosslinked gels improves with a reduction in solution pH, but is still poor. GTA and DVS crosslinked gels are robust and elastic when water swollen, with glass transition values around 20 degrees C. SEC results show that the water soluble degradation products of the gels show a reduction in the radius of gyration at any particular molecular weight and this is interpreted as indicating increased hydrophobicity arising from chemical modification.     

Characterization of the kinetic behavior of resin modified Glass-ionomer cements by DSC, TMA and ultrasonic wave propagation

In this study the isothermal kinetic behavior of two resin modified glass ionomer cements (RMGIC) and a dental composite have been compared by differential scanning calorimetry (DSC) and thermo-mechanical analysis (TMA). The simultaneous evolution of the multiple reactions occurring in RMGIC has been analyzed not only by DSC and TMA but also by ultrasonic wave propagation using the pulse-echo technique. The propagation of ultrasonic waves, acting as a dynamic mechanical deformation at high frequencies, is proportional to the longitudinal bulk moduli of the material and may be used to measure the changes of mechanical properties induced by a chemical reaction as occurs in RMGIC. TMA and ultrasonic analysis have been used to monitor the acid-base reaction of RMGIC in dark conditions. Moreover an RMGIC presenting a double reactive mechanism in dark conditions, a thermally activated radical polymerization and an acid-base reaction are studied using these experimental techniques. Finally DSC and TMA results obtained during photopolymerization of an RMGIC and of a dental composite have been compared.     

Influence of Al2O3 addition on thermal and structural properties of erbium doped glasses

Changes in the structural properties of Er³⁺ doped soda-lime silicate glasses were investigated as a function of Al₂O₃ content. A combined approach of experimental techniques and molecular dynamic simulations (MD) was used to evaluate the structural features directly correlated to the glass properties. The experimental results in term of density, thermal properties as well as microstructural and mineralogical data showed a significant variation when increasing the alumina content from 10 mol% to 15 mol%. These results were compared to the MD information and discussed: changes in erbium and aluminium local configuration, due to the glass structural evolution as a function of the alumina concentration, have been investigated.     

Properties of polyethylene-polypropylene blends

Differential scanning calorimetry, wide-angle X-ray scattering, swelling in n-hexane and mechanical tensile tests have been performed on cylindrical specimens with a fibrous morphology of high-density polyethylene-isotactic polypropylene blends. Such specimens were obtained by cold-drawing unoriented samples (obtained directly by extrusion, whose properties were studied in a previous paper) in an Instron machine at 60° C. The resulting behaviours of fibrous specimens have been compared with those of the initial isotropic samples having a spherulitic morphology. The mechanical properties of unoriented samples have also been compared with the data of other works found in the literature. Such a comparison suggests that, especially for blends of two semicrystalline polymers, not only must the molecular characteristics be accurately specified but also other parameters such as crystallinity, melting points and morphological features, in order to clearly explain the different types of behaviour observed.     

Ab-initio and DFT methodologies for computing hyperpolarizabilities and susceptibilities of highly conjugated organic compounds for nonlinear optical applications

In this talk, after a short introduction on the methodologies used for computing dipole polarizability (α), second and third-order hyperpolarizability and susceptibility; the results of theoretical studies performed on density functional theory (DFT) and ab-initio quantum mechanical calculations of nonlinear optical (NLO) properties for a few selected organic compounds and polymers will be explained. The electric dipole moments (μ) and dispersion-free first hyperpolarizabilities (β) for a family of azo-azulenes and a styrylquinolinium dye have been determined by DFT at B3LYP level. To reveal the frequency-dependent NLO behavior, the dynamic α, second hyperpolarizabilities (γ), second (χ⁽²⁾) and third-order (χ⁽³⁾) susceptibilites have been evaluated using time-dependent HartreeFock (TDHF) procedure. To provide an insight into the third-order NLO phenomena of a series of pyrrolo-tetrathiafulvalene-based molecules and pushpull azobenzene polymers, two-photon absorption (TPA) characterizations have been also investigated by means of TDHF. All computed results of the examined compounds are compared with their previous experimental findings and the measured data for similar structures in the literature. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by configuration interaction (CI) method. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO–LUMO band gaps have been revealed by DFT at B3LYP level for azo-azulenes, styrylquinolinium dye, push–pull azobenzene polymers and by parametrization method 6 (PM6) for pyrrolo-tetrathiafulvalene-based molecules.     

Binary and Ternary Mixtures of Biopolymers and Water: Viscosity,Refractive Index,and Density

Biopolymers have been the focus of intense research because of their wide applicability. The thermophysical properties of solutions containing biopolymers have fundamental importance for engineering calculations, as well as for thermal load calculations, energy expenditure, and development of new products. In this work, the thermophysical properties of binary and ternary solutions of carboxymethylcellulose and/or high methoxylation pectin and water at different temperatures have been investigated taking into consideration different biopolymer concentrations. The experimental data related to the thermophysical properties were correlated to obtain empirical models that can describe the temperature–concentration combined effect on the density, refractive index, and dynamic viscosity. From data obtained from the experiments, the density, refractive index, and dynamic viscosity increase with increasing biopolymer concentration and decrease with increasing temperature. The polynomial models showed a good fit to the experimental data and high correlation coefficients (\(R^{2}\ge \) 0.98) for each studied system.     

Study of poly (methyl methacrylate)/poly (ethylene oxide) blends in solution. II

In this paper, the equilibrium properties for the poly (methyl methacrylate)/poly (ethylene oxide) system have been studied in 1, 2,dichloroethane and methyl acetate separately. Viscometry and laser light scattering techniques have been employed. The results obtained from both methods can be compared. From this comparison it turns out that the compatibility decreases as the PEO molecular weight increases at constant molecular weight of PMMA. On the contrary, the compatibility increases as the PMMA molecular weight increases for the same PEO molecular weight.     

Effect of the long chain extender on the properties of linear and castor oil cross-linked PEG-based polyurethane elastomers

Polyurethane (PU) elastomers were elaborated from polyethylene glycol of high molecular weight (MW = 4,000), 1,6-hexamethylene diisocyanate and polyethylene glycol (PEG₁₅₀₀) (MW = 1,500) as a long linear chain extender and/or castor oil as a cross-linker and were obtained in the form of transparent films. These poly(ether urethanes) elastomers are obtained by replacing the short-chain diol monomers with high molecular weight polyethylene glycols (PEG₁₅₀₀). High molecular weight polyethylene glycol (MW = 4,000 and 1,500, respectively) have greater chain length thus producing networks with lower cross-linking densities and higher average molecular weight between two consecutive cross-links. The PU properties were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, mechanical analysis and thermogravimetry. The results showed that the prepared polyurethanes (PUs) had very good tensile properties. The stress–strain data show that the PU elastomers obtained using a 60/40% OH_PEG1500/OH_{castor oil} ratio have the best mechanical properties. The thermal degradation of the castor oil cross-linked PU elastomers starts at 280–300 °C, compared to the thermal degradation of linear PUs which begins at 220 °C. During storage at 25 °C, the morphology and mechanical properties of the elastomer films have been observed to change in time.     

A model for evaluating physico-chemical substance properties required by consequence analysis models

Modeling systems for analyzing the consequences of chemical emergencies require as input values a number of physico-chemical substance properties, commonly as a function of temperature at atmospheric pressure. This paper presents a mathematical model "CHEMIC", which can be used for evaluating such substance properties, assuming that six basic constant quantities are available (molecular weight, freezing or melting point, normal boiling point, critical temperature, critical pressure and critical volume). The model has been designed to yield reasonably accurate numerical predictions, while at the same time keeping the amount of input data to a minimum. The model is based on molecular theory or thermodynamics, together with empirical corrections. Mostly, model equations are based on the so-called law of corresponding states. The model evaluates substance properties as a function of temperature at atmospheric pressure. These include seven properties commonly required by consequence analysis and heavy gas dispersion modeling systems: vapor pressure, vapor and liquid densities, heat of vaporization, vapor and liquid viscosities and binary diffusion coefficient. The model predictions for vapor pressure, vapor and liquid densities and heat of vaporization have been evaluated by using the Clausius-Clapeyron equation. We have also compared the predictions of the CHEMIC model with those of the DATABANK database (developed by the AEA Technology, UK), which includes detailed semi-empirical correlations. The computer program CHEMIC could be easily introduced into consequence analysis modeling systems in order to extend their performance to address a wider selection of substances.     

Electromechanical properties of nanotube-PVA composite actuator bimorphs

Oxidized multiwalled carbon nanotube (oxidized-MWNT)/polyvinyl alcohol (PVA) composite sheets have been prepared for electromechanical actuator applications. MWNT have been oxidized by nitric acid treatments. They were then dispersed in water and mixed with various amounts of PVA of high molecular weight (198?000?g?mol(-1)). The composite sheets were then obtained through a membrane filtration process. The composition of the systems has been optimized to combine suitable mechanical and electrical properties. Thermogravimetric analysis, mechanical tensile tests and conductivity measurements show that the best compromise of mechanical and electrical properties was obtained for a PVA weight fraction of about 30?wt%. In addition, one face of the sheets was coated with gold to increase the conductivity of the sheets and promote uniform actuation. Pseudo-bimorph devices have been realized by subsequently coating the composite sheets with an inert layer of PVA. The devices have been tested electromechanically in a liquid electrolyte (tetrabutylammonium/tetrafluoroborate (TBA/TFB) in acetonitrile) at constant frequency and different applied voltages, from 2 to 10?V. Measurements of the bimorph deflections were used to determine the stress generated by the nanotube-PVA sheets. The results show that the stress generated increases with increasing amplitude of the applied voltage and can reach 1.8?MPa. This value compares well with and even exceeds the stress generated by recently obtained bimorphs made of gold nanoparticles.     

Partial structure factors of a simulated polymer melt

Fully atomistic molecular dynamic simulations were carried out by using the Insight (Insight II 4.0.0 P version) and the Discover-3 programs from MSI with the polymer consortium force field. The model system used in these simulations was built using the Amorphous Cell module. The polymer system simulated was glassy polyisoprene (PI) as used in previous neutron scattering (NS) measurements. A first molecular dynamics at 363 K was run for 1 ns using the Discover-3 program collecting data every 0.01 ps and a subsequent one (taking the previous output sample as an input for the following dynamics) was run for 2 ns collecting data every 0.5 ps. The results of the second run agreed to those of the first run, indicating that the sample was well equilibrated at this high temperature. Starting from the obtained atomic trajectories we have calculated the partial static structure factors for NS corresponding to different PI samples with different levels of deuteration (PId3, i.e., methyl group deuterated and main chain protonated; PId5, i.e., methyl group protonated and main chain deuterated; PId8, i.e., fully deuterated and PIh8, i.e., fully protonated). The results obtained are compared to the coherent NS cross-sections measured on real samples by means of D7 spectrometer with polarization analysis (ILL, Grenoble). A good agreement is obtained between experimental and simulated data validating the simulated sample. Moreover, the dynamic evolution of these correlations has also been calculated from the simulations. With these time dependent functions, the magnitude measured in a neutron spin echo (NSE) experiment can be constructed. Here we present two examples dealing with the fully deuterated sample PId8 and a partially deuterated sample, PId5, that show how computer simulation constitutes an invaluable tool for interpreting NSE results.