Mixed matrix membrane materials with glassy polymers. Part 1

Mixed matrix materials comprising molecular sieve entities embedded in a polymer matrix can economically increase membrane permselectivity, thereby addressing a key challenge hindering the widespread use of membrane‐based gas separations. Prior work has clarified the importance of proper selection of the dispersed sieve phase and the continuous matrix phase based on their intrinsic transport properties. Proper material selection for the two components, while necessary, is not sufficient since the interfacial contact zone appears to be equally important to achieve optimum transport properties. Specifically, it was found that chemical coupling of the sieve to the polymer can lead to better macroscopic adhesion but to even poorer transport properties than in the absence of the adhesion promoter. This counterintuitive behavior may be attributed to a nanometric region of disturbed packing at the polymer sieve interphase. The poor properties are believed to result from “leakage” of gas molecules along this nanometric interface. The Maxwell model was modified to take into account these complexities and to provide a first order quantification of the nanometric interphase. The analysis indicates that optimization of the transport properties of the interfacial region is key to the formation of ideal mixed matrix materials. This approach is used in the second part of this paper to form successful mixed matrix membrane materials.     

Epoxy-silica polymers as restoration materials. Part II

Room temperature reaction of the epoxy resin poly(bisphenolA-co-epichlorohydrin), glycidyl end-capped with the coupling agent (3-aminopropyl)triethoxysilane, in 1:2 (1), 1:1 (2) and 2:1 (3) molar ratios, leads, after curing for three months at room temperature, to glassy, transparent, crack-free solids which were investigated by SEM, TGA, DSC, NIR and Raman spectroscopy. SEM investigations show substantially a great homogeneity over the entire area with absence of cracks, veins and/or fissures and without formations of clusters and/or aggregates. The conversion of oxirane rings, as found by Raman spectroscopy, decreases by increasing the epoxy/amine ratio, with conversion percentages ranging from 95.3 to 81.3%. As a common feature, the presence in 1, 2 and 3 of Si-O-Si linkages increases the polymer degradation temperature and thermal oxidative stability relative to the parent epoxy resin by shifting the weight loss to higher temperatures. Differently from mixtures 2 and 3, which show the T_g at 90 °C, the mixture 1 does not exhibit any detectable glass transition.     

Effect of crosslink density on the molecular relaxations in diepoxide-diamine network polymers. Part 1. The glassy region

The effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide-diamine polymers are reported. Activation enthalpies and intensities for the β relaxation have been measured using a torsion pendulum at 1 Hz. The glyceryl groups, which are thought to be responsible for this process, are divided into a number of categories defined by the structure of the surrounding matrix. Concentrations of these units are calculated using probability theory, and a correlation is obtained with three measures of the relaxation Intensity, In the case of non-stoichiometric networks, variations in the intensity of the β relaxation are interpreted in terms of the simultaneous motion of each class of glyceryl group. The manner in which these processes combine to produce a composite peak appears to be unimportant. For the γ relaxation (?140°C), it is shown that at least four methylene units are needed in the diamine component before the process is observable, whereas only two consecutive methylene units in the center of the diepoxide molecule produce the relaxation.     

Thermal stability of high-temperature materials. Part 2

Experimental methods for determining thermal stability of high-temperature materials under dynamic and static thermal loading conditions are considered. Experimentally, thermal stability is characterized by the destructive temperature difference or critical (destructive) rate of change of the temperature field in the bulk or at the surface of the material. It is shown that, with the observance of special conditions, the thermal-shock method, based on sharp cooling of heated specimens in water, provides an acceptable destructive temperature difference for a particular material, in agreement with theory. At present, however, no unique method for experimental determination of the thermal stability of high-temperature materials has been developed. A route towards standardizing static methods for determining the destructive temperature difference is proposed.Translated from Novye Ogneupory, No. 8, August, 2004, pp. 38–48.     

Anomalous penetrant transport in glassy polymers: 4. Stresses in partially swollen polymers

The equilibrium swelling process and stress evolution of glassy polymer systems undergoing Case-II penetrant transport were examined using a rubber elasticity theory. Consideration of coupling between stresses and penetrant concentration permitted calculation of equilibrium stress and concentration profiles for a variety of molecular and geometric factors.     

Realization of the properties of carbon fibres in composite materials. Part 2. Carbon fibre composites with a metal matrix (review)

The features of fabrication of metal composites complicates realization of the strength of CF in comparison to carbon-filled plastics. Disordering of the fibres and matrix is possible due to excessive interaction of the components. Three types of structure of metallic carbon materials (MCM) corresponding to insufficient, optimum, and excessive interaction of the components of CM are described. The principles of a quantitative theory of interaction of components in fabrication of MCM are examined and can be used to estimate the optimum parameters of this process.Avtor Scientific and Industrial Co., Mytishchi. Translated from Khimicheskie Volokna, No. 3, pp. 37–42, May–June, 1995.     

Principal features of structural relaxation in glassy polymers. A Review

The principal features of models of structural relaxation in the glassy state were reviewed. The concepts of fictive temperature as the structural parameter and nonexponentiality and nonlinearity of structural relaxations were described. Various expressions for the structural relaxation time were presented and compared. One particular model was selected and utilized in a parametric optimization study of structural relaxation. Model predictions were checked against experimental results obtained by volumetric and calorimetric measurements.     

Transport properties of dichloromethane in glassy polymers. I. Atactic polystyrene films

Sorption and diffusion of dichloromethane vapor were measured in atactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior is characterized by three zones, depending on temperature and penetrant activity. In Zone I, at low activity, the diffusion coefficient is independent of vapor concentration; Zone II is characterized by concentration-dependent diffusion, whereas in Zone III structural transformations are possible. The study of diffusion at three temperatures allowed building of a temperature-penetrant concentration diagram, which is very useful to visualize the different zones of behavior. The aging at room temperature has no effect on the curve of sorption as a function of vapor activity, whereas it determines two effects on the diffusion: a decrease of the zero concentration diffusion coefficient and a more and more anomalous behavior with the aging time. The aging at 70°C produces the same effects on the diffusion behavior as the aging at room temperature; in addition, a decrease sorption is observed at low penetrant activity. The possible presence of ordered domains, impermeable to the vapor, in the samples stored at 70°C, was suggested on the basis of sorption results.     

Controlled release of perfumes from polymers. II. Incorporation and release of essential oils from glassy polymers

Release of essential oils from glassy hydrophilic copolymers of 2-hydroxyethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) was studied in a range of releasing media at 30°C. The release of carvone, limonene, and eugenol was investigated using swelling-controlled release systems based on these copolymers. By changing the crosslinking ratio of the copolymers it was possible to achieve zero-order release. The amount of essential oil release was correlated to the thermodynamic compatibility of the oil-polymer pair, as judged by the solubility parameter difference. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 509–513, 1997     

2-2 Piezoelectric cement matrix composite: Part II. Actuator effect

In this paper, experimental results of the actuator effect of a 2-2 piezoelectric cement matrix composite are presented. A desirable actuator effect was observed in the composite. In the first part of this study, the actuator effect of the composite under free conditions was studied. It was found that the amplitude of the response increases, but the phase angle of the response decreases, both almost linearly with the frequency of the actuator effect. The second part of the study focused on the behavior of the actuator in a structure. Distinct differences were observed in the behaviors of the composite under free conditions and in a structural system (simulated by precompression in the frame of an MTS machine). Clearly, the behavior of the actuator in a structure is influenced by factors including the properties of other components of the structure and the interaction between the actuator and other components, which was represented here by the precompression level in the experiment.     

基于共轭微孔聚合物的二维膜材料构筑及其应用

共轭微孔聚合物(CMPs)是典型的多孔有机聚合物,具有丰富的微纳孔和结构可调控性.具有二维结构的CMPs膜材料既保留了CMPs材料的π-共轭骨架和纳米多孔结构,又兼具二维材料优异的可加工性.重点总结了近年来CMPs膜材料的制备方法,包括电化学法、界面聚合法、模板法等;同时介绍了CMPs膜材料在纳滤、分离、抑菌等领域的应用现状;最后指出宏观大尺度CMPs膜的制备技术开发及其微观结构、化学组成与性能调控是未来二维CMPs膜材料的重点发展方向.     

The effect of carbonyl group on sorption of CO2 in glassy polymers

The interaction of CO₂ and polymers was investigated by examining the sorption isotherms and the desorption time variation of characteristic IR absorption bands. From the time variation of the bending mode (ν₂) of CO₂ at near 660 cm⁻¹ and the antisymmetric stretching mode (ν₃) of CO₂ at near 2340 cm⁻¹, the CO₂ within the polymer film containing carbonyl groups (e.g. poly(methyl methacrylate) (PMMA)) was much more difficult to outgas than the polymer film containing phenyl rings (e.g. polystyrene (PS)). From the red shift of the stretching mode of carbonyl groups at near 1740 cm⁻¹ for the PMMA film upon CO₂ treatments, the bonding force of the carbonyl group–CO₂ interaction is much weaker than that of the conventional hydrogen bonding and Lewis acid–base interaction. The CO₂ was surprisingly found to be present within PMMA for about 6 months after CO₂ treatments as demonstrated by the shifting of loss maxima of dynamic mechanical analyses (DMA) toward low temperatures.     

Physical aging in particulate-filled composites with an amorphous glassy matrix

Physical aging was studied on particulate -filled glassy network polymers by means of mechanical -dilatational, differential scanning calorimetry (DSC) and density measurements on specimens that were aged at room temperature. The composites aged for 0.5 day fractured in a brittle manner at a constant ultimate stress, which is close to the tensile strength of the unfilled material, regardless of the filler content and the presence of a coupling agent. This type of mechanical behavior is caused by the compressive residual stresses that are present due to curing and differential thermal shrinkage. As aging takes place, the compressive residual stresses are relieved; as a result the ultimate tensile strengths of the composites decrease. The 120 -day -old untreated glass bead containing composites exhibited dilatation and yield in mechanical -dilatational testing. This type of behavior is described as “having no adhesion” between the filler and the matrix. The 120 -day -old composites with coupling agent -treated glass beads fractured at a tensile stress which is equal to 1/1.6 the tensile strength of the unfilled material. These materials did not exhibit dilatation and yield in mechanical -dilatational testing. Density and DSC data indicate densification and enthalpy relaxation upon again and support the hypothesis presented for the observed change in the mechanical -dilatational behavior.     

Anomalous penetrant transport in glassy polymers V. Cyclohexane transport in polystyrene

Transport of liquid cyclohexane through well characterized, initially glassy, crosslinked polystyrene slabs was investigated. The samples were produced by bulk polymerization of styrene and divinyl benzene using benzoyl peroxide as an initiator at 90°C for 48 h; they had initial crosslinking ratios, X, between 0.005 and 0.025 mol DVB/mol styrene, initial thickness of 0.25 mm to 1.80 mm, and the aspect ratio was maintained above 10 to achieve one-dimensional transport. The results of cyclohexane uptake as a function of time were used to elucidate the effects of degree of crosslinking and sample geometry on the mechanisms of penetrant transport. These results were interpreted in terms of relaxational and diffusional mechanisms.     

Transport properties of dichloromethane in glassy polymers. II. Amorphous syndiotactic polystyrene films

Sorption and diffusion of dichloromethane vapor were measured in amorphous syndiotactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior, at the temperature of 25°C, was characterized by three stages, depending on penetrant activity. In the first stage, at low activity, the diffusion coefficient was independent of vapor concentration; the second stage was characterized by concentration-dependent diffusion, whereas in the third stage, at high activity, the strong interaction solvent–polymer increased the mobility, allowing the polymer crystallization. The different cooling conditions neither have an effect on the diffusional behavior nor on the sorption curve. The aging, both at room temperature and at 70°C, did not change the diffusion parameters, but led to the appearance of more and more anomalous sorption behavior. The sorption curve, as a function of vapor activity, did not show any difference for the fresh and the aged-at-room temperature samples, whereas the samples aged at 70°C presented a lower sorption at low activity. The presence of ordered domains, impermeable to the penetrant at low activity, was suggested on the basis of sorption results. The solvent-induced crystallization was investigated for all the samples. Crystallization was induced at an activity of 0.45 for the fresh and the aged-at-room temperature samples; at variance, the samples aged at 70°C crystallize at a slightly higher activity, reaching, nevertheless, a higher level of crystallinity. © 1993 John Wiley & Sons, Inc.     

Anomalous penetrant transport in glassy polymers VI. Effect of temperature on transport

Transport of liquid cyclohexane through well characterised, initially glassy, crosslinked polystyrene slabs was Investigated at 20, 30, 40, and 50°C. The samples used were produced by bulk polymerization of styrene and divinyl benzene (DVB) at 90°C for 43 hr using benzoyl peroxide as an initiator. The samples tested had initial cross-linking ratios, X, between 5 and 25 × 10^?3 mol DVB/mol styrene. The initial thickness of the samples tested varied from 0.25 mm to 1.80 mm, and the aspect ratio (length to thickness ratio) was maintained above 10;1 in order to analyze the results by one-dimensional transport equations. Cyclohexane uptake was followed as a function of time along with dimensional changes in the thickness and area of the samples. The results of penetrant uptake as a function of time were analyzed using a simplified exponential expression and employing all the data points from the beginning of the experiment until the time of observation of the maximum in uptake. Good correlations were established between the penetrant uptake and the transport temperature. These results were interpreted in terms of competitive relaxational and diffusional mechanisms.     

Residual stress,aging and fatigue fracture in injection-molded glassy polymers. II. Polycarbonate

Fatigue test have been conducted on notched polycarbonate bars molded using different conditions and having different post-molding conditioning. Fatigue crack propagation rates were not significantly modified by mechanical preconditioning prior to notching, but annealing in air caused an increase in crack growth rate. Annealing in vacuum did not cause the same effect, but specimens annealed in air or in vacuum showed a fracture surface morphology different from that obtained with unannealed bars. Changes in birefringence during cyclic loading and measurements of skin and core densities as a function of aging time were recorded, but a comprehensive interpretation of the fatigue behavior has not yet been achieved.     

Transport properties of dichloromethane in glassy polymers. VI. Poly(ethylene terephthalate)

Sorption and diffusion of dichloromethane vapor in amorphous poly(ethylene terephthalate) (PET) were investigated, with the aim of studying how aging phenomena, at different temperatures, influence the transport properties. It has been found that aging produces the appearance of non-Fickian behavior in the sorption curves as well as the reduction of the diffusion coefficients. Furthermore, aging at 60°C reduces the sorption of vapor at low activity, and this led to the hypothesis of the presence of ordered domains in the aged samples. In this case, the process of solvent-induced crystallization is favored, and it appears at lower activity. © 1996 John Wiley & Sons, Inc.     

Sequestration of electroactive materials in a high Tg, insulating polymer matrix for optoelectronic applications. Part 2. Photovoltaic devices

The incorporation of high levels of electroactive compounds into a high T_g matrix polymer was investigated in photovoltaic (PV) devices. The combination of electron donor-electron acceptor pairs with optionally light harvesting organics (e.g. laser dyes) in the high T_g polymer matrix yielded PV performance in the range of literature data typically reported for organic based PV devices. The advantages for using a high T_g matrix include increasing the T_g of the electroactive compounds, preventing crystallization, improving the mechanical properties of the active layer(s) and the ability to employ lower cost fabrication processes. While the basic concept has been demonstrated, further optimization would be required to achieve a useful combination of photovoltaic properties. As in the companion paper on utilization of a high T_g polymer to sequester low molecular weight electroactive species for LED devices, this paper demonstrates the same concept for PV devices. The approach to solve the issues with low molecular weight electroactive species noted in the literature to date often involves covalent bonding of these compounds to polymeric backbones. This and the companion paper well-illustrates the blend approach is equally viable and offers a much simpler methodology.