Evaluation of gas sorption parameters and prediction of sorption isotherms in glassy polymers

A model of continuous‐site distribution for gas sorption in glassy polymers is examined with sorption data of CO₂ and Ar in polycarbonate. A procedure is presented for determining from a measured isotherm the number of sorption sites in a polymer, an important parameter that previously had to be assumed. With this parameter value and solubility data obtained at zero pressure, the model can reasonably predict sorption isotherms of CO₂ in glassy polycarbonate for a wide temperature range. The number of sorption sites and the average site volume evaluated from CO₂ sorption isotherms are employed for the prediction of Ar sorption isotherms with zero‐pressure solubility data and the independently measured partial molar volume of Ar. A reasonable fit to the measured isotherms of Ar is achieved. With the proposed procedure, the continuous‐site model shows several advantages over the conventional dual‐mode sorption model. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 883–888, 2000     

Simulation of experimentally observed dilation phenomena during integral gas sorption in glassy polymers

A molecular modeling investigation of dilation effects induced by sorbed gas molecules in two glassy polymers is presented. As experimental reference, integral sorption of CO₂ and CH₄ was measured for polysulfone (PSU) and a polyimide (6FDA‐TrMPD, PI4) at 308 K and a pressure of 10 bar. Simultaneously, the gas induced swelling effect was measured with a dilatometer based on a capacitive distance sensor recorded. The experimental evidence of the (on the observed time scale and concentration levels) elastic nature of the gas induced dilation is supported by the dilation and contraction behavior observed in molecular dynamics (MD) simulations of respective detailed atomistic packing models. These models were constructed in accordance with gas concentration levels obtained from the experimental sorption results. Quantitative deviations between simulated and measured dilations are discussed as a consequence of an anelastic response of the polymer matrix which is too fast to be resolved in the experiments whose kinetics is dominated by diffusional processes. In the simulation, the initial insertion of penetrant molecules into equilibrated packing models “circumvents” the slow diffusional process of the experiment and allows a reasonable representation of the dilation process as well as a closer investigation. Our simulation approach reveals a different behavior for PSU and PI4 on the corresponding time scale. Most likely, the different chain mobility of the two polymers is responsible for the respective response to the inserted amount of gas molecules which is discussed in terms of the different chain mobilities of the two polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 59–71, 2008     

The effect of lattice compressibility on the thermodynamics of gas sorption in polymers

A compressible lattice model with holes, the glassy polymer lattice sorption model (GPLSM), was used to model the sorption of carbon dioxide, methane, and ethylene in glassy polycarbonate and carbon dioxide in glassy tetramethyl polycarbonate. For glassy polymers, an incompressible lattice model, such as the Flory–Huggins theory, requires concentration-dependent and physically unrealistic values for the lattice site volumes in order to satisfy lattice incompressibility. Rather than forcing lattice incompressibility, GPLSM was used and reasonable parameter values were obtained. The effect of conditioning on gas sorption in glassy polymers was analyzed quantitatively with GPLSM. The Henry's law constant decreases significantly upon gas conditioning, reflecting changes in the polymer matrix at infinite dilution. Treating the Henry's law constant as a hypothetical vapor pressure at infinite dilution, gas molecules in the conditioned polymer are less “volatile” than those in the unconditioned polymer. Flory–Huggins theory was used to model the sorption of carbon dioxide, methane, and ethylene in silicone rubber. Above the glass transition temperature, the criterion of lattice incompressibility for Flory-Huggins theory was satisfied with physically realistic and constant values for the lattice site volumes. © 1992 John Wiley & Sons, Inc.     

Sorption and swelling of semicrystalline polymers in supercritical CO2

The equilibrium sorption and swelling behavior of four different polymers—poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene–perfluoromethylvinylether–in supercritical CO₂—are studied at different temperatures (from 40 to 80 °C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO₂ in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to “freeze” during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1531–1546, 2006     

Effects of hard‐segment polymers on CO2/N2 gas‐separation properties of poly(ethylene oxide)‐segmented copolymers

Poly(ethylene oxide)‐segmented polyurethanes (PEO‐PUs) and polyamides (PEO‐PAs) were prepared, and their morphology and CO₂/N₂ separation properties were investigated in comparison with those of PEO‐segmented polyimides (PEO‐PIs). The contents of the hard and soft segments in the soft and hard domains, W_HS and W_SH, respectively, were estimated from glass‐transition temperatures with the Fox equation. The phase separation of the PEO domains depended on the kind of hard‐segment polymer; that is, W_HS was in the order PU > PA ≫ PI for a PEO block length (n) of 45–52. The larger W_HS of PUs and PAs was due to hydrogen bonding between the oxygen of PEO and the NH group of urethane or amide. The CO₂/N₂ separation properties depended on the kind of hard‐segment polymer. Compared with PEO‐PIs, PEO‐PUs and PEO‐PA had much smaller CO₂ permeabilities because of much smaller CO₂ diffusion coefficients and somewhat smaller CO₂ solubilities. PEO‐PUs also had a somewhat smaller permselectivity because of a smaller solubility selectivity. This was due to the larger W_HS of PEO‐PUs and PEO‐PAs, that is, a greater contamination of PEO domains with hard urethane and amide units. For PEO‐PIs, with a decrease in n to 23 and 9, W_HS became large and CO₂ permeability decreased significantly, but the permselectivity was still at a high level of more than 50 at 35 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1707–1715, 2000     

Diffusion in gas separation membrane materials: A comparison and analysis of experimental characterization techniques

Typically, materials with high-performance transport properties such as zeolites, carbon molecular sieves, or hyper rigid polymers are inherently difficult or impossible to characterize by steady-state membrane permeation experiments used for conventional polymers. Diffusion coefficients determined by transient sorption, a measurement easily performed on brittle media, are analyzed here and compared to those determined by steady-state permeation/sorption and transient permeation for a glassy polymer and a carbon molecular sieve. Average and local diffusion coefficients are extrapolated to zero upstream partial pressure to eliminate effects caused by concentration dependence. Good agreement between the techniques was observed for the glassy polymer. On the other hand, carbon molecular sieves, possessing a more complex morphology, exhibit a greater difference in diffusion coefficients determined by the various techniques. Nevertheless, comparison of the analysis techniques is shown to provide potentially valuable insights into the morphological features of such carbon molecular sieves. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1747–1755, 1998     

Tuning Pore Size in Square‐Lattice Coordination Networks for Size‐Selective Sieving of CO2

Porous materials capable of selectively capturing CO₂ from flue‐gases or natural gas are of interest in terms of rising atmospheric CO₂ levels and methane purification. Size‐exclusive sieving of CO₂ over CH₄ and N₂ has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore‐size in a coordination network, [Cu(quinoline‐5‐carboxyate)₂]_n ( Qc‐5‐Cu ) ena+bles ultra‐high selectivity for CO₂ over N₂ (S_CN≈40 000) and CH₄ (S_CM≈3300). Qc‐5‐Cu‐sql‐β , a narrow pore polymorph of the square lattice ( sql ) coordination network Qc‐5‐Cu‐sql‐α, adsorbs CO₂ while excluding both CH₄ and N₂. Experimental measurements and molecular modeling validate and explain the performance. Qc‐5‐Cu‐sql‐β is stable to moisture and its separation performance is unaffected by humidity.     

Binding characteristics of molecularly imprinted polymers based on fungicides in hydroalcoholic media

An iprodione‐imprinted polymer was prepared by copolymerization of methacrylamide and ethylene glycol dimethacrylate using a noncovalent imprinting approach. Methacrylamide was chosen using molecular dynamics simulations. To concentrate iprodione from hydro‐alcoholic solutions, batch sorption of iprodione on the imprinted polymer were conducted. The equilibrium time for iprodione sorption is 20 min, and the corresponding kinetic mechanism follows the pseudo‐second order indicating a strong interaction between iprodione and the imprinted polymer. Langmuir, Freundlich, and Dubinin–Radushkevich models were used to fit the isotherm of iprodione sorption. The imprinted polymer was found to be more efficient than the nonimprinted polymer for the uptake of iprodione, as revealed by its higher adsorption energy, affinity, and capacity. Finally, a selectivity study was conducted on the imprinted and the nonimprinted polymers to sorb three fungicides. It shows that the imprinted polymer could be used as a preconcentration phase in a multiresidue analysis of fungicides in hydroalcoholic medium.     

Multiscale description of polymeric foam behavior: A new approach based on discrete element modeling

The mechanical behavior of polymeric foams depends on several parameters, such as temperature, material density, and strain rate. The studied foams are multiscale materials; agglomerated beads (bead scale is millimetric) are composed of microscopic closed cells (a few tens of microns). The response of the material to dynamic loading consists of three regions: an elastic phase, a plastic phase, and densification. The first part of this work has been the identification of the behavior of these multiscale foams in terms of density and strain rate. Some results are presented in this paper. From these first dynamic results, the second step has been the observation and the analysis of the physical phenomena initiated during the yield plateau. Buckling of the bead and cell wall and strong damage localization were studied with several devices and techniques such as high-speed camera, SEM, and microtomography. The final objective is the development of a model adapted to the multiscale structure of the foam. The first step of this numerical approach consists in the modeling of the microstructure. Due to the microscopic discrete aspect of the foam, a Discrete Element Model has been developed to study the relationship between microscopic properties and the macroscopic behavior of foam. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 6, pp. 1037–1050. This article was submitted by the authors in English.     

A new approach to photorecording based on hindering a phase transition in photochromic chiral liquid crystalline polymers

The phase transition from an 'isotropic smectic phase' to the proper SmA* phase in a new photochromic chiral copolymer can be prevented by illumination with non-polarized white light of low intensity. On the basis of the effect observed, a novel photorecording technique is suggested, so that the shadow image appears as a white scattering texture of the SmA* phase on the background of the transparent, optically isotropic TGB A-like phase. Optical, DSC, and X-ray studies of the polymer are reported, the photorecording set-up is described, and the first written photoimage is presented.     

A model for structural relaxation in amorphous glassy polymers based on the aggregation–fragmentation theory

Governing equations are derived for the kinetics of physical aging in polymeric glasses. An amorphous polymer is treated as an ensemble of cooperatively rearranged regions (CRRs). Any CRR is thought of as a string of elementary clusters (ECs). Fragmentation of the string occurs at random times at any border between ECs. Two strings aggregate at random instants to produce a new string. Aggregation and fragmentation are treated as thermally activated processes, and the rate of fragmentation is assumed to grow with temperature more rapidly than the rate of coalescence. A nonlinear differential equation is developed for the distribution of CRRs with various numbers of ECs. Adjustable parameters of the model are found by the fitting of experimental data for polycarbonate, poly(methyl methacrylate), polystyrene, and poly(vinyl acetate) (PVA). Fair agreement is established between observations and results of numerical simulation. For PVAc, the relaxation spectrum found by matching data in a calorimetric test is successfully employed to predict experimental data in a shear relaxation test. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1312–1325, 2001     

A new approach to construct a doubly interpenetrated microporous metal-organic framework of primitive cubic net for highly selective sorption of small hydrocarbon molecules

A new approach has been realized to construct a three‐dimensional doubly interpenetrated cubic metal–organic framework Zn₂(PBA)₂(BDC) ? (DMF)₃(H₂O)₄ ( UTSA‐36 , HPBA=4‐(4‐pyridyl) benzoic acid, H₂BDC=1,4‐benzenedicarboxylic acid) through the self‐assembly of the pyridylcarboxylate linker 4‐(4‐pyridyl) benzoate and bicarboxylate linker 1,4‐benzenedicarxylate with paddle‐wheel [Zn₂(COO)₄]. The activated UTSA‐36 a exhibits highly selective gas sorption of C₂H₆, C₂H₄ and C₂H₂ over CH₄ with the Henry law’s selectivities of 11 to 25 in the temperature range of 273 to 296 K attributed to the unique 3D intersected pore structure of about 3.1 to 4.8 Å within the framework, indicating that UTSA‐36 a is a potentially very useful and promising microporous material for such industrially important separation of C₂ hydrocarbons over methane.     

A novel oxidative reaction of 2-nitro-1-phenylpropane with sodium nitrite. A new approach to prepare 1-oximino-1-phenylacetones

A useful method for preparation of 1-oximino-1-phenylacetones via a novel oxidative reaction of 2-nitro-1-phenylpropanes with sodium nitrite was reported.     

Structural analysis of poly(amidoamine) dendrimer immobilized in crosslinked poly(ethylene glycol)

Polymeric membranes comprised of poly(amidoamine) (PAMAM) dendrimer immobilized in a poly(ethylene glycol) (PEG) network exhibit an excellent CO₂ separation selectivity over H₂. The CO₂ permeability increases with PAMAM dendrimer concentration in the polymeric membrane and becomes 500 times greater than H₂ permeability when the dendrimer content was 50 wt % at ambient conditions (5 kPa of CO₂ partial pressure). However, the detailed morphology of the membrane has not been discussed. The immiscibility of PAMAM dendrimer and PEG matrix results in phase separation, which takes place in a couple of microns scale. Especially, laser scanning confocal microscope captures a 3D morphology of the polymeric blend. The obtained 3D reconstructions demonstrate a bicontinuous structure of PAMAM dendrimer‐rich and PEG‐rich phases, which indicates the presence of PAMAM dendrimer channel penetrating the polymeric membrane, and CO₂ will preferentially pass through the dendrimer channel. In addition, Fourier transform of the 3D reconstructions indicates the presence of a periodic structure. An average size of the dendrimer domain calculated is 2–4 μm in proportion to PAMAM dendrimer concentration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

一种基于硝酸纤维素膜的新颖便捷的芯片对循环肿瘤细胞的高效捕获

开发了一种新颖便捷的循环肿瘤细胞(CTC)捕获芯片用于癌细胞的分离和检测。CTC芯片以硝酸纤维素膜为基底制备,利用其对蛋白质的超强吸附能力来结合抗体,简便高效,便于将来大规模的推广应用。以非小肺癌细胞NCI-H1650为目标靶细胞,证明了CTC芯片对癌细胞具有很高的捕获效能。向1 mL正常人血液中加入500个癌细胞模拟病人血样的分析中成功检测到了182个癌细胞,预示了CTC芯片将来在临床应用上的巨大潜力。     

A thermodynamic analysis on the coincidence of extrema conditions in the sorption equilibrium for ternary polymer systems

Flory-Huggins theory of polymer solutions has been used to express the condition of extrema values in the total sorption, as well as the inversion point in the preferential adsorption parameters for termary polymer systems. Two approaches have been followed, the first considers the binary and ternary interaction parameters independent of polymer concentration and solvent composition. In the second one, this dependence has been introduced. Our attention is focused on the volume fraction of solvent mixture dependence of the above parameters, in order to confirm or not the coincidence between the extrema values and the inversion point. Several cosolvent and cononsolvent ternary polymer systems, have been used to test the validity of the equations obtained. Also, it has been verified, from an experimental point of view, that in cosolvent ternary polymer systems there is coincidence in both compositions while in cononsolvent ternary polymer systems, such coincidence does not appear.     

Synthesis, X-ray crystal structures, and gas sorption properties of pillared square grid nets based on paddle-wheel motifs: implications for hydrogen storage in porous materials

A systematic modulation of organic ligands connecting dinuclear paddle-wheel motifs leads to a series of isomorphous metal-organic porous materials that have a three-dimensional connectivity and interconnected pores. Aromatic dicarboxylates such as 1,4-benzenedicarboxylate (1,4-bdc), tetramethylterephthalate (tmbdc), 1,4-naphthalenedicarboxylate (1,4-ndc), tetrafluoroterephthalate (tfbdc), or 2,6-naphthalenedicarboxylate (2,6-ndc) are linear linkers that form two-dimensional layers, and diamine ligands, 4-diazabicyclo[2.2.2]octane (dabco) or 4,4'-dipyridyl (bpy), coordinate at both sides of Zn(2) paddle-wheel units to bridge the layers vertically. The resulting open frameworks [Zn(2)(1,4-bdc)(2)(dabco)] (1), [Zn(2)(1,4-bdc)(tmbdc)(dabco)] (2), [Zn(2)(tmbdc)(2)(dabco)] (3), [Zn(2)(1,4-ndc)(2)(dabco)] (4), [Zn(2)(tfbdc)(2)(dabco)] (5), and [Zn(2)(tmbdc)(2)(bpy)] (8) possess varying size of pores and free apertures originating from the side groups of the 1,4-bdc derivatives. [Zn(2)(1,4-bdc)(2)(bpy)] (6) and [Zn(2)(2,6-ndc)(2)(bpy)] (7) have two- and threefold interpenetrating structures, respectively. The non-interpenetrating frameworks (1-5 and 8) possess surface areas in the range of 1450-2090 m(2)g(-1) and hydrogen sorption capacities of 1.7-2.1 wt % at 78 K and 1 atm. A detailed analysis of the sorption data in conjunction with structural similarities and differences concludes that porous materials with straight channels and large openings do not perform better than those with wavy channels and small openings in terms of hydrogen storage through physisorption.     

Glass transition. A new approach based on cluster model of glasses

The structure of real glasses has been considered to be microheterogeneous, composed of clusters and connective tissue. Particles in the cluster are assumed to be highly correlated in positions. The tissue is considered to have a truly amorphous structure with its particles vibrating in highly anharmonic potentials. Glass transition is recognized as corresponding to the melting of clusters. A simple mathematical model has been developed which accounts for various known features associated with glass transition, such as range of glass transition temperature,T _g, variation ofT _g with pressure, etc. Expressions for configurational thermodynamic properties and transport properties of glass forming systems are derived from the model. The relevence and limitations of the model are also discussed. Contribution No. 251 from Solid State and Structural Chemistry Unit.     

A new approach to molecular phylogeny of H5N1 avian influenza viruses in Asia

In this article, we introduce a new method to analysis avian influenza virus (AIV) of subtype H5N1 and study the similarity of these sequences. We make a comparison for some nucleic acid sequences of H5N1 AIV in Asia by using the 2D and 3D graphic representation. Comparing these sequences, we structured a phylogenetic tree and discussed the evolutional relationship among these viruses. The sequences analysis shows that there are some obvious traits depending on different areas, periods, and hosts. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Syntheses,crystal structures,and catalytic activities of three new Cu(II) coordination polymers based on 2-(1H-1,2,4-triazole)-1-acetic acid

Three new coordination polymers, {[Cu(trza)(2,2′-bipy)(H₂O)]?·?(ClO₄)} _n (1), {[Cu(trza)(2,2′-bipy)(H₂O)]?·?(BF₄)} _n (2), and {[Cu(trza)(4,4′-bipy)]?·?(H₂O)?·?(ClO₄)} _n (3) (Htrza?=?2-(1H-1,2,4-triazole)-1-acetic acid), have been synthesized and characterized by single-crystal X-ray diffraction analysis. Both 1 and 2 exhibit 1-D chain structure while 3 displays 2-D layer structure. The catalytic activities of 1 and 3 in the green oxidative coupling of 2,6-dimethylphenol have been investigated.