Classical density functional theory for methane adsorption in metal‐organic framework materials

Natural gas is considered as a promising alternative to petroleum as the next generation of primary transportation fuel owing to relatively smaller carbon footprint and lower SO_x/NO_x emissions and to fast developments of shale gas in recent years. Since the volumetric energy density of methane amounts to only about 1% of that of gasoline at ambient conditions, natural gas storage represents one of the key challenges for prevalent deployment of natural gas vehicles. In this work, we present a molecular thermodynamic model potentially useful for high‐throughput screening of nanoporous materials for natural gas storage. We investigate methane adsorption in a large library of metal‐organic frameworks (MOFs) using four versions of classical density functional theory (DFT) and calibrate the theoretical predictions with extensive simulation data for total gas uptake and delivery capacity. In combination with an extended excess entropy scaling method, the classical DFT is also used to predict the self‐diffusion coefficients of the confined gas in several top‐ranked MOFs. The molecular thermodynamic model has been used to identify promising MOF materials and possible variations of operation parameters to meet the Advanced Research Projects Agency‐Energy (ARPA‐E) target set by the U.S. Department of Energy for natural gas storage. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3012–3021, 2015     

Dewetting and microphase separation in symmetric polystyrene‐block‐polyisoprene diblock copolymer ultrathin films

The kinetics of surface structure evolution in ultrathin films of low‐molecular‐weight polystyrene‐block‐polyisoprene (M_w: 7300 g mol^?1–7300 g mol^?1) diblock copolymer at temperatures below the bulk order‐to‐disorder transition temperature are presented. Films with two different thicknesses were studied as a function of annealing temperature using atomic force microscopy. These film thicknesses enabled the investigation of the competition between microphase separation and dewetting that resulted in two different morphologies: long‐range bicontinuous structures and random holes. Three distinctive stages of structure evolution were observed in bicontinuous structure, with the underlying mechanism compared with spinodal dewetting. Thicker films presented holes on their surfaces upon annealing at elevated temperatures, and kinetics of formation of the holes were discussed. We found that the molecular mobility determined the rates of dewetting, while the microphase separation hardly affected the dewetting process. © 2015 Society of Chemical Industry     

Dynamic mechanical properties in blends of poly(styrene‐b‐isoprene‐b‐styrene) with aromatic hydrocarbon resin

The damping properties in blends of poly(styrene‐b‐isoprene‐b‐styrene) (SIS) and hydrogenated aromatic hydrocarbon (C₉) resin were investigated by dynamic mechanical analysis. SIS exhibited two independent peaks of loss factor (tan δ) corresponding to the glass transition of polyisoprene (PI) and polystyrene (PS) segments, respectively. The addition of hydrogenated C₉ resin had a positive impact on the damping of SIS. With the increasing softening point and content of the resin, the main tan δ peak shifted to higher temperatures and the useful damping temperature range was broadened. Addition of mica or PS was found to widen the effective damping range evidently in the high‐temperature region, especially when PS was mixed in the solid state. It was concluded that the dispersed PS domains played a role of reinforcing fillers at low temperatures and served as a polymer component with a tan δ peak due to its glass transition at the high temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4157–4164, 2006     

Matrix effect of mixed‐matrix membrane containing CO2‐selective MOFs

Facilitated mixed‐matrix membranes (MMMs) containing Cu‐metal organic frameworks (Cu‐MOFs) with high CO₂ selectivity on an asymmetric polysulfone support were fabricated and examined the effect of gas separation performance using different matrices. An amorphous poly(2‐ethyl‐2‐oxazoline) (POZ) and semicrystalline poly(amide‐6‐b‐ethylene oxide) (PEBAX^®MH 1657) block copolymer were chosen as the polymeric matrix and the effect of the matrix on CO₂ separation for MMMs containing Cu‐MOFs was investigated. The interaction of CO₂ in different matrix was investigated theoretically using the density functional theory method, and it was found that the amide segment in PEBAX would contribute more to the CO₂ solubility than ether segment. The morphological changes were investigated by differential scanning calorimetry, field emission scanning electron microscope and X‐ray diffractometer. The ideal selectivity of CO₂/N₂ was enhanced significantly with the addition of a Cu‐MOF, and the values are higher in the Cu‐MOF/PEBAX MMM compared with that in a POZ based asymmetric MMM. Improvement in the CO₂/N₂ selectivity of a Cu‐MOF/PEBAX MMM was achieved via facilitated transport by the CO₂‐selective Cu‐MOFs due to both their high adsorption selectivity of CO₂ over N₂ and the decreased crystallinity of PEBAX due to the presence of the Cu‐MOFs, which would provide a synergic effect on the CO₂ separation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42853.     

Materials genomics‐guided ab initio screening of MOFs with open copper sites for acetylene storage

Discovering high‐performance metal‐organic frameworks (MOFs) with open metal sites has become an increasingly hot research topic in the field of safe storage and transportation of acetylene. Following the concept of Materials Genomics proposed recently, a database of 502 experimental MOFs was built by searching the structures deposited in the CSD with the dicopper paddle‐wheel node Cu₂(COO)₄ as the characteristic materials gene. On the basis of the developed ab initio force field, a high‐throughput computational screening was conducted to examine the property‐performance relationships of MOFs containing Cu‐OMS for C₂H₂ storage at ambient conditions. The optimal ranges of the structural and energetic features for the design of such MOFs were suggested. From our computational screening, three potentially promising MOFs were identified which exhibit a performance outperforming those MOFs reported experimentally so far with record high gravimetric C₂H₂ uptakes, both in the total and deliverable adsorption capacities. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1389–1398, 2018     

The effect of crystallites on the rheological properties of microphase‐separated PVC‐PBA‐PVC triblock copolymers obtained by single electron transfer‐degenerative chain transfer living radical polymerization

Linear and nonlinear rheological properties of poly(vinyl chloride) (PVC)‐poly(n‐butyl acrylate)‐PVC triblocks of different compositions, obtained by single electron transfer‐degenerative chain transfer living radical polymerization, are investigated, focusing on the effect of crystallites. Dynamic mechanical thermal analysis results show the existence of two glass transition temperatures, denoting microphase segregation. However, rather than phase separation, it is the presence of two types of crystals that melt at T_m1 = 127 ± 0.8°C and T_m2 = 185 ± 2°C, respectively, the factor that determines the rheological response of the copolymers. To the difference with PVC homopolymers, extrusion flow measurements at very low temperatures (T = 100°C) are possible with the copolymers. A change in the viscosity‐temperature dependence is observed below and above the lowest melting temperature. Notwithstanding the microphase separation and the presence of crystallites, experiments carried out in conditions similar to industrial processing reveal a remarkable viscosity reduction for our copolymers with respect to PVC obtained by single electron transfer‐degenerative chain transfer living radical polymerization, conventional PVC, and PVC/[diethyl‐(2‐ethylhexyl) phthalate] compounds. Extrudates free of surface instabilities are obtained at low extrusion temperatures, such as 90–100°C. J. VINYL ADDIT. TECHNOL., 21:24–32, 2015. © 2014 Society of Plastics Engineers     

Dynamic mechanical properties of polystyrene‐block‐poly[ethylene‐co‐(ethylene‐propylene)]‐block‐polystyrene triblock copolymer/hydrocarbon oil blends

Blend systems of polystyrene‐block‐poly(ethylene‐co‐(ethylene‐propylene))‐block‐polystyrene (SEEPS) triblock copolymer with three types of hydrocarbon oil of different molecular weight were prepared. The E″ curves as a function of temperature exhibited two peaks; one peak at low temperature (? ?50°C), arising from the glass transition of the poly[ethylene‐co‐(ethylene‐propylene)] (PEEP) phase and a high temperature peak (? 100°C), arising from the glass transition of the polystyrene (PS) phase. The glass transition temperature (T_g) of the PEEP phase shifted to lower temperature with increasing oil content. The shifted T_g depended on the types of oil and was lower for the low molecular weight oil. The T_g of PS phase of the present blend system, were found to be constant and independent of the oil content, when molecular weight of the oil is high. However, for the lower molecular weight oil, the T_g of the PS phase also shifted to lower temperatures. This fact indicates that the oil of high molecular weight is merely dissolved in the PS phase. The E′ at (75°C, at which temperature both of PEEP and PS phases are in glassy state, was found to be independent of oil content. In contrast, at 25°C, at which temperature the PEEP phase is in rubbery state, the E′ decreased sharply with increasing oil content. This result indicates that the hydrocarbon oil was a selective solvent in the PEEP phase. It mainly dissolved in the PEEP phase, although slightly dissolved into the PS phase as well, when molecular weight of oil is low. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties of plastic‐bonded explosive binder materials as a function of strain‐rate and temperature

Compression measurements were conducted on three explosive formulation binders, extruded Estane, plasticized Estane, and plasticized hydroxyl‐terminated polybutadiene, as a function of temperature and strain rate. The mechanical response of the Estane was found to exhibit the strongest dependency on strain rate and temperature and higher flow strength for similar test conditions of the three materials tested. Plasticized Estane was less sensitively dependent on strain rate and temperature, followed by the plasticized HTPB. The visco‐elastic recovery of all three binders is seen to dominate the mechanical behavior at temperatures above the glass transition temperature (T_g). There is a pronounced shift in the apparent T_g to higher temperatures as the strain rate is increased. Two distinct behaviors are observed in the binders below the T_g. At low strain rates, the binders exhibit a yield behavior, followed by a drop in the flow stress, which may or may not recover. At high strain rates, the load drop does not occur and the flow stresses either gradually increase, as in plasticized HTPB, or it levels out as seen in the Estane‐based binders. POLYM. ENG. SCI., 46:812–819, 2006. © 2006 Society of Plastics Engineers     

Polyurethanes derived from carbohydrates and cystine‐based monomers

Linear [m,n]‐type polyurethanes (PUs) fully based on renewable materials are synthesized by interfacial polycondensation reaction of diamines derived from the amino‐acid cystine with (bis)chloroformates derived from alditols having L‐arabino or xylo configuration. The degradability of the new PUs has been enhanced by the introduction of disulfide linkages into the polymer backbone leading to a new group of stimulus‐responsive sugar‐based polyurethanes able to be degraded by glutathione under physiological conditions. All these polyurethanes are stable up to around 245°C, decomposing at higher temperatures through a one‐stage mechanism. The new materials display high chemical homogeneity and degradability in both hydrolytic and reductive environments, with reductions of above 90% in M_w. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41304.     

Enhanced proton conductivity from phosphoric acid‐incorporated 3D polyacrylamide‐graft‐starch hydrogel materials for high‐temperature proton exchange membranes

To enhance anhydrous proton conductivity of high‐temperature proton exchange membranes (PEMs), we report here the realization of H₃PO₄‐imbibed three‐dimensional (3D) polyacrylamide‐graft‐starch (PAAm‐g‐starch) hydrogel materials as high‐temperature PEMs using the unique absorption and retention of crosslinked PAAm‐g‐starch to concentrated H₃PO₄ aqueous solution. The 3D framework of PAAm‐g‐starch matrix provides enormous space to keep H₃PO₄ into the porous structure, which can be controlled by adjusting crosslinking agent and initiator dosages. Results show that the H₃PO₄ loading and therefore the proton conductivities of the membranes are significantly enhanced by increasing the amount of crosslinking agent and initiator dosages. Proton conductivities as high as 0.109 S cm^?1 at 180°C under fully anhydrous state are recorded. The high conductivities at high temperatures in combination with the simple preparation, low cost, and scalable matrices demonstrate the potential use of PAAm‐g‐starch hydrogel materials in high‐temperature proton exchange membrane fuel cells. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40622.     

Toughness optimization of elastomer‐modified glass–fiber reinforced PA6 materials

To investigate the influence of moisture and EPR‐g‐MA content on the fracture behavior of glass–fiber reinforced PA6 materials, brittle‐to‐tough transition temperatures (T_btt) were determined. Water absorption was taken into account by conditioning the analyzed materials. Tensile tests could reveal the temperature range of the largest moisture dependence of mechanical properties between 10 and 50°C. J‐integral values were used to describe the fracture behavior under conditions of impact load as a function of temperature. The brittle‐to‐tough transition of reinforced polyamides was found to be less approximate than in unreinforced materials. Two different characteristic temperature points T_s and T_e were identified, which were the intercept between elastic and elastic–plastic deformation on the one hand and the starting point of dominating stable crack propagation with strong plastic deformation on the other hand. Characteristic brittle‐to‐tough transition temperatures T_btt could be calculated as the arithmetic average of these two points. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ceramic tubular MOF hybrid membrane fabricated through in situ layer‐by‐layer self‐assembly for nanofiltration

Nanofiltration has been playing an important role in water purification, in which the developments of novel membrane materials and modules are among significant. Herein, a metal‐organic framework (MOFs) hybrid membrane, ZIF‐8/PSS was fabricated on a tubular alumina substrate through a layer‐by‐layer self‐assembly technique. ZIF‐8 particles in situ grow into PSS layers to improve their compatibility and dispersion, thereby getting high quality membrane, which was loaded into a steel tubular module for nano‐filtrating dyes from water. Under optimized conditions, it shows outstanding nanofiltration properties toward methyl blue, with the flux of 210 Lm^?2 h^?1 MPa^?1 and the rejection of 98.6%. Furthermore, the good pressure resistance ability and running stability of the membrane were revealed, which can be attributed to use the ceramic substrate and the inherent stability of ZIF‐8. This work thus illustrates a simple approach for fabricating MOFs hybrid membranes on tubular ceramic substrates, having great potential for industrial applications. © 2015 American Institute of Chemical Engineers AIChE J, 62: 538–546, 2016     

Investigation on Resonant Vibration Performances of Fe‐Doped BiScO3–PbTiO3 Ceramics in High‐Temperature Environment

The high‐temperature performance of a series of Fe‐doped BiScO₃‐PbTiO₃ (BSPT) piezoelectric ceramics at the morphotropic phase boundary was investigated. The effects of different Fe contents on the piezoceramics were assessed with regard to variations in structure, morphology, dielectric properties, piezoelectric properties, and high‐temperature resonant vibration. X‐ray diffraction (XRD) results indicated that the Fe‐doped BSPT ceramics show a single perovskite structure and that the c/a ratio undergoes a slight increase with increasing Fe concentrations. It was also found that, as the proportion of Fe in the ceramics was increased, the grain size was enlarged somewhat, the dielectric loss (tan δ) decreased, the mechanical quality factor (Q_m) was gradually improved, and the Curie temperature (T_C) was increased from 426°C to approximately 460°C. Despite these complex effects, it was evident that Fe doping can improve the high‐temperature resonant vibration performance of BSPT ceramics, and that these materials exhibit stable resonant vibration velocities at temperatures as high as 225°C. Our results indicate that Fe‐doped BSPT ceramics have the potential to be used as piezoelectric power devices intended for high‐temperature environments.     

Low‐Temperature Magnetic and Dielectric Anomalies in Rare‐Earth‐Substituted BiFeO3 Ceramics

In this work, we report on the magnetic and dielectric anomalies observed in dense Bi_1–xRE_xFeO₃ ceramics (RE = Dy, Tb; 0 ≤ x ≤ 0.3) at cryogenic temperatures. For compositions with a high content of rare‐earth ions, thermomagnetic experiments revealed a distinct anomaly in the magnetization curves at temperatures below 200 K. The temperature of the magnetic anomaly along with a thermal hysteresis was found to be dependent on the rare‐earth concentration and magnetic field strength. Low‐temperature dielectric measurements showed an anomalous relaxor‐like behavior of the relative permittivity and dielectric loss in highly doped ceramic samples. The anomalies in low‐temperature magnetization and dielectric response are suggested to result from the presence of GdFeO₃‐like orthoferrite phase and/or bismuth rare‐earth‐mixed iron garnet impurities.     

High‐Temperature Properties and Ferroelastic Phase Transitions in Rare‐Earth Niobates (LnNbO4)

Phase transition and high‐temperature properties of rare‐earth niobates (LnNbO₄, where Ln = La, Dy and Y) were studied in situ at high temperatures using powder X‐ray diffraction and thermal analysis methods. These materials undergo a reversible, pure ferroelastic phase transition from a monoclinic (S.G. I2/a) phase at low temperatures to a tetragonal (S.G. I4₁/a) phase at high temperatures. While the size of the rare‐earth cation is identified as the key parameter, which determines the transition temperature in these materials, it is the niobium cation which defines the mechanism. Based on detailed crystallographic analysis, it was concluded that only distortion of the NbO₄ tetrahedra is associated with the ferroelastic transition in the rare‐earth niobates, and no change in coordination of Nb⁵⁺ cation. The distorted NbO₄ tetrahedron, it is proposed, is energetically more stable than a regular tetrahedron (in tetragonal symmetry) due to decrease in the average Nb–O bond distance. The distortion is affected by the movement of Nb⁵⁺ cation along the monoclinic b‐axis (tetragonal c‐axis before transition), and is in opposite directions in alternate layers parallel to the (010). The net effect on transition is a shear parallel to the monoclinic [100] and a contraction along the monoclinic b‐axis. In addition, anisotropic thermal expansion properties and specific heat capacity changes accompanying the transition in the studied rare‐earth niobate systems are also discussed.     

Synthesis of highly transparent and heat‐resistant polyimides containing bulky pendant moieties

A new diamine with bulky pendant biphenyl and ortho‐position dimethyl structures, 4,4′‐((1,1′‐biphenyl)‐4‐ylmethylene)bis(2,6‐dimethylaniline), was synthesized via a one‐pot reaction of 4‐biphenyl carboxaldehyde and 2,6‐dimethylaniline. The diamine was employed to polymerize with several dianhydrides via one‐step condensation under high‐temperature conditions. The light yellow or colorless polyimide (PI) films obtained were found to have cut‐off wavelengths in the range 286–358 nm and transmittance over 80% in the visible region (400–780 nm). Meanwhile, these PIs possessed excellent solubility in common organic solvents, even in low‐boiling‐point solvents such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂) and tetrahydrofuran. The glass transition temperatures (T_g) of the PIs were determined to exceed 343 °C, even to 456 °C. All PI films were flexible with a tensile strength of 78–119 MPa, a Young's modulus of 2.0–2.5 GPa and elongation at break of 4.0%–8.2%. Therefore, these colorless PIs can be used as candidate materials for flexible display substrates. © 2019 Society of Chemical Industry     

Novel High‐Temperature Antiferroelectric‐Based Dielectric NaNbO3–NaTaO3 Solid Solutions Processed in Low Oxygen Partial Pressures

The (1?x)NaNbO₃–(x)NaTaO₃ solid solution was investigated for x ≤ 0.4 in terms of new high‐temperature and high‐permittivity dielectric system that is suitable for base metal inner electrode capacitor applications. The addition of Ta significantly enhanced the resistivity of the dielectric, resulting in superior resistivity than the dielectrics‐formulated BaTiO₃ systems that dominate the multilayer ceramic capacitor dielectric devices. The voltage dependence of the permittivity was also superior to BaTiO₃‐based materials, providing higher capacitance at higher temperatures. A transmission electron microscopy study illustrated that the grains had so‐called core‐shell structure. According to the electron diffraction analysis, the core region had an inhomogeneous structure between antiferroelectric and ferroelectric phases, and shell region had an incommensurate ferroelectric‐like structure. The core and shell region had Nb‐ and Ta‐rich composition, respectively, and their interface was compositionally sharp, implying that shell region was formed via a liquid phase during the sintering process with an incongruent Ta dissolution reprecipitation. We anticipate that these or similar materials based on the alkali‐niobate perovskites can be further enhanced to provide capacitor solutions from 150°C to 250°C, which is an important range for a number of new AC–DC invertor and engine control units.     

Ultradrawing properties of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends prepared at various formation temperatures

The ultradrawing behavior of ultrahigh‐molecular‐weight polyethylene/low‐molecular‐weight polyethylene film specimens prepared at various concentrations and formation temperatures was studied. The critical draw ratio (D_rc) of UL_?0.7 film specimens was found to depend significantly on the formation temperature used to prepare the film specimens. At any fixed drawing temperature, the D_rc values of UL_?0.7 specimens prepared at various formation temperatures increased significantly as the formation temperatures were reduced. In fact, with an optimum drawing temperature of 95°C, the D_rc values of UL_?0.7 specimens prepared at a formation temperature of 0°C reached 488, about 50% higher than that of UL_?0.7 specimens prepared at a formation temperature of 95°C. These interesting phenomena were investigated in terms of the thermal, birefringence, and tensile properties of these undrawn and drawn UL_?0.7 specimens. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3728–3738, 2003     

Oligomeric poly(ether‐imide)s bearing ortho trifluoromethyl groups: Solubility,thermal studies,and optical properties

In the development of processable high‐temperature materials, six new aromatic poly(imide)s based on diamines containing ortho trifluoromethyl groups, ether linkages and R,R‐methylenes moieties (R = Me or Ph) and previously reported dianhydrides have been synthesized vía polycondensation reactions. All polymers were obtained with good yields, were soluble in a variety of polar aprotic solvents, and exhibited inherent viscosity (η_inh) values between 0.15 and 0.20 dL g^?1, which is indicative of low molecular‐weight species. Preliminary studies of their physical properties were carried out. The new materials were transparent in the visible region and they exhibited thermal decomposition temperatures ranging from 475 to 545 °C and glass‐transition temperatures varying from 288 to 304 °C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46613.     

Study on time‐dependent resistance of carbon black‐loaded high‐density polyethylene composites during the isothermal course

Carbon black (CB)‐loaded high‐density polyethylene composites were prepared using conventional blending. The resistance and temperature (R‐T) relations under constant heating rates and the resistance and time (R‐t) relations at different isothermal temperatures have been studied. The results of the R‐T and differential scanning calorimetry (DSC) curve demonstrated a correlation between the positive temperature coefficient/negative temperature coefficient transition and the melting course. At isothermal temperatures below T_PTC/NTC, the resistance displayed a sharp increase and thereafter a mild decrease with time. The time to reach the highest resistance became shorter with rise in the isothermal temperature. The ratio between highest resistance and initial resistance was maximum at T_peak of the DSC curve. When the isothermal temperature was higher than T_PTC/NTC, the resistance attenuated with time. The attenuation fits to a first order exponential decay function. The calculated time constant τ decreased with rise in isothermal temperature. The attenuation discrepancy under different isothermal temperatures reduced as the heating rate before the isothermal courses was higher. A model based on polymer chain diffusion and CB movements at high temperature is proposed. The model can explain the results obtained in R‐T and R‐t measurements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2258–2263, 2001