Br treated graphite nanoplatelets for improved electrical conductivity of polymer composites

The graphite nanoplatelets (GNP) were treated by vapor-phase bromination. The increase in weight and atomic concentration of Br indicated the bromine uptake. The intercalation of Br between graphene layers of GNP was confirmed by the X-ray diffraction result, showing an increase in the interlayer spacing from 3.342 Å to 3.361 Å. Two types of bonds between C and Br were introduced simultaneously, ionic and covalent bonds, both of them increased with bromination duration. The fraction of ionic bond reached the highest value by 3 h Br exposure, which corresponded to the highest electrical conductivity of GNP. Although the bromination treatment did not change the percolation threshold of composites, it increased the absolute value of electrical conductivity of composites when the filler content was higher than the percolation threshold.     

Imidazolium poly(butylene terephthalate) ionomers with long-term antimicrobial activity

Imidazolium poly(butylene terephthalate) ionomers with ionic groups located randomly along the polymer chain or selectively as end-groups (telechelic) have been prepared in order to determine their antimicrobial (AM) activity. Two different approaches have been followed for the linkage of the imidazolium to the polymer backbone: a covalent bond and an ionic aggregation to sulfonated groups covalently bonded to the polymer. The ionic groups have been linked to the polymer in order to improve the long-term AM activity since the low molecular weight additives commonly used tends to migrate toward the surface during use. We have found that imidazolium ionomers present AM activity comparable with that of commercial antimicrobial agents such as Triclosan. The AM activity depends on the polymer architecture, the telechelic approach being more active compared to the random approach. We have proved that imidazolium ionomers retain their high AM activity even after 6 days in water at 60 °C while Triclosan consistently loses his activity.     

Bond characteristics,mechanical properties,and high-temperature thermal conductivity of (Hf1−xTax)C composites

Bond characteristics, mechanical properties, and high-temperature thermal conductivity of ultrahigh-temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first-principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high-temperature thermal conductivity.     

Effect of methylsisesquioxane filler on the properties of ionic liquid based polymer electrolyte

Composite electrolyte comprising methylsisesquioxane (MSQ) filler and 1-butyl-3-methyl-imidazolium-tetrafluoroborate (BMImBF₄) ionic liquid (IL) in poly(2-hydroxyethyl methacrylate) (PHEMA) matrix had been prepared. The polymer matrix was formed by free radical polymerization of HEMA macromer, and MSQ was produced in situ from methyl-trimethoxysilane by the sol-gel method. Infrared spectroscopy and dynamic mechanical analysis were employed to give insight into the interactions among the methylsisesquioxane filler, BMImBF₄ and the PHEMA polymer matrix. The PHEMA-IL-MSQ hybrids and the PHEMA-IL electrolyte without MSQ were investigated regarding their ionic conductivity and thermal and electrochemical properties. BMImBF₄ increased the thermal stability of the polymer and provided the ion conductivity; MSQ filler as the additive increased the mechanical strength of the polymer and provided the ion conductive pathway. The electrolyte with MSQ at the 10 wt% showed the highest ionic conductivity of 5×10⁻⁴ S cm⁻¹ which was five times higher than that of the electrolyte without MSQ, and the electrochemical window was up to 3.6 V.     

Poly(β,L-malic acid)/Doxorubicin ionic complex: A pH-dependent delivery system

Poly(β,L-malic acid) (PMLA) was made to interact with the cationic anticancer drug Doxorubicin (DOX) in aqueous solution to form ionic complexes with different compositions and an efficiency near to 100%. The PMLA/DOX complexes were characterized by spectroscopy, thermal analysis, and scanning electron microscopy. According to their composition, the PMLA/DOX complexes spontaneously self-assembled into spherical micro or nanoparticles with negative surface charge. Hydrolytic degradation of PMLA/DOX complexes took place by cleavage of the main chain ester bond and simultaneous release of the drug. In vitro drug release studies revealed that DOX delivery from the complexes was favored by acidic pH and high ionic strength.     

Ionocovalency and applications 1. Ionocovalency model and orbital hybrid scales

Ionocovalency (IC), a quantitative dual nature of the atom, is defined and correlated with quantum-mechanical potential to describe quantitatively the dual properties of the bond. Orbiotal hybrid IC model scale, IC, and IC electronegativity scale, X(IC), are proposed, wherein the ionicity and the covalent radius are determined by spectroscopy. Being composed of the ionic function I and the covalent function C, the model describes quantitatively the dual properties of bond strengths, charge density and ionic potential. Based on the atomic electron configuration and the various quantum-mechanical built-up dual parameters, the model formed a Dual Method of the multiple-functional prediction, which has much more versatile and exceptional applications than traditional electronegativity scales and molecular properties. Hydrogen has unconventional values of IC and X(IC), lower than that of boron. The IC model can agree fairly well with the data of bond properties and satisfactorily explain chemical observations of elements throughout the Periodic Table.     

磁性介孔硅胶负载碱性离子液体催化剂的制备与性能

用巯丙基硅氧烷对磁性介孔硅胶改性,并通过烯丙基官能化离子液体的双键与巯基之间的自由基加成反应将具有不同侧链烷基的离子液体负载到磁性介孔硅胶表面,制备了磁性介孔硅胶负载碱性离子液体催化剂.采用红外光谱分析、X射线衍射、有机元素分析、氮气物理吸附/脱附分析和样品振动磁强计对催化剂的结构和磁性能进行了表征,最后通过催化三油酸甘油酯与甲醇酯交换反应对其催化性能进行了评价.结果表明,随着离子液体侧链烷基碳个数的增多,磁性介孔硅胶负载离子液体催化剂的离子液体负载量降低,比表面积和孔体积降低.当离子液体侧链烷基为辛基、十二烷基或十六烷基时,油酸甲酯产率均高于95%,并且反应3次后油酸甲酯产率依然高于90%.     

An artificial neural network to calculate pure ionic liquid densities without the need for any experimental data

In this study, a feed-forward artificial neural network, with three layers and seventeen neurons, was constructed to estimate the densities of a wide range of ionic liquid families including those based on the imidazolium, ammonium, pyridinium, pyrrolidinium, and isoquinolinium cations, together with various anions, as well as varying lengths of alkyl side chain lengths. The model is a function of the molecular weight and structure of the ionic liquid, and the system condition of temperature and pressure, which covers a temperature range of (273.15 to 393.17) K and a pressure range of (0.1 to 100) MPa. Therefore, no additional experimental data on the ionic liquid is required as input parameter(s), which makes this technique quite versatile. It was observed that the estimated values of densities of pure ionic liquids have very good agreement with the experimental data. The training correlating coefficient (R), the training performance (MSE), and the average absolute error on the training dataset were 0.99997, 6.04 × 10⁻⁶, and 0.019%, respectively. The average absolute error value on the test dataset is 0.014%.     

A model of charge transport and electromechanical transduction in ionic liquid-swollen Nafion membranes

Ionomeric polymer transducers (sometimes called “ionic polymer-metal composites,” or “IPMCs”) are a class of electroactive polymers that are able to operate as distributed electromechanical actuators and sensors. Traditionally, these transducers have been fabricated using water-swollen Nafion membranes. This work seeks to overcome the hydration dependence of these transducers by replacing water with an ionic liquid. In the current work, two ionic liquids are studied as diluents for ionomeric polymer transducers based on Nafion membranes. The two ionic liquids used are 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-Im). These two ionic liquids were chosen for their low viscosity and high conductivity. Furthermore, although many of the physical properties of the two ionic liquids are similar, the EMI-Tf ionic liquid is water miscible whereas the EMI-Im ionic liquid is hydrophobic. These important similarities and differences facilitated investigations of the interactions between the ionic liquids and the Nafion polymer.This paper examines the mechanisms of electromechanical transduction in ionic liquid-swollen transducers based on Nafion polymer membranes. Specifically, the morphology and relevant ion associations within these membranes are investigated by the use of small-angle X-ray scattering (SAXS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. These results reveal that the ionic liquid interacts with the membrane in much the same way that water does, and that the counterions of the Nafion polymer are the primary charge carriers in the ionic liquid-swollen films. The results of these analyses are compared to the macroscopic transduction behavior in order to develop a molecular/morphological model of the charge transport mechanism responsible for electromechanical coupling in these membranes.     

Ab Initio Calculations of the Atomic and Electronic Structure of β-Silicon Nitride

The atomic and electronic structure of the β-silicon nitride (β-Si₃N₄) crystal have been determined using the ab initio pseudopotential method based on the density functional theory. We have obtained the stable lattice parameters and the stable positions of 14 atoms in the unit cell for the structure P 6₃/ m for the first time. The electronic structure and the charge distribution indicate that the Si–N bond has both ionic and covalent characters. The band structure is in good agreement with the other first-principles results and consistent with the experiments.     

Tailor-made fumed silica-based nano-composite polymer electrolytes consisting of BmImTFSI ionic liquid

In this work, nano-sized fumed silica (SiO₂) was embedded in poly(methyl methacrylate) (PMMA)?Cpoly(vinyl chloride) (PVC) blend with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide) (BmImTFSI) as ionic liquid. These composite polymer electrolytes (CPEs) were prepared by solution casting technique. The samples followed Arrhenius behavior in the temperature-dependence of ionic conductivity and further proved the ionic hopping mechanism in the polymer electrolyte. It is suggested the formation of three-dimensional polymer network among the aggregates weakens the interaction of polar group of the polymer backbone and initiates the ionic decoupling process. The mobile ions from adjacent sites would occupy this vacant site and reform the interactive bond with the polymer backbone whereby the ionic hopping mechanism is generated. The activation energy (E _a) is further determined. The higher the ionic conductivity, the lower the activation energy. The maximum ionic conductivity of (8.26?±?0.02) mScm^?1 was achieved at 80?°C upon inclusion of 8 wt% of SiO₂. X-ray diffraction (XRD) analysis revealed the higher amorphous region with increasing SiO₂ mass loadings. The coherence length is further determined by using Debye?CScherrer equation. Higher amorphous region in the polymer matrix is conferred by showing the lower coherent length. Scanning electron microscopy (SEM) was applied to examine the morphology of polymer electrolytes. Based on the differential scanning calorimetry (DSC) study, glass transition temperature (T _g) and melting temperature (T _m) were decreased. Highly flexible polymer chain is produced when the T _g was lowered down. On the other hand, thermal stability of polymer electrolytes was increased by SiO₂ dispersion, as depicted in thermogravimetric analysis (TGA).     

Highly ion conductive flexible films composed of network polymers based on polymerizable ionic liquids

Ionic liquid-type polymer brushes having different hydrocarbon (HC) chain lengths between polymerizable group and imidazolium ring were synthesized. When the carbon number of HC chain was 6, the ionic liquid-type polymer brush exhibited the highest ionic conductivity of 1.37×10⁻⁴ S cm⁻¹ at 30 °C, reflecting low T_g of −60 °C. Moreover, for the first time, we succeeded in obtaining transparent and flexible films without considerable decrease in the ionic conductivity as compared with that of corresponding monomers by using suitable cross-linkers. The most ion conductive (1.1×10⁻⁴ S cm⁻¹ at 30 °C) film was obtained when tetra(ethylene glycol)diacrylate was used 0.5 mol% to ionic liquid monomer as the cross-linker. This film is one of excellent conductive films among single-ion conductive materials.     

Installation of a reactive site for covalent wiring onto an intrinsically conductive poly(ionic liquid)

Post-polymerization radical bromination of a nanostructured poly(ionic liquid) that selectively introduces a reactive bromo-group onto the polyalkylthiophene backbone is described. Raman and FT-IR spectroscopy proves that the bromine is successfully introduced at the 3-methyl position of the thiophene and that the molecular structure of the polymer remains largely intact with only minimal chain scission detected. FT-IR and Vis-NIR spectroscopy indicates that incorporation of the bromine induces twisting (loss of co-planarity) of the polythiophene backbone. WAXS confirms retention of an ordered lamellar structure with minor lattice spacing contraction. Cyclic voltammetry confirms spectroscopic findings that the bromination reaction yields a stable p-doped polymer. The installed bromine is susceptible to nucleophilic displacement permitting the covalent attachment of other functional molecules, such as a dialkylphosphonate. Elemental analysis of such a transformation established that 100% functionalization can be achieved. These results collectively demonstrate that post-modification of a π-conjugated polymer can be used to both tune electronic and photonic properties, as well as install a chemoselective attachment point for the covalent wiring of other molecules.     

Interfacial behavior of epichlorohydrin–ethyleneoxide–allylglycidyl ether/fluorinated carbon black observed from mechanical and dielectrical properties

The purpose of this work was to study the effect of carbon black (CB) surface state on the interaction between CB and polymer matrix, as well as the polymer chain mobility. The mobility of polymer chain absorbed on the CB surface was estimated by using a dynamic mechanical analyzer and an impedance analyzer. The interaction parameter (B) and immobilized polymer layer thickness (ΔR) were estimated from the dynamic mechanical analysis. It was observed that values of B and ΔR decreased with increasing fluorine content on the CB surface. On the other hand, from the dielectric measurement, the Maxwell–Wagner–Sillars (MWS) relaxation peak, accompanied by migration of the charge carriers, accumulated at the interface between polymer and CB, observed at temperatures higher than the glass‐transition temperature (T_g) of the polymer matrix. The activation energy (E_{a MWS}), calculated from the relaxation frequency of MWS relaxation, was decreased with increasing surface fluorine content. Good agreement was found between the B and the ΔR values estimated from the dynamic mechanical analysis and the E_{a MWS} calculated from the MWS relaxation frequency estimated from dielectric measurement. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2928–2933, 2004     

Structure and Born effective charge determination for planar-zigzag β-poly(vinylidene fluoride) using density-functional theory

Two structures have been proposed in the literature for the β-phase of the ferroelectric polymer, poly(vinylidene fluoride) (β-PVDF); planar-zigzag and alternatively-deflected forms. Using density-functional theory, we have found the planar-zigzag structure is the preferred form and upon atomic relaxation, the alternatively-deflected structure attains a structure very similar to the planar-zigzag structure. In order to better understand the atomic origin of the ferroelectricity in β-PVDF, we have for the first time determined the dynamic Born effective charges (Z*) for the planar-zigzag structure using a Berry-phase approach. When compared to their nominal ionic values, the Z* show anomalous differences. Using these effective charges, we describe the polarity of the bonds with β-PVDF and show the extent of atomic-motion-induced (or dynamic) charge transfer within this ferroelectric material. In addition, our effective charges are different to previously-determined Mulliken charges, due to the inherent differences between static and dynamic charges.     

Structurally modified poly(vinyl alcohol) ionic composites as efficient humidity indicators

Synthesis of structurally modified poly(vinyl alcohol) (PVA) ionic composites is presented. Low‐molecular‐weight PVA (M_n = 18,000 g mol⁻¹) is prepared and blended together with either copper or borate ions under ambient conditions to yield PVA–Cu and PVA–B ionic composites, respectively. The borate ions coalesce together with different polymeric chains of PVA, forming a 3D network structure, which is identified by the weakening of  OH absorption in the infrared spectrum. On the other hand, copper ions yield a weakly crosslinked polyelectrolyte by forming a coordinated complex with the hydroxyl groups of PVA, which leads to an increase in the λ_max value in the ultraviolet–visible spectrum. The surface morphology of these PVA‐based ionic composites is studied via atomic force microscopy. Furthermore, the quantitative estimation of copper in PVA–Cu composites is performed by atomic absorption spectroscopy. Among these PVA ionic composites, the PVA–Cu exhibits excellent moisture absorption capability and dramatic changes in the color of thin composite film, when exposed to 75% humidity atmosphere. The absolute recovery, recyclability, and stability of the PVA–Cu ionic composites not only enable them to be good humidity indicators but the results show that these composites can be employed as efficient humidity‐sensitive material on suitable transducers for environmental and industrial applications. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Acidic ionic liquid polymers: <Emphasis Type="Italic">poly</Emphasis>(<Emphasis Type="Italic">bis</Emphasis>-imidazolium-<Emphasis Type="Italic">p</Emphasis>-phenylenesulfonic acid) and applications as catalysts in the preparation of 1-amidoalkyl-2-naphthols

A new class of polymeric acidic ionic liquids with imidazolium hydrogen sulfate and p-phenylene sulfonic acid units built into the main polymer chain were prepared by a simple two step method in 87–89% yield. These new polymers were characterized by elemental analysis, ¹H, ¹³C NMR, FT-IR, TGA and GPC. The catalytic activity of sulfonic acid group functionalized ionic liquid polymers was demonstrated through the synthesis of 1-amidoalkyl-2-naphthols in 78–90% yield by condensation of 2-naphthol, benzaldehyde and amides without a solvent at 100 °C.     

基于可聚合离子液体的功能高分子材料研究进展

阳离子或阴离子带不饱和键、可发生均聚或共聚反应的离子液体可用于合成高分子材料。本文综述了可聚合离子液体合成的智能响应性材料、高分子分散剂、导电高分子材料、吸液保液材料、气体吸收材料、高分子催化剂、新型碳材料、多孔材料、生物医用高分子材料、色谱分离材料、微波吸收材料的合成、性能及应用的研究进展, 提出可聚合离子液体的种类多、阴离子与阳离子的组合具有可设计性、离子液体具有特殊的电离属性, 可赋予主链含离子液体结构单元的高分子材料具有特殊的性能, 在诸多领域具有潜在的应用前景。     

Brønsted酸强度对正碳离子转化方向影响的分子模拟

采用密度泛函理论（DFT）系统地研究了Brønsted酸强度与催化反应过程中正碳离子转化活性之间的关系。通过调整B酸模型电子分布构建5种酸强度模型,其酸强度范围覆盖弱酸、强酸以及超强酸。将C₄正碳离子作为模型化合物,计算其氢转移、异构化、脱氢、β断裂4种反应。计算结果表明氢转移的反应能垒与酸强度呈指数关系,其他3个反应能垒与酸强度呈线性关系。在弱酸范围内各反应对酸的敏感度由高到低排列如下：氢转移反应 > 异构化反应 > β断裂反应 > 脱氢反应,而在强酸范围内氢转移的酸敏感度最低。通过计算过渡态离子携带的电荷可知,反应活性对酸的敏感度与过渡态离子携带的Mulliken电荷有关。过渡态离子携带电荷越多,与酸性位的相互作用越强,所以提高酸强度时能更有效地降低反应能垒。该反应规律与实验结论相匹配,并且从原子层面解释了不同酸强度时实验产率变化的原因,对开发新型催化材料或者催化剂改性有重要意义。     

Polyethylene oxide electrolyte membranes with pyrrolidinium-based ionic liquids

Two pyrrolidinium-based ionic liquids (ILs) with ether groups, and namely N-methoxyethyl-N-methylpyrrolidinium bis-trifluoromethanesulfonimide (PYRA_1,2O1) and 1-(2-(2-(2-methoxyethoxy) ethoxy)ethyl)-1-methylpyrrolidinium bis-trifluoromethanesulfonide (PYRA_1,2(O2)2O1), were used as plasticizers for the PEO₂₀-LiTFSI solid polymer electrolyte. The ionic liquids differ for the number of oxygens and lateral chain length.The properties of the plasticized polymer electrolytes were investigated by means of thermal analysis, impedance spectroscopy, XRD, FTIR spectroscopy and voltammetry. Both the ILs enhanced the conductivity of PEO₂₀-LiTFSI of about one order of magnitude at 40 °C. The polymer electrolyte plasticized with PYRA_1,2O1 showed a higher transport number, and a wider electrochemical window.