Ion-induced manipulation of photochemical pathways in crown ether compounds based on fluorinated oligophenylenevinylenes: the border between ultrafast photoswitches and photoproduced nanomaterials

The photochemical and photophysical properties of the crown ethers trans,trans-1,4-bis[2-(3',4'-benzo 15-crown 5)ethenyl]-2,3,5,6-tetrafluorobenzene (1) and trans,trans-1,4-bis[2-(3',4'-benzo 18-crown 6) ethenyl]-2,3,5,6-tetrafluorobenzene (2) were investigated in the absence and presence of groups I and II metal ions. The photophysical methods used include steady state flurescence, uv spectroscopy, and ultrafast transient absorption spectroscopy. Both compounds showed solvatochromic behavior, due to intramolecular charge transfer state formation, and efficient fluorescence in polar solvents. Photophysical behavior was dependent on the metal ion. The addition of metal ions that completely fit into the crown ether cavity resulted in significant blue shifts in the fluorescence emission spectra (chemosensing properties). Partially fitting ions changed the fluorescence spectra slightly. Transient absorption measurements revealed fast and slow decay components with time constants of 10-20 and 500-600 ps for all fitting ions, respectively. The latter is assigned to a trans-cis photoisomerization process, which decreased in efficiency in the presence of partially fitting ions, i.e., increasing ion size. Steady state irradiation showed clear evidence of a change in the absorption spectra. Trans-cis photoisomerization and [2 + 2] photocycloaddition were found to compete with fluorescence. The ions Li+, Na+, and Ca2+, which fit into the cavity, direct the photoisomerization. Larger ions (K+, Rb+, Sr2+ and Ba2+) that partially fit the cavity cause photocycloaddition. Quantum yields of the photoreaction are between 0.1 and 0.3. Analysis of the photo-product obtained for the 1-Sr2+ system revealed a compound with a molecular weight of nanosize dimension, which was equivalent to seven mass units of 1. The higher molecular weight product was formed due to alternately stacked supramolecular assemblies.     

Poly (ether ether ketone) derivatives: Synthetic route and characterization of nitrated and sulfonated polymers

Nitrated and sulfonated poly (ether ether ketone) [SNPEEK] samples were prepared through sulfonation of nitrated PEEK (NPEEK) at different temperatures resulting in polymers with distinct sulfonation degrees (SD). The sulfonation occurred preferentially in the hydroquinone segment even after 81% of this moiety had been nitrated. Sulfonation in the benzophenone moiety was achieved only in 16% of this segment at the reaction temperature of 80 °C. The substitution degree was obtained through the TG curves, and values were in agreement with ¹H NMR data when SD is much higher as ND (nitration degree). The highest SD obtained was 72%. Membranes of the sulfonated and nitrated PEEK (SNPEEK) were prepared by casting and showed good ductility depending on the substitution degree, with proton conductivity in the order of 10^? 2 S cm^? 1, an important characteristic in some applications, such as in fuel cells.     

Preparation of polyurethane with zwitterionic side chains and their protein resistance

Polyurethane (PU) with zwitterionic side chains has been prepared to resist nonspecific adsorption of proteins. First, dihydroxy-terminated poly(2-(dimethylamino)ethyl methacrylate) (PDEM(OH)(2)) is synthesized by free radical polymerization with 3-mercapto-1,2-propanediol as the chain transfer agent, which polyadds with diisocyanate to yield a PU with PDEM side chains. Such side chains are zwitterionized by 1,3-propane sultone. Proton nuclear magnetic resonance spectroscopy ((1)H NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) show that the zwitterionic side chains are incorporated into the PU. Thermal analysis demonstrates the thermal stability is greatly affected by the content of the side chains. By use of quartz crystal microbalance with dissipation (QCM-D), we have investigated the adsorption of fibrinogen, bovine serum albumin, and lysozyme on a surface constructed by such a PU. It shows the PU has a controllable protein resistance depending on the content of the zwitterionic side chains.     

Synthesis and characterization of aromatic and aliphatic ether bridged polymers containing carbazole moieties

In this study, the polymers were synthesized ether bridged containing carbazole moieties via HBr elimination. Also, these polymers include the aliphatic chains at the different lengths and aromatic groups in their structures. However, the polymers were characterized by FT-IR, NMR and UV–vis spectroscopy, and their thermal stabilities were determined via TGA measurements. Fluorescence measurements were performed using N,N′-dimethyl formamide solutions and also, the optimization of the concentrations to obtain maximal emission intensity was investigated in N,N′-dimethyl formamide. The morphologic properties of the polymers were investigated at different particle sizes by using Scanning Electron Microscopy (SEM). Additionally, the number average molecular weight (M_n), weight average molecular weight (M_w) and polydispersity index (PDI) values of the polymers were determined by size exclusion chromatography (SEC) technique. Resultantly, the remarkable properties related to the fluorescence and thermal measurements of the polymers were obtained. Therefore, these polymers could be used in various application fields because of the fluorescent and thermal properties.     

Application of dimethyl ether to arcjet thruster as propellant

We proposed applying dimethyl ether (DME) to arcjet thrusters and conducted experiments to demonstrate the operation, since DME has good storage properties. DME has a freezing point of −143 °C and a boiling point of −54 °C, and it liquefies at 6 atm under room temperature. Thus, DME is stored in liquid without any complex temperature management device such as cryogenic devices. DME also has little toxicity and is chemically stable. Its molecular structure contains no direct binding between carbon atoms; instead, the carbon atoms bind with an oxygen atom in between, and it is expected that soot generation is lower. We have shown that a DME arcjet thruster produced arc plasma with a discharge power ranging from 1000 to 1600 W with a resulting specific power from 20 to 40 MJ/kg. Furthermore, the plenum chamber pressure reached 160 kPa. We have thus confirmed that our DME arcjet thruster is capable of operating under almost equivalent conditions to conventional arcjet thrusters.     

Preparation and characterization of polymeric plasticized membranes (PPM) embedding a crown ether carrier application to copper ions transport

Polymeric plasticized membranes (PPM) are a new perspective to solve the stability problems of supported liquid membranes to perform the simultaneous separation, concentration and purification of valuable species from aqueous solutions.Cellulose triacetate (CTA) membranes containing the crown ether dibenzo-18-crown-6 (DB18C6) as a fixed carrier were prepared and their performance tested for the transport of copper(II) ions. This study showed that PPM properties were influenced by the membrane composition. The transport studies revealed that diffusion rate was dependent on film thickness, the presence of a plasticizer, 2-nitrophenyloctylether, which plays also a critical role on the membrane physical characteristics (especially malleability) and the quantity of fixed crown ether. Porosimetry analyses showed conversely to other works with different carriers that all the membranes prepared are not porous for all membrane compositions. However, SEM analysis revealed a porous texture when the quantity of crown ether is higher than that of CTA. FTIR, X-ray and TGA characterizations showed that all the constituents of the membrane remain unaltered within the membrane without chemical interactions between them (no presence of new bonds in the FTIR spectra). Hence, transport mechanism of the copper(II) ions seems to be a jumping from site to site.     

侧链枝化的磷酸酯型聚合物电解质的合成与性能研究

以聚乙二醇200、二乙二醇单甲醚等与三氯氧磷反应制备得到枝化结构的磷酸酯单体,其末端为丙烯酸酯基团。紫外引发聚合制备聚合物电解质,考察了磷酸酯单体的分子量、温度、盐浓度对聚合物电解质电导率的影响。研究表明,在测试盐浓度下,复合体系的最大室温电导率对应的LiClO4盐浓度都为5%,PEP200_3与LiClO4复合后室温电导率最高,可达1.80×10-5S/cm。     

Application of fractal fracture mechanics to polymers and polymeric composites

It is shown that the fundamental concepts of fractal fracture mechanics can be applied both to polymers and polymeric composites and to metals and ceramics. The critical crack opening displacement can be chosen as a scale of fracture of polymeric materials. The results obtained for polymers and polymeric composites are described by the same sigmoidal dependence, which means that the regularities of fracture processes in these materials are common.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 53–57, July–August, 2004.     

Application of mass spectrometry to the characterization of polymers

Recent advances in soft ionization techniques for mass spectrometry of polymeric materials make it possible to determine the mass of intact molecular ions exceeding 1 × 10⁶ Da. Developments in high resolution mass spectrometers have additionally led to impressive advances in our ability to characterize polymers. The entire molecular mass distribution of a polymer sample can be accurately measured. From the molecular mass, the molecular formulae and information regarding polymer composition and end-groups can be deduced. The two techniques which have received the most attention are matrix-assisted laser desorption/ionization and electrospray ionization. In recent work, these techniques have been combined with chromatographic separations, and a series of mass spectra are acquired for each fraction of the distribution. This simplifies the analysis by reducing the number of components present in each mass spectrum, and additionally improves quantitation.     

PID调阀在变频空调器中的应用

通过对PID控制原理的介绍,将增量式PID控制算法应用于变频空调器电子膨胀阀的控制。对比试验研究结果表明:PID调阀响应迅速,达到稳定的时间比机械调阀快30%以上,这一优势在中低频上更加明显,机械调阀在低频时会出现调阀振荡致使系统长时间无法稳定运行现象; PID调阀系统排气温度与目标排气温度几乎没有回差,而机械调阀系统排气温度与目标排气温度存在不同程度的回差; PID调阀系统在低温制热工况下排气温度跟随性好,额定低温制热一个周期的平均制热量比机械调阀系统提高8. 2%。     

Application of link adjacency values to detect isomorphism among kinematic chains

The present work deals with problem of detection of isomorphism which is frequently encountered in structural synthesis of kinematic chains. A new method has been proposed using two invariants called as First adjacency chain link string [FACLS] and Second adjacency chain link string [SACLS]. These invariants take into account the degree of links and type of joints and are used as the composite identification number of a KC. The proposed method is easy to compute, reliable and capable of detecting isomorphism in all types of compound KC, i.e. chains of single or multi degree of freedom with simple or multiple joints. This study will help the designer to select the best KC and mechanisms to perform the specified task at conceptual stage of design. Some examples are provided to demonstrate the effectiveness of this method.     

Double stranded chains and interwoven structures: the role of conformational isomerism in coordination polymers

The 1:3 and 1:1.5 coordination complexes of 1,3–bis(4–pyridyl)propane, 1, [Ni(1)₂(H₂O)₂][NO₃]₂⋅(1)⋅(H₂O), 2 and [Cd₄(1)₆(NO₃)₈], 3 form a double stranded chain and four-fold interwoven structures, respectively. Complex 2 is an unusual coordination complex where the ligand not only coordinates with the metal salt but also cocrystallizes with the coordination complex. The double stranded linear chains in 2 have 24 membered rings with a Ni···Ni intra-chain distance of 11.53 Å and close-pack to form a two dimensional layered structure. The anions, non-coordinating ligands, and the solvated water molecules sandwich between the layers in a bilayer fashion. Complex 3 forms an open network owing to its T-shaped geometry but the conformational flexibility of the ligand blurs the difference between the expected brick wall pattern and the distorted hexagonal network. The internal dimensions between opposite Cd metal centers in the distorted non-planar network are ca 18.3×23.2×28.5 Å. These open networks readily undergo four-fold parallel interpenetration and result in a carpet like structure.     

Tuning structural and mechanical properties of two-dimensional molecular crystals: the roles of carbon side chains

A key requirement for the future applicability of molecular electronics devices is a resilience of their properties to mechanical deformation. At present, however, there is no fundamental understanding of the origins of mechanical properties of molecular films. Here we use quinacridone, which possesses flexible carbon side chains, as a model molecular system to address this issue. Eight molecular configurations with different molecular coverage are identified by scanning tunneling microscopy. Theoretical calculations reveal quantitatively the roles of different molecule-molecule and molecule-substrate interactions and predict the observed sequence of configurations. Remarkably, we find that a single Young's modulus applies for all configurations, the magnitude of which is controlled by side chain length, suggesting a versatile avenue for tuning not only the physical and chemical properties of molecular films but also their elastic properties.     

Extractive solubilization, structural change, and functional conversion of cytochrome c in ionic liquids via crown ether complexation

This article reports on the extraction behavior of heme proteins from an aqueous phase into ionic liquids (ILs) with dicyclohexano-18-crown-6 (DCH18C6), and the structure-function relationship of cytochrome c (Cyt-c) dissolved in ILs. We have found that DCH18C6 enables transfer of Lys-rich proteins into ILs via supramolecular complexation. The hydrophobicity and functional groups of ILs have a great influence on protein partitioning, and a hydroxyl group-containing IL with DCH18C6 is capable of the quantitative partitioning of Cyt-c. On the other hand, protein transfer using conventional organic solvents is negligibly small. UV-visible, CD, and resonance Raman spectroscopic characterizations indicate that the sixth ligand Met 80 in the heme group of the Cyt-c-DCH18C6 complex in IL is replaced by other amino acid residues of the peptide chain and that a non-natural, six-coordinate, low-spin ferric heme structure is induced in IL. Solubilization of Cyt-c in IL causes the environmental change of the heme vicinity of Cyt-c, which triggers the functional conversion of Cyt-c from an electron-transfer protein to peroxidase. The Cyt-c-DCH18C6 complex in IL provides remarkably high peroxidase activity compared with native Cyt-c, because of enhancement of the affinity for H2O2.     

Application of activated barrier hopping theory to viscoplastic modeling of glassy polymers

An established statistical mechanical theory of amorphous polymer deformation has been incorporated as a plastic mechanism into a constitutive model and applied to a range of polymer mechanical deformations. The temperature and rate dependence of the tensile yield of PVC, as reported in early studies, has been modeled to high levels of accuracy. Tensile experiments on PET reported here are analyzed similarly and good accuracy is also achieved. The frequently observed increase in the gradient of the plot of yield stress against logarithm of strain rate is an inherent feature of the constitutive model. The form of temperature dependence of the yield that is predicted by the model is found to give an accurate representation. The constitutive model is developed in two-dimensional form and implemented as a user-defined subroutine in the finite element package ABAQUS. This analysis is applied to the tensile experiments on PET, in some of which strain is localized in the form of shear bands and necks. These deformations are modeled with partial success, though adiabatic heating of the instability causes inaccuracies for this isothermal implementation of the model. The plastic mechanism has advantages over the Eyring process, is equally tractable, and presents no particular difficulties in implementation with finite elements.     

A new class of supersaturated design: Application to a sensitivity study of a photochemical model

The use of experimental designs in the field of numerical simulation improves global sensitivity analysis compared to Monte Carlo based method by decreasing the number of simulations. More particularly, supersaturated designs can be applied to decrease the number of calculations, because the number of simulations is inferior to the number of studied factors but its use is risky and depends on “parsimony principle”. This paper shows new supersaturated designs that use the a priori knowledge and thus overcome this difficulty.     

Molecular dynamics simulations of orientation induced interfacial enhancement between single walled carbon nanotube and aromatic polymers chains

In this work, molecular dynamics simulations were utilized to probe the interfacial enhancement between aromatic polymers and single walled carbon nanotube (SWCNT) induced by molecular orientation. Two aromatic polymers, polyphenylene sulfide (PPS) and polystyrene (PS) were chosen for comparison study. It was found that orientation of polymer chain could bring about an obvious promotion in interfacial interaction for both systems. In PPS/SWCNT systems, the increased interfacial interaction energy was due to the easy formation of offset π–π stacking, while in PS/SWCNT systems the formation of edge-to-face π–π stacking contributed to the enhancement. Polymer/SWCNT composites were also constructed and a similar interfacial enhancement was observed as well. The mechanism of the orientation induced enhancement was a combination of forming more π–π stacking and better coating effect. This will help to deepen the understanding of interfacial interaction in aromatic polymers/carbon nanotubes composites and guide the fabrication of high performance materials.