Thermodynamic Analysis of the FR(LT)-FR(HT) Phase Transition in the Pb(Zr,Ti)O3 System under a Hydrostatic Pressure

Effects of hydrostatic pressure on the ferroelectric phase transition between the two rhombohedral phases in the Zr-rich Pb(Zr,Ti)O₃ (PZT) system have been investigated using the Landau-Devonshire phenomenological theory. For this purpose, the rotostrictive coefficients related to the coupling between the oxygen octahedron and the stress were evaluated first. It was shown that the transition temperature between the two rhombohedral phases F_R(LT) and F_R(HT) decreased with increasing tensile hydrostatic pressure. Contrary to this, an opposite trend was predicted under the condition of compressive hydrostatic pressure.     

Influence of a core/shell rubber phase on the morphology and the impact resistance of a PC/SAN blend (75/25)

At 75/25 concentration ratio, bisphenol a polycarbonate (PC)/styreneacry-lonitrile copolymer (SAN) blend has poor impact resistance compared to PC/ABS. A rubber phase methacrylate-butadiene-styrene (MBS) of core/shell type was dispersed in PC/SAN blend. The morphology of the unmodified and modified blend was investigated. The influence of the acrylonitrile ratio in the SAN on the microstructure was studied. It clearly shows that core/shell resides at the interface between PC and SAN. It seems that core/shell particles enhance the adhesion between the different phases. Their presence influences the interface mobility; i.e., the coalescence of the dispersed phase observed in pure PC/SAN is considerably reduced when the MBS particles are added. The impact resistance of the samples was correlated with the morphology.     

Short-range structures of poly(dicarbon monofluoride) (C2F)n and poly(carbon monofluoride) (CF)n

The short-range structures of the so-called graphite fluorides, poly(dicarbon monofluoride) ((C₂F)_n) and poly(carbon monofluoride) ((CF)_n), have been discussed, based on the neutron diffraction data. The C-C and C-F bond lengths in these compounds are determined to be 0.157-0.158 and 0.136 nm, respectively, which slightly differ from those previously evaluated and coincide with those found in polytetrafluoroethylene (PTFE). The structure models of (C₂F)_n (both AB-type and AA′-type) and (CF)_n have been refined so as to give the best fit of the atomic pair distribution functions calculated for them (G_calc(r)’s) to those experimentally observed for the compounds (G_obs(r)’s). Since the G_obs(r) of (C₂F)_n better fits to the G_calc(r)’s of AB-type model rather than those for AA′-type model, the latter model is ruled out. The a-lattice parameter and the C-C-C bond angle in the refined structure model of (CF)_n (0.260-0.261 nm and 111°, respectively) are slightly larger than those of (C₂F)_n (0.256-0.257 nm and 109-110°, respectively).     

Crystallinity of poly(tetramethyl-p-silphenylenesiloxane) and (tetramethyl-p-silphenylenesiloxane)-(dimethyl siloxane) copolymers

An X-ray method is described for determining the degree of crystallinity of poly(tetramethyl-p-silphenylenesiloxane) (TMPS) homopolymers and copolymers of tetramethyl-p-silphenylenesiloxane (TMPS—DMS) of wt % TMPS—DMS ratio of $\text{48}\text{52}$, $\text{65}\text{35}$ and $\text{85}\text{15}$, respectively. The specimens had an average DMS block size of 30 monomeric units. Polymers ranging from 100 wt % TMPS to approximately 50 wt % of TMPS were studied. Over this composition range the crystallinities varied from 75 to 30% approximately. Crystallinity determinations were also made using a density gradient column and differential scanning calorimetric methods for comparison purposes to check the validity of the X-ray procedure described herein. The results of the three techniques were in satisfactory agreement although some refinements are still in order.     

Characterisation and crosslinking properties of a poly(ethylene-co-divinylsiloxane)

This characterisation and crosslinking study has been carried out on a new low density polyethylene, a poly(ethylene-co-divinylsiloxane), copolymerised via a free radical mechanism in a high pressure reactor. This copolymer enabled a study of the role of vinyl groups in the peroxide crosslinking mechanism without the interference of allylic hydrogens; such interference has been present in previous studies. The copolymers contain varying amounts of siloxane vinyl groups, which depend on the concentration of divinylsiloxane in the monomer mix added in the reactor. Peroxide crosslinking experiments show that the siloxane vinyl groups are rapidly consumed, demonstrating that allylic hydrogens are not needed for the reaction of vinyl groups. The effects of a high concentration of long chain branches are also discussed.     

Synthesis and physicochemical characterization of a well-defined poly(butadiene 1,3)-block-poly(dimethylsiloxane) copolymer

For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D₃), and subsequently characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies.     

P(St/MAH)和P(St/MAH/BA)施胶剂的改性及应用

以苯乙烯(St)和马来酸酐(MAH)为主要原料、单链脂肪醇(脂肪醇中碳原子数n=4、5、6、8)为改性剂,通过在主链中引入软单体丙烯酸丁酯(BA),成功制备出改性P(St/MAH/BA)和P(St/MAH)系列施胶剂。结果表明:在相同条件下,经改性P(St/MAH)或P(St/MAH/BA)施胶剂施胶后,不同施胶纸具有不同的施胶效果;对文化书写纸而言,前者的油墨吸收率高于后者、平滑度小于后者,但两者的拉伸强度和施胶度差别不大;对瓦楞纸而言,前者的施胶度和环压强度均高于后者。随着单链脂肪醇中碳原子数的不断增加,文化书写纸的油墨吸收率增大、平滑度和拉伸强度下降,而瓦楞纸的环压强度增大、拉伸强度略有下降,但两种施胶纸的施胶度均呈先升后降态势。     

Evaluation of nutritional potential of fish in diets based on beans (Phaseolus vulgaris) and a cereal/corn (Zea mays) and/or rice (Oryza sativa)

p6e complementation between corn and fish, and rice and fish was evaluated for the purpose of establishing the required levels of each constituent in the mixture to obtain the optimum value in the biological evaluations for each diet. The optimum fish levels were around 10 and 6% for the corn and rice diets, respectively. Complementary levels of fish in the bean: corn and bean:rice diets were evaluated in the same manner. The best values in the biological evaluation were obtained with only 2% of fish. The economical analysis of these mixtures revealed that the nutritional value of the Central American rural diets can be increased with the introduction of fish in small quantities in the habitual diets, without increasing the family food expenses.     

Relationship between the isoelectric point (pHpzc) and the potential of zero charge (Epzc) for passive metals

The potential of zero charge of oxide-covered metals (E_pzc) is shown to be linear function of the isoelectric point of the oxide film (pH_pzc). The linearity is displayed for 14 different metals having n-type semiconductor oxide films and for three metals having p-type semiconductor oxide films. Using experimental values from the literature, the slope of the linear plot of E_pzc vs. pH_pzc is observed to be −0.142 V for n-type oxides and −0.115 V for p-type oxides. The theoretical slope is −0.120 V, which is derived in this communication.     

Synthesis and characterization of (star polystyrene)-block-(polyisoprene)-block-(star polystyrene) copolymers

A (star polystyrene)-block-(linear polyisoprene)-block-(star polystyrene) copolymer, (S)_nI(S)_n, was prepared. The star polystyrene was produced via anionic polymerization of polystyrene macromonomers each containing an unsaturated double bond (vinyl) at the chain end. This vinyl-terminated polystyrene macromonomer (SSTM) was obtained beforehand via the synthesis of a living polystyrene using alkyllithium and the termination with p-chloromethylstyrene (PCMS). The living site in the core of the star polystyrene enabled the construction of the succeeding polyisoprene block resulting in the living (star polystyrene)-block-(linear polyisoprene) copolymer, (S)_nI. This living diblock copolymer was then coupled with 1,2-dibromoethane (DBE) to form the well-defined (S)_nI(S)_n. Compared to a linear polystyrene-block-polyisoprene-block-polystyrene, SIS, with the same molecular weight, (S)_nI(S)_n had a higher T_g and exhibited a lamellae-forming phase separation in conjunction with many dislocation defects. The thermal stability appeared independent of the molecular structure, and the radius of gyration and viscosity of (S)_nI(S)_n were much smaller than SIS.     

Structure of poly (p-phenylenebenzobisoxazole) (PBZO) and poly (p-phenylenebenzobisthiazole) (PBZT) for proton exchange membranes (PEMs) in fuel cells

The structures of membranes of PBZO and PBZT extruded with counter rotating dies (CRD) were studied by wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), atomic force, scanning electron and transmission electron microscopy (AFM, SEM, and TEM). The structure of CRD-extruded PBZO was compared with that of a solution-cast membrane. The extruded membranes have sheet structures typical of rigid-rod polymers. The heterocyclic rings of the extruded membranes are oriented approximately parallel to the membrane surface, while those of the cast membrane are oriented perpendicular to the surface. The parallel orientation of the rings of the extruded membranes may be due to the normal force exerted during extrusion. The polymer molecules near the surfaces of the extruded membranes are oriented along the shear directions of the extruder, while those in the middle are oriented randomly. There is little cholesteric nature. These materials have potential as microporous PEMs holding ion conducting polymers (ICPs).     

离子阱气质联用测定水中苯并(a)芘

利用选择离子监测(SIM)检测苯并(a)芘的特征离子峰,建立了离子阱气相色谱质谱联用测定饮用水中苯并(a)芘的方法,苯并(a)芘的最小检出限为0．002ug/L。建立的方法灵敏度高、预处理简单、精密度高(4．7％-6．9％)、回收效果好(85．1％-100．8％),适宜用作水中的苯并(a)芘的定性定量检测。     

Synthesis and microstructure of (LaSr)MnO3 and (LaSr)FeO3 ceramics by a reaction-sintering process

(La_xSr_1−x)MnO₃ (LSMO) and (La_xSr_1−x)FeO₃ (LSFO) (x = 0.2–0.4) ceramics prepared by a simple and effective reaction-sintering process were investigated. Without any calcination involved, La₂O₃ and SrCO₃ were mixed with MnO₂ (LSMO) or Fe₂O₃ (LSFO) then pressed and sintered directly. LSMO and LSFO ceramics were obtained after 2 and 4 h sintering at 1350–1400 and 1200–1280 °C, respectively. Grain size decreased as La content increased in LSMO and LSFO ceramics.     

Polyimides from a Novel Monomer 3,6-Bis(dimethylamino)acridine(p-cymene)dichlororuthenium(II) for a Catalytic Application

Tricyclic heteroaraomatic dye-based monomer containing NMe₂ units, 6-bis(dimethylamino)acridine(p-cymene)dichlororuthenium (II), was used to prepare novel polyimides via a one-stage solution polycondensation due to their stability under a variety of oxidative and reductive conditions. The Ru(II) complex monomer was synthesized starting from [RuCl₂(p-cymene)]₂ and 3,6-bis(dimethylamino)acridine. A series of stable polyimides was synthesized from the Ru(II) complex of 3,6-bis(dimethylamino)acridine and various aromatic dianhyrides. The polymers had inherent viscosities ranging from 1.72 to 2.11 dL/g and were soluble in polar solvents. The glass transition temperatures were 192–278 °C, and the 10% weight loss temperatures were above 503–635 °C. Ruthenium-substituted polyimides were tested for catalytic activity in the furan formation reaction of (Z)-3-methylpent-2-en-4-yn-1-ol. The polymeric catalyst was added to (Z)-3-methylpent-2-en-4-yn-l-ol without a solvent and the pure furan was isolated by distillation under reduced pressure. The conversion of the starting, enynol, was determined by gas chromatography (GC).     

The rheology of a high-concentration triaminotrinitrobenzene/trinitrotoluene (TATB/TNT) suspension

The rheology of a slurry of 1,3,5-triamino-2,4,6-trinitrobenzene(TATB) in molten 2,4,6-trinitrotoluene (TNT) suspension has been investigated. It was found that at high concentrations these suspensions are thixotropic. It has also been shown that these suspensions possess a shear-dependent maximum packing fraction. This fact is relevant to the processing of these suspensions. A thixotropic model has been developed that successfully predicts flow curves for a chosen high concentration suspension.     

Catalytic dehydrofluorination of CF3CH3(HFC143a) into CF2CH2(HFC1132a)

The catalytic dehydrofluorination of CF₃CH₃ was studied over various metal phosphate catalysts in a fixed-bed reactor. The Mg₂P₂O₇ catalyst exhibited the moderate activity and high selectivity of CF₂CH₂, and it is the most suitable catalyst for the dehydrofluorination of CF₃CH₃. Deactivation did not take place during the 100 h reaction over the Mg₂P₂O₇ catalyst, and XRD patterns of the catalyst were unchanged after 100 h reaction. However, small amounts of F⁻ ions were present on the surface of the catalyst from results of XPS. The active sites for CF₂CH₂ formation are weak acid sites of the catalysts, and carbon deposition and/or polymerization take place on strong acid sites. Results of CF₃CH₃-TPD indicated that the dehydrofluorination proceeds through a

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carbonium-ion mechanism over Mg₂P₂O₇ catalyst, and the rate-determining step is the cleavage of the C–F bond.     

Properties of some polysilane polymers: (n-PrSiMe)n, (i-PrSiMe)n, and (sec-BuSiMe)n

Three polysilane polymers, (n-PrSiMe) _n , (i-PrSiMe) _n , and (sec-BuSiMe) _n , were synthesized and characterized by DSC. UV spectroscopy, wide-angle X-ray diffraction, and optical microscopy, all at variable temperatures. The known thermochromic transition of (n-PrSiMe) _n at 48 C is associated with a change from an orthorhombic to an isotropic phase. (i-PrSiMe) _n was examned as an insoluble and soluble (lowM _w) fraction, both existing mainly in an orthohombic lattice at room temperature. (sec-BuSiMe) _n has a mesophase structure at 25 C, undergoes a weak endothermic transition to a second (nematic) mesophase near 65 C, and becomes isotropic at 160 C.Dedicated to the memory of Professor Zygmunt Lasocki, a fine chemist and a kind and gentle person.     

Fluid dynamics of a fluidized-moving bed (flumov)

The fluid dynamics and other features of a gas-solid contactor based on a combination of FLUidized and MOVing beds (flumov) were studied. The fluidized zone is below the moving one; the mov/flu diameter ratio ranges between 2 and 3. The two zones are joined by means of a conical part and no mechanical elements are used between the bottom of the moving bed and the top of the fluidized bed. The gas is fed at the bottom of the fluidized bed; the solid is fed at the top of the moving bed and, consequently, it moves in countercurrent to the gas and in a continuous mode. The adequate regime is reached when a stable vault between the bottom of the moving bed and the top of the fluidized bed is formed and maintained. The solid circulation from the moving to the fluidized bed is controlled by injecting air pulses from the bottom of the moving bed, at different points of the conical zone. The study comprises the influence of both the contactor geometry and the solid type on the pressure drop profiles and the general flumov performance. The angle of the conical device joining the two zones is an important geometrical parameter and, in the range studied, the flumov performance does not depend on the tested solid size and type.     

Crystallization and vitrification effect in a poly(styrene)-g-poly(ethylene oxide) graft copolymer

Crystallization and solid state structure of a poly(styrene)-graft-poly(ethylene oxide) (PS-g-PEO) graft copolymer with crystallizable side chains were studied using simultaneous small angle X-ray scattering/wide angle X-ray scattering/differential scanning calorimetry (SAXS/WAXS/DSC). It is found that the glass transition temperature (T_g) of PS main chain is remarkably higher than that of PS homopolymer. The start cooling temperature (T_o) has a great influence on crystallization of the PEO side-chain. When the graft copolymer is cooled from the temperature above T_g, phase separation is suppressed due to the low mobility of the PS main chain and the homogeneous melt is vitrified. The unfavorable conformation of the rigid main chain results in a single crystallization peak and lower crystallinity. When PS-g-PEO is only heated to a temperature lower than the T_g and then cooled, phase separation is retained. Both the PEO side chains with high and low crystallizability can crystallize in the phase-separated state, leading to double crystallization peaks and higher crystallinity. The effect of solvent on crystallization of the graft copolymer was also examined. It is observed that addition of toluene reduces the T_g of the PS main chain and leads to the disappearance of the vitrification effect.