Microstructural and Microwave Dielectric Properties of Bi12GeO20 and Bi2O3‐Deficient Bi12GeO20 Ceramics

Bi₁₂GeO₂₀ ceramics sintered at 800°C had dense microstructures, with an average grain size of 1.5 μm, a relative permittivity (ε_r) of 36.97, temperature coefficient of resonance frequency (τ_f) of ?32.803 ppm/°C, and quality factor (Q × f) of 3137 GHz. The Bi_12‐xGeO_20‐1.5x ceramics were well sintered at both 800°C and 825°C, with average grain sizes exceeding 100 μm for x ≤ 1.0. However, the grain size decreased for x > 1.0 because of the Bi₄Ge₃O₁₂ secondary phase that formed at the grain boundaries. Bi_12‐xGeO_20‐1.5x (x ≤ 1.0) ceramics showed increased Q × f values of >10 000 GHz, although the ε_r and τ_f values were similar to those of Bi₁₂GeO₂₀ ceramics. The increased Q × f value resulted from the increased grain size. In particular, the Bi_11.6GeO_19.4 ceramic sintered at 825°C for 3 h showed good microwave dielectric properties of ε_r = 37.81, τ_f = ?33.839 ppm/°C, and Q × f = 14 455 GHz.     

The effect of side chains on the reactive rate and surface wettability of pentablock copolymers by ATRP

The reactive rate and surface wettability of three pentablock copolymers PDMS‐b‐(PMMA‐b‐PR)₂ (R = 3FMA, 12FMA, and MPS) obtained via ATRP for coatings are discussed. Poly(dimethylsiloxane) (PDMS) is used as difunctional macroinitiator, poly(methyl methacrylate) (PMMA) as the middle block, while poly(trifluoroethyl methacrylate) (P3FMA), poly(dodecafluoroheptyl methacrylate) (P12FMA) and poly(3‐(trimethoxysilyl)propyl methacrylate) (PMPS) as the end block, respectively. Their reactive rates obtained by gas chromatography (GC) analysis indicate that 3FMA gains 8.053 × 10^?5 s^?1 reactive rate and 75% conversion, higher than 12FMA (4.417 × 10^?5 s^?1, 35%), but MPS has 1.9389 × 10^?4 s^?1 reactive rate and 96% conversion. The wettability of pentablock copolymer films is characterized by water contact angles (WCA) and hexadecane contact angles (HCA). The PDMS‐b‐(PMMA‐b‐P12FMA)₂ film behaves much higher advancing and receding WAC (120° and 116°) and HCA (60° and 56°) than PDMS‐b‐(PMMA‐b‐P3FMA)₂ film (110° and 106° for WAC, 38° and 32° for HAC) because of its fluorine‐rich surface (20.9 wt % F). However, PDMS‐b‐(PMMA‐b‐PMPS)₂ film obtains 8° hysteretic contact angle in WAC (114°–106°) and HAC (32°–24°) due to its higher surface roughness (138 nm). Therefore, the fluorine‐rich and higher roughness surface could produce the lower water and oil wettability, but silicon‐rich surface will produce lower water wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40209.     

Stress growth and relaxation of a molten polyethylene in a modified weissenberg rheogoniometer

A Weissenberg rheogoniometer was modified^1-3 to improve sample temperature uniformity and constancy (to within ±0.5°C) and to give a quicker response to normal thrust changes (estimated gap change ≤0.1 μm/kg thrust; gap angle = 8.046°; gap radius = 1.2 cm; servomechanism replaced by an open-loop cantilever spring of 10 kg/μm stiffness). Low-density polyethylenes (IUPAC samples A and C, melt index at 190°C = 1.6) at 150°C were used in step-function shear rate experiments. Inspection of marked sectors in the samples showed substantial uniformity of shear at values of ? = 0.1, 2, and 5 sec^?1; for ? = 10 sec^?1 and S ≤ 2 shear units (S = ?t), the shear was highly nonuniform at and near the free boundary. Using selected premolded samples A, scatter in seven replicate tests at ? = 1.0 sec^?1 did not exceed ±6% for N₁(t) and ±5% for σ(t) (N₁ = primary normal stress difference; σ = shear stress; t = time of deformation from the initiation of experiment at zero time). N₁(t) and σ(t) data agreed with Meissner's¹; for ? = 0.1, 2.0, 5.0, and 10.0 sec^?1, torque maxima occurred at S = 6 shear units, and thrust maxima occurred in the range of 10 to 20 shear units. σ(t) and N₁(t) data do not satisfy the van Es and Christensen⁴ test for rubber-like liquids with strain rate invariants included in the memory function. On cessation of shear (after a shear strain S at constant shear rate ?), initial values of ?dσ(t)/dt and ?dN₁(t)/dt were found to depend strongly on S, in some cases passing through maxima as S was increased. After shearing at ? = 0.1 sec^?1 for 500 sec, such that stresses became constant, stress relaxation data satisfied Yamamoto's⁵ equation of dN₁(t)/dt = ?2?σ(t).     

Ionic occupation,structures, and microwave dielectric properties of Y3MgAl3SiO12 garnet‐type ceramics

The Y₃MgAl₃SiO₁₂ ceramics with pure phase were successfully synthesized by solid‐state sintering reaction method for the first time. Their microwave dielectric properties were investigated as a function of sintering temperature. Their microstructure characteristics and ionic occupation sites of tetrahedral and octahedral units were characterized and analyzed by SEM& energy dispersive spectrometer (EDS) and Rietveld refinement of X‐ray powder diffraction data. Crystal structure of Y₃MgAl₃SiO₁₂ is isostructural to Y₃Al₅O₁₂ with a cubic garnet structure and space group of Ia‐3d, which contains YO₈ dodecahedra, (Mg/Al_oct)O₆ octahedral, and (Si/Al_tet)O₄ tetrahedral units. The Qf and ε_r values of different samples are strongly dependent on the distribution of grain sizes, grain sizes, and porosity. The samples sintered at 1550°C exhibit optimized microwave dielectric properties with relative permittivity (?_r) of 10.1, Qf values of 57 340GHz (at 9.5 GHz), and τ_f values of ?32 ppm/°C. Such properties indicate potential application of Y₃MgAl₃SiO₁₂ as microwave substrates.     

Synthesis and properties of TLCPs with 2,6‐naphthalene‐based mesogen,polymethylene spacer,and nonlinear 4,4′‐thiodiphenyl links

A series of new thermotropic main‐chain liquid crystalline copolyesters were prepared by polycondensation of 2,6‐naphthalenedicarbonyl chloride, 4,4′‐thiodiphenol, and α,ω‐alkanediols (n = 4–10) in diphenyl ether at 200°C. Thermal transition behaviors of these copolyesters were investigated by differential scanning calorimetry. Moreover, their thermal stabilities and mesomorphic textures were studied by thermogravimetric analysis and polarizing optical microscopy, respectively. Corresponding model compounds with terminal mesogenic units and central polymethylene spacers were also synthesized for comparison. Both copolymers and model compounds exhibit odd–even dependency of melting temperatures, transition enthalpy (ΔH_m), and entropy (ΔS_m) on the number of methylene units in the spacer. However, the odd–even effects in model compounds are much more distinctive. Nematic mesophases are the only texture observed in melts, except the model compounds with longer methylene units (n = 8, 10), in which smectic mesophases can be observed. The T_m values of the copolyesters (TDP/HD = 1/1) are between 233 and 259°C, depending on spacer length. The initial decomposition temperatures of the copolyesters are above 419°C under N₂ atmosphere. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1536–1546, 2002     

Synthesis and photo-induced transformation of helical aromatic polyamides consisting of axially dissymmetric biphenylene joints and azobenzene segments in the backbone

Wholly aromatic polyamides having a novel helical structure were prepared by the reaction of axially dissymmetric (R)- or (S)-6,6′-dimethylbiphenyl-2,2′-dicarbonyl chloride with aromatic diamines, which are soluble in common solvents such as tetrahydrofuran and N,N-dimethylformamide. Photo-irradiation of a tetrahydrofuran solution of the polymer obtained with 4,4′-diaminoazobenzene induced a change of the helical conformation because of the trans–cis isomerization of the azobenzene units in the polymer chain. No change in the specific rotation of the polymer was observed on heating at 100°C for 4h, indicating thermal stability of its helical structure. CD spectra showed that the helical conformation was maintained in methanesulphonic acid. © 1998 SCI.     

Monomer unit sequence distribution and linkage configurations at citraconic anhydride units in the copolymers of citraconic anhydride and styrene prepared in carbon tetrachloride

The triad monomer unit sequence distribution and the cis and trans linkage configurations at the cyclic citraconic anhydride units are quantitatively determined for the copolymers of citraconic anhydride (α-methylmaleic anhydride) (CA) and styrene (ST) prepared with AIBN in CCl₄ solutions at 50 °C. Semi-alternating copolymers are obtained for most feed compositions with rigidly alternating copolymers being formed when CA in feed is more than 90%. Greater than 50% of the linkages at CA units are found to be in cis configuration in semi-alternating copolymers. This may be explained if the donor-acceptor complex formed between CA and ST participates in the copolymerization. Received: 14 November 1996/Revised: 5 March 1997/Accepted: 10 March 1997     

Structural and Piezoelectric Properties of (Na1−xKx)NbO3 Platelets and Their Application for Piezoelectric Nanogenerator

(Na_1?xK_x)NbO₃ (NKN) platelets synthesized at 600°C for 12 h have an Amm2 orthorhombic structure. However, the structure of NKN platelets synthesized at 500°C is a mixture of R3m rhombohedral and Amm2 orthorhombic structures. The formation of a rhombohedral structure is attributed to the presence of OH^? and H₂O defects in the NKN platelets. The piezoelectric strain constant (d₃₃) of NKN platelets synthesized at 600°C for 12 h is 100 pmV^?1, whereas that of NKN platelets synthesized at 500°C is lesser (50 pmV^?1) due to the presence of these defects. Piezoelectric nanogenerators (PNGs) are fabricated using composites consisting of NKN platelets and polydimethylsiloxane. A large output voltage of 25 V and output current of 2.7 μA were obtained for the PNG with NKN platelets synthesized at 600°C for 6 h. This PNG shows a high output electrical energy of 3.0 μW at an external load of 5.1 MΩ.     

The Influence of Alkyl Chain Length and Steric Effect on the Stability Constants and Extractability of Co(II) Complexes with 1-Alkyl-2-Methylimidazoles

Using the liquid-liquid partition method, the formation of Co(II) complexes with 1-alkyl-2-methylimidazoles (where alkyl = C₄H₉ trough C₁₂H₂₅) at 25°C and at a fixed ionic strength of the aqueous phase (I = 0.5, (HL)NO₃, KNO₃) were studied. Dichloromethane, trichloromethane, and 2-ethylhexanol were used as diluents. The tetrahedral and octahedral complexes were formed. Stability constants (β_n) of the complexes as well partition ratios (P_n) of the extracted species were determined. It was shown that both β_n and P_n increased with an increasing 1-alkyl chain length. Tetrahedral complexes are more readily extractable by organic solvent. Their P_n values are the highest.     

Multinuclear Metal Carbonyl Alkoxide and Aryloxide Derivatives as Models for Metal Carbonyls Adsorbed on Metal Oxide Supports

The synthesis and characterization of two tungsten carbonyl dimers containing bridging alkoxide or aryloxide ligands are described. The crystal and molecular structures of [PPN]₂[W₂(CO)₈(OCH₂CF₃)₂], 1, and [Et₄N]₃[W₂(CO)₆-(OPh)₃]-CH₃CN, 2 , are reported and compared with the structures of tetranuclear tungsten derivatives previously described. The dimer 1 crystalizes in the triclinic space group P 1 with unit cell parameters a = 13.460(11) Å, b = 12.318(5) Å, c = 13.842(10) Å, α = 82.73(5)°, β = 59.11(5)°, γ= 80.09(5)°, V = 1938(2) ų, and Z = 1. The complex 2 crystalizes in the monoclinic space group P2₁/n with unit cell parameters a = 11.954(2) Å, b = 19.359(4) Å, c = 26.462(5) Å, β = 102.50(16)°, V = 5979(2) ų, Z = 4. Molecular modeling software was utilized to construct a tetranuclear derivative from 1 similar to the structurally characterized [W(CO)₃OH]₄₋⁴ tetramer. The two tetramers were found to possess similar molecular parameters. This supports the contention that dimers of type 1 are the precursors of the tetramers. Comparisons of the tungsten alkoxides and aryloxides with the behavior of W(CO)₆ on γ-alumina are provided.     

Effect of Polar Organic Solvents on Self‐Aggregation of Some Cationic Monomeric and Dimeric Surfactants

Surface and micellization behavior of some cationic monomeric surfactants, viz., cetyldiethylethanolammonium bromide (CDEEAB), cetyldimethylethanolammonium bromide (CDMEAB), tetradecyldiethylethanolammonium bromide (TDEEAB) and dimeric surfactants, i.e., alkanediyl‐α, ω‐bis(dimethylhexadecylammonium bromide) (C₁₆‐s‐C₁₆, 2Br^? where s = 4, 12), butanediyl‐1,4‐bis(dimethyldodecylammonium bromide (C₁₂‐4‐C₁₂, 2Br^?) and 2‐butanol‐1,4‐bis(dimethyldodecylammonium bromide) (C₁₂‐4(OH)‐C₁₂, 2Br^?), was studied in water‐organic solvents [10 and 20 % v/v ethylene glycol (EG) and diethylene glycol (DEG)] by conductivity, surface tension and steady‐state fluorescence methods at 300 K. The main focus of the present work is on the study of the effect of organic solvents on the critical micelle concentration (CMC), Gibbs free energy of micellization (ΔG°_m), Gibbs free energy of transfer (ΔG°_trans), Gibbs adsorption energy (ΔG°_ads) and some interfacial parameters such as the surface excess concentration (Γ_max), minimum area per surfactant molecule (A_min) and surface pressure (π_CMC). The aggregation number (N_agg) and Stern‐Volmer quenching constant (K_SV) were also determined by the steady‐state fluorescence method. It was observed that N_agg decreased with increasing volume percent of organic solvent. The results exhibited an increase in CMC in water‐organic solvents as compared to the respective surfactants in pure water. The negative values of ΔG°_m and ΔG°_ads indicate a spontaneous micellization process. The thermodynamics of micellization revealed that the micellization‐reducing efficiency of glycols increases with the concentration and the number of ethereal oxygens in the glycol.     

Synthesis of high molecular weight copolymer of styrene and butadiene bearing high 1,4‐cis butadiene unit from copolymerization with CpTiCl3/methylaluminoxane catalyst

Copolymerization of styrene (St) and butadiene (Bd) with CpTiCl₃/methylaluminoxane (MAO) catalyst in the presence or absence of chloranil (CA) was investigated. The CpTiCl₃/MAO catalyst showed a high activity for the copolymerization of St with Bd. The 1,4‐cis contents in the Bd units for the copolymerization of St and Bd with the CpTiCl₃/MAO catalyst was observed, and the 1,4‐cis content was optimum at a MAO/Ti mole ratio of around 225. The effect of the polymerization temperature on the copolymerization was noted, as was the effect of the 1,4‐cis microstructure in the Bd units for the copolymerization of St and Bd. The addition of CA to the CpTiCl₃/MAO catalyst was found to influence the molecular weight of the copolymer. The high weight‐average molecular weight copolymer (M_w = ca. 50 × 10⁴) consisting of mainly a 1,4‐cis microstructure of Bd units (1,4‐cis = 80.0%) was obtained from the copolymerization with the CpTiCl₃/MAO catalyst in the presence of CA (CA/Ti mole ratio = 1) at 0°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2942–2946, 2003     

Thermal expansion and order-disorder polymorphic transformation in the family of borates BaNaMe(BO3)2, Me = Sc, Y

The thermal behavior of BaNaMe(BO₃)₂, Me = Sc, Y (space group R-3) is studied by the methods of high-temperature X-ray powder diffraction, differential scanning calorimetry, and thermogravimetry in the range from room temperature to 1300°C. It is shown that a polymorphic transition with a two-fold reduction of the unit cell volume is observed at 775 ± 20°C (Sc) and 375 ± 30°C (Y). New polymorphic modifications are solid solutions (Ba, Na)Me(BO₃)₂, (Me = Sc, Y) with a disordered distribution of Ba and Na atoms. Eigenvalues of the thermal expansion tensor of the polymorphic modifications are calculated for BaNaSc(BO₃)₂ and BaNaY(BO₃)₂. The solid solutions are stable approximately up to 819°C (Sc) and 770°C (Y); at higher temperatures, the solid-state decomposition of these phases begins.     

Some properties of β-D-Glucosidase from Trichoderma harzianum C1R1

β-D-Glucosidase from Trichoderma harzianum C₁R₁ consists of several isocomponents having isoelectric points in the pH range of 4.85-7.50. All the components exhibit both cellobiase and 4-nitrophenyl β-D-glucosidase (4NPGase) activity. The enzyme affinity for cellobiose (K_m = 3.92 mmol dm^?3) is 14.5 times weaker than for 4NPG (K_m = 0.27 mmol dm^?3). The hydrolysis of both substrates is competitively inhibited by glucose, the inhibition of 4NPG hydrolysis (K₁ = 2.00 mmol dm^?3) being about 4.2 times stronger compared to the hydrolysis of cellobiose (K₁ = 8.43 mmol dm^?3). The 4NPG hydrolysis is also competitively inhibited by the presence of cellobiose and D-glucono-1,5-lactone (K_i(cellobiose) = 5.00 mmol dm^?3; K_{i(D-glucono-1,5-lactone}) = 22 μmol dm^?3). The optimal hydrolysis conditions are the same for both substrates (pH 4.5,55° C). The half-lives of thermal inactivation at 61° C are 27 and 10min for cellobiase and 4NPGase, respectively.     

X-Ray crystal structure of the Dye 2,4,6-Tricyano-4'-N,N-diethylaminoazobenzene

The crystal structure and molecular conformation of 2,4,6-tricyano-4'-N,N-diethylaminoazobenzene (C₁₉H₁₆N₆, mol. wt. 328.4a.m.u.) has been determined from X-ray diffraction data: monoclinic P2₁/c, a = 9.302(7)Å, b = 8.733(5)Å, c = 20.98(1) Å, β = 94.93(6)°, V = 1699(2)ų, Z = 4, D_c = 1.284gem^?3, F(000) = 688, λ(MoKα) = 0-71069Å, μ(MoKα) = 0.76cm^?1. The structure was solved by MULTAN andrefined by full-matrix least-squares toR = 0.050 for 1358 independent observed reflections. The azobenzene skeleton is planar to within 0.12Å. Most significant bonding data are: NN, 1.286(4) Å; mean C-N (azo) 1.383(4) Å; mean C-C (cyano) 1.439(5) Å; mean CN 1.146(5)Å; NN-C, 112.8(2)° and 115.9(2)°; N-C-C (cis relative to NN) 127.6(2)° and 124.3(2)° ; N- C- C(trans) 115.2(2)° and 117.7(2)°.     

Thermal Decomposition of Energetic Materials XVIII. Bis (cyanomethyl)nitramine and Bis(cyanoethyl)nitramine

The crystal structures of two potentially useful cyanonitramines are reported. Bis(cyanomethyl)nitramine (BCMN), (NCCH₂)₂NNO₂: monoclinic, C2, a = 10.247(1), b = 7.771(1), c = 12.230(2) [Å], β = 107.45 (2)^°, Z = 6, D_calc = 1.502 g.cm⁻³, R_F = 2.8%, R_wF = 3.1%. A syn (C₂) and anti (C_s) isomers of BCMN crystallize together in a 2:1 ratio in the unit cell. Bis(cyanoethyl)nitramine (BCEN), (NCCH₂CH₂)NNO₂: monoclinic, P2₁/c, a = 7.512(2), b = 10.840(3), c = 10.181(3) [Å], β = 97.39(2)^°, Z = 4, D_cale = 1.357 g.cm⁻³, R_F = 4.6%, R_wF = 4.7%. Only one conformation of the BCEN molecule having no symmetry is present in the unit cell. The IR spectrum shows that BCEN forms an amorphous phase when the melt is cooled or when an acetone or acetonitrile solution is rapidly evaporated. The amorphous phase slowly crystallizes at room temperature. High-rate thermolysis of BCMN liberates NO₂ as the predominant initial product. This difference is qualitatively predictable on the basis of the variation in the N-N bond distance in these two compounds.     

The Structure of Cyclo-Di-β-Alanyl

The crystal structure of cyclo-di-β-alanyl (monoclinic; a = 11.85, b = 5.20, c = 10.66 Å, β = 94.83°; space group C2/c; Z = 4) has been determined by X-ray analysis, using direct methods, and refined by full-matrix least-squares calculations. The two cis-peptide groups, related by a twofold axis, are almost exactly planar, and the molecule occurs in a “flexible” chair conformation with N-CH₂CH₂-C torsion angle of 27°.     

Medium-Ring Compounds 30. cis-1,6-Cyclodecanediol: Molecular Compounds with the trans Isomer and with Itself

The crystal structures of cis-1,6-cyclodecanediol ( 1 ) and of the molecular compound formed between cis and trans-1,6-cyclodecanediol in the ratio 2:1 (2) have been established by X-ray diffraction. The two substances are closely isostructural. (Crystal data: both monoclinic, P2₁/c, Z = 6; ( 1 ) a = 6.665(6), b = 18.074(3), c = 14.351(8) Å, β = 119.77(6)°, V = 1500(2) ų; (2) a = 6.679(8), b = 18.074(4), c = 14.314(10) Å, β = 119.64(8)°, V = 1502(3) ų). The asymmetric unit of the molecular compound contains one cis molecule in a general position and one trans molecule at a center of symmetry. In the crystal of the pure cis diol a set of disordered cis molecules mimics the corresponding centrosymmetric trans molecules in the molecular compound. The molecules have the stable BCB cyclodecane ring conformation, except for the disordered cis molecules, which have a conformation about 2 kJ mol⁻¹ higher in energy (molecular mechanics calculations). The intricate three-dimensional hydrogen-bond network found in both crystals is presumably especially favorable from an energetic viewpoint.     

Principal element design of garnets to access structure stability and excellent microwave dielectric properties

Guided by the tolerance factor and average electronegativity difference, two stable garnets with compositions Ca₃BTiGe₃O₁₂ (B = Mg, Zn) were designed, synthesized followed by structural, and dielectric characterization. The phase purity and structural characteristics were analyzed using X-ray, Rietveld refinement, and microstructural analysis through scanning electron microscopy. A cubic structure with an Ia-3d space group was confirmed for synthesized compositions. A combination of microwave dielectric properties for both garnets suggested that Ca₃MgTiGe₃O₁₂ ceramic possessed a much higher quality factor (Q × f) ∼ 84 000 ± 3000 GHz coupled by a higher dielectric constant (ε_r) ∼ 12.97 ± 0.03, and a smaller temperature coefficient of resonance frequency (τ_f) ∼ −29.4 ± 1.5 ppm/°C compared to its Zn counterpart (Q × f ∼ 45 000 ± 2000 GHz, ε_r ∼ 12.84 ± 0.03, and τ_f ∼ −33.19 ± 1.6 ppm/°C). Such differences in dielectric performances were further explored utilizing packing fraction, ion polarizability, bond valence, Raman, and infrared spectrum to understand structure–property relationship.     

Enhanced piezoelectricity and temperature stability in LaFeO3-modified KNN-based lead-free ceramics

(0.96-x)K_0.48Na_0.52NbO₃-0.04Bi_0.5Na_0.5ZrO₃-xLaFeO₃ ceramics (abbreviated as KNN-BNZ-LF1000x) with enhanced piezoelectric performance and temperature stability were prepared by the conventional solid-state sintering method. It was found that the incorporation of LaFeO₃ gradually shifted the O-T phase boundary toward room temperature, while maintaining the Curie temperature above 300°C. The optimal piezoelectricity was found at x = 0.006, with relatively high piezoelectric constant d₃₃ of 345 pC/N as well as a high level of unipolar strain (0.126% at 3 kV/mm). Benefiting from the diffused phase transition induced by appropriate amount of LaFeO₃ content, the KNN-BNZ-LF6 sample possessed greatly enhanced the temperature stability of , which varied less than 8% in the temperature range of 20°C-100°C.