SnO2/SiO2 and Sn/Sb-oxide/SiO2 gel-derived composites. Part 1: Structural evolution from a Mössbauer study

The lasing photostability of the red perylimide dye (RPD) in various solid matrices was measured under frequency-doubled Nd:YAG laser excitation. The RPD: composite glass laser intensity decayed to 50% of its initial value after approximately 20,000 pump pulses of 13 mJ/pulse. The output of RPD:ormosil glass and RPD:PMMA glass lasers decayed to 50% of their initial value after 1,200 and 1,000 pump pulses of the same energy, respectively. For rhodamine-6G:silica-gel and rhodamine-6G:ormosil glass lasers, the 50% decay occurred already after 1,000 and 300 pulses, respectively. The decay was non-exponential, suggesting that the dye bleaching was not a single-photon process. The average laser output decay rates increased linearly with the pump energy. Singlet-singlet excited state absorption of the RPD dye in the solid matrices was also measured between 550 and 730 nm. At ～600 nm the cross section was ～2×10^?16 cm²/molecule. The excited-state absorption competes with the lasing, and is a main factor that limits the laser efficiency.     

Investigation of IrO2/SnO2 thin film evolution by thermoanalytical and spectroscopic methods

The formation mechanism of thermally prepared IrO₂/SnO₂ thin films has been investigated under in situ conditions by thermogravimetry combined with mass spectrometry (TG-MS) and infrared emission spectroscopy (IRES). Mixtures of varying composition of the precursor salts (SnCl₂·2H₂O dissolved in ethanol and IrCl₃·3H₂O dissolved in isopropanol) were prepared onto titanium metal supports. Then the solvent was evaporated and the gel-like films were heated in an atmosphere containing 20% O₂ and 80% Ar to 600°C. The thermogravimetric curves showed that the evolution of the oxide phases take place in several decomposition stages and the final mixed oxide film is formed between 490 and 550°C, depending on the noble metal content. Mass spectrometric ion intensity curves revealed that below 200°C crystallization water, residual solvent, and hydrogen-chloride (formed as a result of an intramolecular hydrolysis) are liberated. The decomposition of surface species (surface carbonates, carbonyls and carboxylates) formed via the interaction of the residual solvent with the precursor salts takes place up to 450°C as evidenced by emission Fourier transform infrared spectrometry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of SiO2 nanoparticles on electro-optical and thermophysical properties of polyacrylate/liquid crystal composites

ABSTRACT

In this paper, SiO₂ nanoparticle-doped polymer dispersed liquid crystal (PDLC) lenses are made from a mixture of prepolymer, 5CB liquid crystal and SiO₂ nanoparticles by the polymerisation induced phase separation (PIPS) process. The effect of SiO₂ nanoparticles on the electro-optical properties of PDLC ?lms are studied. It is established that SiO₂ nanoparticles affect the microstructure of PDLC ?lms signi?cantly because of the formed agglomerates of SiO₂ nanoparticles. Results show an improvement in the electro-optical properties and a decrease in the response time for doped systems with small amount of SiO₂ nanoparticles. We also observe a shift of nematic–isotropic transition temperature as a function of SiO₂ nanoparticle contents. A good agreement between the electro-optical study and thermophysical properties is reached.     

Thermal behavior of poly(hexamethylene terephthalate) oligomers. I. Melting behavior and morphology of the crystalline phase

The thermal behavior of poly(hexamethylene terephthalate) (PHT) oligomers containing variable amounts of isophthalic (IPA) monomer has been investigated. Poly(hexamethylene terephthalate‐co‐isophthalate) 3400 was first studied. This polymer has a M n of 3400, is constituted by heterodisperse PHT units (crystallizable units) with a M n of 2000, contains an average number of 2.6 IPA per chain, and has carboxylic chain ends. DSC results have shown that this polymer exhibits multiple melting endotherms. These are described in terms of (i) the existence of two melting zones located on both sides of T_c and associated with two polymer fractions differentiated by their crystallizable unit length, (ii) different crystalline populations growing at T_c, (iii) a reorganization process. A simultaneous small (SAXS) and wide (WAXS) angle time resolved X‐ray scattering study using synchrotron radiation has revealed that the different crystalline populations are characterized by different lamellar structures rather than by different crystalline lattices. Other PHTcoIs and PHTs differing from PHTcoI 3400 by their molecular weight and IPA content were also studied using DSC. IPA acts as a defect for crystallinity and causes T_m and ΔH_m depression in the PHTcoIs. When the molecular weight of PHT increases, T_m increases and ΔH_m decreases as usually reported in the literature. Finally, two crosslinked polymers (PHTcoI 3400 and PHTcoI 4700) were investigated. The insoluble fraction of crosslinked PHTcoI 3400 does not crystallize anymore while the one of PHTcoI 4700 does. This results from shorter crystallizable units and from the distance between the crosslinks of the former. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1–18, 1999     

Kinetic Equations for Thermal Dissociation Processes. Part II. Equations R2 and F0

Relationships have been established between the average conversion degree and the dissociation time for polydisperse granular material, taking into account its grain size distribution. It has been checked in which cases the kinetic curves, obtained by a numerical solution, can be described in terms of equations R2 and F0. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rheology and phase structure of PP/EPDM/SiO2 ternary composites

In this article, the rheological properties of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM)/silicon dioxide (SiO₂) ternary composites were systematically investigated. Two kinds of nano-SiO₂ particles (with hydrophobic (denoted as A-SiO₂) or hydrophilic (denoted as B-SiO₂)) as well as two processing methods (one-step or two-step) were first employed to prepare PP/EPDM/SiO₂ ternary composites. Then the deep mixing and morphology evolution of polymer composite with mixing time were assessed by rheological method, on the focus of formation of filler-network, and compared with scanning electron microscopy (SEM) observations. Linear viscoelastic behavior was observed for PP/EPDM and PP/SiO₂ binary system, showing no evidence of the formation of filler-network structure. However, a solid-like rheological behavior, which was attributed to the formation of the filler-network structure as confirmed by SEM observation, could be observed in some PP/EPDM/SiO₂ ternary systems, depending on the SiO₂ surface property, processing method and EPDM content. It seemed that SiO₂ with hydrophilic surface was necessary for the formation of filler-network in PP/EPDM/SiO₂ ternary system. Besides, two-step processing method made the solid-like behavior occurred at an earlier stage compared with that of a one-step processing method, also, the higher elastomer content facilitated the formation of the filler-network structure. The results were in good agreement with those reported in our previous publications [Yang H, Zhang Q, Guo M, Wang C, Du R, Fu Q. Polymer 2006;47:2106] [Yang H, Zhang X, Qu C, Li B, Zhang L, Zhang Q, et al. Polymer 2007;48:860].     

Structural and mechanical behavior of nylon 6 films part I. Identification and stability of the crystalline phases

The crystalline phase of polyamide 6 (otherwise nylon 6) films produced following various physical treatments is investigated by means of thermal analysis, X‐ray diffraction, and infrared spectroscopy. A recently published procedure for treating infrared spectra of multicomponent compounds without a priori knowledge of the individual component spectra allowed us to perform a semiquantitative analysis of the structural changes upon annealing, including data from drawn samples. Melt‐cast films display a mesomorphic state that is thermally stable up to about 120 °C. This structure partly reorganizes into the stable monoclinic α form above 120 °C. Films in major γ form produced by iodine treatment are thermally stable up to 200 °C. Films in major α form are also prepared by superheated water treatment. No evidence is given for a Brill transition about 170 °C. This is an important fact for further understanding of the drawing behavior of PA6 at temperatures above and below this domain. The mesomorphic phase can hardly be separated from the amorphous component both from X‐ray and infrared analysis. However, scanning calorimetry, which is often criticized due to possible reorganization of unstable species during the heating scan, turned out to be a very useful technique. Indeed, recrystallization from the amorphous phase or improvement of ordering from the mesomorphic state both result in exothermic effects in quite different temperature domains that allow to discriminate the two phenomena. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 484–495, 2001     

A Spectro-Microscopic Approach for Thin Film Analysis: Grain Boundaries in mc-Si and Sn/SnO2 Nano Particles

 Synchrotron radiation based spectro-microscopy is shown to be an exciting tool for elemental analysis in the field of heterogeneous interfaces, thin films, and device technology. Results are reported, taken with a spectrometer that enables the combination of a photoemission electron microscope (PEEM) with photoelectron spectroscopies (XPS, UPS) operated at a high brilliance undulator beam line at BESSY. The properties of mc-Si (multi crystalline silicon) are of interest because of their applications in low priced photovoltaic devices. An example of how to analyze the surface potentials of such surfaces without removing the native oxide is given. Tin nano-scale particles are shown to be the decisive factor affecting the corrosion prevention of passivated tinplate surfaces.     

High-pressure modifications of CaZn2, SrZn2, SrAl2, and BaAl2: Implications for Laves phase structural trends

High-pressure forms of intermetallic compounds with the composition CaZn₂, SrZn₂, SrAl₂, and BaAl₂ were synthesized from CeCu₂-type precursors (CaZn₂, SrZn₂, SrAl₂) and Ba₂₁Al₄₀ by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl₂ and BaAl₂), X-ray single-crystal diffraction (CaZn₂), and electron microscopy (SrZn₂). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu₂ (C15) structure, the dizincides adopt the hexagonal MgZn₂ (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions.     

Mercury(II) Compounds with 1,3-Benzothiazole-2-thione. Spectral, Thermal, and Crystal Structure Studies

Mercury(II) halides, HgX₂ (X = Cl^–, Br^–, I^–) react with 1,3-benzothiazole-2-thione (btztH) in methanol solutions giving the HgX₂(btztH) and HgX₂(btztH)₂ types of compounds. Mercury(II) acetate gives the thiolato compound Hg(btzt)₂ because of the deprotonation of btztH. Hg(btzt)₂ reacts with 2,2-bipyridine (bipy) giving a 1:1 complex. IR, ¹H, and ¹³C NMR spectral studies indicate that btztH acts as a monodenatate ligand through the S thione donor atom in all complexes. The X-ray crystal structure determinations of [HgI₂(btztH)]₂, HgBr₂(btztH)₂, Hg(btzt)₂, and Hg(btzt)₂(bipy) have been carried out revealing tetrahedrally coordinated mercury atom in [HgI₂(btztH)]₂ and HgBr₂(btztH)₂, while in Hg(btzt)₂(bipy) 2 + 2 coordination is achieved through strong Hg (N(bipy) contacts. A linear coordination in Hg(btzt)₂ is not affected by the Hg N contacts, which are longer than in Hg(btzt)₂(bipy), but still shorter than the van der Waals sum of mercury and nitrogen covalent radii. [HgI₂(btztH)]₂ exists as centrosymmetrical dimer with a Hg₂I₂ bridging core. The dimeric molecules are linked by the intermolecular hydrogen bonds between the terminal iodine atom and the NH group [3.63(1) Å] into infinite chains along the z-axis. There are N–H Br(bridging) intermolecular hydrogen bonds in HgBr₂(btztH)₂ joining molecules into endless chains along the x-axis. The Br(bridging) atom acts as double proton acceptor and two NH groups as proton donors [NH Br(bridging) 3.278(9) and 3.338(7) Å]. The mercury to sulfur and mercury to halogen bond distances in [HgI₂(btztH)]₂ and HgBr₂(btztH)₂ are discussed in relation to the analogous compounds, revealing strong influence of hydrogen bonds on their relative strengths as well as crystal packing requirements of the ligand. The sulfur and halogen atoms are more tightly bound to mercury implicating severe distortion of the coordination polyhedron in the structures in which they do not take part in hydrogen bonds formation. The influence of steric requirements of the ligands in Hg(btzt)₂ and Hg(btzt)₂(bipy) on the distortion of the mercury coordination polyhedra accompanied with the relative strength of Hg N contacts is considered.     

Spectrum analysis of U-doped LaBr3 single crystals. Part 1: crystal-field analysis

Single crystals of U³⁺:LaBr₃ were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm⁻¹ range. Sixty-four experimental crystal-field energy levels of the U³⁺ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm⁻¹. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f³→5f³ transitions. The effects of selected CCF operators on the splitting of some specific U³⁺ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses.     

Octadecyltrichlorosilane adsorption kinetics on Si(100)/SiO2 surface: contact angle,AFM, FTIR and XPS analysis

Octadecyltrichlorosilane (OTS) adsorption kinetics on Si(100)/SiO₂ surface has been studied as a function of concentration by sequential and nonsequential dipping techniques. The contact angle technique is used to evaluate growth kinetics and thermal stability and to determine critical surface tension of the OTS layer. Atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) are used to confirm OTS adsorption. Langmuir isotherms are employed to analyze the kinetics data to obtain adsorption and desorption rate constants (k_a & k_d) as well as Gibbs free energy, (ΔG_ads). These parameters, k_a, k_d and ΔG_ads(y) are found to depend exponentially (y = y₀ + A.exp(?x/t)) on the OTS concentration (x). The OTS layers are found to be thermally stable up to a temperature of 230 °C and the critical surface tension obtained from the Zisman plot is found to be ～19.8 dynes/cm. OTS monolayer coverage obtained by AFM measurement agrees quite closely with that obtained from contact angle measurements. FTIR and XPS results confirm OTS adsorption. Copyright © 2006 John Wiley & Sons, Ltd.     

Vibrational properties and first hyperpolarizability of cyclopentadiene homologues C4H4XH2 (X=C, Si, Ge, Sn): ab initio HF and DFT investigation

IR and Raman spectra and static electronic and vibrational first hyperpolarisabilities, β, of the cyclopentadiene homologues C₄H₄XH₂ (X=C, Si, Ge, Sn) have been calculated by conventional ab initio and DFT-B3LYP methods using Sadlej POL and correlation consistent Dunning basis sets to investigate on the role of the heteroatom on the response property. The pure vibrational contribution to β has been evaluated within the double harmonic oscillator approximation. A clear heavy atom effect was found in the vibrational frequencies and intensities localised on the XH₂ and C–X–C fragments, which decrease and increase, respectively, as the size of the heteroatom increases. Both β^e and β^v show an increase along the series, the vibrational contribution to β being modest in cyclopentadiene, but substantial in metalloles, especially for silole, where it is about two times greater than the electronic counterpart. The β^v/β^e ratio is strongly dependent on the basis set, decreasing as the quality of the basis set increases. Both β^v and total β^e+β^v values of the cyclopentadiene homologues are higher than the corresponding ones in the furan series, except for stannole and tellurophene which have close total β^e+β^v values.     

The Crystal Structure, Vibrational Spectra, and Thermal Behavior of Piperazinium(2+) Selenate Monohydrate and N, N′-Dimethylpiperazinium(2+) Selenate Dihydrate

The crystal structure of piperazinium(2+) selenate monohydrate has been resolved; this substance crystallizes in the monoclinic space group P2₁/n, a=6.4586(8), b=11.8335(7), c=11.8065(7) Å, β=100.990(8)°; V=885.80(13) Å⁵, Z=4, R=0.0446 for 1556 observed reflections. A similar compound, N,N′-dimethylpiperazinium(2+) selenate dihydrate, crystallizes in a triclinic system with space group P and lattice parameters a=6.7370(8), b=7.9845(9), c=12.3802(12) Å, α=92.435(9)°, β=100.219(9)°, γ=114.699(10)°; V=590.34(11) ų, Z=2, R=0.0311 for 2071 observed reflections. While, in the former structure, the cations of piperazinium(2+) in the chair conformation are arranged roughly plane-parallel above one another, in the second substance, the N,N′-dimethylpiperazinium (2+) ions lie approximately perpendicularly above one another. The FTIR and FT Raman spectra of both test substances have been measured and studied. The thermoanalytical properties were studied using TG, DTG, and DTA methods in the temperature range 293–533 K. DSC measurements were carried out in the temperature range 95–343 K. No phase transition was found in this temperature region for either of the compounds.     

Structure evolution in the PbO-ZrO2-TiO2 sol-gel system: Part II—Pyrolysis of acid and base-catalyzed bulk and thin film gels

The pyrolysis behavior of acid and base-catalyzed bulk and thin film Pb(Zr, Ti)O₃, or PZT, gels as well as their components have been studied using Thermo-Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA), and Dynamic Mass Spectrometric Analysis (DMSA). The TGA/DTA data reflected the structural differences of the acid and base-catalyzed gels. Gels obtained using an acid catalyst were less cross-linked, denser, and more homogeneous than base-catalyzed gels. Based on the understanding of structure evolution in the silica system, the various events in the TGA/DTA studies of acid-catalyzed PZT gels were attributable to specific mechanisms. The DMSA showed that primarily water, 2-methoxyethanol, acetone, and carbon dioxide were evolved for both acid and base catalyzed PZT gels. The presence of the latter two volatiles was associated with the decomposition of the acetate group via the carbonate route. Acetate and carbonate groups were determined by Fourier Transform Intrared Spectroscopy (FTIR) to be present in the gel structure prior to pyrolysis. Differences in the synthesis of the prehydroiyzed solution were found to affect the amount of residual alkoxy groups, gel structure, pyrolysis behavior, and therefore, the resulting microstructures of sol-gel derived PZT thin films. Finally, some suggestions for improving the processing of sol-gel PZT thin films are given.     

Biodegradable liquid crystalline aromatic/aliphatic copolyesters. Part I: Synthesis, characterization, and hydrolytic degradation of poly(butylene succinate-co-butylene terephthaloyldioxy dibenzoates)

To increase the thermal and mechanical properties of the aliphatic polyester poly(butylene succinate) (PBS), a series of potentially biodegradable liquid crystalline aromatic/aliphatic random copolyesters were prepared by melt polycondensation of new mesogenic monomers dimethyl 4,4′-(terephthaloyldioxy) dibenzoate (MTB), dimethyl succinate, and 1,4-butanediol. The synthesized copolyesters were characterized by means of proton nuclear magnetic resonance spectroscopy (¹H NMR), gel permeation chromatography (GPC), viscosity measurements, differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), polarizing light microscopy (PLM) and mechanical property measurements. The MTB content was varied so that the effects of the mesogen content on the thermal and mechanical properties, degradable behaviours and mesophase were examined. It was found that introducing the rigid rod mesogens could increase the thermal stability and the mechanical properties, while it reduced the melting temperature (T_m), the crystallization temperature (T_c), the degree of relative crystallinity (X_c) and the hydrolytic degradation rate. Only the homopolyester poly(butylenes terephthaloyldioxy dibenzoates) was able to show the schlieren texture characteristic of nematics.     

Thermal stability study of some azo-derivatives and their complexes,Part 2. New azo-derivative pigments and their Cu(II) complexes

This paper deals with the investigation concerning the thermal stability of two new azo-derivatives and their Cu(II) complexes of type [Cu(L¹)₂] and, respectively, ((C₄H₉)₄N)₂[Cu(L²)₂]. The thermal decomposition steps have been put in evidence. For the kinetically workable ones, the values of the activation energy vs. conversion degree were determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

ChemInform Abstract: Molecular Structure and Thermal Stability of B2H4 and B2H+ 4 Species.

B₂H₄ is produced by reaction of B₂H₆ with fluorine atoms generated in a microwave discharge.