Relation between chemical composition of sols and surface free energy of inorganic-organic films

The presented study deals with relation between chemical composition of precursor sols and surface free energy of inorganic-organic films. Inorganic-organic films were prepared from precursor sols in “tetraethoxysilane (TEOS) - triethoxy(octyl)silane (OTES) - distilled water - nitric acid - isopropyl alcohol” system. The fifteen sols were prepared, where the ratio of K?=?x(OTES)/(x(TEOS)?+?x(OTES)) varied from 0 to 0.5 and ratio of R?=?x(H₂O)/(x(TEOS)?+?x(OTES)) varied from 2 to 6. The relationship between chemical composition and surface free energy of inorganic-organic films was quantified by model selection approach. Model, which describes the studied relationship in the best way, was selected on the basis of Akaike information criterion. Based on the analysis of selected (the best describing) model, it was found out that the surface free energy as well as its dispersion and polar component are dependent only on K ratio in observed range of K and R values. Form the physico-chemical aspect, the observed dependences of surface free energy, its dispersive and polar component on chemical composition of precursor sols are explained by the influence of octyl groups on the sequences of hydrolysis and condensation reactions leading to formation of particles in precursor sol. In addition, the arrangement of octyl groups is used for explanation of particles arrangement on film surface.

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Two new mononuclear cobalt(II) complexes of pyrazole-based ligands: synthesis,structures and magnetic studies

We have synthesized two mononuclear cobalt(II) complexes (1 and 2) of pyrazole-based bidentate (NN) and tridentate (NNN) tripodal ligands. X-ray crystal structure determination reveals that complex 1 has a tetrahedral geometry, while complex 2 has a trigonal–bipyramidal geometry. Both the complexes have been characterized by variable-temperature magnetic measurements between 2 and 300 K. A weak ferromagnetic exchange interaction (J = +1.5 cm^?1) is observed for complex 2. Due to the presence of supramolecular CH···Cl and π···π interactions, a good magnetostructural correlation was found between the D parameter and angular distortion (δ) for complex 1 and related complexes reported in the literature.     

Evidence and modelling of physical aging in green wood

Physical aging typical of semi-crystalline polymers was evidenced in green (never dried) wood from three tropical hardwood species. The assumption of uniform aging rate was verified by the construction of master curves from series of tensile creep tests in the fibre direction, performed at increasing time elapsed after a quench following heating above the glassy transition. The rheological response during periods of creep small enough to neglect the progress of aging was described by a model made of a spring in series with a parabolic dash-pot where only the characteristic time depends on the aging time. The model was able to describe results obtained by a previous author on softwood loaded transversally to the fibres. The possible role of a transient adsorption process consecutive to the quench is discussed.

Development and applications of a relaxation-inducing cluster expansion theory for treating strong relaxation and differential correlation effects

We present in this paper a multi-reference coupled cluster (MRCC) formulation for energy differences which treats orbital relaxation and correlation effects on the same footing, by invoking a novel cluster ansatz of the valence portion of the wave operator Ω_v. Unlike in the traditional normal-ordered exponential representation of Ω_v, our new relaxation-inducing ansatz, represented symbolically as E _r(S), allows contractions between the spectator lines and also certain other special contractions. By an extensive theoretical analysis, taking as an example the case of one-hole model space (the IP problem), we demonstrate that our ansatz incorporates in a manifestly spin-free form the orbital relaxation to all orders. The traditional Thouless-type of exponential transformation via one-body excitations can induce the same effect, as is done in the valence-specific or the quasi-valence-specific MRCC formalisms, but they have to be done in the spin-orbital basis – making the spin adaptation of the problem a complicated exercise. In contrast, we use a spin-free representation of the cluster operators right from start, but expand the rank of the cluster operators by involving spectator orbitals to distinguish the various spin possibilities. The combinatorial factors entering the contracted power series in E _r(S) are chosen in such a way that they correspond to what we would have obtained if we had used a Thouless-like transformation to induce the orbital relaxation. Our working equations generally have only finite powers of the cluster operators S, resulting in a very compact formulation of the relaxation problem. Pilot numerical applications for the IP computations of HF and H₂O in the core, the inner valence and the outer valence regions show very good performance of the method vis-a-vis those obtained using the traditional normal ordered ansatz for Ω_v. The improvement in the core IP value is particularly impressive, although even for the valence regions there is an overall improvement of the IP values. Received: 3 August 1998 / Accepted: 30 September 1998 / Published online: 15 February 1999     

Frictional contact of elastomer materials on rough rigid surfaces

The frictional behavior of elastomer materials is still unexplored, but very important for many industrial applications. Special attention is turned to rubber friction on rough road tracks. Due to the non‐rigid material characteristics of the rubber it is not sufficient to use a constant friction coefficient like Coulombs law. The frictional qualities depend on many different influences like sliding velocity, applied normal stress, surface roughness, material properties and the temperature in the contact zone. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of precursor sol pH on microstructural, optical and photocatalytic properties of vacuum annealed zinc tin oxide thin films on glass

Dip coated vacuum annealed zinc tin oxide thin films on soda lime silica glass have been deposited from the precursor sols containing zinc acetate dihydrate and tin (IV) chloride pentahydrate (Zn:Sn = 67:33, atomic ratio in percentage) in 2-methoxy ethanol by varying sol pH (0.85–5.5). Crystallinity, morphology, optical and photocatalytic properties of the films strongly depend on sol pH. Measurement of grazing incidence X-ray diffraction confirms the presence of hexagonal nano ZnO in the films derived from the sols of pH < 5.5. Film crystallinity deteriorates on increasing sol pH and the film deposited from the sol of pH 5.5 shows XRD amorphous but the selected area diffraction pattern and HRTEM image evidence the presence of nano Zn₂SnO₄ (size, 5–6 nm). Direct band gap energy of films increases on increasing sol pH. To visualize the film surface microstructure, FESEM study has been done and a rod-like surface feature is revealed in the film deposited from the sol of pH 2.85. A dependence of precursor sol pH on the photocatalytic activity of films towards degradation of Rhodamine 6G dye under UV (254 nm) irradiation is found and the highest decomposition rate constant, ‘k’ value is obtained from the film prepared from the sol of pH 5.5. The presence of zinc deficient nano Zn₂SnO₄ in the film may consider for generating the highest ‘k’ value. We also measure gelling time, viscosity of sols as well as UV and FTIR studies on the films and propose chemical reactions.     

[N‐(Carboxyl­ato­methyl)­aspartato(3–)](ethyl­enedi­amine)­cobalt(III) trihydrate

The mononuclear title complex, [Co(C₆H₆NO₆)(C₂H₈N₂)]·3H₂O, contains an octahedrally coordinated Co^III atom. The N‐(carboxy­methyl)­aspartate moiety is coordinated as a tetradentate ligand, providing an OONO‐donor set and forming two trans five‐membered chelate rings and one six‐membered chelate ring. A seven‐membered chelate ring is also formed, which consists of part of the six‐membered chelate ring and part of one of the five‐membered chelate rings. The crystal structure of the complex is stabilized by hydrogen bonds with three water mol­ecules.     

2‐Bromo‐6‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)pyridine,a new unexpected bifunctional building block for combinatorial chemistry

The first reported structure of a pyridin‐2‐ylboron derivative, viz. the title compound, C₁₁H₁₅BBrNO₂, (I), is compared with its regioisomer 2‐bromo‐5‐(4,4,5,5‐tetra­methyl‐1,3,2‐dioxa­borolan‐2‐yl)­pyridine, (II) [Sopková‐de Oliveira Santos, Lancelot, Bouillon & Rault (2003). Acta Cryst. C59, o111o113 ]. Structural differences are observed, firstly in the orientation of the dioxaborolane ring with respect to the pyridine ring and secondly in the bond angles of the BO₂ group. These differences do not explain the experimentally observed differences in chemical reactivity between (I) and (II) but do confirm the relatively lower stability of (I). However, ab initio calculations of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), based on the known crystal structures of the two compounds, show different distributions, which correspond to the differences observed during chemical reactions.