Effects of the nanoassociation of hexadecyltrimethoxysilane precursors on the sol–gel process

Modifications to the refractive indices of meso-structured organic–inorganic films caused by variations in the mole fraction of precursors in ethanolic solutions were investigated. The refractive indices were dependent on the mole fraction of C₁₆TMS (hexadecyltrimethoxysilane) and of the C₁₆TMS/TMOS (tetramethoxysilane) (1/1) mixture in ethanol. The dependency was determined to be nonlinear, and the phenomenon was attributed to self-assembly caused by the long alkyl groups (C₁₆) on the C₁₆TMS. Changes in the maximum decreasing rate of d_n/d_x values [(d_n/d_x)_max—for d_n/d_x estimation, the curves from Fig. 1 were associated with a polynomial; using a dedicated program, d_n/d_x was calculated; maximum values of d_n/d_x were taken into account and were included in Table 1)] were used to distinguish the behavior of alcoholic precursor mixtures. In the case of using pyrene as a fluorescent probe, the ratio between two peaks from the pyrene emission spectra (I₁/I₃) strongly decreased as hydrophobic micro-surroundings formed due to the self-assembly process. The UV–VIS spectra of a cationic dye solution, R6G, was studied because dilute solutions of the dye in equilibrium form measurable ratios of dimers and monomers. The absorbance was modified as micro-surroundings with different polarities were formed. These three methods demonstrated that nano-structuration was present prior to the occurrence of the sol–gel process. The combination of C₁₆TMS with other alkyltrialkoxysilane precursors having hydrocarbon chain lengths between C₁ and C₈ provided further evidence for a nonlinear dependence of the refractive indice and fluorescence spectra of pyrene. The properties of the final hybrids obtained by the sol–gel process were significantly affected by the precursor hydrocarbon chain lengths. DSC, XRD and FTIR measurements were used to show the plasticizing phenomena of C₁₆ as other alkyltrialkoxysilanes (i.e., C₁–C₈) were added.

The influence of the temperature on the liquid–liquid equilibrium of the ternary system 1-pentanol–ethanol–water

Liquid–liquid equilibrium data for the ternary system 1-pentanol–ethanol–water have been determined experimentally at 25, 50, 85 and 95°C. These results have been correlated simultaneously by the uniquac method obtaining two sets of interaction parameters: one of them independent of the temperature and the other with a linear dependence. Both sets of parameters fit the experimental results well.     

Effect of the Acid–Base Properties of the Support on the Activity of Pd–Zeolite Catalysts for CO Oxidation

The effect of the acid–base properties of zeolite Y on the activity of palladium–zeolite catalysts for CO oxidation was studied. The modification of the support with basic additives was found to improve the catalyst activity. A linear correlation between the ratio between the amounts of O₂and CO adsorbed on the surface of palladium and the catalyst activity was established.     

Study on the effects of flame retardants on the thermal decomposition of wood by TG–MS

The effect of three flame retardants, K₂CO₃, Na₂SiO₃·9H₂O, and Na₂B₄O₇·10H₂O on the process and composition of volatile products of the thermal degradation of wood has been investigated by the thermogravimetric (TG), differential thermogravimetry (DTG), differential thermal analysis (DTA), and the synchronous thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the ion current intensity and ion peak area of m/z = 18 and 44 MS signals were increased by the flame retardants but the ion peak area of m/z = 28 MS signal was decreased (except K₂CO₃) at the meantime. What’s more, the ion current intensity and ion peak area of m/z = 60 and 68 MS signals were also decreased (except K₂CO₃), which mean that Na₂B₄O₇ can significantly enhances the dehydration and inhibits the depolymerization of wood. Although K₂CO₃ accelerates the dehydration reaction, it cannot inhibit the depolymerization reaction effectively, so the flame retardant efficiency of K₂CO₃ is decreased with the higher concentration. The catalysis of dehydration reaction of Na₂SiO₃ is the worst one.     

Effects of microhydration on the characteristics of cation–phenol complexes

The properties of complexes formed by phenol and K⁺, Na⁺, Li⁺ and Mg²⁺ in the presence of up to four water molecules have been studied by means of computational methods. The interaction becomes stronger as the size of the cation decreases, showing almost no preference between coordinating to the aromatic ring or to the hydroxyl oxygen. As water molecules are introduced, a variety of stable structures arise, where water molecules establish hydrogen bonds among themselves and with the hydroxyl group of phenol. For the most polarizing cations, the strong cation···water interaction gives most stable minima corresponding to arrangements with water molecules and phenol coordinated directly to the cation, with no significant hydrogen bonds among them. However, in Na⁺ complexes and especially in K⁺ ones, the interaction with the cation is weaker, so hydrogen bond formation starts to be competitive as more water molecules are included, the most stable minima corresponding to structures where not all water molecules or phenol are directly bound to the cation. This behavior is also reflected on the predicted vibrational spectra, which agree with those determined experimentally. Up to three water molecules, only for K⁺ and to a less extent Na⁺, stable minima are found showing red-shifted O–H stretching bands corresponding to water···water and water···phenol hydrogen bonds. With four water molecules, at least one water molecule is located in a second solvation shell, all cations exhibiting red-shifted bands.     

Effect the conditions of the acid–thermal modification of clinoptilolite have on the catalytic properties of palladium–copper complexes anchored on it in the reaction of carbon monoxide oxidation

The dependence of the physicochemical and structural–adsorption properties of natural and acid–thermal modified clinoptilolite, and of Pd(II)–Cu(II) catalysts based on them, on the duration of acid–thermal modification is investigated. The samples under study are described via XRD and thermal gravimetric (DTG and DTA) analysis, IR, DR UV–Vis, EPR spectroscopy, and water vapor adsorption. Values of both the specific surface area (S_sp) and pH of aqueous suspensions are determined. The resulting catalysts are tested in the reaction of low-temperature carbon monoxide oxidation with air oxygen. A conclusion is drawn about the nature of surface bimetallic Pd(II)–Cu(II) complexes. The greatest catalytic activity is shown by complexes based on clinoptilolite and modified with 3 M HNO₃ for 0.5 and 1 h.     

Influence of the anisometry of magnetic particles on the isotropic–nematic phase transition

The influence of the shape anisotropy of magnetic particles on the isotropic–nematic phase transition was studied in ferronematics based on the nematic liquid crystal (LC) 4-(trans-4-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT). The LC was doped with spherical or rod-like magnetic particles of different size and volume concentrations. The phase transition from isotropic to nematic phase was observed by polarising microscope as well as by capacitance measurements. The influence of the concentration and the shape anisotropy of the magnetic particles on the isotropic–nematic phase transition in LC are demonstrated here. The results are in a good agreement with recent theoretical predictions.     

Influence of the zirconia transformation on the thermal behavior of zircon–zirconia composites

During a heating?Ccooling cycle, zirconia (ZrO₂) undergoes a martensitic transformation from monoclinic to tetragonal structure phases, which presents special hysteresis loop in the dilatometry curve at temperatures between 800 and 1100?°C. Monoclinic zirconia (m-ZrO₂) particles reinforced ceramic matrix composites not always present this behavior. In order to elucidate this fact a series of zircon?Czirconia (ZrSiO₄?CZrO₂) ceramic composites have been obtained by slip casting and characterized. The final properties were also correlated with the zirconia content (0?C30?vol.%). The influence of the martensitic transformation (m?Ct) in well-dispersed zirconia grains ceramic composite on the thermal behavior was analyzed. Thermal behavior evaluation was carried out; the correlation between the thermal expansion coefficients with the zirconia content showed a deviation from the mixing rule applied. A hysteresis loop was observed in the reversible dilatometric curve of composites with enough zirconia grains (??10?vol.%). Over this threshold the zirconia content is correlated with the loop area. The transformation temperatures were evaluated and correlated with the zirconia addition. When detected the m?Ct temperature transformation is slightly influenced by the zirconia content (due to the previously evaluated decrease in the material stiffness) and similar to the temperature reported in literature. The reverse (cooling) transformation temperature is strongly decreased by the ceramic matrix. The DTA results are consistent with the dilatometric analysis, but this technique showed more reliable results. Particularly the endothermic m?Ct transformation temperature showed to be easily detected even when the only m-ZrO₂ present was the product of the slight thermal dissociation of the zircon during the processing of the pure zircon material.     

Influence of Fe concentration on the properties of the electrodeposited Zn–Fe coatings

Electrodeposition of Zn–Fe alloys on a copper substrate from a sulfate bath with different Fe²⁺ concentration (0.05, 0.10 and 0.20 mol L^?1) at room temperature was investigated using cyclic voltammetry. The influence of the Fe²⁺ content in the plating bath on the surface morphology, structural and magnetic properties of the coatings were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Vibrating Sample Magnetometer (VSM). The results show that the morphology of Zn–Fe films changes with different Fe²⁺ concentration. The EDS analysis demonstrated that the Fe content of the coatings increased with increasing the Fe concentration in the bath. XRD measurements shows the presence of ?Zn (hcp), δ1ZnFe (hcp) and the ΓZnFe (bcc) phases with a (101) preferential orientation in all the electrodeposited films. The magnetic analysis of Zn–Fe films indicated that the saturation magnetization was largely enhanced in comparison to pure Zn, especially with 0.2 at. % Fe, while the coercivity decreased.     

Influence of the nickel content on the electrocatalytic activity of thin nanostructured Co–Te–Ni–O films

The influence of nickel addition in Co–Te–O catalytic films, obtained by vacuum co-evaporation of Co, Ni, and TeO₂ on electrocatalytic activity toward oxygen reactions in alkaline media has been investigated. Bifunctional gas-diffusion oxygen electrodes were prepared by direct deposition of catalyst films on gas-diffusion membranes consisting of hydrophobized carbon blacks. The method used allows the deposition of nanostructured films consisting of intertwined nanowires with high surface area. Thus, obtained electrodes with different atomic ratio R _(Co+Ni)/Te of the catalyst, fresh and thermally treated at 100 °C temperatures were electrochemically tested by means of cyclic voltammetry and steady-state voltammetry. It has been shown that the partial replacement of Co with about 30 at.% Ni leads to the increase in the film catalytic activity toward oxygen evolution reaction.     

Investigations on the electrochemical preparation of gold–nanoparticle composites

The role of electrical charges in the double layers of the electrode and in particles during the electrochemical preparation of dispersion coatings was studied for the systems Au/diamond and Au/Al₂O₃. The surface charge of the electrode under the conditions of electroplating will depend on the potential of zero charge (p.z.c.). For the nanoscaled particles the sign of the surface charge was estimated from the zeta potential in dilute solutions. Successful inclusion of Al₂O₃ and diamond nanoparticles was observed when the particles and the electrode were oppositely charged. The Vickers hardness of the layers was increased by the codeposition of Al₂O₃, whereas it decreased in the case of nanodiamond.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Influence of Sr addition on microstructure of the hypereutectic Zn–Al–Cu alloy

Journal of Thermal Analysis and Calorimetry - The purpose of the presented work is to answer the questions: how does the addition of strontium to the Zn–8Al–1Cu alloy crystallisation...     

The influence of polyoxypropylenetriamine on the properties of epoxy–thiokol mixtures

The influence of Jeffamine T-403 polyoxypropylenetriamine on the physico-mechanical, adhesion, and relaxation properties of polymeric compositions based on the products of preliminary thioesterification reaction of epoxy resin with liquid thiokol was studied. It was shown that the introduction of polyoxypropylenetriamine leads to a significant increase of the adhesive and cohesive strength, the elongation at break, and the work of destruction of the material.     

A perspective on the localizability of Hartree–Fock orbitals

A common perception about molecular systems with a nonlocal electronic structure (as manifested by a nonlocal Hartree–Fock (HF) density matrix), such as conjugated π-systems, is that they can only be described in terms of nonlocal molecular orbitals. This view is mostly founded on chemical intuition, and further, this view is strengthened by traditional approaches for obtaining local occupied and virtual orbital spaces, such as the occupied Pipek–Mezey orbitals, and projected atomic orbitals. In this article, we discuss the limitations for localizability of HF orbitals in terms of restrictions posed by the delocalized character of the underlying density matrix for the molecular system and by the orthogonality constraint on the molecular orbitals. We show that the locality of the orbitals, in terms of nonvanishing charge distributions of orbitals centered far apart, is much more strongly affected by the orthogonality constraint than by the physical requirement that the occupied orbitals must represent the electron density. Thus, the freedom of carrying out unitary transformations among the orbitals provides the flexibility to obtain highly local occupied and virtual molecular orbitals, even for molecular systems with a nonlocal density matrix, provided that a proper localization function is used. As an additional consideration, we clear up the common misconception that projected atomic orbitals in general are more local than localized orthogonal virtual orbitals.     

Study on the effect of chain-length compatibility of mixed anionic–cationic surfactants on the cloud-point extraction of selected organophosphorus pesticides

The chain-length compatibility of mixed anionic-cationic surfactants was investigated for the extraction of organophosphorus pesticides (OPPs). Cationic surfactants with different chain lengths (n = 12 and 16) were mixed with sodium dodecyl sulfate (SDS; n = 12) for the mixed anionic-cationic surfactants-based extraction. Six OPPs were studied including azinphos-methyl, parathion-methyl, fenitrothion, diazinon, chlorpyrifos, and prothiophos. Reversed-phase high-performance liquid chromatography was used for the determination of the studied OPPs. The extraction was performed using mixtures of SDS and cationic surfactants including dodecyltrimethyl ammonium bromide or dodecyltrimethylammonium bromide (DTAB; n = 12) and cetyltrimethyl ammonium bromide or cetyltrimethyl ammonium bromide (CTAB; n = 16). The parameters affecting the extraction efficiencies of two extraction systems were studied and discussed. The optimum condition for SDS-DTAB was 15 mmol L(-1) SDS and 1 mmol L(-1) DTAB in the presence of 15% (w/v) sodium chloride (NaCl). Meanwhile, the condition for SDS-CTAB was 10 mmol L(-1) SDS and 1.0 mmol L(-1) CTAB with 10% (w/v) NaCl. Under the optimum conditions, the extraction efficiency of SDS-DTAB (66-85%) was slightly higher than that of SDS-CTAB (61-82%). In addition, the SDS-DTAB system also gave greater enrichment factor than SDS-CTAB for all the studied OPPs. This result may be due to the compatibility of chain length between SDS and DTAB. The extraction using SDS-DTAB was successfully applied to determine OPPs in fruit samples (i.e., pomelo, apple, and pineapple). No contamination by the studied OPPs in samples was observed. Good accuracy with recoveries ranging from 77 to 105% was obtained. Low limits of detection were in the range of 0.003-0.01 mg kg(-1) which are below the MRLs established by EU-MRLs for the OPPs residues in fruit samples.     

Temperature dependence on the dose response of the Fricke–gelatin–xylenol orange gel dosimeter

The effect of temperature during optical absorbance measurements and irradiation on the values of the molar absorption coefficient, (ε_m)_t, and radiation chemical yield, G_t^′, respectively, for the Fricke–gelatin–xylenol orange (FGX) gel dosimeter were investigated. At 20 °C, the product (ε_m)_tG_t^′ was found to be 6.76×10^?3 m² J^?1. While an irradiation temperature coefficient, k₂, was evident (?0.53% °C^?1), no temperature effect was found during measurement in the range 16–25 °C.     

Influence of phosphorus concentration on the state of the surface layer of Pd–P hydrogenation catalysts

Phase composition and surface layer state of the Pd–P hydrogenation catalyst formed at various P/Pd ratios from Pd(acac)₂ and white phosphorus in a hydrogen atmosphere were determined. Palladium on the catalyst surface is mainly in two chemical states: as Pd(0) clusters and as palladium phosphides. As the P/Pd ratio increases, the fraction and size of palladium clusters decrease, and also the phase composition of formed palladium phosphides changes: Pd₃P_0.8 → Pd₅P₂ → PdP₂. The causes of the modifying action of phosphorus on the properties of palladium catalysts for hydrogenation of unsaturated compounds were considered.     

Effect of the structural change of an iron–iron oxide mixture on the decomposition of trichloroethylene

The effect of the structure of a mixture of industrially produced iron and iron oxide on the decomposition of trichloroethylene (TCE) was investigated by gas chromatography, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffractometry, and ⁵⁷Fe-Mössbauer spectroscopy. The concentration of 10 mg L^?1 TCE aqueous solution decreased to 0.41, 0.52, 0.26, and 0.09 mg L^?1 when stirred for 7 days with iron–iron oxide mixtures having mass ratios of 2:8, 3:7, 4:6, and 5:5, respectively. The Mössbauer spectra of the mixtures after leaching were composed of two sextets with respective isomer shifts (δ) and internal magnetic fields (H) of 0.29_±0.01 mm s^?1 and 48.8_±0.1 T, and 0.64_±0.01 mm s^?1 and 45.5_±0.1 T, attributed to the Fe³⁺ species in tetrahedral (T _d) and the Fe²⁺ and Fe³⁺ mixed species (Fe^2.5+) in octahedral (O _h) sites, respectively. Mössbauer spectra of a 3:7 mass ratio iron–iron oxide mixture showed a gradual decrease in the absorption area (A) of zero valent iron (Fe⁰) from 40.6. to 12.6, 13.2, 3.8 2.8, and 1.0_±0.5 % and an increase in A of Fe₃O₄ from 31.8 to 59.4, 71.4, 93.2, 95.6, and 98.0_±0.5 % after leaching with 10 mg L^?1 TCE aqueous solution for 1, 2, 3, 7, and 10 days, respectively. Consistent values of the first-order rate constant were calculated as 0.32 day^?1 for Fe⁰ oxidation, 0.34 day^?1 for Fe₃O₄ production, and 0.30 day^?1 for TCE decomposition, which indicates that the oxidation of Fe⁰ was the rate-controlling factor for Fe₃O₄ production and TCE decomposition. It is concluded from the experimental results that an iron–iron oxide mixture is very effective for the decomposition of TCE.     

Prediction and experimental verification of the salt effect on the vapour–liquid equilibrium of water–ethanol–2-propanol mixture

Experimental vapour–liquid equilibria of water–ethanol–2-propanol saturated with NaNO₃, NaCl, KCl and containing 0.05 mol CH₃COOK/mol total solvent compared well with those predicted by Tan–Wilson and Tan–non-random two liquid (NRTL) models for multicomponent solvent–solute mixture using a set of solvent–solvent interaction parameters obtained from the regression of the vapour–liquid equilibrium of the solvent mixture without the dissolved solute and a set of solute–solvent interaction parameters calculated from the bubble points of the individual solvent components saturated or containing the same molar ratio of solute/total solvents as the mixture. The results also showed that a solvent component i is salted-in or out of the liquid phase relatively more than solvent component j would depend on whether A_sj/A_si (Tan–Wilson model) or exp(τ_is−τ_js) (Tan–NRTL model) is less or greater than 1. This is consistent with earlier publications on the effect of dissolved solutes (electrolytes and non-electrolytes) on the binary solvents mixtures. These findings confirmed that Tan–Wilson and Tan–NRTL models for multicomponent solvent–solute system can provide an accurate and rapid screening of electrolytes and non-electrolytes for their suitability in facilitating solvent separation by salt distillation of ternary solvent mixtures simply by determining the relative ratios of the solute–solvent interaction parameters from the respective bubble points of the solvent components containing the dissolved solute. The results also suggest that this may also be extended to other multicomponent solvent mixtures.