The surface energy of monolithic silica xerogels was examined by measuring the interaction of organic probes with xerogels heated at temperatures close to the gel-to-glass transition temperature. Values of the dispersive component of the surface energy,
, between 60 and 80 mJ m-2 have been observed using n-alkanes for silica xerogels heated at 700, 800 and 900°C. At 1000°C,
decreases to 8.37 mJ · m-2. Also the differential heat of adsorption, variation of standard free energy and entropy of adsorption decrease when the silica xerogel is heated at 1000°C, showing a lower interaction potential of the organic probes with the silica surface. For the silica xerogels heated between 700 and 900°C, the acid character varies in accordance with the variation of the chemical nature of the silica. Upon heating at 1000°C, both acid and base characters are very close in accordance with a neutral surface. Within the experimental conditions used in this work, the surface of the obtained monolithic silica xerogels behaves as a glass surface when the treating temperature is 1000°C. 相似文献
Inverse gas chromatography (IGC) was applied to characterize the surface energy of organically modified silicates (ormosils) by measuring the interaction of molecular organic probes with the ormosil surface. Ormosils were prepared by the sol-gel method by the reaction of TEOS (tetraethoxysilane), PDMS (polydimethylsiloxane) and different types of silica (Aerosil 130, Aerosil 200 and Aerosil 380). The isosteric heat of adsorption, qst, and the dispersive component of the surface energy, sD, were estimated by using the retention volume of different nonpolar and polar probes at infinite dilution. The dispersive component shows an increase as the specific surface area of the silica is increased from 29.6 mJ/m2 to 51.4 mJ/m2 at 60°C. Such values are lower than that obtained for aerosil particles meaning that PDMS chains impede the interaction with silanol groups located on the silica surface. The specific interaction parameter, ISP, and the enthalpy of specific adsorption, HaSP, of polar probes on the ormosil surface were also measured in order to obtain the acid-base character of ormosil surface. The HaSP, was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, KA, and the basic, KB, parameters of the substrate surface. The obtained results suggest that the silica particles were covered by PDMS chains in a different way depending on the type of silica used. The values of KA and KB suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites. 相似文献
This study deals with the use of ethanol as washing solvent in the preparation of the silica gels from sodium silicate in order to enhance the textural properties, especially surface area. We here examined the effect of ethanol-washing on surface area, micro- and mesopore volume, and average pore size. The silica xerogels prepared from sodium silicate solution exhibited an extremely high surface area of 1139 m2/g by washing their hydrogels with ethanol. Compared to water-washed xerogels, ethanol-washed xerogels showed higher surface areas, total pore volumes, and larger average pore sizes. Unlike the surface area of water-washed xerogel, that of the ethanol-washed xerogel was not affected by the silica concentration of initial solution. This study indicates that the textural properties of sodium silicate-derived xerogels are further enhanced by using ethanol as washing solvent. 相似文献
The B‐ala/AIBN PBZ system has a high extent of ring‐opening of oxazine because phenol‐containing oligomers are formed at the early stage of the curing process. As a result, the B‐ala/AIBN PBZ system possesses a relatively stronger intramolecular hydrogen bonding and lower surface energy than the pure B‐ala system at low temperature curing. In this context, poly(4‐vinyl pyridine), poly(4‐vinyl phenol) thin films and polycarbonate substrates, which lack liquid resistance, possess low surface free energy after modification with B‐ala/AIBN = 5/1 PBZ.
The adsorption of water vapor and the heat of wetting of hydrophilic hydromica and hydrophobized samples of kaolinite and
Silochrom were studied. The contact angles for the wetting of the investigated materials with water were obtained. The thermodynamic
characteristics of the surface of the sorbents and the interfacial region at their boundary with water were calculated from
the obtained data. It was shown that the boundary water layers close to the hydrophilic surface of the hydromica are more
ordered while those close to the hydrophobic surfaces of the modified samples of kaolinite, Silochrom, and the reference sample
(extremely hydrophobic Teflon) are less ordered than liquid water.
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Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 87–91, March–April, 2006. 相似文献
Since antimicrobials were banned as feed additives, coccidiostats with favorable anticoccidial action and growth promotion have been widely used in the breeding industry. The monitoring of coccidiostats in feed is necessary, while the current methods based on mass-spectrometer analysis have limited applicability and matrix effects could interfere with the results. Accordingly, in the present paper, a rapid analytical strategy for the simultaneous determination of six synthetic coccidiostats in feed using high-performance liquid chromatography coupled with diode-array detection was developed. Coccidiostats in chicken feeds were extracted with the trichloroacetic acid–acetonitrile solution. The cleanup was performed by dispersive solid-phase extraction after the optimization of the response surface methodology. The method exhibited good linearity for target coccidiostats within the range of 0.05~20 µg/mL. Recoveries for six compounds in fortified feed samples were from 67.2% to 107.2% with relative standard deviations less than 9.6%. The limit of detection was 0.2~0.3 mg/kg. The successful application of the method in commercial feed verified that it is effective and sensitive for the rapid determination of multiple coccidiostats in chicken feeds. 相似文献
The potential energy surface for the electronic ground state of the HXeBr molecule is constructed from more than 4200 ab initio points calculated using the internally contracted multi-reference configuration interaction method with the Davidson correction (icMRCI + Q). The stabilities and dissociation barriers are identified from the potential energy surface. The three-body dissociation channel is found to be the dominant dissociation channel for HXeBr. Low-lying vibrational energy levels of HXeBr calculated using the Lanczos algorithm are found to be in good agreement with the available experimental band origins. 相似文献
For any biomaterial placed into a biological medium, the surface properties of the material, such as porosity, crystallinity, presence and distribution of electrical charge and functional groups are very critical parameters that determine the acceptance or rejection of the material. Applications, especially tissue engineering require some surface modifications at the molecular level without disturbing the bulk properties of the implants in order to enhance the cell attachment on the material. An appropriate technique is the application of glow discharge plasma which employs no solvents, takes place at ambient temperatures, and alterations take place only at the surface by changing the surface chemistry along with surface free energy (SFE) and efficiency for cell-material interaction. In this study, poly(methyl methacrylate) (PMMA) film surfaces were modified with oxygen plasma. SFE and its dispersive and polar (acidic-basic) components of the modified surfaces were calculated by means of several theoretical approaches including geometric mean, harmonic mean and acid-base equations. The relation between SFE and its dispersive and polar components and cell attachment on surfaces were studied. The highest 3T3 cell attachment was obtained for the surface with the total SFE of 61.77 mJ/m2 and polar component of 50.91 mJ/m2 according to Geometric mean. The total SFE of this surface was calculated to be 61.06 mJ/m2 and the polar component as 40.96 mJ/m2 using the Harmonic mean method. 相似文献
A modified carbon paste electrode with SiO2/SnO2/Phosphate/Meldola's blue, SSPMelB, was used to study the electrocatalytic oxidation of ascorbic acid by cyclic voltammetry and chronoamperometry. The adsorbed dye mediates ascorbic acid oxidation at an anodic potential of 0.04 V vs. saturated calomel electrode (SCE) at pH 7.0, in 0.5 mol L?1 solution. The linear range of the sensor is between 4.0×10?7 and 2.0×10?3 mol L?1, with a limit of detection of 4.0×10?7 mol L?1. This novel electrode shows good analytical performance for determination of ascorbic acid in medicine and commercial fruit juice. 相似文献
The structural, electronic, and energy parameters of the metal-containing clusters (H3SiO)3Si−O−XMen (X=H, B, Al, or Zn;n=0, 1, or 2), which model organometallic groups on a SiO2 surface modified with B-, Al-, and Zn-containing alkyls, have been studied by quantum-chemical methods. Full geometry optimization
for these clusters was carried out by the SCF MO LCAO method taking into account the electron correlation within the frameworks
of the MP2 and B3LYP schemes using the 6-31G(d) (6-311G(d) for Zn) basis set. The effect of the crystal environment was taken
into account in calculations of siliconoxygen clusters containing 10 and 30 silicon atoms using theab initio SCF/6-31G(d) and semiempirical MNDO-PM3 methods. Various modes of coordination and interactions of organometallic groups
with oxygen atoms of surface groups were studied. For the organoaluminum group on the surface, two stable conformations were
found, namely, the three-coordinate structure with the chain −O−AlMe2 ligand and the four-coordinate (quasicyclic) structure with the Al atom that forms two nonequivalent bonds with the O atoms
at the same Si atom. The four-coordinate structure is energetically more favorable. No stable structures were found for the
organoboron and organozinc fragments.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1296–1303, July, 1998. 相似文献
The fundamental understanding of the behavior of a solid is intimately related to the understanding of the interactions on the surface of the latter, a major challenge in particular if the material is natural and ecological. The infinite dilution-inverse gas chromatography was used to evaluate the surface thermodynamic properties of several phases (grafted and/or coated) diatomite. A series of non- or polar-solute probes were injected at temperatures of 45?°C and 90?°C. The dispersive surface free energies values of the supports decrease with increasing temperature and their active surface is amphoteric with predominantly acidic character. 相似文献