Surface Energy Changes of Heat Treated TEOS Derived Silica Xerogels

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.     

Surface Energy of Silica-TEOS-PDMS Ormosils

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, q _st, and the dispersive component of the surface energy, _s ^D, 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, I^SP, and the enthalpy of specific adsorption, H _a ^SP, of polar probes on the ormosil surface were also measured in order to obtain the acid-base character of ormosil surface. The H _a ^SP, was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, K _A, and the basic, K _B, 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 K _A and K _B suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites.     

二氧化钛干凝胶热分解及热处理对表面有机官能团变化的影响

利用X射线衍射(XRD)、差示扫描量热法(DSC)、红外光谱(FTIR)、X射线光电子能谱(XPS)等技术手段研究了溶胶-凝胶(sol-gel)法制备的二氧化钛干凝胶粉末在不同温度下煅烧后表面成分和结构变化,并对不同煅烧温度的粉末样品表面有机官能团的种类及所占的比例进行了探讨。结果表明:二氧化钛干凝胶粉末随着煅烧温度的提高,O-Ti-O结构逐步由复杂的无序网链状结构向有序的晶体结构转变,粉末表面的有机官能团中羧基通过反应产生的螯合物影响二氧化钛晶化;在200~300℃温度范围二氧化钛表面存在大量羟基;300℃左右羧基螯合物分解,在350℃时,憎水碳链官能团已基本除去,在300~350℃,有机官能团加速减少。     

Ethanol Washing Effect on Textural Properties of the Sodium Silicate-Derived Silica Xerogel

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.     

反气相色谱法测定苯乙烯-氧乙烯-苯乙烯三嵌段聚合物的表面能

 采用反气相色谱法测定了苯乙烯 氧乙烯 苯乙烯三嵌段聚合物 (PS PEO PS)的色散成分的表面能 (γsd) ,研究探讨了温度及嵌段聚合物链段结构组成对γsd 的影响 ,并确定了γsd 与温度的数学关系式。研究结果表明 :在 70℃～ 12 0℃范围内 ,PS PEO PS的表面能较低 ;随着PS PEO PS表面组成中氧乙烯 (EO)成分的增加 ,色散成分的γsd 增大 ,且对温度的变化极其敏感 :随温度的升高 ,γsd 急剧地呈线性下降。     

Modification of Polymer Substrates with Low Surface Free Energy Material by Low‐Temperature Cured Polybenzoxazine

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.

     

Surface energy of hydrophobic adsorbents

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. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 87–91, March–April, 2006.     

两亲聚合物表面的反相气相色谱分析

采用反相气相色谱探针技术研究了苯乙烯－氧乙烯－苯乙烯三嵌段两亲聚合物的表面物理化学性质。包括表面吸附热力学函数,表面能的色散分量以及表面分子链与探针的分子间相互作用,。探讨了共聚物中亲油性链段聚苯乙烯（PS）和亲水性链段聚氧乙烯（PEO）的组成比例与其表面性质的关系。结果表明共聚物表面组成中随PEO含量的增加,其表面能增大,表面分子链与探针分子的相互作用增强,表面吸附能力也增强。     

二氧化硅分散体系在应力剪切过程中粘弹性及能耗研究

通过动态应力剪切研究了以乙二醇、丙二醇和丁二醇为分散介质的雾化二氧化硅分散体系的粘弹性以及能耗. 研究发现, 随着应力的增大, 体系都经历了线性粘弹区、剪切变稀区以及剪切增稠区. 在线性粘弹区, 储能模量(G′)、耗能模量(G′′)随着应力(σ)的增大保持不变；在剪切变稀区, G′随着σ的增大而减小, 且乙二醇、丙二醇、丁二醇分散体系的减小幅度依次递减, 而G′′基本保持不变；在剪切增稠区, G′、G′′都随着σ的增大而增大. 在所研究的应力范围内, G′′都大于G′, 体系主要体现粘性, 消耗能量为主. 同时还发现在低剪切应力区, 体系所消耗的能量(Ed)都随着最大应变(γ0)成二次方关系增长, 而在剪切增稠区, 当n=2.79、4.93、4.88时, EG/SiO2、PG/SiO2、BG/SiO2的Ed分别随γ0以指数关系增长.     

Response Surface Optimization of Dispersive Solid-Phase Extraction Combined with HPLC for the Rapid Analysis of Multiple Coccidiostats in Feed

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.     

煅烧温度对TiO2/SiO2混合氧化物表面酸量的影响

采用共沉淀法制备了高钛含量的复合氧化物TiO2／SiO2．用BET、XRD、FT-IR和正胺吸附等分析手段，研究了煅烧温度对TiO2／SiO2表面酸量的影响．研究发现，随着煅烧温度的升高，TiO2／SiO2表面羟基密度、比表面积逐渐减少，TiO2晶粒尺寸变大，造成TiO2／SiO2表面酸量降低．当煅烧温度达到600℃到800℃之间，表面酸量基本不再改变．     

Theoretical Studies on the Potential Energy Surface and Vibrational Energy Levels of HXeBr

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.     

Influence of Oxygen Plasma Modification on Surface Free Energy of PMMA Films and Cell Attachment

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.     

Meldola's Blue Immobilized on a SiO2/SnO2/Phosphate Xerogel,a New Sensor for Determination of Ascorbic Acid in Medicine and Commercial Fruit Juice

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.     

二氧化钛(TiO2)表面能的理论研究

用密度泛函理论和虚拟原子轨道方法对二氧化钛-金红石(TiO2)(110)表面的表面能进行了理论计算. 结果表明, 二氧化钛的表面能与表面缺陷的百分率相关. 完整的表面具有最低的表面能, 表面能随着表面缺陷百分率的增大而升高, 这与自然环境下二氧化钛-金红石(TiO2)具有规整的(110)表面一致. 在光催化实验中利用二氧化钛表面的缺陷作催化剂需要考虑到表面的稳定性. 另一方面, 在完整的表面五配位Ti4+上填加氧原子与表面作用时, 表面能起初变化很小, 直到50%的五配位Ti4+被填充后表面能才开始升高.     

Structure and coordination of organometallic groups on a chemically modified SiO2 surface

The structural, electronic, and energy parameters of the metal-containing clusters (H₃SiO)₃Si−O−XMe _n (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.     

SO2-4/SiO2表面酸性的红外光谱和密度泛函理论研究

对介孔SiO2及硫酸根促进的SiO2样品进行了原位吡啶吸附红外光谱测试,分别建立了硫酸根促进前后的SiO2表面原子簇模型,用密度泛函理论对其吡啶吸附行为进行了计算,分析了SO2-4/SiO2表面酸性产生的机理. 实验和计算结果表明, SO2-4/SiO2表面不存在Lewis酸中心,原位红外谱图中表征Lewis酸性的特征峰对应于氢键吸附吡啶的环振动,这种氢键作用因SiO2表面的硫酸根促进而得到加强. HSO-4螯合结构为SO2-4/SiO2表面Br(φ)nsted酸中心,其酸强度强于表面磺酸基团修饰的介孔SiO2材料SO3H-MSU, 而弱于HZSM-5. SO2-4/SiO2的酸催化活性源于其表面的Br(φ)nsted酸性.     

Characterization of an Algerian diatomite by inverse gas chromatography: Specific and non-specific contribution and Lewis acid–base parameters

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.     

BH+2与C2H2反应势能面的量子化学研究

用B3LYP/6-311G(d,p) 密度泛函方法和高级电子相关的CCSD(T)/6-311G(2df,p)偶合簇法研究BH+2与C2H2反应势能面. 结果表明 该势能面上存在(a) H2B+*C2H2, (b) HBCHCH2+, (c) H2BCCH+2和(d) H2*BHCCH+四种异构体, 其中(b)能量最低且在动力学上最稳定, (a), (c)和(d)在动力学上均不稳定; BH+2通过对C2H2的分步亲电加成以及随后的氢迁移和H2消除等反应形成离解产物HBCCH++H2, 该反应不需要活化能且大量放热. 计算结果有助于深入了解BH+2等缺电子硼氢正离子的反应行为.     

SO2基态势能面和振转能级的理论研究

在键长-键角坐标下,精确求解SO₂的核振动方程,并通过与实验数据比较来优化势能参数,由所得势能面计算得到38个振动能级,与实验值相比,均方根误差为0.93cm^-1.计算了³⁴SO₂的部分振动能级以及³²SO₂的J=6以下的部分振动能级,所得结果均与实验值较为吻合