氢氧化镁纳米片的合成及其润滑性能的研究

以硫酸镁和氢氧化钠为原料,油酸为表面修饰剂,采用原位合成的方法制备出了疏水性的Mg(OH2)纳米片.研究了反应温度、反应物浓度等因素对氢氧化镁纳米片平均粒径的影响.用X-射线粉末衍射(XRD)、红外(IR)和热重(DTA-TGA)及扫描电子显微镜(SEM),对制备出的Mg(OH)2纳米片的结构和形貌进行了表征,证实制备出的Mg(OH)2纳米片具有良好分散性,纳米片尺度为200～300nm,厚度10nm.摩擦实验证明Mg(OH2)纳米片可以作为润滑油中的添加剂来应用.     

Periodic precipitation of cobalt(II) oxinate in agar gel: factors influencing the flocculation

The influence of concentration, ageing and pH of the gel medium on the periodic precipitation of cobalt oxinate in agar gel is reported. The results are explained on the basis of Shinohara’s revised flocculation theory. The flocculation value (F) increases with increase in the gel concentration whereas it decreases with increase in ageing and pH of the gel. The raise in temperature of the gel increases the solubility of the sparingly soluble substance and hence theF value. The effect of additives on the periodic precipitation of cobalt (II) oxinate is reported.     

Synergistic effects of layered double hydroxide with hyperfine magnesium hydroxide in halogen-free flame retardant EVA/HFMH/LDH nanocomposites

The synergistic effects of layered double hydroxide (LDH) with hyperfine magnesium hydroxide (HFMH) in halogen-free flame retardant ethylene-vinyl acetate (EVA)/HFMH/LDH nanocomposites have been studied by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI), mechanical properties' tests, and dynamic mechanical thermal analysis (DMTA). The XRD results show that the exfoliated EVA/HFMH/LDH can be obtained by controlling the LDH loading. The TEM images give the evidence that the organic-modified LDH (OM-LDH) can act as a disperser and help HFMH particles to disperse homogeneously in the EVA matrix. The TGA data demonstrate that the addition of LDH can raise 5-18 °C thermal degradation temperatures of EVA/HFMH/LDH nanocomposite samples with 5-15 phr OM-LDH compared with that of the control EVA/HFMH sample when 50% weight loss is selected as a point of comparison. The LOI and mechanical tests show that the LDH can act as flame retardant synergist and compatilizer to apparently increase the LOI and elongation at break values of EVA/HFMH/LDH nanocomposites. The DMTA data verify that the T_g value (−10 °C) of the EVA/HFMH/LDH nanocomposite sample with 15 phr LDH is much lower than that (T_g = −2 °C) of the control EVA/HFMH sample without LDH and approximates to the T_g value (−12 °C) of pure EVA, which indicates that the nanocomposites with LDH have more flexibility than that of the EVA/HFMH composites.     

二氧化硅脱除羟基的动力学研究

醇盐水解法制备的纳米二氧化硅粉体中含有大量羟基,结合差热分析,采用Doyle-Ozawa法和Kissinger法研究二氧化硅粉体脱除羟基的动力学,得到反应表观活化能为134.78kJ.mol-1;并采用Coats-Redfern法进行验证,结果为140.22 kJ.mol-1.采用SEM和XRD对样品进行检测,表明非晶态二氧化硅样品颗粒大小没有变化,晶态没有改变.     

Influence of Fe‐MMT on the fire retarding behavior and mechanical property of (ethylene‐vinyl acetate copolymer/magnesium hydroxide) composite

In this work, Fe‐montmorillonite (Fe‐MMT) is synthesized and used as a synergistic agent in ethylene vinyl acetate/magnesium hydroxide (EVA/MH) flame retardant formulations. The synergistic effect of Fe‐MMT with magnesium hydroxide (MH) as the halogen‐free flame retardant for ethylene vinyl acetate (EVA) is studied by thermogravimetric analysis (TGA), limiting the oxygen index (LOI), UL‐94, and cone calorimetry test. Compared with that of Na‐MMT, it indicates that the synergistic effects of Fe‐MMT enhance the LOI value of EVA/MH polymer and improve the thermal stability and reduce the heat release rate (HRR). The structure and morphology of nanocomposites are studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of the EVA composites have also been studied here, indicating that the use of Fe‐MMT reduces the amount of inorganic fillers. MH hence enhances the mechanical properties of the EVA composite while keeping the UL‐94 V‐0 rating. Copyright © 2008 John Wiley & Sons, Ltd.     

NO2^-/NO2体系电子转移的外电场效应和温度效应

用半经典模型研究NO2^-/NO2体系自交换电子转移的反应机理和速率常数, 探讨了外电场对反应过程势能面, 反应能垒及电子转移速率常数的影响, 确定了能垒崩溃的阈值; 讨论了低能垒条件下电子转移反应的速率常数随温度变化的特征。研究表明, 一定方向的外电场能显著降低电子转移反应的活化能垒并提高反应速率常数k, 而对非绝热电子转移反应, 当温度T和活能能垒Ec满足T=2Ec/R时, k取得极大值。     

Hydrophobic nature of sugars as evidenced by their differential affinity for polystyrene gel in aqueous media

Partition coefficients K _av for the partition of sugars between a polystyrene gel and aqueous solvents were determined. The results show that monosaccharides have different affinities for polystyrene. Their K _av values increase markedly in NaCl solution but reduce to nearly the same value in solutions of NaSCN and LiSCN, both highly chaotropic salts. The K _av of maltodextrins increase with their molecular weight. These partition peculiarities are attributed to the hydrophobic nature of sugars presumably due to their CH surface. The order of increasing hydrophobicity based on K _av is: D-galactose < D-glucose < D-mannose < (D-arabinose, D-xylose) < D-ribose. This order is consistent with that based on the free energy change pertaining to the transfer of sugar molecules from water to 1-butanol.     

Influence of the size of the formed cycle on the reactivity of free radicals in cyclization reactions

Numerous experimental data for the cyclization of free radicals C·H₂(CH₂)_nCH=CH₂ cyclo-[(CH₂)_n+1CH(C·H₂)], and C·H₂(CH₂)_nCH=CHR cyclo-[(CH₂)_n+1C·HCHR] were analyzed in the framework of the parabolic model. The activation energy of thermoneutral (H _e = 0) cyclization E _e0 decreases linearly with an increase in the energy of cycle strain E _rsc: E _e0(n) (kJ mol–1) = 85.5 – 0.44E _rsc(n) (n is the number of atoms in the cycle). The activation entropy of cyclization S ^# also depends on the cycle size: the larger the cycle, the lower S ^#. A linear dependence of S ^# on the difference between the entropies of formation S° of cyclic hydrocarbon and the corresponding paraffin was found: S ^# = 1.00[S°(cycle) – S°(C_nH_2n+2)]. The E _e0 values coincide for cyclization reactions with the formation of the six-membered cycle and the bimolecular addition of alkyl radicals to olefins.     

A comparative electrochemical study of diffusion in room temperature ionic liquid solvents versus acetonitrile.

Measurements on the diffusion coefficient of the neutral molecule N,N,N',N'-tetramethyl-para-phenylenediamine and the radical cation and dication generated by its one- and two-electron oxidation, respectively, are reported over the range 298-348 K in both acetonitrile and four room temperature ionic liquids (RTILs). Data were collected using single and double potential step chronoamperometry at a gold disk electrode of micrometer dimension, and analysed via fitting to the appropriate analytical expression or, where necessary, to simulation. The variation of diffusion coefficient with temperature was found to occur in an Arrhenius-type manner for all combinations of solute and solvent. For a given ionic liquid, the diffusional activation energies of each species were not only closely equivalent to each other, but also to the RTIL's activation energy of viscous flow. In acetonitrile supported with 0.1 M tetrabutylammonium perchlorate, the ratio in diffusion coefficients of the radical cation and dication to the neutral molecule were calculated as 0.89 +/- 0.05 and 0.51 +/- 0.03, respectively. In contrast, amongst the ionic liquids the same ratios were determined to be on average 0.53 +/- 0.04 and 0.33 +/- 0.03. The consequences of this dissimilarity are considered in terms of the modelling of voltammetric data gathered within ionic liquid solvents.     

Dechlorination of poly(vinylidene chloride) in NaOH/ethylene glycol as a function of NaOH concentration, temperature, and solvent

The wet dechlorination treatment of poly(vinylidene chloride) (PVDC) was evaluated at atmospheric pressure in a solution of NaOH in ethylene glycol (EG), as a function of NaOH concentration, temperature, and solvent. Hydroxide ion from NaOH was required for dechlorination with EG acting solely as a solvent. The wet treatment exhibited significantly enhanced dechlorination efficiency over traditional thermal techniques, with a reaction efficiency as high as 92.8% in 1.0 M NaOH at 190 °C. Dechlorination reactions of PVDC in both NaOH/EG and NaOH/H₂O were expressed by an apparent first-order reaction. At 190 °C, the apparent rate constant in 1.0 M NaOH/EG was approximately 1.4 times larger than in 1.0 M NaOH/H₂O, with an apparent activation energy of 82.8 kJ mol⁻¹, indicating that the reaction proceeded under chemical control. The degree of dechlorination increased with increasing reaction temperature, favouring the elimination of HCl over the hydroxyl substitution of chloride.     

Influence of media polarity on the rate of activation of “dormant” chains in nitroxide‐mediated radical polymerization

Rate constants of decomposition of “living” polymeric adducts polystyrene (PS)‐TEMPO, poly‐4‐vinylpyridine‐TEMPO, PS‐SG1, and polyacrylic acid‐SG1 in different solvents were determined by the method of a competitive inhibition by means of electron spin resonance. It was found that with the increase in polarity of solvent, the values of constants become higher for all systems studied. This effect opens a new way of activating chains in nitroxide‐mediated radical polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012