Variation in surface fractal of graphite due to the adsorption of polyoxyethylene sorbitan monooleate

The fractal analysis is carried out to study the influence of adsorption of polyoxyethylene sorbitan monooleate (Tween 80) on the surface properties of graphite. The surface fractal dimension (d_SF), BET surface area (S_BET) and pore size distribution (PSD) are calculated from low temperature nitrogen adsorption isotherms. The decline in the d_SF of graphite surface is found as the adsorption amount of Tween 80 increases, which suggests that the adsorbed Tween 80 smoothes the graphite surface. Additionally, the observation of atomic force microscopy (AFM) proves that the original slit pores in pure graphite are blocked up and the step defect sites are screened by Tween 80, which may result in the reduction of graphite roughness. The PSD pattern of graphite changes after the adsorption due to the pore blocking effect. S_BET of the graphite decreases as the adsorption amount of Tween 80 increases, which is attributed to both pore blocking effect and surface screening effect.     

（AgI）n团簇熔化行为的分子动力学模拟

用遗传算法结合经验势搜索了 (AgI)n(n=3-15) 团簇的可能稳定结构,并用微正则分子动力学方法研究了它们的熔化行为.(AgI)n 团簇的稳定结构主要以四叫元环和六元环相接的笼状结构为主.大多数(AgI)n会在一个较大的温度范围内随温度升高结构不断扭曲,原子间距涨落及动能涨落不断增大,直到在某个温度下熔化,结构变得完全无序.(AgI)6 的结构具有很高的对称性,熔化发生在一个较窄的温度范围.对于(AgI)5,会在熔化前较大的温度范围内发生最稳定结构与能量较高的环状异构体之间的转化,并可能出现负热容现象.     

吸附聚丙烯酸对纳米碳管表面特征影响的研究

利用低温氮气吸附法系统研究了吸附聚丙烯酸 (PAA)的量对纳米碳管表面特征的影响 .分析结果表明 :当PAA吸附量增加到 2 68 98mg·g-1时 ,纳米碳管的比表面积下降了 46 97% ;虽然吸附PAA后的纳米碳管在 1 8nm以上的孔径分布特征基本上与原样一致 ,但孔容减少 ,这部分孔对比表面的贡献明显降低 ,同时出现 1 8nm以下的孔 ;通过氮气吸附等温线利用热力学方法计算的纳米碳管的表面分维值 (surfacefractaldimension)dSF由原样的 2 5 4下降至吸附后的 2 48,表明吸附PAA分子能够降低纳米碳管的粗糙度 .这些说明堵孔效应和屏蔽效应是纳米碳管表面特征改变的主要因素 ,这一研究对纳米碳管在吸附、催化等方面的应用有着非常重要的意义 .     

(AgI)n团簇熔化行为的分子动力学模拟

用遗传算法结合经验势搜索了(AgI)n(n=3-15)团簇的可能稳定结构, 并用微正则分子动力学方法研究了它们的熔化行为. (AgI)n团簇的稳定结构主要以四元环和六元环相接的笼状结构为主. 大多数(AgI)n会在一个较大的温度范围内随温度升高结构不断扭曲, 原子间距涨落及动能涨落不断增大, 直到在某个温度下熔化, 结构变得完全无序. (AgI)6的结构具有很高的对称性, 熔化发生在一个较窄的温度范围. 对于(AgI)5, 会在熔化前较大的温度范围内发生最稳定结构与能量较高的环状异构体之间的转化, 并可能出现负热容现象.