Tree-gel and loop-gel conversions in nonlinear polymerization

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脉冲激光光声量热装置的研制及用之对香豆素激光染料无辐射跃迁过程的研究

本文报道了一套适用于液相体系的高灵敏度脉冲激光光声量热装置的建立。用此仪器对香豆素激光染料C428, C47和C120的无辐射过程进行了研究, 测得它们在无水乙醇中的无辐射跃迁量子产额分别为0.50, 0.47和0.38。     

气相色谱-质谱法测定油炸淀粉类食品中的丙烯酰胺

 建立了油炸淀粉类食品中丙烯酰胺的溴衍生化气相色谱-质谱(GC-MS)测定方法。样品经水提取、高速离心、石墨化 炭黑柱净化、溴衍生化后,以GC-MS选择离子进行定性,同位素稀释技术定量。该方法的检出限为5 μg/kg,回收率为90％ ～105％,相对标准偏差为6.3％。利用该方法对市场上某些油炸淀粉类食品进行了初步测定,发现薯片和炸薯条中含有27 8~4518 μg/kg的丙烯酰胺。     

Preparation of flame retardant polyamide 6 composite with melamine cyanurate nanoparticles in situ formed in extrusion process

This paper is focused on in situ preparation of melamine cyanurate (MCA) nanoparticles from reaction of melamine (MEL) and cyanuric acid (CA) and their flame retardant polyamide 6 (PA6) composite in the extrusion process through a novel reactive processing method. Fourier transform infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were utilized to characterize the in situ formed MCA nanoparticles and their blends with PA6. Introduction of pentaerythritol (LTP) and water-bound plasticizer dioctyl phthalate (DPT) into the extrusion reaction system greatly inhibits the evaporation of water required for melamine and cyanuric acid reaction at high temperature (higher than 180 °C), laying a foundation for successful in situ preparation of MCA through reactive processing. XRD and FT-IR measurements indicate that under the effect of pentaerythritol, dioctyl phthalate and water, melamine really reacts with cyanuric acid to in situ form MCA in extrusion process. The reaction degree is close to 100%. A very important finding through SEM is that the in situ formed MCA particles, which were found to have aspect ratio of about 7.5, radial size in the range of 70-300 nm (mostly 70-90 nm) and crystallite size of less than 22 nm, are uniformly dispersed in the matrix PA6 at nanoscale. The in situ formed MCA nanoparticles greatly improve the flame retardancy and the mechanical properties of flame-retarded PA6 materials, and the introduced plasticizer dioctyl phthalate also ameliorates the related impact property. The obtained flame-retarded PA6 materials have good comprehensive performance with flame retardancy UL-94 V-0 rating at 1.6 and 3.2 mm thickness, tensile strength 48.0 MPa, elongation at break 106.3% and Izod notched impact strength 8.92 kJ/m². Compared with flame-retarded PA6 material with in situ formed MCA, the one prepared through conventional blending of PA6 with commercial MCA product has improved tensile strength but deteriorated impact strength and flame retardancy.     

表面能与晶体生长/溶解动力学研究的新动向

界面现象使物质在结晶过程中出现了临界现象.但最近的研究指出在物质溶解过程中,在表面能量的控制下也存在着临界现象以及尺寸效应.实验发现,当晶体自身小到一 定的程度时(通常在纳米尺度上并和临界蚀坑的大小相近),在溶解过程中其速度会自发降 低,反应被抑制乃至停止.尽管在热力学上表面能的因素可以赋予小颗粒晶体较大的溶解度 ,但表面能却也能通过对临界条件的控制而使这些微粒在动力学上不被溶解.这个发现不仅 解决了纳米颗粒在水溶液中稳定性的问题,而且还从动力学的角度解释了生物矿物选择纳米 尺度作为其基本构成单元的原因.由于表面能和晶体生长/溶解的动力学有着密切的关系, 我们可以通过对表面能的调节来修改它们的动力学速度和晶体的形貌.反过来,也可以用动力学的方法来测定表面能及表面吸附/脱附常数等.相对于常规的界面研究手段,通过生 长和溶解动力学途径所得的数据有着很好的可靠性及重复性.我们认为,晶体生长和溶解的 动力学和表面能的研究相结合,不仅为界面研究提供了新的思路和方法,而且也会推动晶体生长和材料科学的发展.     

Molecular simulation of water behaviors on crystal faces of hydroxyapatite

The water behavior on (001) and (100) crystal faces of hydroxyapatite (HAP) were studied using molecular dynamics (MD) simulations. The study showed that the water molecules between the HAP faces were under conditions of strong electrical field and high pressure, and hence formed 2–3 well-organized water layers on the crystal surfaces. These structured water layers had ice-like features. Compared with the crystallographic [100] direction of HAP, the polarity along the [001] direction was stronger, which resulted in more structured water layers on the surface. The interaction of water molecules with the calcium and phosphate sites at the HAP-water interface was also studied. The results indicated the multiple pathways of water adsorption onto the HAP surfaces. This study revealed the formation and the detailed structure of water layers on HAP surfaces and suggested that the interfacial water played an important role in stabilizing the HAP particles in aqueous solutions. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(8): 1392–1400 (in Chinese)     

混合价聚十五钒酸盐[V_(15)O_(36)Cl](NH_4)_3Na_7·30H_2O的合成与晶体结构

以XRD法确定制得的标题晶体属空间群D_(3A)~3,a=13.111,c=11.130。结构由帕特逊-极小函数法结合差值法解出,经精修得一致性因子R_w=0.0344。晶胞中坐落在6m2特殊位置上的是包合1个Cl~-的聚十五钒酸根[V_(15)O_(36)Cl]~(10-),配合键价法确认这是四价钒占主导地位的一类特种混合价同多酸根。