Optical control of layered nanomaterial generation by pulsed-laser ablation in liquids

ABSTRACT

Pulsed-laser ablation in liquids capitalizes on combining chemical and optical control to rapidly generate size, composition, and phase-controlled nanostructures, without the need for surfactants. Very high temperatures, which we determined to be ca. (8,400?±?1,300) K, pressures, and ion densities exist in the laser-induced liquid-confined plasma. These unique conditions, coupled with the rapid cooling during which nanoparticles are formed, permitted access to new extreme regions of materials’ phase diagrams. This way, we produced metastable layered copper and zinc hydroxide-based nanocrystals with interesting physical properties that can serve as precursors for two-dimensional inorganic semiconductor nanomaterials.     

纳米甘薯渣纤维素对糖尿病大鼠血糖及血脂水平的影响

目的：探讨纳米甘薯渣纤维素对糖尿病大鼠血糖及血脂的影响。方法：选用40 只雄性Sprague-Dawley（SD）大鼠随机分组为5 组,其中1 组大鼠喂食基础饲料作为空白组,另外4 组采用链脲佐菌素（streptozotocin,STZ）诱导大鼠建立糖尿病模型,分为模型对照组（MC组）、普通甘薯渣纤维素组（OC组）、微晶甘薯渣纤维素组（MCC组）和纳米甘薯渣纤维素组（CNC组）,实验期28 d,测定大鼠体质量、采食量、空腹血糖、糖化血清蛋白、血清胰岛素、肝糖原及血脂水平等指标。结果：模型对照组大鼠的采食量,空腹血糖、糖化血清蛋白、血脂水平均显著高于空白组（P＜0.05）,体质量、胰岛素和肝糖原含量明显下降（P＜0.05）,说明造模成功,糖尿病大鼠表现出相应的症状。喂食不同粒度甘薯渣纤维素的糖尿病大鼠,其体质量、血清胰岛素和肝糖原水平有所增加,而空腹血糖、糖化血清蛋白、血脂水平等都有所下降,其中喂食纳米甘薯纤维素的糖尿病大鼠指标变化具有显著性差异（P＜0.05）。结论：从甘薯渣纤维素粒度分析,可以看出随着甘薯渣纤维素粒度的减小,其对糖尿病大鼠血糖血脂的调节作用愈加明显,其中纳米甘薯渣纤维素具有较好的调节血糖血脂水平的作用。     

Theoretical Simulation of AlN Nanobelts and Nanorings

An extension of our previously reported periodic cluster model (J. Phys. Chem. C 2008, 112, 6667-6676 ) to nanorings and nanobelts is presented. This new scheme allows for accurately calculating reasonably large nanostructures while preserving a very small number of optimization parameters. The model has been applied to a number of AlN semiconducting structures using ab initio pair potentials. Attention has been paid to the variation of the B1-B4 phase transition pressure as the the size of the structures is varied.     

丝素蛋白含量对纳米羟基磷灰石仿生矿化和体外细胞相容性的影响

通过制备含有不同丝素蛋白(SF)含量的丝素蛋白/纳米羟基磷灰石复合材料, 着重研究丝素蛋白含量对纳米羟基磷灰石(n-HA)仿生矿化过程中晶体成核与生长及体外细胞相容性的影响. 结果表明: SF的加入对n-HA晶体的成核和生长具有明显的调控作用; 丝素含量的大小对n-HA晶体成核和生长没有明显的区别, 但对晶粒在有机大分子中的聚集状态有明显的影响: 当SF含量不超过20wt%时, n-HA晶粒呈现放射状团簇, 当SF含量超过20wt%时, n-HA晶粒无序团聚. 体外细胞相容性结果显示, SF的加入可以促进材料与细胞的界面亲和性, 但SF含量对这种亲和性的影响不明显, 20wt%和30wt%的SF含量对增殖能力具有较强的促进作用.     

Preparation and properties of starch nanocrystals/carboxymethyl chitosan nanocomposite films

Waxy maize starch was hydrolyzed with sulfuric acid in aqueous solution. The remaining starch granules after acid hydrolysis were characterized by TEM and wide‐angle XRD. Starch nanocrystals with size between 40 to 80 nm and relative crystallinity of 63% were obtained after 6 days of hydrolysis. Starch nanocrystals/carboxymethyl chitosan composite films were prepared by casting‐evaporation method. When the starch nanocrystals content was below 30 wt%, the filler dispersed uniformly in the carboxymethyl chitosan matrix, whereas aggregation of starch nanocrystals and phase separation between aggregates and matrix were observed when the starch nanocrystals content was higher than 30 wt%. The maximum tensile strength (TS) of composite films approached ∼29 MPa, which was two times higher than that of the carboxymethyl chitosan film without filling starch nanocrystals. The percentage elongation at break (EB%) of nanocomposite films decreased with the increasing of the starch nanocrystals content. The water absorption and water vapor barrier property of carboxymethyl chitosan film were significantly improved by adding starch nanocrystals.     

Oil-in-water emulsions stabilized by chitin nanocrystal particles

The aim of the present study was to investigate the oil-in-water emulsion stabilizing ability of chitin nanocrystals (colloidal rod-like particles) and the factors that may influence the properties of such systems. Chitin nanocrystal aqueous dispersions were prepared by acid hydrolysis of crude chitin from crab shells and oil-in-water emulsions were generated by homogenizing appropriate quantities of a chitin nanocrystal stock aqueous dispersion with corn oil, using an ultra-sonic homogenizer. The resulting emulsions were visually evaluated for their creaming behaviour upon storage. Additionally, the samples were studied with static light scattering, small deformation oscillatory rheometry and optical microscopy, under different conditions of nanocrystal concentration, ionic strength, pH and temperature. The chitin nanocrystals were proven quite effective in stabilizing o/w emulsions against coalescence, over a period of one month, as evidenced by static light experiments and microscopy, and this could be attributed to the adsorption of the nanocrystals at the oil–water interface. The rheological data provided evidence for network formation in the emulsions with increasing chitin nanocrystal concentration. Such a gel-like behaviour was attributed to an inter-droplet network structure and the formation of a chitin nanocrystal network in the continuous phase. The stability of the emulsions to creaming increased with an increase in nanocrystal concentration. Finally, by raising the temperature (20–74 °C), NaCl concentration (up to 200 mM) or pH (from 3.0 to 6.7) there was an enhancement of the emulsion elastic character and creaming stability.     

Mixed aqueous chitin nanocrystal–whey protein dispersions: Microstructure and rheological behaviour

Chitin nanocrystals (ChN) and whey protein isolate (WPI) aqueous dispersions (at pH 3.0) of different polymer concentrations were mixed and examined with small deformation oscillatory measurements and polarized optical microscopy, under different conditions of ionic strength and temperature. The ChN–WPI mixed dispersions displayed a gel-like behaviour with increasing either the ChN or the WPI concentration. The network formation could be attributed to phase separation phenomena, as evidenced by the micrographs obtained, due to thermodynamic incompatibility between the two components; i.e. the addition of WPI, as a globular biopolymer mixture, in a dispersion of rod-like particles (ChN) leads to the formation of ChN-rich and ChN-poor domains. Increasing ionic strength did not significantly affect the viscoelastic properties of the network. However, heating of the ChN–WPI mixed dispersions resulted in further increase of the elastic modulus, which was irreversible upon cooling.     

表面修饰CdTe量子点的合成及其光学特性

在水相中合成高发光性能的CdTe量子点,研究以巯基乙酸(TGA)为稳定剂对CdTe表面进行修饰,制备在水中分散性良好的纳米晶,通过对CdTe量子点合成反应条件的摸索,掌握了其合成的反应规律.同时用紫外分光光度计、荧光分光光度计和透射电子显微镜对其进行了表征.结果表明,回流时间、n(Cd2+):n(HTe-)、反应物浓度、TGA用量、反应体系pH值,对纳米晶的光学性质具有显著影响.回流2 h制得的CdTe纳米粒子直径约为5 nm,其发射峰窄且对称,表现出良好稳定的光学性质.     

Stabilization of PbS Nanocrystals by Bovine Serum Albumin in its Native and Denatured States

PbS nanocrystals (NCs) are synthesized in aqueous phase within a temperature range of 40–80 °C in the presence of native and denatured states of bovine serum albumen (BSA) as the capping/stabilizing agent. The NCs are characterized with the help of field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray analysis. At 40 °C, large ball‐shaped NCs (145 ± 37 nm) with small surface protrusions are formed when 1 × 10^?4 g mL^?1 BSA is used. As the reaction temperature is increased towards 80 °C, the size of NCs decreases and they acquire somewhat cubic geometries (49.1 ± 7.0 nm) due to a change in the capping behavior of BSA between its native and denatured states. The native and denatured states of BSA are simultaneously studied by fluorescence spectroscopy using tryptophan emission, and pH measurements with respect to time and temperature. Gel electrophoresis is used to determine the polarity of the BSA capped NCs. Only the small sized NCs conjugated with relatively larger amounts of BSA show a displacement towards the positively charged electrode in comparison to larger NCs with lower amounts of BSA capping. It was concluded that the denatured state of BSA is more effective in controlling the crystal growth of PbS than its native state especially in the low concentration range.     

反应时间对球状及棒状ZnO纳米晶的影响

本实验采用溶液法合成球状及棒状ZnO纳米晶。X射线衍射分析(XRD)显示合成的纳米晶为六方纤锌矿结构ZnO。紫外可见光(UV-vis)光谱和透射电镜(TEM)图表明通过改变反应时间可以控制ZnO纳米棒的长度。随着反应时间从90min延长到360min,纳米棒的长度可以从25nm长大到60nm。同时,纳米晶的室温光致发光谱(PL)具有强烈的近带边发射,在LED和LD等光电器件上有一定的应用前景。