Nucleation of Polypropylene with Gold Nanoparticles. Part 1: Introduction of Sandwich Method for Evaluation of Very Weak Nucleation Activity

Although gold particles are known to nucleate isotactic polypropylene (PP), the nucleating effect of chemically pure 5 nm Au, prepared in vacuum sputter coater, was found to be hardly observable. In order to detect such a weak effect, we deposited a homogeneous layer of Au nanoparticles between thin PP films and evaluated the nucleation activity by a combination of three independent methods: polarized light microscopy (PLM), differential scanning calorimetry (DSC), and 2D wide-angle X-ray scattering (2D-WAXS). This new technique, which was called sandwich method, allowed us to demonstrate that gold nanoparticles were able to nucleate PP crystallization, although the effect was much weaker than that produced by commercial α-nucleant [1,2,3,4-bis(3,4-dimethylbenzylidene)sorbitol] and β-nucleant (N,N-Dicyclohexyl-2,6-naphthalene dicarboxamide). The sandwich method appeared to be quite universal and applicable for any micro-sized nucleants or nanonucleants.     

Crystallization Morphology and Behavior of Polypropylene Composites Containing Microencapsulated Flame Retardant

With shells of melamine-formaldehyde (MF), urea-melamine-formaldehyde (UMF), or poly(vinyl alcohol)-melamine-formaldehyde (VMF), microencapsulated ammonium polyphosphate (APP) was prepared by in-situ polymerization for use as a flame retardant in polypropylene (PP). Microencapsulated APP showed rougher surface, smaller size, and narrower size distribution compared with APP. The results of polarized optical microscopy (POM) showed that the additives resulted in a decrease of the spherulite size and less perfection in crystal geometry of PP composites. Due to the interaction and alignment of the PP polymer chains at the surface, the surface modification of APP influenced the formation and further development of PP crystals remarkably. The crystallization and melting behaviors of the PP composites were affected by the rough surface of the microencapsulated APP, which was helpful for the formation of β-crystals and decreased the crystal growth rate compared with APP.     

The Crystallization and Morphology of Isotactic Polypropylene Nucleated by Magnesium Sulfate Whiskers Surface Modified by Pimelic Acid

Pimelic acid (PA) was used to modify the surface of magnesium sulfate whiskers (M-HOS). The treated M-HOS and its effects as a function of concentration on the crystallization and morphology of isotactic polypropylene (iPP) were investigated. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), thermogravimetic analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) revealed that PA reacted with M-HOS and formed magnesium pimelate on the surface after the reaction. The results of differential scanning calorimetry (DSC) and polarized light microscopy (PLM) showed that the treated M-HOS had the ability to induce β-spherulites, increase the crystallization temperature and decrease the size of spherulites in iPP. It was the most effective to form β-spherulites when the content of PA treated M-HOS was 5 wt%.     

海胆状金纳米粒子表面形貌对表面增强喇曼散射特性的影响

采用改进的一步还原法合成了多种海胆状金纳米粒子,并对它们的表面增强喇曼散射特性与其表面形貌的关系进行了实验研究.实验表明,合成的海胆状金纳米粒子的直径及表面的尖刺大小可以通过改变加入到氯金酸溶液中的硝酸银的量来调节.当加入到氯金酸溶液中的硝酸银为1μL时,合成的海胆状金纳米粒子的直径最小而尖刺最长.同时测量的紫外-可见-近红外吸收光谱表明,海胆状金纳米粒子的局域表面等离子体共振带会随着加入到氯金酸溶液中的硝酸银量的增加而变宽.此外,通过喇曼标记分子对巯基苯甲酸(4MBA)的喇曼光谱测量发现,较小直径和较长尖刺的海胆状金纳米粒子具有更强的表面增强喇曼散射活性.     

Biological Production of Gold Nanoparticles at Different Temperatures: Efficiency Assessment

The study aims to compare different approaches and efficacies during the biological production of nanoparticles (NPs). Gold nanoparticles (AuNPs) are produced by Fusarium oxysporum at two different temperatures. One flask is incubated at 37 °C (“Common”) and the other is directly heated for 5 min at 80 °C (“Heat-treated”). Obtained AuNPs are analyzed and compared by spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Graphite furnace atomic absorption spectroscopy (GF-AAS) is used to determine the particle concentration after the AuNPs production. The AuNPs prepared by both (the Common and the Heat-treated) methods exhibit maximum absorption peaks at 541 and 528 nm, respectively, and have round shapes and sizes of less than 50 nm. Their zeta potential is about −28 mV. GF-AAS shows that the efficiency of AuNP production in Common- and Heat-treated samples is equal, between 65% and 68%. Since the Heat-treated sample shows a better size distribution, the use of higher temperature and shorter time period is preferable for the bioproduction of AuNPs. It seems that shortening the time for the production of AuNPs prevents the formation of larger NPs.     

Colloidal Nanoparticles: Formation of Large 2D Arrays of Shape‐Controlled Colloidal Nanoparticles at Variable Interparticle Distances (Part. Part. Syst. Charact. 1/2013)

A method for the production of homogeneous layers of nanoparticles of arbitrary shape is presented. The method relies on a ligand exchange with a functionalized polymer and a subsequent self‐assembly of a thin film on the substrates. The interparticle distances in the layer can be adjusted by the length of the polymer. In the case of spherical particles, the approach yields quasi‐hexagonal structures; in the case of anisotropic particles, the minimum distance between adjacent particles is controlled. Regular arrangements of the nanoparticles covering areas of several square centimeters are achieved.     

Facile Functionalization of Gold Nanoparticles with PLGA Polymer Brushes and Efficient Encapsulation into PLGA Nanoparticles: Toward Spatially Precise Bioimaging of Polymeric Nanoparticles

Nanocarriers prepared from poly(lactide‐co‐glycolide) (PLGA) have broad biomedical applications. Understanding their cellular uptake and distribution requires appropriate visualization in complex biological compartments with high spatial resolution, which cannot be offered by traditional imaging techniques based on fluorescent or radioactive probes. Herein, the encapsulation of gold nanoparticles (GNPs) into PLGA nanoparticles is proposed, which should allow precise spatial visualization in cells using electron microscopy. Available protocols for encapsulating GNPs into polymeric matrices are limited and associated with colloidal instability and low encapsulation efficiency. In this report, the following are described: 1) a facile protocol to functionalize GNPs with PLGA polymer followed by 2) encapsulation of the prepared PLGA‐capped GNPs into PLGA nanocarriers with 100% encapsulation efficiency. The remarkable encapsulation of PLGA‐GNPs into PLGA matrix obeys the general rule in chemistry “like dissolves like” as evident from poor encapsulation of GNPs capped with other polymers. Moreover, it is shown that how the encapsulated gold nanoparticles serve as nanoprobes to visualize PLGA polymeric hosts inside cancer cells at the spatial resolution of the electron microscope. The described methods should be applicable to a wide range of inorganic nanoprobes and provide a new method of labeling pharmaceutical polymeric nanocarriers to understand their biological fate at high spatial resolution.     

Micro and Macro Injection Molded Parts of Isotactic Polypropylene/Polyethylene Blends: Shear-Induced Crystallization Behaviors and Morphological Characteristics

The present study focused on the importance of scale effect (micro- and macro-injection molded parts) and iPP content to the formation of epitaxial crystallization and crystal structure formed in injection-molded bars of high-density polyethylene (HDPE)/isotactic polypropylene (iPP) blends. After making the blends with different iPP content via melt mixing, the injection-molded bars were prepared via both micro and conventional injection molding. Hot stage polarized light microscopy (HS-PLM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were used to investigate their morphological and crystal features. The results indicated that an appropriate matching of micro-part and relative high iPP content was most favorable for epitaxial crystallization. The micro-parts had a large fraction of shear layer in comparison with macro-parts. The SEM observations showed that the shear layer of the former consisted of a highly oriented shish-kebab structure. The memory effect of the crystalline structure of the micro-parts and macro-parts at high temperature, investigated in detail through HS-PLM experiments, showed that micro-part had a relatively high memory effect of the preceding crystallization process.     

Effect of Spherical Nanoparticles on the Motion of Macromolecular Chains and Segments of Isotactic Polypropylene. I. Dynamic Mechanical and Thermal Properties

The role of spherical nano-CaCO₃ particles treated with 2 wt% and 6 wt% stearic acid (SA), respectively, on the motion of macromolecular chains and segments of isotactic polypropylene (iPP) was studied through the dynamic mechanical analysis and nonisothermal crystallization. Higher nucleation activity of the particles and more nucleating sites were achieved in the 6 wt% SA treated particle nanocomposites with respect to the 2 wt% SA counterpart. The increased nucleation efficiency caused high inhomogeneity and thus large mobility of the amorphous phase of iPP, which favored a low glass transition temperature (T_g ) in the nanocomposites. However, the spherical nanoparicles also spatially restrained the motion of macromolecular chains and segments, and the better the nanoparticles dispersed, the stronger the restriction was. Thus the glass transition temperature (T_g ) of the nanocomposites decreased with increasing filler loading but recovered at a certain particle concentration. At this filler content, the maximal α-transition temperature (T_α ) and the main melting peak temperature (T_m1 ) as well as the lowest degree of crystallinity (X_PP ) also occurred. This critical filler loading appeared at lower value (20 wt%) in 6 wt% SA treated nano-CaCO₃ composites with respect to 2 wt% SA counterpart (25%) due to the better dispersion of particles in the former. It was concluded that the mobility of the macromolecular chains and segments of iPP was dominated by the competition of the spatial confinement and nucleation effect of nano-CaCO₃ particles in the matrix.     

金-二氧化钛（Au-TiO_2）复合薄膜的制备及局域表面等离子体共振（LSPR）效应

利用溶胶凝胶法在玻璃衬底上制备了金-二氧化钛（Au-TiO2）复合纳米薄膜,研究了热处理温度对复合薄膜表面纳米颗粒沉积的影响。利用原子力显微镜对样品进行了形貌表征,结果显示：复合薄膜是由纳米微晶组成的致密膜,温度越高越有利于Au粒子的形成。在550℃的热处理温度下,薄膜表面沉积的纳米微晶的粒径约为100nm。利用紫外-可见分光光度计测量了反射谱线,结果表明：由于局域表面等离子体共振（LSPR）的产生,在不同的热处理温度下,第一个反射峰（短波长处）不发生变化,第二个反射峰（长波长处）发生漂移（红移）。     

非晶一次晶化过程微观组织演化和生长动力学的相场法研究

在晶化物理模型中添加扩散系数对晶化过程的影响, 采用相场方法研究初始形核率和初始形核半径对一次晶化过程中微观组织和生长动力学的影响。结果表明: 随着初始形核率的增加, 相同时间内非晶一次晶化的晶粒数量逐渐增加, 晶粒尺寸逐渐减小。晶化分数随着演化时间和初始形核率的增加逐渐增大, 初始形核率越大, 相同演化时间内的晶化分数越高。不同初始形核半径情况下, 非晶一次晶化过程中的晶粒数量和尺寸随着演化时间的增加基本保持不变。晶化分数随着演化时间的增加而增大。不同初始形核率和初始形核半径情况下所对应的生长指数均小于1, 表明初始形核率和初始形核半径对晶化方式无影响, 均为一次晶化。改变初始形核率和初始形核半径可调控一次晶化微观组织结构, 而晶粒尺寸及晶化分数直接关系到合金性能。     

Comparing the Contribution of Visible‐Light Irradiation,Gold Nanoparticles,and Titania Supports in Photocatalytic Nitroaromatic Coupling and Aromatic Alcohol Oxidation

Under visible‐light irradiation, gold nanoparticles (Au NPs) supported by titania (TiO₂) nanofibers show excellent activity and high selectivity for both reductive coupling of nitroaromatics to corresponding azobenzene or azoxylbenzene and selective oxidation of aromatic alcohols to corresponding aldehydes. The Au NPs act as active centers mainly due to their localized surface plasmon resonance (LSPR) effect. They can effectively couple the photonic energy and thermal energy to enhance reaction efficiency. Visible‐light irradiation has more influence on the reduction than on the oxidation, lowering the activation energy by 24.7 kJ mol^?1 and increasing the conversion rate by 88% for the reductive coupling, compared to merely 8.7 kJ mol^?1 and 46% for the oxidation. Furthermore, it is found that the conversion of nitroaromatics significantly depends on the particle size and specific surface area of supported Au NPs; and the catalyst on TiO₂(B) support outperforms that on anatase phase with preferable ability to activate oxygen. In contrast, for the selective oxidation, the effect of surface area is less prominent and Au NPs on anatase exhibit higher photo‐catalytic activity than other TiO₂ phases. The catalysts can be recovered efficiently because the Au NPs stably attach to TiO₂ supports by forming a well‐matched coherent interface observed via high‐resolution TEM.