Sol–gel concave micro-lens arrays fabricated by combining the replicated PDMS soft mold with UV-cured imprint process

Photosensitive TiO₂/organically modified silane organic–inorganic hybrid thin films were synthesized by combining a low-temperature sol–gel process with a spin-coating method. Optical transmittance properties and the photochemical activities of the planar hybrid films were characterized by UV–Visible spectroscopy and Fourier transform infrared spectroscopy. Advantages for fabrication of the concave micro-lens arrays (MLAs) based on the photosensitive hybrid films were demonstrated by using the replicated polydimethylsiloxane (PDMS) soft mold as the imprint mold and a UV soft imprint technique. Morphological and surface profile properties of the master, the PDMS soft molds and the as-fabricated sol–gel concave MLAs were observed by scanning electron microscopy and laser confocal scanning microscopy. Contact angles of water on the PDMS soft molds baked at different temperatures were studied. Optical imaging properties of the as-fabricated concave MLAs were confirmed by a self-made optical test system. Results indicate that the as-prepared photo-patternable hybrid materials have great applicability for the fabrication of photonic components, thus providing an effective method to fabricate concave MLAs based on the as-synthesized hybrid films by combining the UV-cured imprint technique with the replicated PDMS soft mold, which has advantages of simplicity, cost-effective and mass production and potential application in industry production.     

Melting behavior of isotactic polystyrene revealed by differential scanning calorimetry and transmission electron microscopy

The triple melting behavior and lamellar morphologies of isotactic polystyrene isothermally crystallized from the glassy state have been investigated by differential scanning calorimetry (DSC), temperature-modulated DSC and transmission electron microscopy (TEM). The combination of thermal analysis measurements and morphological observations indicates that: (1) The lowest endothermic peak, the so-called “annealing peak” (T_a), is not associated with the melting of the subsidiary crystals formed by secondary crystallization as often suggested in the literature, but probably with a constrained interphase between the amorphous and crystalline regions; (2) Within spherulites two lamellar populations with different degrees of perfection (or thermal stability) are confirmed by direct TEM observations following partial melting experiments, which are responsible for the so-called double melting peaks (T_m,1 and T_m,2) at higher temperatures observed in DSC curves; (3) The highest endothermic peak (T_m,2) is partially originated from the melting of the recrystallized lamellae formed during heating process in DSC.     

Effect of moisture on the dynamic mechanical relaxation of polyamide-6/clay nanocomposites

This article investigates the effect of moisture on the dynamic mechanical behavior of polyamide-6 (PA6)/clay nanocomposites with dynamic mechanical analysis from −130 to 110 °C. The storage moduli increase with the clay loading for dried and moisture-absorbed samples because of the enhancing effect from the high-aspect-ratio nanoclay. Storage moduli for moisture-exposed samples are lower than those for dried samples; the longer the moisture absorption period is, the lower the moduli are for neat PA6 and PA6/clay nanocomposites. At temperatures below about 10 °C, however, samples exposed to moisture for longer periods tend to be stiffer than dried samples, probably because of the stiffening effect of ice. The peak temperature of the β relaxation shifts from −53 to −65 °C as the moisture content increases. The glass-transition temperature (T_g) or α relaxation dramatically shifts; its position is significantly lowered from 62 to 17 °C as the moisture content increases (longer moisture absorption period) and from 62 to 50 °C as the clay loading increases. The observed depression of the storage modulus and T_g may be attributed to the plasticization effect of moisture absorption. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1823–1830, 2004     

High-Dimensional Mixed Graphical Models

While graphical models for continuous data (Gaussian graphical models) and discrete data (Ising models) have been extensively studied, there is little work on graphical models for datasets with both continuous and discrete variables (mixed data), which are common in many scientific applications. We propose a novel graphical model for mixed data, which is simple enough to be suitable for high-dimensional data, yet flexible enough to represent all possible graph structures. We develop a computationally efficient regression-based algorithm for fitting the model by focusing on the conditional log-likelihood of each variable given the rest. The parameters have a natural group structure, and sparsity in the fitted graph is attained by incorporating a group lasso penalty, approximated by a weighted lasso penalty for computational efficiency. We demonstrate the effectiveness of our method through an extensive simulation study and apply it to a music annotation dataset (CAL500), obtaining a sparse and interpretable graphical model relating the continuous features of the audio signal to binary variables such as genre, emotions, and usage associated with particular songs. While we focus on binary discrete variables for the main presentation, we also show that the proposed methodology can be easily extended to general discrete variables.     

以棓酸为底物的Belousov-Zhabotinskii振荡反应研究

In perfect mixture of CSTR, oscillation behavior of B-Z reaction system with gallic acid as organic substrates have been studied.We have found the regular oscillation curves, the sharp colur changes (purple red to blue) in reaction solution; and oscillation periods keep unchange. The dependence of oscillation behavior upon temperature is investgated. Oscillation behavior only take place in the temperature range 317 KIn this paper, we have also discussed the mechanism of this oscillation reaction. Some special regularity of this system can well be explained by modified FKN mechanism. The theonetical analysis is in accordance with the experiment results.     

反相高效液相色谱测定敦煌壁画胶结材料中氨基酸

用邻苯二甲醛（OPA）柱前衍生，反相高效液相色谱法测定了敦煌壁画中15种氨基酸成份，采用Watersodsc18柱分离，PH=6.5的醋酸钠缓冲溶液和甲醇二元梯度洗脱，荧光检测，24min内15种氨基酸标准样品达到分离，待测样品中氨基酸也有很好的分离效果。     

Synthesis and characterization of highly stable blue‐light‐emitting hyperbranched conjugated polymers

Polyfluorene homopolymer ( P1 ) and its carbazole derivatives ( P2 – P4 ) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography, ¹H NMR, ¹³C NMR, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry, UV–vis absorption, photoluminescence, and cyclic voltammetry (CV). The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties has been investigated. Both carbazole addition and the hyperbranched structure increase the thermal and photoluminescent stability. The CV shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer ( P1 ). The EL devices fabricated by these polymers exhibit pure blue‐light‐emitting with negligible low‐energy emission bands, indicating that the hyperbranched structure has a strong effect on the PLED characteristics. The results imply that incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue‐light‐emitting conjugated polymers, and it is possible to adjust the property of light‐emitting polymers by the amount of carbazole derivative incorporated into the polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 790–802, 2008     

Novel Method to Graft Chitosan on the Surface of Hydroxyapatite Nanoparticles via ＂Click＂ Reaction

In order to tune the surface properties of hydroxyapatite（HA） nanoparticles and prevent them from ag- gregation, an efficient method was proposed to graft chitosan（CS） molecules on the surface of HA via ＂click＂ reac- tion. Thermal gravimetric analysis（TGA） shows that CS was successfully grafted on the surface of HA nanoparticles and the grafting amount was about 8.9 g of CS on per hundred grams of HA. The grafted chitosan chains can prevent HA nanoparticles from aggregation and greatly enhance the colloidal stability of HA in water. The 3-（4,5-dimethylthiazoyl-2-yl）-2,5-diphenyltetrazolium bromide（MTT） assay demonstrats that the cytotoxicity of CS modified HA（HA-CS） is negligible and thus HA-CS may find potential application in biomedical fields.