Houbin Li

Impregnation of imidazole functionalized polyhedral oligomeric silsesquioxane in polymer electrolyte membrane for elevated temperature fuel cells

Imidazole functionalized polyhedral oligomeric silsesquioxane (ImPOSS) is synthesized and introduced into a polymer electrolyte membrane for elevated temperature applications. Aggregates of ImPOSS containing 30–40 blocks of POSS cages are observed. The synthesized ImPOSS are well distributed in the hybrid membrane without further aggregation during the membrane formation process. The resulting hybrid membrane exhibits strong Coulombic interaction between sulfonic acid groups on Nafion and imidazole moieties on ImPOSS, leading to increased glass transition temperature and improved thermal stability of the membranes. Under anhydrous conditions, Vogel–Tamman–Fulcher type temperature-dependent proton conductivity is observed, suggesting that structural reorganization of incorporated imidazole moieties dominates the long-range proton transfer in the hybrid membrane. The anhydrous proton conductivity of hybrid membranes containing 35 wt% of ImPOSS reaches 0.0256 S cm−1 at 140 °C. The output voltage of a single cell assembled from the hybrid membrane is observed to be 0.41 V at 600 mA cm−2 under 120 °C and 25% relative humidity using hydrogen and oxygen as reaction gases. The results show the potential applicability of ImPOSS-Nafion hybrid membranes for elevated polymer electrolyte membrane fuel cells.

Waterborne UV-curable polyurethane acrylate/silica nanocomposites for thermochromic coatings

Waterborne UV-curable polyurethane acrylate/silica (PUA/SiO2) nanocomposites were prepared by a sol–gel method. SiO2 nanoparticles were modified by γ-methacryloxypropyltrimethoxysilane (KH-570) and then introduced to the ends of the PUA main chains through radical polymerization. According to the transmission electron microscopy (TEM) results, the size of the PUA/SiO2 nanocomposite particles was approximately 70–100 nm. It was easier to get a uniform emulsion by the sol–gel method than by the physical blending method. Surface tension and contact angle tests both demonstrated the good wettability of the nanocomposites. Besides, the kinetics of the curing process of the PUA/SiO2 films were analyzed by ATR-FTIR and gel content. This revealed that the modified SiO2 could accelerate the curing speed of PUA coatings. Scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) indicated that the nanosilica were well dispersed in the PUA matrix and the soft and hard segments of PUA/SiO2 were well phase mixed. Furthermore, the nanocomposite films displayed enhanced rigidity, hardness, abrasion resistance and good weather resistance. Finally, waterborne UV-curable PUA/SiO2 nanocomposites were applied to thermochromic coatings, showing excellent temperature sensitivity and reversibility.

UV-curable coating crosslinked by a novel hyperbranched polyurethane acrylate with excellent mechanical properties and hardness

A novel hyperbranched polyurethane acrylate (HBPUA), successfully synthesized based on a reaction of hyperbranched polyether (HBP-OH) with toluene diisocyanate (TDI) and hydroxy-ethyl acrylate (HEA), was incorporated into photosensitive polyurethane acrylate (PUA) as crosslinker to prepare a series of high-performance UV-curable coatings. The structure of HBPUA was characterized by Fourier transform infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance (1H NMR). The kinetics of the curing process was monitored using real-time IR. The results indicated that the final double bond conversion was associated with acrylate double bond concentration and the initial viscosity of the curing system. The properties of cured films were investigated by tensile tests, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The hardness, abrasion resistance, adhesion on plastics and transparency of the cured coatings were also tested. The results revealed that tensile strength and storage modulus of the cured film could be improved by 148% and 74%, respectively, by adding HBPUA, and that the hardness of the cured coating could reach 9H. Furthermore, the cured coatings also showed excellent adhesion on PC and PVC sheets, enhanced abrasion resistance and thermal properties as well as outstanding transparency.

Novel Waterborne UV-Curable Hyperbranched Polyurethane Acrylate/Silica with Good Printability and Rheological Properties Applicable to Flexographic Ink

Novel waterborne UV-curable hyperbranched polyurethane acrylate/silica (HBWPUA/SiO2) nanocomposites were prepared by a three-step procedure and sol–gel method. 1H NMR and 13C NMR results indicate that HBWPU is successfully synthesized. Surface tension and contact angle tests both demonstrate the good wettability of the nanocomposites. Besides, the kinetics of photopolymerization of HBWPUA/SiO2 films were analyzed by attenuated total reflection-Fourier transform infrared spectroscopy, which reveals that the modified SiO2 could accelerate the curing speed of HBWPUA coatings. Thermal gravity analysis indicates that the HBWPUA/SiO2 hybrid films have a better thermal stability than the pure HBWPUA cured films. Furthermore, the hybrid films show enhanced pencil hardness, abrasion resistance, and adhesion. On the basis of the above, HBWPUA/SiO2 nanocomposites were finally applied to waterborne UV-curing flexographic printing ink, which is printed on poly(ethylene terephthalate) and glass. The nanocomposite presents good rheological behavior because the ink has a lower Z0, a higher Z∞, and the viscosity rebuild time is 375 s. Three colors (red, yellow, and blue) of ink were used to test its printing quality, the curing time was below 30 s, and the adhesion was excellent without being stripped. All of the inks show good water resistance and abrasion resistance. Moreover, the red and blue inks possess better solid densities than the value of 1.07 of yellow ink, and are 1.83 and 1.84, respectively. The current study suggests that the process has promise in applications of food packages.

Properties and Applications of High Emissivity Composite Films Based on Far-Infrared Ceramic Powder

Polymer matrix composite materials that can emit radiation in the far-infrared region of the spectrum are receiving increasing attention due to their ability to significantly influence biological processes. This study reports on the far-infrared emissivity property of composite films based on far-infrared ceramic powder. X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray powder diffractometry were used to evaluate the physical properties of the ceramic powder. The ceramic powder was found to be rich in aluminum oxide, titanium oxide, and silicon oxide, which demonstrate high far-infrared emissivity. In addition, the micromorphology, mechanical performance, dynamic mechanical properties, and far-infrared emissivity of the composite were analyzed to evaluate their suitability for strawberry storage. The mechanical properties of the far-infrared radiation ceramic (cFIR) composite films were not significantly influenced (p ≥ 0.05) by the addition of the ceramic powder. However, the dynamic mechanical analysis (DMA) properties of the cFIR composite films, including a reduction in damping and shock absorption performance, were significant influenced by the addition of the ceramic powder. Moreover, the cFIR composite films showed high far-infrared emissivity, which has the capability of prolonging the storage life of strawberries. This research demonstrates that cFIR composite films are promising for future applications.

Monitoring of oxygen using colorimetric indicator based on graphene/TiO2 composite with first-order kinetics of methylene blue for modified atmosphere packaging

Oxygen is crucial in food preservation and food spoilage. For the purpose of monitoring intact of modified atmosphere packaging (MAP) by nondestructive testing and controlling the reaction rate during recovery stage, we report a convenient and visual colorimetric oxygen indicator based on a graphene /titanium oxide composite, incorporating glycerol, methylene blue (MB), hydroxyethyl cellulose (HEC) and poly (vinyl alcohol) (PVA). The graphene/titanium oxide (GNT) composite was synthesized through a modified Hummers synthesis of graphene oxide, followed by the hydro-thermal treatment with butyl titanate without using any reducing agent, then the morphology and structure characteristics were analyzed by XRD, FT-IR, Raman spectra, UV-vis, SEM and TEM. According to the performance tests using UV-vis and CIElab, the indicator demonstrated the pseudo first-order kinetics of MB for modified atmosphere packaging in detecting stage. It is confirmed with the results that the prepared colorimetric indicator can actually detect the intact of MAP without destruction. Additionally, the reaction time of indicator in recovery stage can be controlled by changing the concentration of MB, because of pseudo first-order kinetics.

Modification of liquid silicone rubber by octavinyl-polyhedral oligosilsesquioxanes and silicon sol

To develop an efficient and bio-compatible way to improve the thermal and mechanical properties of addition type liquid silicone rubber (LSR), a series of modified LSR samples were prepared by introducing octavinyl-polyhedral oligosilsesquioxanes (VPOSS) and high purity silicon sol singly or in combination before vulcanization. Significant correlation was found between the loading rate of VPOSS and thermal properties. However, mechanical properties were negatively correlated with VPOSS content within the range experimented, which may be ascribed to material defect caused by uneven distribution and aggregation. Furthermore, test results approved that the introducing of silicon sol indeed affected the stabilities of the polymer by restraining the material defect caused by the aggregation of POSS molecules and improving cross link density. For example, adding 10%-20% of silicon sol into VPOSS(1.0%) modified LSR will increase tear resistance by 43.9%-85.7%, elongation at break by 31.7%-57.3%, residue at 800 °C in N2 atmosphere by 32.0%-37.9%, residue at 650 °C in air atmosphere by 70.9%-91.6%, respectively. This work proves that, to incorporate VPOSS into LSR by hydrosilylation, and to use silicon sol as dispersant and reinforce filler can become an efficient way to improve the mechanical property, thermal stability and bio-compatibility of LSR in the future.

Simulation of temperature distribution around media heat spot in heat assisted magnetic recording

The super-fast growth in recording areal density and the correlative decrease of the exterior dimension has been greatly beneficial to the widespread use of hard disk drives (HDDs). In the pursuit of high areal recording density, the heat assisted magnetic recording (HAMR) has been promised to be a new and feasible technology for the next generation of HDDs. In this paper, the temperature distribution around media heat spot in HAMR drive is studied. Firstly, a three-dimensional HAMR drive finite element model consisting of the disk, voice coil motor (VCM), suspension, slider, and filter is built. Then, the flow characteristics and temperature distributions in HAMR drives filled with air and helium are investigated respectively. Finally, the cooling effects of the high speed disk rotation and the heat convection in head-disk interface (HDI) are analyzed and compared.

The Preparation and Characterization of a Compatibilizer: Silicon Dioxide Nanoparticles Grafted with L-Lactic Acid Oligomer

It is found that the blending of inorganic materials and organic materials are usually thermodynamically immiscible with each other. The compatibility between the two blending materials can be enhanced by adding a component which is miscible with both parent materials. Therefore, the as-synthesized silicon dioxide grated by L-lactic acid (OLLA-g-SiO2) was used as a compatibilizer to enhance the compatibility of the PLLA and silicon dioxide (SiO2). In the paper, we prepared OLLA-g-SiO2 by using Tin (II) 2-octanoate Sn(Oct)2 as catalyst. Meanwhile, the surface-grafting reaction was characterized by Fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TG). We also studied the mechanical properties of the composite PLLA/OLLA-g-SiO2/SiO2 films which can be used as package materials. It was found that the tensile strength of PLLA/SiO2 films could still be kept when OLLA-g-SiO2 were introduced, even if there were a large amount of SiO2 nanoparticles (>10 wt%) during blending. So the OLLA-g-SiO2 could be used as a compatibilizer in the films prepared by blending PLLA with SiO2.