Characterization of the morphology and hydrophilicity of chitosan/caffeic acid hybrid scaffolds

The morphology and affinity of a scaffold influence the attachment of cells to its surfaces. In this study, the morphology and hydrophilicity of chitosan/caffeic acid hybrid scaffolds were investigated. Grafting caffeic acid onto chitosan hybrid scaffolds by using high levels of potassium persulfate produced scaffolds with looser morphology and higher porosity, as indicated by scanning electron microscopy (SEM) and porosity analysis. SEM analysis showed that the prepared scaffolds had a macroporous morphology with interconnected pores. Differential scanning calorimetry (DSC) revealed that the scaffolds’ hydrophilicity decreased after caffeic acid grafting. The scaffolds were cultured with human osteosarcoma UMR-106 cells, but SEM analysis showed that cell attachment was poor. However, calcification of the scaffolds promoted the attachment of UMR-106 cells onto the scaffold. This study shows that calcified chitosan/caffeic acid hybrid scaffolds could be suitable for use in hard-tissue engineering.     

A novel and rapid fabrication for microlens arrays using microinjection molding

This work reports a novel and effective procedure for manufacturing the mold insert of microlens arrays. First, the microlens arrays master is formed using room‐temperature imprint lithography and photoresist reflow process. Next, electroforming is carried out to fabriccate the metal mold insert from the master. Finally, microinjection molding is used to replicate the molded microlens arrays. The 200 × 200 arrays of molded microlens, with a diameter of 150 μm, a pitch of 200 μm, and a sag height of 11.29 μm for polycarbonate (PC) material and 11.24 μm for polymethylmethacrylate (PMMA) material have been successfully fabricated. The moldability for PMMA material is better than PC material on molded microlens arrays. The average surface roughness of the molded microlens arrays is 4.53 nm for PMMA material and 4.81 nm for PC material. The mold temperature is the most important processing factor for the focal length and sag height of molded microlens arrays. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Coupled nanowire-based hybrid plasmonic nanocavities on thin substrates

We theoretically analyze nanowire-based hybrid plasmonic nanocavities on thin substrates at visible wavelengths. In the presence of thin suspended substrates, the hybrid plasmonic modes, formed by the coupling between a metal nanowire and a dielectric nanowire with optical gain, exhibit negligible substrate-mediated characteristics and overlap better with the gain region. Consequently, the confinement factor of the guided hybrid modes is enhanced by more than 42%. However, the presence of significant mirror loss remains the main challenge to lasing. By adding silver coatings with a sufficient thickness range on the two end facets, we show that the reflectivity is substantially enhanced to above 50%. For a coating thickness of 50 nm and cavity length of about 4 μm, the quality factor is above 100.     

Model Experiment on Thermodynamic Stability of Retained Intergranular Amorphous Films

To test the stability of intergranular amorphous films against crystallization, a model experiment was conducted wherein a thin SiO2 film was deposited on a single-crystal TiO₂ substrate, annealed to form a eutectic liquid in equilibrium with the substrate, then quenched and crystallized below the eutectic temperature. This geometry is free of residual stresses and capillary effects proposed by others as kinetic limitations to complete crystallization. Furthermore, using a binary system removes solute rejection barriers to complete crystallization. A remnant amorphous film ∼1.5 nm thick retained at the hetero-interface shows unequivocally that the amorphous film is thermodynamically preferred to a crystal/crystal interface in this system.     

Epitaxial nucleation model for chiral-selective growth of single-walled carbon nanotubes on bimetallic catalyst surfaces

An epitaxial nucleation model for single-walled carbon nanotube (SWCNT) growth on bimetallic catalysts surfaces is reported in support of experimental observations of chiral enrichment. We model the bimetallic catalyst surfaces as a 2D (1 1 1) surface consisting of Ni or a combination of Ni and Fe atoms, with varying average bond length between nearest neighbor atoms which corresponds to the crystal structure of the alloys. The energies associated with nanotube cap formation on these various surfaces are calculated using density functional theory (DFT). We find that certain cap chiralities, such as (8, 4), are more stably bound to a surface that resembles a Ni_0.27Fe_0.73 bimetallic catalyst, whereas other chiralities, such as (9, 4), are more stable on a pure Ni surface. These results help explain the predominance of certain chiralities on specific bimetallic catalysts and provide a potential route to controlling the chirality of as-grown SWCNTs.     

Enhancement of intrinsic emission from ultrathin ZnO films using Si nanopillar template

Highly efficient room-temperature ultraviolet (UV) luminescence is obtained in heterostructures consisting of 10-nm-thick ultrathin ZnO films grown on Si nanopillars fabricated using self-assembled silver nanoislands as a natural metal nanomask during a subsequent dry etching process. Atomic layer deposition was applied for depositing the ZnO films on the Si nanopillars under an ambient temperature of 200°C. Based on measurements of photoluminescence (PL), an intensive UV emission corresponding to free-exciton recombination (approximately 3.31 eV) was observed with a nearly complete suppression of the defect-associated, broad-range visible emission peak. As compared to the ZnO/Si substrate, the almost five-times-of-magnitude enhancement in the intensity of PL, which peaked around 3.31 eV in the present ultrathin ZnO/Si nanopillars, is presumably attributed to the high surface/volume ratio inherent to the Si nanopillars. This allowed considerably more amount of ZnO material to be grown on the template and led to markedly more efficient intrinsic emission.     

Synthesis and characterization of novel copolymers with the trimethylsilyl group for deep‐UV photoresists

N‐(4‐Acetoxyphenyl) maleimide (APMI) and three kinds of comonomers bearing a trimethylsilyl group were copolymerized at 60°C in the presence of azobisisobutyronitrile (AIBN) as an initiator in 1,4‐dioxane to obtain the three IP, IIP, and IIIP copolymers. These copolymers were removed from the acetoxy group in a transesterification process into new IVP, VP, and VIP copolymers with a pendant hydroxyl group. Two modified processes were adopted to prepare photoresists using these copolymers. The first process involved mixing the dissolution inhibitor, o‐nitrobenzyl cholate, with the new copolymers. Second, o‐nitrobenzyl cholate was introduced into the copolymers using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in dimethylformamide (DMF). The cyclic maleimide structure is responsible for the high thermal stability of these copolymers. After irradiation using deep–UV light and development with aqueous Na₂CO₃ (0.01 wt %), the developed patterns showed positive images and exhibited good adhesion to the silicon wafer without using any adhesion promoter. The resolution of these resists was at least 0.8 μm and an oxygen‐plasma etching rate was 1/5.3 to that of hard‐baked HPR‐204. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2791–2798, 2002; DOI 10.1002/app.10255     

Insolubilization of sodium chondroitin sulfate by forming a semi‐interpenetrating polymer network with acrylic acid: A potential carrier for colon‐specific drug delivery

To reduce the highly hydrophilic property of chondroitin sulfate (ChS), a semi‐interpenetrating polymer network (semi‐IPN) of chondroitin sulfate/polyacrylic acid (PAA) was prepared as a drug carrier by crosslinking acrylic acid with diethyleneglycol diacrylate. The swelling properties of the semi‐IPNs with different concentrations of crosslinking agent were correlated. The moisture sorption profiles were evaluated using differential thermal analysis. Ketoprofen was used as a drug probe to evaluate the performance of the drug released from the semi‐IPN matrices. The prepared semi‐IPNs demonstrated significant swelling reduction properties with both gastric and intestinal fluids compared with those of both the pure ChS and the ChSAA blend without the crosslinking agent. The amount of accumulated drug released from the semi‐IPNs was less than 30 wt % at pH 1.2 and up to 80 wt % at pH 7.4. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 114–122, 2002     

MONITORING THE HYDROGEN RELEASE FROM COAL LIQUID SOLVENTS USING A HYDROGEN PROBE

A hydrogen probe made of nickel tubing has been used to monitor the release of hydrogen from coal liquid solvents at elevated temperatures and pressures. A knowledge of this release rate is helpful in determining the overall hydrogen balance for coal liquefaction operations, in choosing among alternative solvents and in evaluating the validity of model compounds. The hydrogen release was found for coal liquids to reach a constant value when the reactor temperature was steady. In the case of some model compounds the amount of hydrogen released continued to increase and equilibrium was not attained during a 10 hours measurement period. For the coal liquids the total pressure of the system was found to increase sharply with time indicating the production of gases other than hydrogen, while for the model compounds the total pressure increases were almost parallel to the increases of the hydrogen partial pressure. A correlation was developed for the percentage of hydrogen released with the aromatic fraction distribution in the coal liquids. The hydrogen probe was a valuable instrument for continuously following the hydrogen changes in these dehydrogenation experiments.