Preparation and characterization of thermoresponsive poly(N-isopropylacrylamide-co-N-isopropylmethacrylamide) hydrogel materials for smart windows

In this study, a series of thermoresponsive cross-linked copolymer poly [N-isopropylacrylamide(NIPAm)-co-N-isopropylmethacrylamide(NIPMAm)] (P-M series samples: P-M-0, 10, 20, 30, 40, where numbers are co-monomer contents) hydrogels were prepared by free radical polymerization using the main monomer N-isopropylacrylamide (NIPAm), co-monomer N-isopropylmethacrylamide (NIPMAm), cross-linking agent N, N-methylenebisacrylamide, initiator (ammonium persulfate)/catalyst, and solvent water. In addition, a series of samples [P-G series samples: P-G-0, 10, 20, 30, 40, where numbers are co-solvent glycerol content) were prepared using P-M-40 as components and water/co-solvent glycerol as a mixed solvent. The effects of co-monomer NIPMAm and co-solvent glycerol contents on the lower critical solution temperature (LCST)/freezing temperature and light transmittance as function of temperature of the prepared copolymer gels were investigated. The resulting thermoresponsive polymer gels had LCSTs in the range of 17.9 to 38.7°C and freezing points in the range of 6.3 to −38.5°C. These gels are suitable materials for smart windows that are responsive to various environmental conditions.     

Tuning of Fe catalysts for growth of spin-capable carbon nanotubes

Growing spin-capable multi-walled carbon nanotube (MWCNT) forests in a repeatable fashion will become possible through understanding the critical factors affecting the forest growth. Here we show that the spinning capability depends on the alignment of adjacent MWCNTs in the forest which in turn results from the synergistic combination of a high areal density of MWCNTs and short distance between the MWCNTs. This can be realized by starting with both the proper Fe nanoparticle size and density which strongly depend on the sheet resistance of the catalyst film. We prove that a simple measurement of the sheet resistance can allow one to reliably predict the growth of spin-capable forests. Further investigation into the properties of pulled MWCNTs sheets demonstrated the relationship between their electrical resistance and optical transmittance. Overlaying either 3, 5, or 10 sheets pulled out from a single forest produces much more repeatable characteristics.     

Reliability analysis and comparison of several structures

In this study, we consider the redundant structure with the function of swithover processing which is assumed to cause the increase of the failure rate of the system. A single component system and a simple redundant system are compared in terms of the four reliability measures such as the reliability function, the MTBF, the failure rate and the mean residual life (MRL). We find the relations of the MTBF, the failure rate, and the MRL between two systems. We also consider a quad configuration system and a parallel string configuration system and evaluate the four reliability measures for two systems. As a numerical example, the total system down of an ATM switching system is considered.     

Battery performance of PMMA-grafted PE separators prepared by pre-irradiation grafting technique

Poly(methyl methacrylate)-grafted polyethylene (PE-g-PMMA) separators were prepared by pre-irradiation grafting technique of methyl methacrylate onto a commercial polyethylene separator. The prepared separators were characterized by using charge/discharge (C/D) cycling test, AC impedance, and thermal stability analyses. Thermal shrinkage (TS) of the PE-g-PMMA separators decreased with an increasing degree of grafting up to 70% above which it was saturated. The PE-g-PMMA separators showed a better oxidation stability on the anode up to 5 V and a better cycle life performance than the original PE separator. These characteristics make the prepared separators suitable for applications in high voltage secondary lithium batteries.     

Curing Behaviors of UV-Curable Temporary Adhesives for a 3D Multichip Package Process

Temporary bonding adhesives for a three-dimensional (3D) multichip package process have been synthesized. To enhance the thermal stability, the adhesives used a fluorinated silicon urethane acrylic binder and ultraviolet (UV) curing for crosslinked network structures. Focusing on different photoinitiator contents and UV doses, the UV-curing behaviors and thermal stability were studied using Fourier-transform infrared spectroscopy attenuated total reflectance, gel fraction, swelling ratio, shrinkage, and thermogravimetric analyses.     

Annealing-induced enhancement of ferromagnetism in SnO2-core/Cu-shell coaxial nanowires

In this study, we have coated tin oxide (SnO₂) nanowires with a Cu shell layer via the sputtering method and subsequently investigated the effects of thermal annealing. The annealing-induced changes in morphologies, microstructures, and compositions of the resulting core-shell nanowires were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and energydispersive X-ray spectroscopy (EDX). The Cu shell layers were agglomerated to form clusters, which were mainly comprised of the Cu₂O phase. For the first time, a hysteresis loop indicating weak ferromagnetism was observed from the pure SnO₂ nanowires. Both the coercivity and the retentivity in the hysteresis loop were slightly increased by Cu-sputtering, indicating a very slight enhancement of ferromagnetism. Also, the ferromagnetic behavior was significantly enhanced by thermal annealing. We discuss the possible mechanisms of annealing-induced enhancement of ferromagnetism in the SiO₂/Cu core-shell nanowires, which include the generation of Cu₂O phase, Cu-doping into the SnO₂ lattice, and the generation of oxygen vacancies in SnO₂ core nanowires.     

Trend change in mean residual life

The authors consider a life distribution which shows a trend change in its mean residual life (MRL). The problem of testing such a trend change has been of great interest in reliability analysis. The authors propose a new procedure for testing the exponentiality against IDMRL or DMIRL, assuming that the proportion of the population, p, that dies at or before the change point of MRL is known. Their test provides a new competitor to the known test procedures, such as the Guess, Hollander, Proschan test and the Aly test. Based on the empirical powers of these tests against lognormal alternatives, their test outperforms the others for most sample sizes and most values of p and that all three tests achieve high power in detecting the trend change of MRL when p is very small and very large     

Isolation and identification of cinnamic acid amides as antioxidants from Allium fistulosum L. and their free radical scavenging activity

Four compounds obtained from the ethyl acetate-soluble neutral fraction of methanol extracts of the Welsh onion (Allium fistulosum L.) were purified by column chromatography using silica gel, octadecyl silane (ODS), and Sephadex LH-20 with a guided DPPH radical scavenging assay. After purification, the compounds were isolated by ODS-HPLC. The isolated compounds were identified as N-trans-feruloyl-3′-methoxytyramine (1), N-cis-feruloyl-3′-methoxytyramine (2), N-trans-p-coumaroyltyramine (3), and 3,5,7-trihydroxyflavone (kaempferol, 4) based on the spectroscopic data of NMR and MS. To the best of our knowledge, this is the first study to identify compound 1–3 in the Welsh onion. Compound 1 and 2 showed significantly (p<0.05) higher DPPH radical scavenging activities than compound 3.     

Effect of the ionic conductivity of a polymer matrix on the electrooptical properties of polymer-dispersed liquid crystal films

Summary The influence of ionic conductivity on the electrooptical response was investigated. A new monomer of 2-(poly(ethylene glycol)oxycarbonyl)-bicyclo[2.2.1] hepta-2,5-diene (PEGOC-BCHD) was synthesized and polymerized. Polymer/liquid crystal composite films are composed of poly(PEGOC-BCHD), E8, and alkali metal salts. The ionic conductivities were measured as a function of the ratio of LiClO₄/ethylene oxide for various molecular weights of poly(ethylene glycol). The results indicate that the threshold field and response rise time can be reduced by increasing ionic conductivity of the matrix polymer. Liquid crystal droplets were observed in a continuous matrix phase in the form of ‘Swiss cheese’ morphology. Received: 13 March 1998/Accepted: 19 May 1998