Thermoreversible gelation of poly[hexyl isocyanate]: Effect of solvent type

The thermoreversible gelation of poly[hexyl isocyanate] (PHIC), a rather stiff polymer, has been studied in two closely-related solvents of the alcane series, namely heptane and octane. Temperature-concentrations phase diagrams have been established for both systems. The occurrence of polymer-solvent compound is suggested in heptane but not in octane. This conclusion receives further support from neutron diffraction investigations through the use of the isotopic labelling technique. Finally, it is observed that the morphology is also affected by the solvent type although still displaying a fibrillar network structure.     

A new family of lipolytic plant enzymes with members in rice, arabidopsis and maize

We have noted a striking similarity between the sequences of proteins in a novel family of lipases we recently reported [Upton, C. and Buckley, J. T. (1995) Trends Biol. Sci. 20, 178-9] and more than 120 sequences from the database of Expressed Sequence Tags (dbEST) which correspond to at least 30 unique genes from arabidopsis, rice and maize. A cDNA (Arab-1) corresponding to one of these sequences was isolated, sequenced and translated. There was significant similarity to sequences in the new lipase family over the entire open reading frame of Arab-1 and when expressed in E. coli, the gene product was lipolytic. Arab-1 and genes for some of the other plant proteins appear to be differentially expressed. They may play a role in the regulation of lipid metabolism during plant development.     

Strain relaxation in SiGe due to process induced defects and their subsequent annealing behavior

Ion implantation and reactive ion etching are known to create defects in silicon which get cured during subsequent annealing operations. In this paper we have reported the annealing behavior of phosphorus implanted into strained SiGe layer at room temperature. The implantation was performed at 155 KeV with a dose of 1×10¹⁴/cm². Post implantation annealing was performed at 600, 700, 800 and 900°C for 10 s in a rapid thermal process furnace. Annealing behavior of defects generated as a consequence of dry etching is also reported. RTP annealing on reactive ion etching (RIE) etched samples were performed at 650, 700, 750 and 800 °C. I–V, C–V and DLTS measurements hint towards the presence of permanent dislocation loops created as a consequence of RIE and implantation causing strain relaxation.     

Rolling textures in nanoscale Cu/Nb multilayers

Rolling textures in nanoscale multilayered thin films are found to differ markedly from textures observed in bulk materials. Multilayered thin films consisting of alternating Cu and Nb layers with columnar grains were produced by magnetron sputtering, with individual layer thickness ranging from 4 μm to 75 nm and Cu/Nb interfaces locally satisfying the Kurdjumov–Sachs (K–S) orientation relations. After rolling to 80% effective strain, samples with a larger initial layer thickness develop a bulk rolling texture while those with a smaller initial layer thickness display co-rotation of Cu and Nb columnar grains about the interface normal, in order to preserve the K–S orientation relations. The resulting K–S texture has 0 0 1Nb parallel to and 1 1 0Cu approximately 5° from the rolling direction. A crystal plasticity model based on the Principle of Minimum Shear captures the K–S texture approximately and suggests that Nb drags Cu along in the rotation process.     

Photomechanical degradation of thermoplastic elastomers

The photodegradation of thermoplastic elastomers designed for outdoor applications was studied with laboratory ultraviolet (UV) exposure in the unstrained state and under tensile strain (25 and 50%). Strained exposure caused a reduction of the strain to failure in subsequent tensile tests. For some combinations of material and exposure conditions, some recovery of extensibility occurred between 2 and 4 weeks. Microscopic examination revealed that this was probably due to embrittlement of the surface region that was sufficiently severe that surface cracks did not propagate into the interior and that the observed recovery did not correspond to repair or improvement of the material. Shielding the sample surface from UV irradiation reduced the formation of surface cracking very significantly, and it was deduced that the principal cause of degradation was photooxidation rather than ozone attack. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 150–161, 2006     

Synthesis and characterization of hindered‐phenol‐containing amine moieties as antioxidants for polypropylene copolymers

(4‐Ethylphenyl)‐3,5‐ditertiarybutyl‐4‐hydroxybenzylamine, 1‐phenyl‐4‐(3,5‐ditertiarybutyl‐4‐hydroxybenzyl)piperazine, and 1‐(3,5‐ditertiarybutyl‐4‐hydroxybenzyl)piperidine were synthesized and characterized, and their performance in polypropylene copolymer (PPCP) was tested by multiple extrusions in a Brabender plasticorder. The thermooxidative stability of PPCP was assessed by the measurement of oxidative induction time at 200 ± 1°C, and the thermal stability was assessed by observation of the change in the melt flow rate. A comparative study of the synthesized antioxidants with the commercially available antioxidant 2,6‐ditertiarybutyl‐4‐methylphenol was made. The presence of phenolic and amino groups influenced the performance of the antioxidants. The performance of the antioxidants influenced the thermal stability of the PPCP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1097–1103, 2004     

Boron-doped hydrogenated amorphous carbon films grown by surface-wave mode microwave plasma chemical vapor deposition

We report the effects of boron (B) doping on optical and structural properties of the hydrogenated amorphous carbon thin films grown by surface-wave mode microwave plasma (SW-MWP) chemical vapor deposition (CVD) on n-type silicon and quartz substrates at room temperature. Argon and acetylene were used as a carrier and carbon source gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy were employed to investigate the properties of the films. Low atomic concentration of B (0.08 at.%) was found in the doped film. The optical band gap of the undoped film was 2.6 eV and it decreased to 1.9 eV for the B-doped film. Structural property shows the crystalline structure of the film and it has changed after incorporating B as a dopant. The structural modifications of the films leading to being more graphite in nature were confirmed by the Raman and FT-IR characterization.     

Phase relations in the Nb-Pd-Hf-Al system

In support of computational design of coherent aluminide strengthened Nb alloys, the phase equilibria in a series of six Nb-Pd-Hf-Al alloys were investigated using scanning electron microscopy (SEM) and x-ray diffraction (XRD). All alloys were heat treated at 1200°C for 200 h, while three alloys were also heat treated at 1500°C for 200 h. Three-phase equilibria and two-phase equilibria were observed in two alloys at both temperatures. Two more alloys also exhibited three-phase equilibria at 1200 °C, while one alloy exhibited two-phase equilibria at 1200 °C. A final alloy revealed four-phase equilibria at both temperatures, confirming the presence of a unique tie-tetrahedron in the Nb-Pd-Hf-Al system. Based on the characterization of phases by SEM and XRD, the Nb-Pd-Hf-Al partial phase diagram at 1200 °C has been constructed. Such phase diagrams provide the basis for designing precipitation-strengthened Nb-based superalloys.