bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of shearing and comonomer content on the crystallization behavior of poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate)
Authors: Chae Dong Wook , Kim Byoung Chul , Kim Dong Kook
Published: June 2004

Poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate) (PBSEMS) random copolymers were prepared with different comonomer compositions. The effects of shearing and comonomer content on the crystallization behavior of these copolymers were investigated at 80 °C. The thermal and morphological properties of the resulting samples were also discussed. The copolymers showed a longer induction time and a slower crystallization rate with increasing comonomer content. The promoting effect of shear on the overall crystallization behavior was more notable for those copolymers containing more 2‐ethyl‐2‐methyl succinic acid (EMSA) units. The melting temperature of ‘as‐prepared’ poly(butylene succinate) (PBS) was ca. 115 °C, while that of the copolymers varied from 112 to 102 °C. Higher comonomer contents in the copolymers gave rise to lower melting temperatures and broader melting peaks. In addition, the isothermally crystallized samples showed multiple melting endothermic behavior, the extent of which depended on the comonomer content. The copolymers showed different wide‐angle X‐ray diffraction (WAXD) patterns from that of neat PBS, depending on the comonomer content and shear applied during crystallization. With increasing comonomer content, the copolymers crystallized without shearing, showing the shifting of a diffraction peak to a higher angle, while those crystallized under shear did not show any peak shift. Copyright © 2004 Society of Chemical Industry
Effects of crystalline and orientational memory phenomena on the isothermal bulk crystallization and subsequent melting behavior of poly(trimethylene terephthalate)
Authors: Supaphol Pitt , Srimoaon Phornphon , Sirivat Anuvat
Published: June 2004

The effects of crystalline and orientational memory phenomena on the subsequent isothermal crystallization and subsequent melting behavior of poly(trimethylene terephthalate) (PTT) were investigated by studying the effect of prior melt‐annealing temperature, Tf, on the subsequent isothermal crystallization kinetics, crystalline structure and subsequent melting behavior of neat and sheared PTT samples. On partial melting, choices of the Tf used to melt the samples played an important role in determining their bulk crystallization rates, in which the bulk crystallization rate parameters studied were all found to decrease monotonically with increasing Tf. The decrease in the values of these rate parameters with Tf continued up to a critical Tf value (ie ca 275 °C for neat PTT samples and ca 280 °C for PTT samples which were sheared at shear rates of 92.1 and 245.6 s−1). Choices of the Tf used to melt neat PTT samples had no effect on the crystal structure formed. The subsequent melting behavior suggested that the Tf used to melt both neat and sheared samples had no effect on the peak positions of the melting endotherms observed and that the observed peak values of these endotherms for all sample types studied were almost identical. Copyright © 2004 Society of Chemical Industry
Impact response of epoxy systems containing short fibres and/or oxide particles as reinforcements
Authors: Kishore  , Harimkar SP , Desai DS
Published: June 2004

This work looks at the role played by constant levels of fibre and/or particles in epoxy matrices on impact responses during dynamic loading. In order to delineate the differing roles of reinforcements, hybrid composites containing different amounts of fibres and particles were prepared. Maximum loads and energies were used to distinguish the responses during and following impact. Scanning electron microscopy (SEM) was used to characterize the surface features before and after failure. Furthermore, such microscopic analyses were also employed to substantiate the deductions arrived at based on mechanical data analysis, which included the deduced parameter in the form of energy for propagation. The experimental results pointed to the fact that the total energy and load generally rise as the fibre content in the epoxy system increases. The hybrids, on the other hand, displayed a trend where the normalized load and the total energy increased as the fibre content in the hybrid was raised from 1 to 5 vol%. This was most evident when the differing levels of fillers and fibres were fixed at a total of 7 vol%. In addition, comparison was made between two sets of compositions of fibres and particles in the composites. The results showed that the higher fibre content in the hybrid allowed greater load bearing and energy absorption and the difference in recorded levels increased with higher fibre content in one hybrid set. Fractography studies indicated flatter surface features for systems with only particles added, whereas the ‘all‐fibre’ bearing systems displayed ‘fast‐fracture’ features resembling ‘river patterns’. Copyright © 2004 Society of Chemical Industry
Crystallization and melting behavior of polyester/clay nanocomposites
Authors: Phang In Yee , Pramoda KP , Liu Tianxi , He Chaobin
Published: June 2004

Polyester/clay nanocomposites were prepared by melt compounding with different clay loadings. Comparing against neat polyester resins, the crystallization and multiple melting behavior of the nanocomposites was investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Nanoclay filler is an effective heterogeneous nucleating agent, as evidenced by a decrease and an increase in the crystallization temperature for both cold and melt crystallization of polyesters, respectively. The degree of crystallinity was found to increase with increasing clay content, due to heterogeneous nucleation effects by the addition of a nanofiller. For the annealed samples, multiple melting peaks were always observed for both neat polyester and its nanocomposites. The origins of the multiple melting behavior are discussed, based on the DSC and XRD results. Interestingly, an ‘abnormal’ high‐temperature endothermic peak (Tm, 3) at about 260 °C was observed when the nanocomposite samples were annealed at higher temperatures (eg ≥240 °C). The constrained polyester crystals formed within intercalated clay platelets due to confinement effects were probably responsible for this melting event at these higher temperatures. Copyright © 2004 Society of Chemical Industry
Intraply and interply hybrid composites based on E‐glass and poly(vinyl alcohol) woven fabrics: tensile and impact properties
Authors: Pegoretti Alessandro , Fabbri Elena , Migliaresi Claudio , Pilati Francesco
Published: June 2004

E‐glass and poly(vinyl alcohol) (PVA) fibres were used to produce both homogeneous and hybrid composites with an orthophthalic unsatured polyester resin. Results are presented regarding the tensile and impact behaviour of both intraply and interply hybrid composites, with particular regard to the effects of the plies stacking sequence and the loading direction. With a proper choice of composition and stacking sequence, E‐glass/PVA hybrid composites were proved to achieve a property profile superior to those of homogeneous E‐glass laminates in terms of specific properties. In particular, hybridization with PVA fibres resulted in improving the specific impact energy of E‐glass laminates. Resistance to impact crack propagation was higher for intraply with respect to interply hybrid composites, as evidenced by their ductility index values. Copyright © 2004 Society of Chemical Industry
Formation of a soluble hyperbranched polymer via initiator–fragment incorporation radical copolymerization of divinyl adipate and isobutyl vinyl ether
Authors: Sato Tsuneyuki , Arima Yukiko , Seno Makiko , Hirano Tomohiro
Published: June 2004

The copolymerization of divinyl adipate (DVA) with isobutyl vinyl ether (IBVE) was conducted at 70 and 80 °C in benzene using azobisisobutyronitrile (AIBN), at a concentration as high as 0.50 mol l−1 as the initiator, where the concentrations of DVA and IBVE were 0.40 and 0.60 mol l−1, respectively. The copolymerization proceeded homogeneously, without any gelation, to yield soluble copolymers in spite of the high molar ratio of DVA as an excellent cross‐linker for IBVE. The copolymer yield increased with time, and the number‐average molecular weight (Mn = 0.9–2.4 × 104 g mol−1) from gel permeation chromatography (GPC) and molecular weight distribution (Mw/Mn = 1.5–7.6) of the resulting copolymer increased with copolymer yield. The cyanopropyl group, as a fragment of AIBN, was incorporated as a main constituent in the copolymer, the fraction of which increased from ca 10 to ca 20 % with copolymer yield, hence indicating that the copolymerization is an initiator–fragment incorporation radical polymerization. The copolymers also contained IBVE units (10–30 %) and DVA units with intact double bond (8–36 %) and without double bond (45 %). The intrinsic viscosity of the copolymer was very low (0.1 dl g−1) at 30 °C in tetrahydrofuran. The results from GPC–multi‐angle laser light scattering (MALLS), transmission electron microscopy (TEM) and MALLS revealed that individual copolymer molecules were formed as hyperbranched nanoparticles. Copyright © 2004 Society of Chemical Industry
Polyurethane ionomer dispersions from a blocked aromatic‐diisocyanate prepolymer
Authors: Subramani S , Park Young‐Jun , Cheong In‐Woo , Kim Jung‐Hyun
Published: June 2004

Aqueous anionic blocked aromatic polyurethane prepolymers were synthesized by a prepolymer mixing process and their dispersions were obtained by adding water to the blocked prepolymer solutions. A series of prepolymers were prepared by using toluene 2,4‐diisocyanate, 4,4′‐diphenylmethane diisocyanate, polytetramethylene glycol, dimethylol propionic acid, methyl ethyl ketoxime and ε‐caprolactam. The aqueous dispersions were characterized by Fourier‐transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. The particle sizes, viscosities, pH and storage stabilities of the dispersions were studied and compared. Some mechanical properties of the cast films obtained from the aqueous dispersions and the adhesive properties of the dispersions were also evaluated. Copyright © 2004 Society of Chemical Industry
Identification of rheological and structural characteristics of foamable poly(ethylene terephthalate) by reactive extrusion
Authors: Xanthos M , Wan C , Dhavalikar R , Karayannidis GP , Bikiaris DN
Published: June 2004

The reactivity and efficiency of five low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers of a bottle grade poly(ethylene terephthalate) (PET) resin were evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Measures of melt viscosity, melt strength, intrinsic viscosity and carboxyl group content were used as criteria of the extent of the modification. Correlations of die pressure with extrudate swell during extrusion, and melt flow index (MFI) with melt strength by off‐line testing of the extrudates permitted the ranking of the modifiers according to their chain‐extending/branching efficiency. For some systems molecular weight increases (related to die pressure/MFI/intrinsic viscosity) accompanied by broadening of the molecular weight distribution (related to die swell/melt strength) were considered excessive. Extrusion foaming experiments with one particular dianhydride modifier that increased the intrinsic viscosity of the resin from 0.71 to 0.9 dl g−1 indicate that production of low‐density foams by a process involving one‐step reactive modification/gas injection foaming is feasible, at conditions not significantly different from those employed in the simple reactive modification of the PET resin. The rheological and structural parameters determined in this work may be used as criteria to specify PET foamable compositions in terms of types and concentrations of modifiers. Copyright © 2004 Society of Chemical Industry
Chain structure of polyethylene/polypropylene in‐reactor alloy synthesized in gas phase with spherical Ziegler–Natta catalyst
Authors: Fu Zhisheng , Fan Zhiqiang , Zhang Yanzhong , Xu Junting
Published: June 2004

Two polyethylene/polypropylene (PE/PP) in‐reactor alloy samples were synthesized by multi‐stage gas‐phase polymerization using a spherical Ziegler–Natta catalyst. The alloys show excellent toughness and stiffness. FTIR, 13C‐NMR and thermal analysis proved that the alloys are mainly composed of polyethylene, PE‐block‐PP copolymer and polypropylene. There are also a few percent of ethylene‐propylene segmented copolymer with very low crystallinity. The block copolymer fraction accounts for more than 25 % of the alloy. The role of the block copolymer as compatibilizer between PE and PP is believed to be the key factor that results in the excellent toughness–stiffness balance of the material. Copyright © 2004 Society of Chemical Industry
Implications of melt compatibility/incompatibility on thermal and mechanical properties of metallocene and Ziegler–Natta linear low density polyethylene (LLDPE) blends with high density polyethylene (HDPE): influence of composition distribution and branch content of LLDPE
Authors: Hussein Ibnelwaleed A
Published: June 2004

In this paper, the implications of melt compatibility on thermal and solid‐state properties of linear low density polyethylene/high density polyethylene (LLDPE/HDPE) blends were assessed with respect to the effect of composition distribution (CD) and branch content (BC). The effect of CD was studied by melt blending a metallocene (m‐LLDPE) and a Ziegler‐Natta (ZN) LLDPE with the same HDPE at 190 °C. Similarly, the effect of BC was examined. In both cases, resins were paired to study one molecular variable at a time. Thermal and solid‐state properties were measured in a differential scanning calorimeter and in an Instron mechanical testing instrument, respectively. The low‐BC m‐LLDPE (BC = 14.5 CH3/1000 C) blends with HDPE were compatible at all compositions: rheological, thermal and some mechanical properties followed additivity rules. For incompatible high‐BC (42.0 CH3/1000 C) m‐LLDPE‐rich blends, elongation at break and work of rupture showed synergistic effects, while modulus was lower than predictions of linear additivity. The CD of LLDPE showed no significant effect on thermal properties, elongation at break or work of rupture; however, it resulted in low moduli for ZN‐LLDPE blends with HDPE. For miscible blends, no effect for BC or CD of LLDPE was observed. The BC of LLDPE has, in general, a stronger influence on melt and solid‐state properties of blends than the CD. Copyright © 2004 Society of Chemical Industry
A study of the products and mechanism of the thermal oxidative degradation of poly(ethylene oxide) using 1H and 13C 1‐D and 2‐D NMR
Authors: Mkhatresh Omar A , Heatley Frank
Published: June 2004

The products and mechanism of the thermal oxidative degradation of poly(ethylene oxide) at 150 °C have been analysed using 1H and 13C 1‐D and 2‐D NMR spectroscopy, including COSY, HMQC, HMBC and DOSY techniques. Peaks from methanoate ester chain ends (in the majority), in‐chain esters, peroxy groups, acetal links and ethanoyl chain ends have been assigned. Two small molecule degradation products, 2‐hydroxyethyl methanoate and ethylene glycol dimethanoate have been identified. Copyright © 2004 Society of Chemical Industry
Effect of acids on in situ polyaniline film formation
Authors: Ayad MM , Sheneshin MA
Published: June 2004

The chemical oxidation of aniline with ammonium persulfate (APS) to form polyaniline (PANI) films has been studied in different aqueous acid media such as sulfuric, nitric, phosphoric and acetic acids. A comparison was made between the yields of PANI film deposition during the polymerization from these media with the corresponding one obtained previously from aqueous HCl solution. The degradation of the formed PANI films at the beginning of polymerization obtained at the higher concentrations of HCl is absent when the other acids under consideration were used. The effect of acid concentration on the yield and growth rate of the PANI film was studied. The variation in the yield and growth rate of the polymer films at different acid concentrations was explained on the basis of the electrostatic repulsion and the screening effects. Copyright © 2004 Society of Chemical Industry
Effects of epoxy content on dynamic mechanical behaviour of PEI‐toughened dicyanate–novolac epoxy blends
Authors: Guo Baochun , Jia Demin
Published: June 2004

By varying the cyanate/epoxy ratio, three polyetherimide(PEI)‐modified bisphenol A dicyanate–novolac epoxy resin blends with different epoxy contents were prepared. The effects of epoxy content on the dynamic mechanical behaviour of those blends were investigated by dynamic mechanical thermal analysis. The results showed that the glass transition temperature of the cyanate–epoxy network (Tg1) in the modified blend decreases with epoxy content. When the epoxy content increases, both the width of the glass transition of the cyanate–epoxy network and its peak density are depressed substantially. Although the tangent delta peak value of PEI is basically independent of epoxy content, the Tg of PEI (Tg2) decreases with epoxy content. Tg1 is independent of the PEI loading. When Tg1 is lower than Tg2, however, the Tg1 in the blend with revised phase structure is substantially lower than other blends. Copyright © 2004 Society of Chemical Industry
pH and salt effects on interpolymer complexation via hydrogen bonding in aqueous solutions
Authors: Khutoryanskiy Vitaliy V , Mun Grigoriy A , Nurkeeva Zauresh S , Dubolazov Artem V
Published: June 2004

The effect of inorganic salts addition on the complex formation of poly(acrylic acid) with various non‐ionic polymers such as poly(vinyl pyrrolidone), poly(acrylamide), poly(ethylene oxide), pol(vinyl methyl ether), poly(vinyl alcohol), poly(N‐isopropylacrylamide), poly(2‐hydroxyethyl vinyl ether), hydroxypropylcellulose and hydroxyethylcellulose has been studied in aqueous solutions. It was found that, depending on the nature of the polymers and pH medium, addition of inorganic salts could increase or decrease the critical pH values of complexation. A new classification of interpolymer complexes based on critical pH values and ionic strength effects is suggested. Copyright © 2004 Society of Chemical Industry
Synthesis and characterization of poly(p‐phenylene)‐graft‐poly(ε‐caprolactone) copolymers by combined ring‐opening polymerization and cross‐coupling processes
Authors: Yurteri Seda , Cianga Ioan , Degirmenci Mustafa , Yagci Yusuf
Published: June 2004

2,5‐Dibromo‐1,4‐(dihydroxymethyl)benzene was used as initiator in ring‐opening polymerization of ε‐caprolactone in the presence of stannous octoate (Sn(Oct)2) catalyst. The resulting poly(ε‐caprolactone) (PCL) macromonomer, with a central 2,5‐dibromo‐1,4‐diphenylene group, was used in combination with 1,4‐dibromo‐2,5‐dimethylbenzene for a Suzuki coupling in the presence of Pd(PPh3)4 as catalyst or using the system NiCl2/bpy/PPh3/Zn for a Yamamoto‐type polymerization. The poly(p‐phenylenes) (PPP) obtained, with PCL side chains, have solubility properties similar to those of the starting macromonomer, ie soluble in common organic solvents at room temperature. The new polymers were characterized by 1H and 13C NMR and UV spectroscopy and also by GPC measurements. The thermal behaviour of the precursor PCL macromonomer and the final poly(p‐phenylene)‐graft‐poly(ε‐caprolactone) copolymers were investigated by thermogravimetric analysis and differential scanning calorimetry analyses and compared. Copyright © 2004 Society of Chemical Industry
Preparation and properties of new thermally stable poly(ether imide amide)s
Authors: Mehdipour‐Ataei Shahram , Amirshaghaghi Ahmad
Published: June 2004

2,6‐Bis(4‐aminophenoxy)pyridine was prepared via reaction of 4‐aminophenol with 2,6‐dichloropyridine in the presence of potassium carbonate. Reaction of the diamine with two mol of trimellitic anhydride afforded a diacid with preformed imide structures. Poly(ether imide amide)s were prepared by polycondensation reactions of the diacid with different diamines in the presence of triphenyl phosphite. All the monomers and polymers were fully characterized and the physical properties of the polymers including solution viscosity, thermal stability, thermal behavior and solubility were studied. Thermal analysis data showed the polymers to have high thermal stability. Copyright © 2004 Society of Chemical Industry
Characteristics of ethylene propylene diene monomer rubber/organoclay nanocomposites resulting from different processing conditions and formulations
Authors: Gatos Konstantinos G , Thomann Ralf , Karger‐Kocsis József
Published: June 2004

Several parameters which affect the nanocomposite formation in a sulfur‐cured ethylene propylene diene rubber (EPDM) containing 10 phr organoclay (montmorillonite modified with octadecylamine; MMT–ODA), were investigated. The parameters varied were linked to processing (mixer type, temperature) and rubber recipe (compatibilizer, accelerator). Increasing temperature and high shear mixing (internal mixer instead of open mill) improved the mechanical performance of the rubber nanocomposites. A more pronounced effect was achieved by using polar EPDM rubbers (maleic anhydride and glycidyl methacrylate grafted version) as compatibilizer. Among the accelerators, zinc diethyldithiocarbamate proved to be most suitable. The microstructure of the rubber/organoclay systems was studied by X‐ray diffraction, transmission electron microscopy and scanning electron microscopy. Organoclay intercalation/exfoliation was accompanied by its more or less severe confinement (reaggregation, deintercalation). This was traced to a partial or full removal of the ODA intercalant from the clay galleries via the formation of a zinc complex in which amine groups of the ODA and sulfur participated. Copyright © 2004 Society of Chemical Industry
Preparation and properties of a novel high‐performance resin system with low injection temperature for resin transfer moulding
Authors: Gu Aijuan , Liang Guozheng
Published: June 2004

A novel high‐performance resin system with low injection temperature for resin transfer moulding, M4506, was developed, which was made of 4,4′‐bismaleimidodiphenylmethane, o,o′‐diallyl bisphenol A, o,o′‐diallyl bisphenol A ether, and 1,1′‐bis(4‐cyanatophenyl)ethane. The processing characteristics, thermal and mechanical properties of the system were studied, and the effect of differing stoichiometries of each component on the processing and performance parameters was discussed. Investigations show that the processing properties of the M4506 system are greatly dependent on the stoichiometries of each component in the formulations, while all the three formulations developed in this paper have good processing characteristics, their suitable injection temperature are between 40 and 50 °C, depending on their respective formulation. The three formulations exhibited outstanding heat resistance (Tg = 294–300 °C) and thermal stability, good toughness and high strength, evidence that the M4506 system is a potential candidate as a high‐performance RTM matrix for advance composites as well as high‐performance paints with no solvents. Copyright © 2004 Society of Chemical Industry
Grafting of dodecyl methacrylate onto hydroxylated polybutadiene by miniemulsion polymerization
Authors: Pham Thi Thuy Binh , Fellows Christopher M. , Gilbert Robert G.
Published: June 2004

Homogeneous copolymer latex particles of dodecyl methacrylate (DMA) and low‐molecular‐weight hydroxy‐terminated polybutadiene (HTPB) oligomers were prepared by free‐radical polymerization using miniemulsion methods. Rate data and latex characteristics were consistent with the classical miniemulsion mechanism where nucleation of monomer droplets is the predominant pathway of particle formation. There is essentially no particle formation by secondary nucleation in the water phase. Characterization of the copolymer latex particles using transmission electron microscopy and modulated differential scanning calorimetry suggested that there is a significant amount of grafted poly(DMA)/HTPB polymer contributing to the miscibility of the HTPB and poly(DMA) phases. Particles were more homogeneous at increased HTPB composition, of relatively narrow polydispersity, and could be prepared reproducibly using a number of different initiation systems. The observed trends can all be rationalized in terms of conventional understanding of miniemulsion polymerization systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3404–3416, 2004
Stereospecific polymerization of methacrylates by metallocene and related catalysts
Authors: Chen Eugene Y.‐X.
Published: June 2004

Stereospecific—isospecific, syndiospecific, and diastereospecific—polymerizations of methacrylates using group 4 metallocene and related catalysts produce polymethacrylates with controlled stereo‐microstructures. The versatility and stereospecificity of these cat‐ alysts for methyl methacrylate polymerization were demonstrated not only in solution‐phase polymerization, but also in polymerizations on silica surfaces and inside silicate nanogalleries. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3395–3403, 2004
Interfacial adhesion mechanisms in incompatible semicrystalline polymer systems
Authors: Lo Chieh‐Tsung , Laabs Francis C. , Narasimhan Balaji
Published: June 2004

The mechanism of adhesion at semicrystalline polymer interfaces between isotactic polypropylene (iPP) and linear low‐density polyethylene (PE) was studied with transmission electron microscopy (TEM) and an asymmetric‐double‐cantilever‐beam test. From the TEM images, both the interfacial width and the lamellar thickness of the polymers were extracted. During annealing, the interfacial width increased with the annealing temperature, and this indicated the accumulation of amorphous polymers at the interface. The interfacial strength, determined from the critical fracture energy (Gc), also increased with the annealing temperature and reached a maximum above the melting temperatures of iPP and PE, whereas the smallest Gc value was obtained below the melting temperatures of the two materials. A mechanism of interfacial strengthening was proposed accounting for the competition between the interdiffusion of PE and crystallization of iPP. As the annealing temperature increased, the rates of PE diffusion and iPP crystallization increased. Although the crystallization of iPP hindered the interdiffusion of PE, both the interfacial width and the fracture energy increased with the temperature, and this indicated that PE interdiffusion dominated iPP crystallization. Below the critical temperature, the fracture surfaces of both iPP and PE were smooth, and chain pullout dominated the fracture mechanism. Above the critical temperature, iPP crystallization still hindered the interdiffusion, and crazes could be seen on the iPP side. Above the melting temperatures of the two materials, ruptured surfaces could also be seen on the PE side, and crazing was the fracture mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2667–2679, 2004
Spectroscopic Diagnostics for a DBD Plasma in He/Air and He/N2 Gas Mixtures
Authors: Chiper Alina S. , Aniţa Viorel , Agheorghiesei Catalin , Pohoaţa Valentin , Aniţa Maria , Popa Gheorghe
Published: June 2004

Summary: Experimental results obtained by emission spectroscopy on dielectric barrier discharges (DBD) in helium/air and helium/nitrogen gas mixtures are presented. The transition between the glow mode and filamentary mode of the dielectric barrier discharge was determined, and the electrical power transferred to the discharge was calculated. Dependence of the rotational temperature versus nitrogen gas‐flow rate was investigated.

Even with a peak power of 2.1 kW and a total energy of 2.3 × 10−4 J per pulse for the FD mode (in comparison to a peak power of 270 W and 5 × 10−5 J per pulse for the GD mode) the line intensity and number of excited species are larger for the GD mode than those of the FD mode.

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Even with a peak power of 2.1 kW and a total energy of 2.3 × 10−4 J per pulse for the FD mode (in comparison to a peak power of 270 W and 5 × 10−5 J per pulse for the GD mode) the line intensity and number of excited species are larger for the GD mode than those of the FD mode.
Influence of Plasma Functionalization of Poly(propylene) with Acrylic Acid on the Nucleation of CaCO3
Authors: Sciarratta Vincenzo , Oehr Christian , Diegelmann Carsten , Löbmann Peer
Published: June 2004

Summary:Poly(propylene) surfaces were modified by polymerization of acrylic acid using an RF plasma technique. Whereas a stable and reproducible hydrophilicity is obtained even after short treatment times, the thickness of the deposited layer, and thus the concentration of COOH functional groups per substrate surface area, increases with plasma exposure time. The modified‐poly(propylene) samples were exposed to aqueous solutions supersaturated with respect to CaCO3. Even though the polymer surfaces show a significant affinity for the adsorption of Ca2+ions, the density of nucleation sites for calcite is reduced in comparison to untreated poly(propylene). This result can be explained by the special conditions in porous (“gelatinous”) growth media and high disorder provided by the plasma‐polymerized layers.

AFM surface profile of a poly(propylene) surface (*) and film segments of plasma‐polymerized acrylic acid (**).

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AFM surface profile of a poly(propylene) surface (*) and film segments of plasma‐polymerized acrylic acid (**).
Formation of Plasma Polymer Layers with Functional Groups of Different Type and Density at Polymer Surfaces and their Interaction with Al Atoms
Authors: Friedrich Jörg , Kühn Gerhard , Mix Renate , Unger Wolfgang
Published: June 2004

Summary:Monotype functionalizations with different types of functional groups (OH, NH2, COOH) on polypropylene and poly(tetrafluoroethylene) surfaces were synthesized using pulsed plasma‐initiated homo‐ or copolymerization of functional group‐carrying monomers. The maximum concentrations of functional groups were 31 OH, 18 NH2or 24 COOH groups per 100 C atoms using allyl alcohol, allylamine or acrylic acid respectively as the monomer. The measured peel strengths of aluminium deposits increased linearly with the concentration of functional groups. Near the maximum concentration of OH (>27 OH/100 C atoms) or at moderate concentrations of COOH groups (>10 COOH/100 C atoms), constant (maximum) peel strengths were measured due to the mechanical collapse of one component in the composite (cohesive failure). Interface failures in Al‐PP composites were found with COOH, NH2and OH groups and cohesive failures were seen when higher concentrations of COOH groups were applied (>10 COOH/100 C atoms).

Dependence of Al peel strength in Al‐plasma polymer‐PP systems on the type and density of functional groups in plasma polymer interlayers.

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Dependence of Al peel strength in Al‐plasma polymer‐PP systems on the type and density of functional groups in plasma polymer interlayers.
A Review of Plasma‐Surface Interactions During Processing of Polymeric Materials Measured Using the IRIS Technique
Authors: Fisher Ellen R.
Published: June 2004

Summary: This work reviews the use of the imaging of radicals interacting with surfaces (IRIS) technique to elucidate chemical mechanisms during plasma modification of polymers. Four systems are examined, NH and NH2 in NH3 plasmas, OH radicals in H2O and O2/NH3 plasmas, OH in SiO2 film deposition systems, and CF2 molecules in a variety of fluorocarbon plasmas. Some of the findings include that NH and NH2 are produced at the surface during NH3 plasma modification of polymers. Their surface interactions are directly connected to each other and are also influenced by other plasma species such as ions. In implantation systems, OH reacts at the surface of polymers, contributing to the creation of hydrophilic polymeric membrane surfaces. In addition, OH surface reactivity is largely controlled by the chemistry of OH and not by other species in the plasma for all three systems studied. In fluoropolymer‐deposition systems, CF2 is scattered from the surface and is strongly influenced by ion bombardment. Most notably, CF2 scatter coefficients can be correlated directly to the percentage of cross‐linking in amorphous fluorocarbon films deposited in a range of plasma systems. Comparisons and contrasts between plasma systems and surface interactions of different species are provided.

Spatially resolved two‐ dimensional ICCD images of the LIF signal for NH with a PI substrate rotated into the path of the molecular beam with a laser–surface distance of 3.5 mm.

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Spatially resolved two‐ dimensional ICCD images of the LIF signal for NH with a PI substrate rotated into the path of the molecular beam with a laser–surface distance of 3.5 mm.
Homogeneous and Micro‐Patterned Plasma‐Deposited PEO‐Like Coatings for Biomedical Surfaces
Authors: Sardella Eloisa , Gristina Roberto , Senesi Giorgio S. , d'Agostino Riccardo , Favia Pietro
Published: June 2004

Summary: Mixtures of diethyl glycol dimethyl ether vapors and argon were used to feed RF (13.56 MHz) glow discharges and coat polystyrene substrates with poly(ethylene oxide) (PEO)‐like thin films. Different power input values have been used to obtain coatings with different cell‐adhesive properties. Cell‐culture experiments showed a tight correlation between the adhesion/morphology of cultured cell‐lines and the chemical composition of the coatings; the ability of PEO‐like coatings to discourage or promote cell adhesion could thus easily be related to the power delivered to the plasma. Combined deposition processes of different PEO‐like coatings have been performed, with the method of physical masking, to produce surfaces micro‐patterned with cell‐adhesive tracks alternating with cell‐repulsive domains. The micro‐arrangement of different cell‐adhesive domains enabled the patterning of cell cultures and induced the alignment of cells along predefined directions.

The adhesion pattern of 3T3 murine fibroblasts on a substrate of PEO10W patterned with a PEO5W coating deposited through a G50p mask after 24 h.

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The adhesion pattern of 3T3 murine fibroblasts on a substrate of PEO10W patterned with a PEO5W coating deposited through a G50p mask after 24 h.
Relations for the high‐pressure melting temperature of alkali halides based on the diffusional driving force models: NaCl as an example
Authors: Fang Zheng‐Hua
Published: June 2004

Two different diffusional driving force models were presented by Sharma et al. [Indian J. Pure Appl. Phys. 29, 637 (1991)] and Singh [J. Phys. Chem. Solids 63, 1935 (2002)], respectively, for estimating the zero‐pressure melting temperatures of alkali halides. Whether the two models are suitable for the analysis of the high‐pressure melting temperature of alkali halides is examined in this paper. It is shown that, supposing that the product of the thermal expansivity and the isothermal bulk modulus is inversely proportional to the volume along the melting curve, then the two diffusional force models are equivalent and the same relation for the high‐pressure melting temperature of solids may be derived. The reasonableness of this assumption is supported by the analysis and test on NaCl up to 1 Mbar, and is presented here. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal tuning and broadening of the spectral lines of trivalent neodymium in laser crystals
Authors: Chen Xuesheng , Di Bartolo Baldassare , Barnes Norman P. , Walsh Brian M.
Published: June 2004

This work reports a large number of experimental investigations of the effects of temperature on the sharp spectral lines of the trivalent neodymium ion in laser‐type crystals. The available theory that explains these effects in simple luminescence systems is applied to the cases examined when possible. Some general conclusions regarding the thermal effects on the systems examined are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Charge‐ordering correlated elastic anomalies in Pr1−xCaxMnO3 perovskite
Authors: Chen C. X. , Qian T. , Zheng R. K. , Wang F. , Li X. G.
Published: June 2004

The temperature dependence of the elastic properties of polycrystalline manganite Pr1−xCaxMnO3 (0.5 ≤ x ≤ 0.85) has been studied systematically by means of ultrasonic measurements. It was found that the longitudinal modulus starts to soften obviously with decreasing temperature from higher temperature to the charge‐ordering transition temperature Tco, and stiffens dramatically just below Tco. The elastic anomalies observed near Tco cannot be explained based on a conventional antiferromagnetic transition. The electron–phonon coupling originating from the Jahn–Teller effect may play an important role in the system. The good fit of the theory to the temperature dependence of the elastic modulus data indicates that the mean‐field theory, which describes the coupling of Jahn–Teller ions to lattice distortions of the Jahn–Teller system, adequately characterizes the behavior. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of the Tl+ center doped in NH4Cl crystals with the CsCl structure
Authors: Kawai Taketoshi , Hashimoto Satoshi
Published: June 2004

We have investigated the optical properties of the Tl+ center doped in NH4Cl single crystals with the CsCl structure. The A, B and C absorption bands due to the cationic transition in the Tl+ ion are observed at 5.22, 6.22 and 6.59 eV at low temperature, respectively. When the A absorption band is photoexcited, the AX luminescence band appears at 4.35 eV, and the AT luminescence band at 3.37 eV. As the temperature increases, the AT band that is dominant at 13 K decreases around 20 and 60 K. On the other hand, the AT band exhibits an increase that compensates the decrease of the AX luminescence intensity. The blue‐shift of the peak energy and the narrowing of the halfwidth with increasing temperature are observed in the temperature ranges from 18 to 25 K for the AX band, and from 25 to 45 K for the AT band. Such complex temperature behaviors of the AX and AT bands are explained on the basis of the thermally activated non‐radiative transitions among four relaxed excited states introduced semiempirically. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fragmentation of multiply charged simple metal clusters in the liquid‐drop stabilized jellium model
Authors: Payami M.
Published: June 2004

In this work, we have used the liquid‐drop model in the context of stabilized jellium model, to study the stability of Z‐ply charged (Z = 1, 2, 3, 4) metal clusters of different species against fragmentation. The liquid drop energy coefficients for each rs value are obtained from fitting of the self‐consistent Kohn‐Sham results for 0 ≤ N ≤ 100. The fission barriers are calculated using the two‐sphere model. Results show that the singly ionized clusters are stable against any spontaneous fragmentation. However, multiply charged clusters of sufficiently small sizes may undergo spontaneous decay via fission processes. The size at which competition between evaporation and fission starts, is predicted in good agreement with experiment for r ≥ 3.99. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability and band gaps of As‐rich and N‐rich GaAsN alloys: Density‐functional supercell calculations
Authors: Jenichen A. , Engler C.
Published: June 2004

Total energies and band gap energies of cubic cells with various arrangements of Ga32As32−nNn (n = 0–8 and n = 28–32 corresponding to 0.0–25.0% N and 12.5–0.0% As) are calculated using the density‐functional supercell method. In the As‐rich limit up to an exchange of 6.2% N isolated N atoms (maximum N distance) are the most stable arrangement and provide the typical reduction of the band gap energy from about 1.5 eV (GaAs) to about 1 eV caused by reduction of the N distance. For higher N content special N distributions are the most stable arrangements. GaNm clusters (m = 2–4) and isolated N atoms are less stable. The band gap remains nearly constant at about 1 eV between 6.2 and 18.8% N. The good agreement between the experimental band gap energies and ones calculated for the most stable arrangements points out that the experimental distribution of the atoms is the thermodynamic equilibrium distribution. In the N‐rich limit, linear As chains in [110] direction or fragments of them are the most stable arrangement. At 9.4% As the band gap disappears. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Preisach modeling on the magnetic properties of Sr1−xCaxRuO3
Authors: Hou Deng‐Lu , Xu Jing , Bai Yun , Zhao Jing , Du Guo‐Qiang , Tang Gui‐De , Nie Xiang‐Fu
Published: June 2004

The samples Sr1−xCaxRuO3 (x = 0.0, 0.2, 0.6) have been synthesized by a solid state reaction, and characterized by the zero field cooled (ZFC), field cooled (FC) magnetic moments and the major hysteresis loops. The data have been analyzed within the framework of a generalized Preisach model, which includes thermal fluctuations, critical phenomenon, and temperature dependent distribution of free energy barriers. The model provides an excellent description of the experimental data, and the simulating results are in good agreement with the experiment results. All the ZFC/FC curves at different applied fields and all the major hysteresis loops at different temperatures can be replicated by the model with one set of parameters. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular dynamics simulation of C60 encapsulated in boron nitride nanotubes
Authors: Moon Won Ha , Son Myung Sik , Lee Jun Ha , Hwang Ho Jung
Published: June 2004

We investigate the C60 chain encapsulated in boron nitride (BN) nanotubes using molecular‐dynamics simulation. The most favorable BN nanotubes for encapsulation of C60 molecules are (10, 10) and (17, 0) with energy gains of 3.83 and 3.61 eV per C60 for (n, n) and (n, 0) BN nanotubes, respectively. For the diffusion of a C60 into the tube, the position of atoms of a C60 must be not located above the outer wall of the BN nanotube. The C60 located above the outer wall is quickly absorbed and moves on the surface of the tube. The C60 absorbed on the surface is not spontaneously encapsulated inside the tube, which is due to the energy barrier (0.48 eV) of the edge of the BN nanotube. We also calculate the energy barrier for drawing C60 outside the (10, 10) BN nanotube, which is above 3.92 eV. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical explanation of EPR parameters for Cu2+ ion in TiO2 crystal
Authors: Dong H. N. , Wu S. Y. , Li P.
Published: June 2004

The EPR parameters anisotropic g‐factors gx, gy and gz for Cu2+ ion and hyperfine structure constants Ax, Ay and Az for 63Cu2+ and 65Cu2+ isotopes in rutile (TiO2) crystal are calculated by the method of diagonalizing the full Hamiltonian matrix. The crystal‐field parameters contact with the crystal structure by the aid of the superposition model. The calculated results are in reasonable agreement with the observed values. The results are discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Binding energies of excitons in II–VI compound‐semiconductor based quantum well structures
Authors: Senger R. T. , Bajaj K. K.
Published: June 2004

We present a brief description of the calculation of the variation of the binding energy of the heavy‐hole exciton as a function of well width in quantum well structures composed of II–VI compound semiconductors including the effects of exciton–optical phonon interaction as formulated by Pollmann and Büttner [J. Pollmann and H. Büttner, Phys. Rev. B 16, 4480 (1977)], and of particle masses and dielectric mismatches between the well and the barrier layers. We compare the results of our calculations with the available experimental data in ZnSe/MgS, ZnSe/Mg0.15Zn0.85Se, and ZnS/Mg0.19Zn0.81S quantum well structures and find a good agreement. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Harmonic generation by molecules in intense laser and magnetic fields: Orientation effects
Authors: Bandrauk André D. , Lu Huizhong
Published: June 2004

We solve exactly the 3‐D time‐dependent Schrödinger equation (TDSE) for the H molecular ion in combination with intense laser fields and static magnetic fields using a newly developed adaptive grid method. This allows for a study of the control of high‐order harmonic generation (HOHG) in molecules by various orientation of the magnetic and laser fields. In particular, we find regimes of pure‐even‐only and even‐with‐odd harmonic generation spectra for particular field and frequency configurations. Furthermore, HOHG plateaus are found to extend to much larger harmonic order in the presence of magnetic fields, thus offering the possibility of obtaining coherent sources in the X–UV region. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Computing enthalpy–entropy interplay for isomeric fullerenes
Authors: Slanina Z. , Zhao X. , Uhlík F. , Lee S.‐L. , Adamowicz L.
Published: June 2004

Fullerenes represent unique species in many respects, one of them being one of the highest temperature regions ever used for preparation of chemical species. This very factor automatically substantially enhances the importance of the TS part of the Gibbs function. The essential feature of fullerenic systems has consistently been ignored in computational studies of fullerenes, almost always drawing their conclusions from potential energies or heats of formation. This report demonstrates that the simplified treatment cannot really describe all the features of complex mixtures of isomeric fullerenes. General formulas are surveyed and illustrated on C96—the biggest set of isomeric fullerenes characterized by 13C NMR spectra to date. Computations are carried out for the complete set of 187 isolated‐pentagon‐rule (IPR) isomers of C96, using four semiempirical quantum chemical methods (MNDO, AM1, PM3, and SAM1). Entropy terms are also computed and the relative‐stability problem is entirely treated in terms of the Gibbs function. In overall, the computed data match the observed data reasonably well, although no method can really reproduce the complete ten‐membered observed set. There are however still several aspects to be checked and several possibilities how to improve quality of the computed terms. In principle, such developments are, however, only a question of available computing power. There are, nevertheless, some remaining questions, such as inclusion of anharmonicity effects, contribution from electronic partition function, or even interactions between individual, yet separated motions. This article also discusses a subsequent, more general task of relative stabilities of carbon cages of different dimensions, i.e., relative stabilities of nonisomeric fullerenes. The computational treatment of isomeric mixtures has several interesting features: the results depend on temperature, but not on pressure; only the relative, and not the absolute, values of the heats of formation are needed; and the form of the master equation allows for an ample cancellation of terms in the partition functions. In contrast, for the more general task—relative stabilities of fullerenes of different dimensions—the absolute values of the heats of formation are required, the mentioned cancellations do not operate there, and the scheme is essentially pressure dependent. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004