bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Poly(ester amide)s Derived from Glycolic Acid and the Amino Acids: β‐Alanine or 4‐Aminobutyric Acid
Authors: Rodríguez‐Galán Alfonso , Vera Montserrat , Jiménez Katia , Franco Lourdes , Puiggalí Jordi
Published: November 2003

The polymerization of metal salts of N‐chloroacetyl‐β‐alanine and N‐chloroacetyl‐4‐aminobutyric acid was investigated. The former gives a mixture of polymer and a seven‐membered cyclic compound constituted of glycolic and β‐alanine units, and its reaction proceeds in the solid state. However, liquefaction is observed in the second case giving rise to a polymer with a moderate molecular weight. Condensation kinetics of both sodium and silver salts of N‐chloroacetyl‐β‐alanine have been studied by differential scanning calorimetry. Copolymers of glycolic acid and β‐alanine with a molar ratio of glycolic acid/β‐alanine varying from 0.5 to 1.0 have been synthesized by thermal reaction of co‐precipitated crystals of the sodium salts of chloroacetic acid and N‐chloroacetyl‐β‐alanine. NMR spectroscopy indicates that copolymers tend to have a random distribution. The resulting new poly(ester amide)s have been characterized by spectroscopy and thermal analysis.

DSC heating runs corresponding to different mixtures of the sodium salts of chloroacetic acid and chloroacetyl‐β‐alanine.

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DSC heating runs corresponding to different mixtures of the sodium salts of chloroacetic acid and chloroacetyl‐β‐alanine.
Synthesis and Characterization of Poly(arylene ether oxadiazole) Telechelics
Authors: Gomes Dominique , Nunes Suzana P.
Published: November 2003

Poly(arylene ether oxadiazole) telechelics with fluorine and hydroxyl end groups were synthesized by nucleophilic substitution polymerizations of 2,5‐bis(4‐fluorophenyl)‐1,3,4‐oxadiazole monomer with bishydroxy compounds containing C(CH3)2, C(CF3)2 and SO2 groups. Fluorotelechelics were obtained with about 3 repeating units (molecular weight about 2 000 g · mol−1) using a rather excess (100 mol‐%) of bis(fluorophenyl) oxadiazole compound. On the other hand, hydroxytelechelics were synthesized with about 9 repeating units (molecular weight about 5 000 g · mol−1) using a small excess of bishydroxy compound (monomer molar ratio of 0.93). Sulfonated poly(arylene ether oxadiazole) hydroxytelechelics were also synthesized using sulfonated and unsulfonated bishydroxy compounds. All sulfonated hydroxytelechelics were partially water soluble, even when only 40 mol‐% of sulfonated monomers was used. The number of repeating units of hydroxytelechelics increased up to 12 (molecular weight about 9 000 g · mol−1) using sulfonated monomers, probably because of the higher reactivity of sulfonated phenoxide. The molecular weights estimated by 1H NMR were in agreement to the results obtained by SEC. The telechelics can be used as precursor for the synthesis of block copolymer.

Structure of the hydroxytelechelics.

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Structure of the hydroxytelechelics.
Study on Doping Behaviors of Vinyl Hydrogels with Pendant Terthiophenes
Authors: Chen Li , Gong Jian Ping , Ohsedo Yutaka , Osada Yoshihito
Published: November 2003

The water‐swollen poly(AA3T‐co‐NaSS) and poly(AA3T‐co‐PEG) gels were synthesized by radical copolymerization of the monomer, [(2,2′:5′,2″‐terthiophen‐5‐yl)methyl acrylate] (AA3T), containing pendant terthiophenes as an electron‐conducting material with a soluble monomer, sodium p‐styrenesulfonate (NaSS), or oligo(ethylene glycol) (PEG); their swelling, spectral, and doping behaviors were investigated. The degree of swelling of the poly(AA3T‐co‐PEG) gel was independent of the pH, whereas that of poly(AA3T‐co‐NaSS) gel increases abruptly below pH 3, which suggests self‐doping between the AA3T and NaSS groups. The self‐doping is not suppressed by cross‐linking. Both poly(AA3T‐co‐NaSS) and poly(AA3T‐co‐PEG) gels can be chemically doped with concentrated HCl or HClO4 solution.

Concentration dependence of the absorbency of the copolymers and gel.

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Concentration dependence of the absorbency of the copolymers and gel.
Polyelectrolyte‐in‐Ionic‐Liquid Electrolytes
Authors: Tiyapiboonchaiya Churat , Pringle Jennifer M. , MacFarlane Douglas R. , Forsyth Maria , Sun Jiazeng
Published: November 2003

Novel polymer electrolyte materials based on a polyelectrolyte‐in‐ionic‐liquid principle are described. A combination of a lithium 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSLi) and N,N′‐dimethylacrylamide (DMMA) are miscible with the ionic liquid, 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIDCA). EMIDCA has remarkably high conductivity (≥ 2 · 10−2 S · cm−1) at room temperature and acts as a good solvating medium for the polyelectrolyte. At compositions of AMPSLi less than or equal to 75 mol‐% in the copolymer (P(AMPSLi‐co‐DMAA)), the polyelectrolytes in EMIDCA are homogeneous, flexible elastomeric gel materials at 10 − 15 wt.‐% of total polyelectrolyte. Conductivities higher than 8 · 10−3 S · cm−1 at 30 °C have been achieved. The effects of the monomer composition, polyelectrolyte concentration, temperature and lithium concentration on the ionic conductivity have been studied using thermal and conductivity analysis, and pulsed field gradient nuclear magnetic resonance techniques.

Comparison of the measured and calculated lithium conductivity at 30 °C.

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Comparison of the measured and calculated lithium conductivity at 30 °C.
Homolysis and Decomposition of Alkoxyamines Containing PROXYL and TEMPO Residues: A Comparison
Authors: Bacon Catherine A. , Cameron Neil R. , Reid Alistair J.
Published: November 2003

Quantitative ESR and 1H NMR spectroscopies have been used to study the homolysis and decomposition, respectively, of alkoxyamines derived from TEMPO and PROXYL nitroxides. It is shown that alkoxyamines substituted in the β position with a tert‐butoxy group have different activation parameters than those bearing a 1‐phenethyl fragment, however, there is compensation between transition state enthalpy and entropy, resulting in most cases in similar transition state free energies and homolysis kinetics. On the other hand, β‐substituted alkoxyamines show a much lower tendency to undergo decomposition, while species derived from TEMPO are more prone to decomposition than those from the substituted PROXYL derivative investigated. These findings are used to explain the observed differences in polymerisation behaviour of the various alkoxyamines.

Alkoxyamines used in the present study.

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Alkoxyamines used in the present study.
Electrical Conductivity of an Individual Polyaniline Nanotube Synthesized by a Self‐Assembly Method
Authors: Long Yunze , Zhang Lijuan , Ma Yongjun , Chen Zhaojia , Wang Nanlin , Zhang Ze , Wan Meixiang
Published: November 2003

Camphor sulfonic acid (CSA) doped polyaniline (PANI) nanotubes (175 nm in outer diameter and 120 nm in inner diameter) were synthesized successfully by a self‐assembly method. It is found that the room‐temperature conductivity of an individual PANI nanotube is 30.5 S · cm−1; in particular, the intrinsic resistance of an individual nanotube (30 kΩ) is much smaller than the contact resistance of crossed nanotubes (500 kΩ).

A SEM image of two crossed PANI‐CSA nanotubes and the attached Pt electrodes.

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A SEM image of two crossed PANI‐CSA nanotubes and the attached Pt electrodes.
Probing Nanoscale Polymer Interactions by Forced‐Assembly
Authors: Liu Richard Y. F. , Jin Yi , Hiltner Anne , Baer Eric
Published: November 2003

When two immiscible polymers are brought into intimate contact, highly localized mixing of polymer chains creates an “interphase” region. Materials that are entirely interphase are fabricated by forced‐assembly using layer‐multiplying coextrusion to form assemblies of thousands of nanolayers. Analysis of the interphase materials with conventional methods of polymer analysis confirms certain theoretical predictions for the first time. The unique properties of the new interphase materials result from lower free volume than the constituents.

Atomic force microscopy phase image from the cross‐section of a PC/PMMA nanolayer film with 4096 layers and average layer thickness of 25 nm.

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Atomic force microscopy phase image from the cross‐section of a PC/PMMA nanolayer film with 4096 layers and average layer thickness of 25 nm.
Encapsulation of Bovine Serum Albumin in Temperature‐Programmed “Shell‐in‐Shell” Structures
Authors: Jo Yun‐Suk , Kim Do‐Kyung , Jeong Young‐Keun , Kim Kyung‐Ja , Muhammed Mamoun
Published: November 2003

A novel approach to load a hydrophilic bovine serum albumin into drug carriers was proposed in terms of temperature‐programmed “shell‐in‐shell” structures, which were fabricated with poly(N‐isopropylacrylamide), poly(lactide), poly(ethylene glycol), and Au nanoparticles. Spherically well‐defined “shell‐in‐shell” structures were constructed by a modified‐double‐emulsion method (MDEM). The lower critical solubility temperature of the structures was manipulated to 36.4 °C which was confirmed by UV/Vis spectroscopy and DSC (Differential Scanning Calorimetry).

TEM image of the Au@PLLA‐PEG@PNIPAAm‐PDLA structure.

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TEM image of the Au@PLLA‐PEG@PNIPAAm‐PDLA structure.
Pioniere in der Supraleiter‐ und Supraflüssigkeitsforschung
Authors: Huebener Rudolf
Published: November 2003

Die Königlich Schwedische Akademie der Wissenschaften vergab in diesem Jahr den Physik‐Nobelpreis zu gleichen Teilen an Aleksej Abrikossow, Witalij Ginsburg und Anthony Leggett für ihre „pionierhaften Beiträge zur Theorie der Supraleiter und Supraflüssigkeiten.”︁

http://www.nobel.se
„Eine neue Eigenschaft der Materie”︁
Authors: Jacobi Manfred
Published: November 2003

Im Jahre 1903 erhielten Henri Becquerel sowie Marie und Pierre Curie den Physik‐Nobelpreis für die Entdeckung der Radioaktivität. Schon damals stellte Pierre Curie die Frage nach Nutzen und Gefahr dieser neuen Eigenschaft von Materie. Er war der Überzeugung, dass der Fortschritt letztlich mehr zum Nutzen als zum Schaden der Menschen beitrage.
Das Elektron auf der Präzisionswaage
Authors: Vogel Manuel , Werth Günther
Published: November 2003

Die Elektronenmasse ist eine der Fundamentalkonstanten der Physik. Entsprechend gibt es viele, zumeist indirekte Ansätze zu ihrer Bestimmung. Physikern der Universität Mainz gelang es jüngst, den Wert um einen Faktor vier zu verbessern. Sie nutzten dafür die Messung des anomalen magnetischen Moments des Elektrons in wasserstoffartigen Ionen.
Neutronen in Hiroshima
Authors: Rugel Georg
Published: November 2003

Münchner Physikern gelang es kürzlich in Zusammenarbeit mit Kollegen aus den USA, in Kupferproben aus Hiroshima Reaktionsprodukte schneller Neutronen von der damaligen Atombomben‐Explosion nachzuweisen. Dies ermöglichte es erstmals, die Neutronendosen, denen die Überlebenden ausgesetzt gewesen waren, experimentell zu bestimmen [1].
Physik mit Gewehr und Eiern
Authors: Loos Andreas
Published: November 2003

Es fing schon gut an: Mit zehn Jahren saß der begabte Junge bereits in der Universität, wo ihn kein Geringerer als sein Vater persönlich unterrichtete. Damit schlug dieser zwei Fliegen mit einer Klappe: Sein Sohn lernte etwas Gescheites, und er war zugleich in sicherer Obhut.
Von Weihnachtsplätzchen und anderen granularen Backwerken
Authors: Vilgis Thomas
Published: November 2003

Weihnachten steht vor der Tür, und aus den Backöfen duften die ersten Plätzchen als Vorboten. Die isst man auch bei Physikers so gern, dass kaum ein Krumen übrig bleibt. Dabei sind die Krümel besonders interessant, denn sie zeigen eine Vielzahl von Merkmalen und lassen auf die verschiedenen Teigarten schließen, deren Reiz nicht nur im Geschmack, sondern auch in Herstellungsweise und Teigklasse liegt.
Synthesis and characterization of fillers of controlled structure based on polyhedral oligomeric silsesquioxane cages and their use in reinforcing siloxane elastomers
Authors: Pan Guirong , Mark James E. , Schaefer Dale W.
Published: November 2003

Four polyhedral oligomeric silsesquioxane (POSS) cages with vinyl groups were linked to a central siloxane core by hydrosilylation. The goal was to obtain filler particles of sizes between those of the POSS cages themselves and the much larger silica particles typically used to reinforce elastomers. The hydrosilylation reaction was monitored with Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the resulting structure was confirmed by mass spectrometry. Simply blending these POSS‐based fillers into silanol‐terminated poly(dimethylsiloxane) (PDMS) had little effect on the mechanical properties, but bonding them to PDMS provided considerable reinforcement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3314–3323, 2003
Influence of polymer matrix composition and architecture on polymer nanocomposite formation: Coarse‐grained molecular dynamics simulation
Authors: Sinsawat Anuchai , Anderson Kelly L. , Vaia Richard A. , Farmer B. L.
Published: November 2003

Coarse‐grained molecular dynamics simulations of stacks of two‐dimensional platelets immersed in a polymer melt were performed to investigate aspects of the polymer matrix that promote the formation of intercalated or exfoliated nanocomposite structures. Such factors include temperature, copolymer architecture, and blend composition. Increasing the polymer‐sheet attractive interaction led to binding of the sheets, where individual beads simultaneously attract two neighboring sheets, thus kinetically blocking intercalation by occupying the perimeter of the affected gallery. Polymers with a small polymer‐sheet attraction, but having a strongly attractive chain end (end‐functionalized polymers) minimized the bonding of adjacent sheets. These systems exhibited some sheet sliding because a majority of the confined polymer beads only interacted weakly with adjacent sheets; however, the number density of intercalated polymer was low. Mixtures of end‐functionalized and nonfunctionalized polymers, however, yielded better intercalation efficiency. For the mixed system, the reduced number of highly attractive beads provided sufficient interaction for intercalation to occur, enabling greater intercalation rates, less sheet‐bridging, and incorporation of the nonfunctionalized polymers into the galleries. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3272–3284, 2003
Melt‐processable syndiotactic polystyrene/montmorillonite nanocomposites
Authors: Wang Z. M. , Chung T. C. , Gilman J. W. , Manias E.
Published: November 2003

Monoalkyl‐ and dialkyl‐imidazolium surfactants were used to prepare organically modified montmorillonites with markedly improved thermal stability in comparison with their alkyl‐ammonium equivalents (the decomposition temperatures increased by ca. 100 °C). Such an increase in the thermal stability affords the opportunity to form syndiotactic polystyrene (s‐PS)/imidazolium‐montmorillonite nanocomposites even under static melt‐intercalation conditions in the absence of high shear rates or solvents. Upon nanocomposite formation, s‐PS exhibited an improvement in the thermal stability in comparison with neat s‐PS, and the β‐crystal form of s‐PS became dominant. This crystallization response agrees with previous studies of s‐PS/pyridinium‐montmorillonite hybrids and is tentatively attributed to a heterogeneous nucleation action by the inorganic fillers. © 2003 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys 41: 3173–3187, 2003
Analysis of small‐angle scattering of suspensions of organically modified montmorillonite: Implications to phase behavior of polymer nanocomposites
Authors: Vaia Richard A. , Liu Weidong , Koerner Hilmar
Published: November 2003

A generalized model for scattering from a collection of independent (isolated) stacks of layers enabled predictions of and parameterized fits to small‐angle X‐ray scattering from layered silicate dispersions. From this fundamental development, example investigations that use small‐angle scattering to examine the structure of organically modified montmorillonite dispersions in toluene and toluene–acetone blends provided detailed information on the distribution of the stacks (relative concentrations, K and fraction of individual layers, χ) and characteristics of the intercalated crystallite (mean number of layers per stack, 〈N〉; layer repeat distance, D; and fractional stack disorder, δ). The analysis initially supported correlations with discotic phase behavior, which provides concise definitions for various morphologies (exfoliated, intercalated, and mixed). Finally, examination of the deviations between the scattering model and the experiment provided insights for improved experimental technique, more complete utilization of the scattering data, a sound basis for real‐time observations, insight into inconsistencies between scattering and microscopy, and minimization of incorrect or overinterpretation of data. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3214–3236, 2003
Glass transition of polymer/single‐walled carbon nanotube composite films
Authors: Pham Joseph Q. , Mitchell Cynthia A. , Bahr Jeffrey L. , Tour James M. , Krishanamoorti Ramanan , Green Peter F.
Published: November 2003

The glass‐transition temperatures (Tg's) of nanocomposites of polystyrene (PS) and single‐walled carbon nanotubes were measured in the bulk and in thin films with differential scanning calorimetry and spectroscopic ellipsometry, respectively. The bulk Tg of the nanocomposites increased by approximately 3 °C and became much broader than that of PS. For the nanocomposite films thinner than 45 nm, Tg decreased with decreasing film thickness [i.e., ΔTg(nano) < 0]. This phenomenon also occurred in thin PS films, the magnitude of the depression in PS [ΔTg(PS)] being somewhat larger. The film thickness dependence and the differences in the magnitude of ΔTg in the two systems were examined in light of current theory, and a quantitative comparison was made. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3339–3345, 2003
Hybrid epoxy‐based thermosets based on polyhedral oligosilsesquioxane: Cure behavior and toughening mechanisms
Authors: Kim G.‐M. , Qin H. , Fang X. , Sun F. C. , Mather P. T.
Published: November 2003

Polyhedral oligosilsesquioxane (POSS)‐reinforced thermosets based on octaglycidyl epoxy polyhedral oligosilsesquioxane cured with 4,4′‐diaminodiphenyl sulfone (DDS) were prepared and studied for their cure, thermomechanical, and microstructural characteristics. Particular attention was paid to nanometer‐scale deformation processes responsible for toughening, as revealed by transmission electron microscopy (TEM) in conjunction with the thermal properties. A cure analysis investigated with calorimetry and rheometry showed a significant dependence of the cure mechanism and kinetics on the DDS content, but all hybrid thermosets reacted completely below 300 °C into rigid solids. A dynamic mechanical analysis of this hybrid resin system showed that increasing the DDS concentration used during cure increased the dynamic storage modulus in the glassy (temperature < glass‐transition temperature) and rubbery (temperature > glass‐transition temperature) states, simply through an increase in the crosslink density. The phase structures revealed by TEM with selective POSS staining were drastically affected by the DDS concentration and manifested as altered nanomechanical deformation structures. It was qualitatively found that the main toughening mechanism in the studied POSS‐reinforced thermosets was void formation at the nanometer scale, possibly templated by limited POSS aggregation. As the crosslinking density increased with the DDS concentration, microshear yielding between voids prevailed, providing a balance of stiffness, strength, and toughness. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3299–3313, 2003
Electrical characterization of poly(ethylene oxide)–clay nanocomposites prepared by microwave irradiation
Authors: Aranda Pilar , Mosqueda Yodalgis , Pérez‐Cappe Eduardo , Ruiz‐Hitzky Eduardo
Published: November 2003

Poly(ethylene oxide) (PEO)–clay (montmorillonite, hectorite, and laponite) nanocomposites were prepared by a melting intercalation procedure induced by microwave irradiation. The influence of parameters such as the time of irradiation, power, amount and relative ratio of the reagents, and relative humidity was investigated. X‐ray diffraction, differential scanning calorimetry, elemental microanalysis, Fourier transform infrared, and scanning electron microscopy techniques were applied to characterize the resulting nanocomposites. Techniques involving impedance spectroscopy, thermoelectric power, and electrical polarization in the solid state were used to characterize the electrical properties of the nanocomposites. The electrical behavior of these PEO–silicate nanocomposites, including those containing an excess of alkaline metal salts in comparison with that of similar systems prepared by alternative procedures such as direct intercalation from polymer solutions or melting intercalation, was also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3249–3263, 2003
Investigation of nanodispersion in polystyrene–montmorillonite nanocomposites by solid‐state NMR
Authors: Bourbigot Serge , VanderHart David L. , Gilman Jeffrey W. , Awad Walid H. , Davis Rick D. , Morgan Alexander B. , Wilkie Charles A.
Published: November 2003

Nanocomposites result from combinations of materials with vastly different properties in the nanometer scale. These materials exhibit many unique properties such as improved thermal stability, reduced flammability, and improved mechanical properties. Many of the properties associated with polymer–clay nanocomposites are a function of the extent of exfoliation of the individual clay sheets or the quality of the nanodispersion. This work demonstrates that solid‐state NMR can be used to characterize, quantitatively, the nanodispersion of variously modified montmorillonite (MMT) clays in polystyrene (PS) matrices. The direct influence of the paramagnetic Fe3+, embedded in the aluminosilicate layers of MMT, on polymer protons within about 1 nm from the clay surfaces creates relaxation sources, which, via spin diffusion, significantly shorten the overall proton longitudinal relaxation time (T). Deoxygenated samples were used to avoid the particularly strong contribution to the T of PS from paramagnetic molecular oxygen. We used T as an indicator of the nanodispersion of the clay in PS. This approach correlated reasonably well with X‐ray diffraction and transmission electron microscopy (TEM) data. A model for interpreting the saturation‐recovery data is proposed such that two parameters relating to the dispersion can be extracted. The first parameter, f, is the fraction of the potentially available clay surface that has been transformed into polymer–clay interfaces. The second parameter, ϵ, is a relative measure of the homogeneity of the dispersion of these actual polymer–clay interfaces. Finally, a quick assay of T is reported for samples equilibrated with atmospheric oxygen. Included are these samples as well as 28 PS/MMT nanocomposite samples prepared by extrusion. These measurements are related to the development of high‐throughput characterization techniques. This approach gives qualitative indications about dispersion; however, the more time‐consuming analysis, of a few deoxygenated samples from this latter set, offers significantly greater insight into the clay dispersion. A second, probably superior, rapid‐analysis method, applicable to oxygen‐containing samples, is also demonstrated that should yield a reasonable estimate of the f parameter. Thus, for PS/MMT nanocomposites, one has the choice of a less complete NMR assay of dispersion that is significantly faster than TEM analysis, versus a slower and more complete NMR analysis with sample times comparable to TEM, information rivaling that of TEM, and a substantial advantage that this is a bulk characterization method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3188–3213, 2003
New poly(butylene succinate)/layered silicate nanocomposites. II. Effect of organically modified layered silicates on structure, properties, melt rheology, and biodegradability
Authors: Okamoto Kazuaki , Sinha Ray Suprakas , Okamoto Masami
Published: November 2003

A series of new poly(butylene succinate) (PBS)/layered silicate nanocomposites were prepared successfully by simple melt extrusion of PBS and organically modified layered silicates (OMLS). Three different types of OMLS were used for the preparation of nanocomposites: two functionalized ammonium salts modified montmorillonite and a phosphonium salt modified saponite. The structure of the nanocomposites in the nanometer scale was characterized with wide‐angle X‐ray diffraction and transmission electron microscopic observations. With three different types of layered silicates modified with three different types of surfactants, the effect of OMLS in nanocomposites was investigated by focusing on four major aspects: structural analysis, materials properties, melt rheological behavior, and biodegradability. Interestingly, all these nanocomposites exhibited concurrent improvements of material properties when compared with pure PBS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3160–3172, 2003
Poly(styrene‐block‐isoprene) nanocomposites: Kinetics of intercalation and effects of copolymer on intercalation behaviors
Authors: Chen Hua , Schmidt Daniel F. , Pitsikalis Marinos , Hadjichristidis Nikos , Zhang Yuangming , Wiesner Ulrich , Giannelis Emmanuel P.
Published: November 2003

In addition to phase morphology, diffusion, and dynamics in the bulk, the behavior of block copolymers in the confined state has been of great interest. Although random and graft copolymers have been used in polymer‐layered silicate nanocomposites, well‐defined block copolymers have received relatively little attention. In this study, the kinetics of intercalation of a series of poly(styrene‐b‐isoprene) block copolymers into a layered silicate were examined via X‐ray diffraction. Intercalation was observed even when the copolymer was in the ordered state, with no discontinuity around the order–disorder transition of the copolymer. As the size of the polystyrene block was increased, slower intercalation kinetics were observed, possibly because of the increased glass‐transition temperature of the polystyrene segment. Finally, the clearing temperature of the copolymer in the nanocomposites as measured by small‐angle X‐ray scattering showed a large heating‐rate dependence suggesting that the nanoparticles act as kinetics barriers to the disordering of the copolymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3264–3271, 2003
The hot carrier dynamics in InGaN multi‐quantum well structure
Authors: Shikanai A. , Kojima K. , Omae K. , Kawakami Y. , Narukawa Y. , Mukai T. , Fujita Sg.
Published: November 2003

We investigated the hot carrier dynamics in InGaN mutli‐quantum wells using phtoluminescence, time‐resolved photoruminescence (TRPL) and white‐light pump and probe methods at room temperature. The pump and probe spectra or ΔOD spectra have not reflected the screening of electric field by photoexcited carriers but the distribution of hot carriers. It reflects the band filling of the tail state in lower energy side and Maxwell–Boltzmann‐like tail of hot carriers on the higher energy side. ΔOD spectra in 1.5 ps rose in the observed spectral region, which indicates that thermalization among carriers is very fast. It is because of carrier‐LO phonon and carrier‐carrier interaction. After 2 ps ΔOD spectra are red shifted as increasing the time delay. At 40 ps time delay, the Maxwell–Boltzmann‐like tail shows still the high temperature of carriers. This slow cooling is likely due to the hot phonon effects where the nonequilibrium phonon population may lead to a reabsorption of phonons by photoexcited carriers. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isoelectronic doping of AlGaN alloys
Authors: Novikov S. V. , Zhao L. X. , Harrison I. , Foxon C. T.
Published: November 2003

Isoelectronic doping of AlxGa1−xN alloys with arsenic in films grown by molecular beam epitaxy has been investigated. In photoluminescence spectra of these AlxGa1−xN layers, there is a gradual increase of the band gap and a smaller progressive shift of the position of blue emission band to the higher energies as the Al content increases. To explain the change in the energy of the blue band in As‐doped AlxGa1−xN alloys a model has been proposed, which predicts the shift in the blue band energy to be equal to the valence band offset from AlGaN to GaN. This prediction is consistent with the experimental results. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of nitrogen on self‐assembled GaInNAs quantum dots grown on GaAs
Authors: Nishikawa A. , Hong Y. G. , Tu C. W.
Published: November 2003

We investigate the effect of nitrogen on self‐assembled GaInNAs quantum dots (QDs) grown on GaAs (001) substrates by gas‐source molecular beam epitaxy. The dot density of GaInNAs QDs decreases with increasing nitrogen. The reduced strain resulted from nitrogen incorporation decreases dot density of QDs. However, we find that the dot density of Ga0.3In0.7N0.02As0.98 QDs is still significantly lower than that of Ga0.4In0.6As QDs, even though they have comparable nominal strain. This difference can be explained by the composition fluctuation in the wetting layer. The inhomogeneous local strain due to the composition fluctuation decreases the number of dots when the dots begin to form, resulting in lower dot density after QD growth. The dot density difference between GaInNAs QDs and GaInAs QDs becomes smaller with decreasing growth temperature. Therefore, the PL intensity of GaInNAs QDs grown at low temperature (450 °C) improved to be comparable to that of GaInAs QDs, while the PL intensity of the GaInNAs QDs grown at high temperature (520 °C) dramatically decreased with increasing nitrogen composition. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Localization characteristics of photoluminescence decay dynamics in an InxGa1−xAs1−yNy/GaAs single quantum well
Authors: Nakayama M. , Tokuoka K. , Nomura K. , Yamada T. , Moto A. , Takagishi S.
Published: November 2003

We have investigated photoluminescence (PL) properties of an InxGa1−xAs1−yNy/GaAs single quantum well from an aspect of carrier localization. The sample was grown on a (001) GaAs substrate by metalorganic vapor phase epitaxy: the InxGa1−xAs1−−yNy thickness is 8 nm, and the alloy compositions of x and y are 0.15 and 0.034, respectively. The PL spectra at low temperatures lie on the low energy side of the band edge confirmed by photoreflectance spectroscopy, and the PL peak energy approaches to the band edge with increasing excitation power. These results demonstrate the localization characteristics of the PL process. It has been found that the PL decay of localized carriers exhibits a stretched exponential profile that is a typical decay phenomenon in a disordered system. From the energy dependence and temperature dependence of the stretched exponential profile, we conclude that the PL decay dynamics at low temperatures are dominated by random potentials due to alloy disordering of InGaAsN. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nitrides as spintronic materials
Authors: Dietl Tomasz
Published: November 2003

A report on the progress in spintronics‐related works involving group III nitrides is given, emphasizing contradictory opinions concerning the basic characteristics of these materials. The actual position of magnetic impurities in the GaN lattice as well as a possible role of magnetic precipitates is discussed. The question as to whether the hole introduced by Mn impurities is localized tightly on the Mn d levels or rather on the hybridized p–d bonding states is addressed. The nature of spin–spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined and the possible origins of the high‐temperature ferromagnetism observed in (Ga, Mn)N are presented. Experimental studies aimed at evaluating characteristic times of spin coherence and dephasing in GaN are described. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of the GaN‐rich side of GaNP grown by metal‐organic chemical vapor deposition
Authors: Tsuda Yuhzoh , Mouri Hirokazu , Araki Masahiro , Ueta Yoshihiro , Yuasa Takayuki , Taneya Mototaka
Published: November 2003

We have investigated the growth of the GaN‐rich side of GaNP films by metalorganic chemical vapor deposition (MOCVD). The GaNP samples were mainly analysed by using X‐ray diffraction (XRD) and Auger electron spectroscopy (AES). From the XRD measurement, we have found that the c‐axial lattice constant and the a‐axial lattice constant of our GaNP were smaller than those of GaN. Moreover, we have confirmed that these lattice constants decreased with increasing PH3 flow rate. According to the AES analysis, the nitrogen concentration in GaNP hardly changed along with increasing the PH3 flow rate, but the gallium concentration tended to decrease. This fact implies that a phosphorus atom would be replaced with not a nitrogen atom but a gallium atom on III‐group site. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Giant second‐harmonic generation due to quasi‐phase matching in a one‐dimensional GaN photonic crystal
Authors: Torres J. , Coquillat D. , Legros R. , Lascaray J. P. , Ruffenach S. , Briot O. , Aulombard R. L. , Peyrade D. , Chen Y. , Le Vassor d'Yerville M. , Centeno E. , Cassagne D. , Albert J. P.
Published: November 2003

We have demonstrated the giant enhancement of second‐harmonic generation in a one‐dimensional GaN photonic crystal structure caused by the simultaneous achievement of strong fundamental field confinement and quasi‐phase matching conditions. We have firstly measured the linear dispersive properties of the resonant modes for various azimuthal directions to predict the quasi‐phase matching conditions. The theory based on a rigorous scattering matrix method has provided a good description of the equi‐frequency surfaces. We have then shown that the equi‐frequency surfaces may be used to identify the angular situations for which the quasi‐phase matching conditions can be satisfied. The SHG enhancement achieved due to the double resonance was 5000 times greater than for the unpatterned GaN layer. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton localization in InGaN/GaN single quantum well structures
Authors: Graham D. M. , Vala A. Soltani , Dawson P. , Godfrey M. J. , Kappers M. J. , Smeeton T. M. , Barnard J. S. , Humphreys C. J. , Thrush E. J.
Published: November 2003

We have performed a detailed investigation of the low temperature (T = 6 K) photoluminescence spectra and recombination lifetimes of localized excitons in a set of InGaN/GaN single quantum wells in which the indium fraction in the quantum well was varied. We found that with increasing indium fraction the photoluminescence peak emission moved to lower energy and the intensities of the phonon replicas relative to the zero‐phonon line increased. From a multi‐Gaussian fit of the experimental data, we extracted the Huang–Rhys factor (S), a measure of the strength of the exciton coupling with LO‐phonons. By comparing experimental S factors with the results of a theoretical model, we found that the excitons localize on a length scale of ∼2 nm in our samples. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoreflectance studiesof N‐ and Ga‐face AlGaN/GaN heterostructures confininga polarisation induced 2DEG
Authors: Winzer A. T. , Goldhahn R. , Buchheim C. , Ambacher O. , Link A. , Stutzmann M. , Smorchkova Y. , Mishra U. K. , Speck J. S.
Published: November 2003

Photoreflectance measurements have been carried out in order to determine the electric field strength F within the topmost layers of Ga‐face polarity AlxGa1−xN/GaN and N‐face polarity GaN/AlxGa1−xN/GaN heterostructures containing high‐mobile polarisation induced 2DEGs. For both types of samples F decreased from 400 kV/cm at room temperature up to 200 kV/cm when cooling down the structure to T = 5 K. Our results strongly emphasise the existence of surface donor and surface acceptor states of the Ga‐ and N‐face samples, respectively. The temperature dependence of F is explained by the change of the piezoelectric and spontaneous polarization. From self‐consistent conduction band calculations the bare surface potential was obtained. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measurement of optical nonlinearities from intersubband transitions in GaN/AlGaN quantum wells at 1.5 μm
Authors: Chen Gang , Rapaport R. , Mitrofanov O. , Gmachl C. , Ng H. M.
Published: November 2003

We measured the resonant nonlinear optical absorption and refraction due to intersubband transitions in GaN/AlGaN multiple quantum well structures at 1.5 μm. The measured values are much smaller than that predicted by theoretical studies. This is attributed to a larger than expected dephasing of excited electrons. At high excitation intensity, the absorption can be saturated. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Angular dependence of the in‐plane polarization anisotropy in the absorption coefficient of strained M‐plane GaN films on γ‐LiAlO2
Authors: Misra Pranob , Sun Y. J. , Brandt O. , Grahn H. T.
Published: November 2003

We investigate the in‐plane polarization properties of GaN films grown by plasma‐assisted molecular‐beam epitaxy on LiAlO2(100). Due to the crystal symmetry of LiAlO2(100), GaN films can be realized in a nonpolar (M‐plane) configuration, i.e., the c‐axis of the wurtzite unit cell lies in the growth plane. For strained M‐plane GaN films, the band structure of the valence band changes in such a way that the optical transmittance is completely linearly polarized for two orthogonal in‐plane directions, where one of these directions is parallel to the c‐axis of the GaN film. The transmittance for an arbitrary in‐plane polarization angle can be described as a linear combination of the transmittance for two orthogonal polarization, one of which is parallel to the c‐axis. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence and Raman study of hexagonal InN and In‐rich InGaN alloys
Authors: Davydov V. Yu. , Klochikhin A. A. , Emtsev V. V. , Smirnov A. N. , Goncharuk I. N. , Sakharov A. V. , Kurdyukov D. A. , Baidakova M. V. , Vekshin V. A. , Ivanov S. V. , Aderhold J. , Graul J. , Hashimoto A. , Yamamoto A.
Published: November 2003

We present results of a detailed study of X‐ray, photoluminescence, and Raman measurements of hexagonal InN, In‐rich InxGa1−xN (0.36 < x < 1) alloys, and InN samples annealed in oxygen. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Localized biexcitons in AlxGa1−xN ternary alloy epitaxial layers
Authors: Yamada Y. , Sasaki C. , Ueki Y. , Taguchi T. , Tanaka S. , Nakagawa Y.
Published: November 2003

Excitonic optical properties of AlxGa1−xN ternary alloy epitaxial layers have been studied by means of photoluminescence (PL), time‐resolved PL, and PL excitation (PLE) spectroscopy. The luminescence line due to radiative recombination of biexcitons was clearly observed in an Al0.08Ga0.92N epitaxial layer. The PL decay time of excitons and biexcitons was estimated to be 350 and 210 ps, respectively. PLE spectroscopy of biexcitons enabled us to observe a two‐photon absorption process of biexcitons. On the basis of the energy separation between exciton resonance and two‐photon biexciton resonance, the binding energy of biexcitons in Al0.08Ga0.92N was estimated to be 15 ± 2 meV. This value was approximately 2.5 times as large as the binding energy of biexcitons in GaN. This value was also found to be comparable to the observed energy separation between the exciton luminescence and the biexciton luminescence, which indicated the strong localization of biexcitons. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of MOVPE‐grown GaN layers on GaAs (111)B with a cubic‐GaN (111) epitaxial intermediate layer
Authors: Sanorpim S. , Takuma E. , Katayama R. , Ichinose H. , Onabe K. , Shiraki Y.
Published: November 2003

We have proposed the use of cubic‐GaN (c‐GaN) as an intermediate layer for the metalorganic vapor phase epitaxy (MOVPE) growth of hexagonal‐GaN (h‐GaN) on GaAs (111)B substrates. Insertion of the c‐GaN layer at the h‐GaN (0001)/GaAs (111) interface significantly improves the crystallinity of the h‐GaN layer. Although, we have used [111]‐oriented c‐GaN layer so far, the lattice‐mismatch between h‐GaN (0001) and c‐GaN (111) is expected to be less than 0.1%, which is much smaller than that for the other commonly used substrate materials. Furthermore, the c‐GaN layer was grown at a relatively low growth temperature (Tg = 600 °C) to prevent the GaAs substrate from thermal decomposition and to provide a strain relief template layer. This technique enables us to succeed in obtaining nearly strain free h‐GaN layers on GaAs (111)B substrates. In this report, the relationship between the nature of the c‐GaN intermediate layer and the cubic‐to‐hexagonal structural transition machanisms are discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Narrow bandgap group III‐nitride alloys
Authors: Wu J. , Walukiewicz W. , Yu K. M. , Ager III J. W. , Haller E. E. , Lu Hai , Schaff William J.
Published: November 2003

High‐quality wurtzite In‐rich In1−xGaxN (0 ≤ x ≤ 0.5) and In1−yAlyN films (0 ≤ y ≤ 0.25) were grown on sapphire substrates by molecular‐beam epitaxy. Optical absorption, photoluminescence and photomodulated reflectance measurements demonstrate that the fundamental bandgap for InN is only about 0.7 eV. The free electron effective mass is found to vary with free electron concentration, the consequence of a strongly non‐parabolic conduction band caused by the k · p interaction with the valence bands across the narrow bandgap. The bandgap gradually increases with increasing Ga or Al content in In1−xGaxN or In1−yAlyN alloys. The composition dependencies of the bandgaps are well described by bowing parameters of 1.4 eV for In1−xGaxN and 3.0 eV for In1−yAlyN. The direct gaps of the group III‐nitride alloy system cover a very broad spectral range from the near‐infrared in InN to deep‐ultraviolet in AlN. This offers unique opportunities for the use of these alloys in a wide range of optoelectronic and photovoltaic devices. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polarization‐induced surface band bendings of GaN films studied by synchrotron radiation photoemission spectroscopy
Authors: Jang Ho Won , Ihm Kyu Wook , Kang Tai‐Hee , Lee Jung‐Hee , Lee Jong‐Lam
Published: November 2003

The change in the surface band bandings of GaN films with crystal polarity and strain was investigated using synchrotron radiation photoemission spectroscopy. The Ga‐face GaN sample showed larger surface band bending than the N‐face one by 1.4 eV due to spontaneous polarization‐induced sheet charges at the surface, resulting in a higher Schottky barrier height of a Pt contact. For both n‐type and p‐type GaN, the shift of the surface Fermi level with longitudinal tensile strain (∼4 × 10−3) is negligible, while that with compressive strain (∼3 × 10−3) is significant. This could be attributable to combined effects of piezoelectric polarization‐induced sheet charges and the change of bandgap energy with the strains near the surface region. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Role of Amylose in the Maintenance of the Configuration of Rice Starch Granules
Authors: Seguchi Masaharu , Hayashi Miho , Suzuki Yasuhiro , Sano Yoshio , Hirano Hiro‐Yuki
Published: November 2003

Amylose contents in 39 strains of rice starch, including waxy starch, low amylose containing starch, and non‐waxy starch, were measured. Seguchi et al. [1] reported that waxy wheat starch exhibits a ghost appearance by staining and swelling with 25% KI/10%I2 solution at 25 °C. We subjected the 39 rice strains to staining in the same manner. We found that the relative ghost area (%) in a rice starch, which is a measure of granule swelling in 25%KI/10%I2 solution, , is related to its amylose content (r = ‐0.78). As the relative ghost area (%) of the rice starch increased rapidly when the amylose content decreased below 5%, we concluded that at least 5% of amylose is required to maintain the structure of rice starch granules. Furthermore, the red‐brown central region in ghostly appearing granules decreases with amylose level and the surrounding light brown region increases. When the starch does not contain amylose, the ghost is entirely light brown. The decrease in the area of the red‐brown central region with decreasing amylose content suggests that amylose is concentrated in the red‐brown central region of the ghost.
Crystallinity and Pasting Properties of Freeze‐Thawed High Amylose Maize Starch
Authors: Jeong Hyo‐Young , Lim Seung‐Taik
Published: November 2003

Native and defatted high amylose (about 70%) maize starch gels were freeze‐dried or repeatedly freeze‐thawed, and the effects of the treatments on the crystallinity, pasting viscosity, and resistance to digestive enzymes of the dried starch were examined. Both native and defatted starches showed a B‐type crystal structure in the X‐ray diffractogram, but the crystallinity was decreased by repeating the freeze‐thawing cycle. In the DSC thermogram, the freeze‐thawed starches exhibited two endothermic transitions in the temperature ranges of 90—110 °C and 130—160 °C, representing amyloselipid complexes and amylose‐amylose double helix crystals, respectively. By defatting, the melting enthalpy for the amylose double helices was increased, indicating that the residual lipids inhibited the amylose crystal formation. Ice crystals in the starch gel matrix became smaller and the ice cell membrane became thinner as freeze‐thawing was repeated. The freeze‐dried or freeze‐thawed starch powders swelled to a paste by heating in water as did typical granular starch, but the setback by cooling was significantly high due to the rapid retrogradation of leached amylose. By the treatments, the resistance of the starch to digestive enzymes was also raised. The defatted starches displayed greater paste viscosity and resistance to digestive enzymes than the native starches. But the overall viscosity was decreased as the number of freeze‐thawing cycles increased.
Impregnation of Kraft Paper with Cassava‐Starch Acetate — Analysis of the Tensile Strength, Water Absorption and Water Vapor Permeability
Authors: Larotonda Fábio D. S. , Matsui Kátia S. , Paes Sabrina S. , Laurindo João Borges
Published: November 2003

Kraft paper is widely used in the manufacture of packing, but its hygroscopic properties and water vapor barrier are not suitable for the storage of dehydrated products for long periods. The objective of this work was to study the influence of the impregnation of this paper with cassava‐starch acetate (CSA, degree of substitution, DS, 1.41) and the consequent modification of tensile strength, water absorption and water vapor permeability. SEM‐micrographs were taken and experiments of water absorption, tensile strength, water vapor permeability and water sorption isotherms were carried out for original and CSA‐impregnated Kraft paper. The results obtained showed that the impregnation of the Kraft paper with CSA significantly decreases the water absorption and the water vapor permeability. Water sorption isotherms showed great differences only at high relative humidity. In relation to mechanical properties, the tensile strength of the Kraft paper increased with its impregnation by CSA. Therefore, CSA impregnation was demonstrated to be a very interesting and new alternative for the use of cassava starch to obtain waterproof paper.