bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methoxymethyl cation [CH3OCH2]+ revisited: Experimental and theoretical study
Authors: Audier H. E. , Bouchoux G. , McMahon T. B. , Milliet A. , Vulpius T. 
Published: May 2005

AbstractThe metastable dissociation of the methoxymethyl cation and a number of its deuterium and 13C variants was examined using a reverse‐geometry double‐focusing mass spectrometer. The loss of methane from the methoxymethyl cation clearly showed a composite peak shape which, when deconvoluted, revealed a bimodal kinetic energy release distribution in the resulting formyl cations. Labelling experiments revealed that the two carbon atoms and all hydrogens become equivalent on the time‐scale of the unimolecular dissociation lifetime of the decomposing ion. A small deuterium isotope effect was found which can be rationalized on the basis of zero point energy effects. The bimodal kinetic energy release distribution was shown, with the aid of a four‐sector instrument, to be due to the production of both formyl cation (with a large kinetic energy release) and isoformyl cation (with a much smaller kinetic energy release). The methoxymethyl cation was also prepared with a precisely defined amount of internal energy in a Fourier transform ion cyclotron resonance (FTICR) spectrometer by the reaction of methyl cation with formaldehyde. Experiments with 13C and deuterium labelling revealed that the dissociation to formyl cation of the methoxymethyl cations formed in the low‐pressure FTICR cell by reaction of methyl cation with formaldehyde is accompanied by complete scrambling of the carbons and incomplete scrambling of the hydrogens. Ab initio calculations were carried out which identified and characterized each of the stable minima and transition states for the appropriate reactions. The calculations were fully consistent with the mechanism deduced on the basis of the experimental data.
Simple determination of relative hydrogen atom affinities by supercritical fluid chromatography/atmospheric pressure chemical ionization mass spectrometry
Authors: Matsumoto Kozo 
Published: May 2005

AbstractCoupled supercritical fluid chromatography and atmospheric pressure chemical ionization mass spectrometry was applied to estimate hydrogen atom affinities. The intensities of the M+ and MH+ peaks in the mass spectra were measured at various drift voltages (collision energies). The ratios of the two peaks were plotted against the drift voltages to obtain threshold drift voltages. The threshold drift voltages of polycyclic aromatic hydrocarbons were plotted and found to be proportional to the values of reported hydrogen atom affinities. The value for acenaphthylene was estimated to be 292.9 kJ mol−1 from this relationship.
Field‐dependent [M – 2H]+. formation in the field desorption mass spectrometric analysis of hydrocarbon samples
Authors: Heine Curt E. , Geddes Marie M. 
Published: May 2005

AbstractHigh‐boiling hydrocarbons often yield abundant [M — 2H]+. ions under the conditions of field desorption mass spectrometry (FDMS). This work evaluated [M — 2H]+. formation from various saturated and aromatic compounds. The most intense [M — 2H]+. signals observed resulted from the analysis of saturated compounds containing long and branched chains. The presence of an aromatic ring in a molecule, however, strongly diminished [M — 2H]+. formation during FDMS. Experiments involving manipulation of the applied potential between the FD anode and cathode reveal the strong field dependence of this phenomenon. At a potential difference of 10 kV, strong [M — 2H]+. formation occurred for samples including squalane, hexatriacontane (C36 n‐alkane) and a Polywax 655 mixture. Analyses of the same samples conducted at a potential difference of 4 kV produced only weak (if measurable) [M — 2H+.] signals. The magnitude of [M — 2H]+. formation also decreased as the sample quantity decreased.
Disparity between solution‐phase equilibria and charge state distributions in positive‐ion electrospray mass spectrometry
Authors: Wang Guangdi , Cole Richard B. 
Published: May 2005

AbstractTwo peptides, bradykinin and gramicidin S, were used to investigate the relationship between protonation in the solution phase and charge state distribution observed in electrospray ionization (ES) mass spectra. The degree of protonation in solution was estimated using acid‐base equilibrium calculations where possible. Protonation in solution was varied by adjusting pH, solvent composition and peptide concentration. Major disparities were observed between calculated solution‐phase peptide protonation and the charge state distributions observed in ES mass spectra. The [(M + 2H)2+]/[(M + H)+] ratio calculated in solution was larger than the abundance ratio (M + 2H)2+ /(M + H)+ in the ES mass spectra of all acidic aqueous (pH < 6.5) and non‐aqueous solutions; in basic aqueous solutions (pH > 9.5) the opposite was true. At high pH, electrophoretic droplet charging may reduce the activity of OH− in positively charged droplets. The results at low pH imply the existence of supplementary factors in the ES ionization process which largely attenuate the degree of charging in the gas phase as compared with solution. Factors such as the increasing intra‐ and intermolecular coulombic repulsion between charge carriers (protons) and increasing attractive forces between protonated sites and counterions at progressively later stages of charged droplet evaporation were hypothesized to be chiefly responsible for this effect. Non‐aqueous solvents of high basicity compete with analytes to some extent for available protons, forming protonated solvent molecules while decreasing the sensitivity and the degree of multiple charging of peptides.
Reaction of ionized propene with methanol: Comparison with CH3OH2+ formation from ionized 2‐methylpropanol
Authors: McAdoo David J. , Zhao Guohong , Ahmed Mohammed S. , Hudson Charles E. , Giam C. S. 
Published: May 2005

AbstractMethanol exchanges its hydroxyl hydrogen with deuteriums in ionized propene during the formation of protonated methanol. This exchange is attributed to the interconversion [CH3CHCH2+. HOCH3⇌][CH2 ⋅CHCH2 +H2OCH3] in single collisions. The exchange in this ion‐molecule reaction is analogous to that observed in the formation of protonated methanol from ionized 2‐methylpropanol, supporting the intermediacy of ion‐neutral complexes in the final step of the latter reaction. Ion‐molecule reactions were studied using a Fourier transform mass spectrometer.
A tandem mass spectrometric study of C2H5I+CH3 ions: A search for the non‐classical ethyl cation stabilized by methyl iodide
Authors: Zagorevskii Dmitri V. , Holmes John L. 
Published: May 2005

AbstractThe results of this study have shown that the C2H5I+CH3 ion containing classical and non‐classical forms of the ethyl group can be generated by gas‐phase ion—molecule reactions. The classical ions fragment by CH4 and CH3⋅ losses, the latter without loss of positional identity of H atoms in the ethyl group. Hydrogen scrambling, however, precedes ethene loss, taking place in an ion of non‐classical form. The latter is produced directly from ion—molecule reactions and from energy‐rich classical ions. The relative energies of the classical and non‐classical ions could not be determined, although the former was proposed to be the global minimum. Finally, the classical ion serves as a source for the ylid ion CH3ICH2+., which previously had eluded preparation.
Water sorption characteristics of grp composite: Effect of outdoor weathering
Authors: Blaga A. 
Published: May 2005

AbstractThe complete sorption‐desorption equilibrium isotherms determined at 23° C indicate that glass fiber‐reinforced polymer (GRP) sheets weathered outdoors for 3 years absorb larger amounts of water vapor than the non‐weathered sheets. Sorption and desorption Kinetic results at 23° and two levels of relative pressure (p/p0 = 0.80 and p/p0 = 0.975) show that the weathered sheets absorb water vapor at considerably higher rates than the non‐weathered sheets. Larger amounts of sorbed water, and faster sorption and desorption will result in respectively greater magnitudes and higher rates of dimensional changes (swelling and shrinking). This accelerates the overall effects of environmentally exerted stress‐fatigue on the GRP composite.
Low‐velocity impact damage in graphite‐fiber reinforced epoxy laminates
Authors: Rhodes Marvin D. , Williams Jerry G. , Starnes James H. 
Published: May 2005

AbstractAn experimental investigation was conducted to identify the failure mechanism and to understand damage propagation in compression‐loaded composite structures. The tests were conducted on several laminates of different ply orientation with thicknesses that ranged from 0.56 to 0.79 cm. The panels were damaged by 1.27‐cm‐diameter aluminum spheres propelled normal to the specimen surface at velocities ranging from 30 m/s to 140 m/s. Results indicate that there is significant internal laminate damage due to low‐velocity impact with no surface damage. The internal damage consists of delamination and intraply cracking. Three damage propagation modes were identified as causing specimen failure; delamination, axial load‐lateral deformation coupling, and local shear failure.
Flexural fatigue of marine laminates reinforced with woven roving of E‐glass and of Kevlar® 49 aramid
Authors: Zweben Carl , Wardle Marilyn W. 
Published: May 2005

AbstractA comparison of the flexural fatigue characteristics of E‐glass and Kevlar® 49 aramid in polyester and vinyl ester resin hand lay‐ups typical of boat hull laminates is presented. Data on unidirectional E‐glass and aramid composites from epoxy preimpregnated tapes are reported for comparison. The data indicate that while the initial flexural strength of E‐glass woven roving laminates is greater than that of aramid laminates, the runout stress of aramid laminates at 106fatigue cycles is similar or superior to glass. S‐N curves for aramid laminates are flatter indicating better flexural fatigue resistance.
Fatigue of glass and carbon fiber reinforced engineering thermoplastics
Authors: Mandell J. F. , Huang D. D. , McGarry F. J. 
Published: May 2005

AbstractCyclic tension fatigue S‐N curves are given for injection moleded Nylon 6/6, polycarbonate, polysulfone, polyphenylene sulfide, and poly(amide‐imide) matrices with glass and carbon fibers as well as for unreinforced material. The S‐N curves for most composites appear linear, with no evidence of a fatigue limit up to 106cycles. Some nonlinearity is evident with the Nylon 6/6 composities, and these appear to fail at a cumulative strain similar to the ultimate static strain. The remainder of the composites appear to fail by a crack propagation mechanism. The glass reinforced materials all degrade at a similar rate in fatigue, while the carbon reinforced materials with brittle matrices degrade more slowly than do those with ductile matrices. The latter effect may be due to greater integrity of the cracked regions for brittle matrix systems.
The resin matrix: Its influence on sheet molding compound mechanical properties
Authors: Pritchard Geoffrey , Rhoades Gary V. 
Published: May 2005

AbstractA series of sheet molding compound (SMC) materials have been prepared in which the only variable was the polyester resin used as the matrix. The polyester resins were all synthesized from maleic anhydride, propylene glycol and 1,2 propane diol. Systematic variations were made in the molar ratio of maleic of to phthalic anhydride used, and also in the hydroxyl values of the polyesters. The resins were also separately crosslinked with styrene, and the fracture toughness of the cast sheets measured. The toughness of the SMC was assumed to be measurable by linear elastic fracture mechanics (LEFM) methods. Results indicated that the resin matrix toughness was inversely related to polyester unsaturation but the SMC toughness was directly related to it. The hydroxyl values of the resins were determined by nuclear magnetic resonance (NMR) of the silyated derivatives. The tensile properties of the SMC were investigated. Modulus increased steadily with resin hydroxyl value, but tensile strength showed a maximum at 50 mg. These observations indicate the importance of hydroxyl value in SMC resin formulation, arising from its effect on fiber‐resin bond strength.
Physical aging in graphite/epoxy composites
Authors: Kong Eric S. W. , Lee Susanna M. , Nelson Howard G. 
Published: May 2005

AbstractMatrix‐dominated mechanical behavior of a graphite/epoxy composite has been found to be affected by sub‐Tg annealing. Postcured (±45°)4S specimens of Thornel 300 graphite/Narmco 5208 epoxy were quenched from above Tg and given a sub‐Tg annealing at 140°C for times up to 105 min. The ultimate tensile strength, strain‐to‐break, and toughness of the composite material were found to decrease as functions of sub‐Tg annealing time. No weight loss was observed during the sub‐Tg annealing. The time‐dependent change in mechanical behavior is explained on the basis of free‐volume changes that are related to the physical aging of the nonequilibrium glassy network‐epoxy. The results imply possible changes in composite properties with service time.
Effect of water and isooctane absorption on the flexural fatigue strength of a sheet molding compound
Authors: Hoa S. V. , Ngo A. D. , Sankar T. S. 
Published: May 2005

AbstractThe effect of water and isooctane absorption on the flexural fatigue strength of a sheet molding compound (SMC‐R30) is investigated. Absorption of water reduces the fatigue life of specimens of SMC‐R30 as compared to the fatigue life of specimens tested in air. Absorption of isooctane reduces the fatigue life much more than absorption of water.
Optimum strength of composites of ceramic particles in poly(methyl methacrylate)
Authors: Atsuta M. , Turner D. T. 
Published: May 2005

AbstractCeramic particles were sedimented in methyl methacrylate, which was then polymerized by exposre to γ‐rays. After annealing, specimens were cut and tested, and the ceramic content determined by ashing. Diamond indentation hardness was found to increase monotonically with increase in ceramic content. In contrast, both Young's modulus and, more markedly, flexural strength were found to give optimum (peak) values for a content of lithium aluminum silicate near 80 wt‐percent. The higher silicate contents were reached with use of a silane coupling agent and by centrifuging, prior to polymerization. Examination of fracture surfaces by scanning electron microscopy indicated that the decrease in mechanical properties was due to the presence of voids in the polymeric matrix. It is suggested that void formation becomes serious when ceramic particles are initially too close‐packed to respond to conraction, during polymerization, by shifting closer together. Consistent with this suggestion, both void formation and peaking in strength can be prevented by continuously centrifuging the composite throughout the polymerization reaction.
Fatigue damage studies in high strength sheet‐molding compound fiberglass composites
Authors: Kundrat R. , Joneja S. , Broutman L. J. 
Published: May 2005

AbstractThe materials considered in this investigation were oriented‐hybrid‐glass‐fiber‐reinforced vinyl ester resin sheet‐molding compound (SMC) composites. The composition of one material was 60 percent continuous glass and 5 percent random fibers, while the other was 45 percent continuous glass and 20 percent random fibers. The S‐N curves for the two materials were determined in the continuous fiber direction. The fatigue stress levels ranged from approximately 20 to 80 percent of each material's respective ultimate tensile strength. The residual tensile strengths of the fiber‐reinforced composites were not seriously reduced until near final fracture. The moduli of the composites in the fiber direction are also not reduced in any detectable manner. Damping measurements have shown that the damping increases during fatigue and that it is a sensitive measure of matrix and interface damage, generally debonding and cracking. It is shown by damping measurements that damage accumulates differently for two materials studied. The material with the higher percent of continuous glass appeared to be more cycle‐dependent, while the other was more stress‐dependent.
Monitoring cure viscosity of epoxy composite
Authors: Tajima Yuji A. 
Published: May 2005

AbstractViscosity is an important process variable that should be monitored and controlled to ensure the consistent and reliable production of graphite‐fiber‐reinforced composite parts by the autoclave/vacuum bag process. Unfortunately, no technique is currently known for the direct measurement of viscosity in this process. However, d.c. conductivity and a.c. phase lag appear to correlate quite well with viscosity, and either electrical property may be followed in order to indirectly monitor viscosity. As the method of measuring d.c. conductivity is so inexpensive, simple, and almost free of electrical interference compared to the method of measuring a.c. phase lag, it appears to be the method of first choice for application in an autoclave environment.
Use of wood fibers in thermoplastic composites
Authors: Kokta Bohuslav V. , Chen Rubie , Daneault Claude , Valade Jacques L. 
Published: May 2005

AbstractWood fibers from aspen and spruce have been used for filler and reinforcement of polystyrene. The wood fibers used were in the form of refined wood. In order to improve compatibility of wood fibers with polymeric matrices, fibers have been modified by copolymerization with styrene. The kanthate method of grafting employing the ferrous‐hydrogen peroxide catalytic system was used for fiber treatment. The following properties of composites have been measured: elastic‐modulus, tensile strength, and energy absorbed at break. In summary, it has been found that the composites from grafted fibers showed superior mechanical properties to those with original fibers. In general, as a filler, the aspen fibers were superior to spruce, and the shorter fibers superior to longer ones. Mechanical properties of composites as compared to polystyrene were improved as follows: elastic modulus +37 percent; tensile strength +35 percent and energy at breakup by 43.5 percent. The best composites properties have been achieved at 40 percent of fiber fraction present.
Evaluation of surface treatments for fibers in composite materials
Authors: Fraser W. A. , Ancker F. H. , Dibenedetto A. T. , Elbirli B. 
Published: May 2005

AbstractAn embedded single filament test has been developed that measures the cumulative distribution of critical fibers lengths for a given fiber‐polymer system. The mean value of critical lengths and the dispersion of values are a function of both the shear transmission characteristics of the interface and the strength characteristics of the fibers. A computer model of the stochastic fracture process has been developed that incorporates a mixed‐element, weakest‐link model to describe the strength properties of the fibers, a random generator to describe the stochastics of multiple fiber fracture, and a shear‐lag analysis to describe the shear transmission across the interface. From the measurement of critical fiber lengths, a value for the magnitude of the shear transmission across the fiber‐polymer interface, τ, can be determined. From measured values fiber strength, the ability of a surface treatment to protect a given fiber can be determined. A variety of surface treatments for E‐glass are evaluated in a number of thermoplastic polymer materials. The experimental technique and the associated analysis are shown to be valuable in separating the coupling and sizing effects of the fiber surface treatment formulations. This should be of particular value in the optimization of commercial fiber treatment formulations.
A review of recent progress in the studies of molecular and microstructure of coupling agents and their functions in composites, coatings and adhesive joints
Authors: Ishida Hatsuo 
Published: May 2005

AbstractRecent progress in the studies of molecular and microstructure of interfaces and interphases in composites, coatings, and adhesive joints is reviewed. Remarkable progress has been made in elucidating the structure of silane coupling agents and their function with respect to dry and wet strengths of multiphase systems. Aminosilanes attracted major effort in the past. It is now understood that the structure of partially cured hydrolyzate is complicated. When adsorbed from a natural pH solution and dried in air at room temperature, approximately half of the amine groups form amine bicarbonate salt with the CO2 in air. The rest of the amine groups are either intra‐ and intermolecularly hydrogen bonded to neighboring silanol groups or free from hydrogen bonding. There exists chemical bonding at the glass/silane or metal/silane interfaces. The surface characteristics, including acidity, topology and homogeneity, influence the structure of the coupling agent. The coupling agent interphase shows a gradient in various properties. Silanes tend to be ordered in the interphase and the degree of organization depends largely on the organofunctionality. The orientation and organization of the silane affects the reinforcement mechanism. There are chemisorbed and physisorbed silanes in the interphase. The coupling agent/matrix interface is a diffuse boundary where intermixing takes place due to penetration of the matrix resin into the chemisorbed silane layers and the migration of the physisorbed silane molecules into the matrix phase. With proper selection of the organofunctionality and the curing conditions, silanes can chemically react with the matrix to form copolymers. The existence of the matrix interphase is now well accepted and the effect of the interphase on the mechanical properties has been studied. It has been recognized that modification of the matrix interphase, such as a coating applied on the fiber using a similar resin as the matrix, has a complex effect on the mechanical performance. It is noteworthy that attempts to synthesize new coupling agents and to utilize the existing coupling agents more effectively still continue. Based on the molecular understanding, new concepts in the reinforcement mechanism have appeared which recognize the importance of interpenetrating networks, the structure of silane in the treating solution, and the microheterogeneity of the glass surfaces. The knowledge obtained through the studies of composites can be applied to organic coatings and adhesive joints provided that the geometrical factors are taken into consideration.
Dynamic mechanical experiments for probing process‐structure‐property relations in amine‐cured epoxies
Authors: Chu Helen S. , Seferis James C. 
Published: May 2005

AbstractDynamic mechanical experiments were performed on an amine‐cured high performance epoxy system containing two types of epoxies and one amine. The system approximates a commercial resin system used widely as matrix material for graphite composites and whose main ingredients and composition are 88.5 percent of tetraglycidyl 4,4′‐diamino diphenyl methane (TGDDM) and 11.5 percent of polyglycidyl ether of Bisphenol A Novalac epoxy with varying compositions of 4,4′‐diaminodiphenyl sulfone (DDS), ranging from 19 to 40 PHR. Specifically, the effects of DDS and Novalac content as well as processing conditions including the particle size of solid components, the mixing speed, mixing temperature, and the mixing duration of the components on the dynamic mechanical properties of the epoxy polymer were investigated. A viscoelastic transition in the dynamic spectrum which was observed to be quite sensitive to the sample's Tg in conjunction with incomplete crosslinking reactions allowed for interrelating the composition and processing variables to the structure and bulk properties of this epoxy system.