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11.
C. Pagnoulle N. Moussaif J. Riga R. Jrme 《Journal of polymer science. Part A, Polymer chemistry》2000,38(19):3682-3689
The grafting kinetics of reactive poly(styrene‐co‐acrylonitrile) (SAN) onto EPR‐g‐MA was studied under isothermal conditions, at the planar interface of an SAN/ethylene‐propylene rubber (EPR) bilayer film in relation to the type of reactive groups, NH2 versus carbamate (which is an amine precursor), attached to SAN. The amount of SAN chemically bound to EPR chains at the interface was estimated by selectively washing off the unreacted SAN chains before X‐ray photon spectroscopic analysis of the released surface. It is clear that the mutual reactivity of the reactive groups, i.e., the NH2–MA pair versus the carbamate–MA pair, has a decisive effect on the amount of SAN that reacts with EPR‐g‐MA at the interface. In case of SAN‐carb, the grafting reaction is controlled by the thermolysis of the carbamate groups into primary amines. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3682–3689, 2000 相似文献
12.
Amanda L. Santos Gilberto O. Chierice Kenneth S. Alexander Alan Riga Ellen Matthews 《Journal of Thermal Analysis and Calorimetry》2009,96(3):821-825
Eugenol is the main volatile compound extracted oil from clove bud, Syzygium aromaticum L., and used in traditional medicine, as a bactericide, fungicide, anesthetic, and others. Its extraction was performed using
hydrodistillation which is the most common extraction technique. Its components and thermal behavior were evaluated using
gas chromatography (GC) and differential scanning calorimetry (DSC), which provide a better characterization of these natural
compounds. This extracted product was compared to the standard eugenol results. The GC results suggested ~90% eugenol was
found in the total extracted oil, and some of its boiling characteristics were 270.1 °C for peak temperature and 244.1 J g−1 for the enthalpy variation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
In this paper, we present simulations of the decay of quantum coherence between vibrational states of I(2) in its ground (X) electronic state embedded in a cryogenic Kr matrix. We employ a numerical method based on the semiclassical limit of the quantum Liouville equation, which allows the simulation of the evolution and decay of quantum vibrational coherence using classical trajectories and ensemble averaging. The vibrational level-dependent interaction of the I(2)(X) oscillator with the rare-gas environment is modeled using a recently developed method for constructing state-dependent many-body potentials for quantum vibrations in a many-body classical environment [J. M. Riga, E. Fredj, and C. C. Martens, J. Chem. Phys. 122, 174107 (2005)]. The vibrational dephasing rates gamma(0n) for coherences prepared between the ground vibrational state mid R:0 and excited vibrational state mid R:n are calculated as a function of n and lattice temperature T. Excellent agreement with recent experiments performed by Karavitis et al. [Phys. Chem. Chem. Phys. 7, 791 (2005)] is obtained. 相似文献
14.
Dhruthiman R. Mantheni M. P. K. Maheswaram Hany F. Sobhi Naullage Indika Perera Alan T. Riga M. Ellen Matthews K. Alexander 《Journal of Thermal Analysis and Calorimetry》2012,108(1):227-233
Novel dielectric behavior of a linear increase in ionic conductivity prior to melt temperature was observed for active pharmaceutical
ingredients (APIs), organic chemicals, amino acids, and carbohydrates. Though, there are solids like polyolefins and long
chain organic compounds (tetracosane, pentacosane) which do not exhibit this premelt behavior (i.e., the temperature where
the onset of increase in ionic conductivity to melt temperature). We have discovered novel electrical conductivity properties
and other physical analytical variations which can lead to unique synthetic routes of certain chemical entities. The above-mentioned
unique variations are not related to solid–solid transitions which are quite often observed in pharmaceutical crystalline
solids. These new properties are related to amorphous crystalline behavior of a solid. We have also studied the effect of
various experimental variables: such as amount of mass tested, applied frequency at a given electric field and heating rate,
which results in varying the onset temperature of the increase in ionic conductivity. Melting of the solids was correlated
using differential scanning calorimetry (DSC). Activation energies for all the solids were measured in the premelt region
using an Arrhenius plot at a specific frequency since we observed changes in the conductivity with frequency. This study focused
on frequencies 0.1 to 10 Hz, since the conductivity at these frequencies related to surface analysis. This new physical properties
are leading to new electro synthetic procedures to modify or prepare chemicals. 相似文献
15.
Libby Yoerg M. Ellen Matthews Lakshmi Kaza Naullage Indika Perera David W. Ball John Moran Alan T. Riga 《Journal of Thermal Analysis and Calorimetry》2012,108(1):19-24
Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts.
Phase transitions, including glass transition (T
g) and melting temperature (T
m), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced
dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each
of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles
were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and
solid–liquid transitions. 相似文献
16.
Lakshmi Kaza Hany F. Sobhi Jeffrey A. Fruscella Chris Kaul Shravan Thakur Naullage I. Perera Kenneth Alexander Alan T. Riga 《Journal of Thermal Analysis and Calorimetry》2012,109(3):1365-1371
A standard protocol was developed to determine the water content by thermal analysis of milk of magnesia (MoM). Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used in a novel manner for examining the physical characteristics of the commercial pharmaceutical suspensions. Moisture analyzer and oven-dry methods validate the proposed protocol. MoM consists primarily of water and magnesium hydroxide [Mg(OH)2]. Experimental design of the thermal analysis parameters were considered including sample size, flowing atmosphere, sample pan, and heating rate for both DSC and TG. The results established the optimum conditions for minimizing heat and mass transfer effect. Sample sizes used were: (5?C15?mg) for DSC and (30?C50?mg) for TG. DSC analysis used crimped crucibles with a pinhole, which allowed maximum resolution and gave well-defined mass (water) loss. TG analysis used a heating rate of 10?°C/min?1 in an atmosphere of nitrogen. The heat of crystallization, heat of fusion, and heat of vaporization of unbound water are 334, 334, and 2,257?Jg?1, respectively (Mitra et al. Proc NATAS Annu Conf Therm Anal Appl 30:203?C208, 2002). The DSC average water content of (MoM) was 80?wt% for name brand and 89.5?wt% for generic brand, based on the relative crystallization, melting and vaporization heats/Jg?1 of distilled water in the recently purchased (2011) MoM samples. The TG showed a two-step process, losing water at 80?C135?°C for unbound water and bound water (MgO·H2O) at 376?C404?°C, yielding a total average water loss of 91.9?% for name brand and 90.7?% for generic brand by mass. The difference between the high-temperature TG and the lower-temperature DSC can be attributed for the decomposition of magnesium hydroxide or MgO·H2O. Therefore in performing this new approach to water analysis by heating to a high temperature decomposed the magnesium hydroxide residue. It was determined that the TG method was the most accurate for determining bound and unbound water. 相似文献
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18.
High resolution X-ray photoelectron spectra are reported for tetraphenyldithiapyranylidene (DIPSσ4), three of its polyiodides, and its diperchlor allows to emphasize the evolution of the structure with iodine contents. The chemical nature of the iodine species is also inferred from the I3d signal shape. The low binding energy of the highest occupied molecular orbital is compared to that of other π-systems, and the Iteration of the electron delocalization is shown to be rel 相似文献
19.
20.
This project investigated the interaction between poly-L-lactic acid (PLLA) and several therapeutic agents. Low percentage crystallinity PLLA (melt-pressed, molded and drawn) was
studied. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the crystallinity and
thermal properties in a thermal cycling process. Repeatable melting and crystallization events were observed. The thermal
properties of a drug-polymer combination using PLLA and an acidic, basic, neutral and zwitterionic material were investigated.
A sufficient quantity of the drug must be present in the polymer to be observed thermally. Release of atropine sulfate from
a PLLA tablet showed a two-phase process. 相似文献