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Amorphous Solids (amorphous + solid)
Selected AbstractsNitrogen Incorporation in an Al0.5Ga0.5PO4 Amorphous Solid Studied with 27Al and 31P NMR.CHEMINFORM, Issue 41 2003Stephanie Delsarte Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Crystalline Aluminum Hydroxy Fluorides , Suitable Reference Compounds for 19F Chemical Shift Trend Analysis of Related Amorphous Solids.CHEMINFORM, Issue 40 2008Rene Koenig Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Dielectric studies of molecular motions in amorphous solid and ultraviscous acetaminophenJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2005G.P. Johari Abstract The dielectric permittivity and loss spectra of glassy and ultraviscous states of acetaminophen have been measured over the frequency range 10 Hz,0.4 MHz. The relaxation spectra show an asymmetric distribution of times expressed in terms of the Kohlrausch exponent, ,, which remains constant at 0.79,±,0.02 over the 305,341 K range. The dielectric relaxation time increases on cooling according to the Vogel,Fulcher,Tammann equation. However, the values of the parameters are considerably different from the values deduced from earlier work by other researchers using the heat capacity of ultraviscous acetaminophen and relating it to its molecular mobility. The calorimetric glass softening temperature of 296 K obtained from differential scanning calorimetry is close to the value measured from dielectric relaxation. The equilibrium permittivity of ultraviscous acetaminophen decreases on heating like that of a normal dipolar liquid, as anticipated from the Curie law. But, its value decreases rapidly with time when it begins to crystallize. The equilibrium permittivity of this crystal phase is ,3.1 at 300 K and increases with temperature, which indicates a partial, orientational-disordering of its structure. The results show limitations of the procedures used in the modeling of the kinetics of molecular motions, that is, estimating physical stability, using thermodynamic considerations based on thermal analyses of the amorphous solid phase of acetaminophen. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2207,2223, 2005 [source] IR Laser-Induced Carbothermal Reduction of SilicaEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2008Markéta Urbanová Abstract Pulsed IR-laser irradiation of silica in the presence of gaseous hydrocarbons (benzene or ethyne) results in carbothermal reduction of silica by hydrocarbon decomposition products and allows deposition of amorphous solids which were analyzed by FTIR, Raman, X-ray photoelectron and Auger spectra and by electron microscopy and revealed as nanosized carbon,silicon oxycarbide composites containing crystalline silica domains. The reported IR laser-induced process is the first approach to deposition of nanosized carbon,silicon oxycarbide composites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Engineering pharmaceutical stability with amorphous solidsAICHE JOURNAL, Issue 6 2002Christopher J. Roberts First page of article [source] Characterization of amorphous solids with weak glass transitions using high ramp rate differential scanning calorimetryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2008Derrick S. Katayama Abstract Measurement of the glass transition temperature (Tg) of proteins and other high molecular weight polymers in the amorphous state is often difficult, since the transition is extremely weak, that is, the ,Cp at the glass transition temperature is small. For example, little is known about the solid-state properties of hydroxyethyl starch (HES), which is beginning to become more commonly evaluated as a bulking agent in pharmaceutical products. For weak thermal events, such as the change in heat capacity at the Tg of a pure protein or large synthetic polymer, increased heating rate should produce greater sensitivity in terms of heat flow. Recent innovations in rapid scanning technology for differential scanning calorimetry (DSC) allow measurements on materials where the thermal events are difficult to detect by conventional DSC. In the current study, measurements of the Tg of proteins in the solid state, amorphous pharmaceutical excipients which have small ,Cp at the glass transition temperature, and bacterial spores, have all been made using high ramp rate DSC, providing information on materials that was inaccessible using conventional DSC methods. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1013,1024, 2008 [source] Physics of amorphous solidsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2004Lori R. Hilden Abstract The physical state of a dosage form, crystalline versus amorphous, is critical in determining its solid-state physical and chemical properties. This minireview describes the physics associated with the preparation and storage of amorphous solids including a review of the common theories of the glass transition and relaxation processes. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:3,12, 2004 [source] Prediction of the relaxation behavior of amorphous pharmaceutical compounds.JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2003Abstract Variability in the time to crystallization is a major technical and economic hurdle in using amorphous solids in dosage forms. It is hypothesized that amorphous solids "age", and that the older they are, the more relaxed they are and the higher the probability of crystallization. At present, there is no method that allows the "effective age" of an amorphous raw material to be assessed relative to its unrelaxed initial condition. A method has been developed that may satisfy this unmet need and provide a first step in subsequent investigation of the crystallization "event". This method consists of using master curves to enable the determination of the effective age (,aging') of an amorphous compound given normal excursions in storage conditions. The present study shows that master curves can be prepared for different storage conditions and subsequently be used to predict the relaxation or aging behavior of amorphous compounds with expected variations in storage conditions. Given the constraint that the system remain within the area enclosed by the equilibrium supercooled liquid line and the glass on the enthalpy,temperature diagram, experimental results using indomethacin and salicin as model compounds show that master curves can be used to predict aging behavior under nonisothermal conditions, with temperature excursions as large as 10°C. The nonisothermal relaxation behavior can be modeled by combining the Kohlrausch,Williams,Watts (KWW) stretched exponential function, the relaxation function, and a shift factor. In addition, a model was developed that extends the range of applicability to time/temperature regions in which partial crystallization occurs. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:1464,1472, 2003 [source] Soil organic matter beyond molecular structure Part II: Amorphous nature and physical agingJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2006Gabriele E. Schaumann Abstract Glassy, rubbery, and crystalline phases are representatives of supramolecular structures which strongly differ in order, density, and other characteristics. In this contribution, the amorphous nature of soil organic matter (SOM) is reviewed with respect to the glassy/rubbery model, glass transition mechanisms, interactions of SOM with water, and physical aging. Glass-transition behavior and physical aging are inherent properties of amorphous solids, and numerous spectroscopic investigations give insights into different domain mobilities of humic substances (HS). The correlation between sorption nonlinearity and glassiness of polymers and HS supports a relation between sorption and amorphicity in Aldrich humic acid. Further evidence is still required for the transfer to soil HS and SOM. Sorption and differential scanning calorimetry (DSC) data suggest a correlation between aromaticity and glassiness in HS, and the available data do currently not allow to decide unambiguously between specific sorption and hole filling as explanation. This needs to be verified in future research. Although parts of the investigations have up to now only been conducted with humic substances, the collectivity of available data give strong support for the glassy/rubbery conception of SOM. They clearly indicate that amorphous characteristics cannot be excluded in SOM. This is further supported by the observation of different types of glass-transition behavior in samples of whole humous soil. In addition to classical glass transitions in water-free soil samples, water surprisingly acts in an antagonistic way as short-term plasticizer and long-term antiplasticizer in a second, nonclassical transition type. Latter is closely connected with physico-chemical interactions with water and suggests water bridges between structural elements of SOM (HBCL-model). The gradual increase of Tg* in SOM indicates physico-chemical aging processes, which are not restricted to polymers. They may be responsible for contaminant aging, changes in surface properties and increased soil compaction in agricultural soils. [source] Influence of a Ceramic Substrate on Aqueous Precipitation and Structural Evolution of Alumina Nano-Crystalline CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007Marie Mahé Either boehmite (,-AlOOH) or gibbsite (,-Al(OH)3) nanocrystalline thin films (h,100 nm) can be precipitated from AlCl3 solution at fixed pH and temperature onto different substrates. It depends on the nature of the substrate (mica flakes, SiO2 flakes, or ,-Al2O3 flakes), on their crystallographic properties (crystalline or amorphous), and on some experimental parameters (agitation rate, addition rate). According to the surface charge of the substrates, different alumina species are involved in the precipitation process. When negative charges are present on the substrate, the [Al3O(OH)3(OH2)9]4+ polycation is promoted, leading to the formation of the (Al4) tetramer ([Al4O(OH)10(OH2)5]o) and then to the precipitation of bohemite. When positive charges are present, a ligand bridge containing complex ([Al3O(OH)3(O2H3)3(OH2)9]+) is likely favored, giving rise to hexagonal ring structures or amorphous solids that lead to the formation of gibbsite. Besides the surface effects, crystalline substrates can act as a template during precipitation of aluminum species as shown for the formation of gibbsite on muscovite. Finally, calcination at 850°C of boehmite samples leads to porous ,-Al2O3 layers, while calcination of gibbsite leads to ,-Al2O3 layers. [source] Quasi-localized low-frequency vibrational modes of disordered solids: Study by single-molecule spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004A. V. Naumov Editor's Choice of this issue of physica status solidi (b) is the article [1] by Andrei V. Naumov et al. This paper is Part II (Part I see [2]) of a study on elementary excitations in glasses, presented at the 11th International Conference on Phonon Scattering in Condensed Matter, St. Petersburg, 25,30 July 2004. For his outstanding talk, Naumov received the new physica status solidi Young Researcher Award which was bestowed for the first time at this conference. The cover picture is a sketch of a glass with a single impurity molecule and one hypothetical quasi-localized vibrational mode. The broadening and shift of the chromophore spectral line are caused by the interaction with this mode. Andrei V. Naumov is senior scientific researcher and deputy head of the Molecular Spectroscopy Department of the Institute of Spectroscopy, Troitsk. His main research interests are experimental and theoretical studies of low-temperature dynamics of amorphous solids (glasses, polymers etc.) via high resolution laser selective spectroscopy techniques. The second Editor's Choice is an article by E. A. Eliseev and M. D. Glinchuk [3]. Eugene A. Eliseev is scientific researcher at the Frantsevich Institute for Problems of Materials Science of the Ukrainian National Academy of Sciences, Kiev. His research areas are the theory of size and correlation effects in ferroelectric materials as well as modelling of disordered ferroelectrics properties. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Probing the Building Blocks of Eumelanins Using Scanning Electron MicroscopyPIGMENT CELL & MELANOMA RESEARCH, Issue 3 2000J. BRIAN NOFSINGER Scanning electron microscopy (SEM) is used to examine the structure of natural and synthetic melanins. Eumelanin from Sepia officinalis and synthetic eumelanin are found to be structurally dissimilar. The natural sample has a significant structural order with subunits that have a lateral dimension of ,15 nm. The synthetic samples, on the other hand, appear to be amorphous solids. These results lend support for the existence of fundamental structural units proposed from the analyses of wide-angle X-ray diffraction measurements and previous mass-spectrometry results. These findings also provide insight into the disparate photophysical behavior of Sepia and synthetic eumelanin. [source] Anderson localization of matter wavesANNALEN DER PHYSIK, Issue 12 2009P. Bouyer The transport of quantum particles in non ideal material media is strongly affected by scattering from impurities of the medium. Even for a weak disorder, semi-classical theories, such as those based on the Boltzmann equation for matter-waves scattering from the impurities, often fail to describe transport properties and full quantum approaches are necessary. The properties of the quantum systems are of fundamental interest as they show intriguing and non-intuitive phenomena that are not yet fully understood. Understanding quantum transport in amorphous solids is one of the main issues in this context, related to electric and thermal conductivities. [source] Order and Disorder in Powder Mixtures: Spatial Distribution Functions as Tools to Assess Powder HomogeneityPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5-6 2008Albert Mihranyan Abstract In interactive mixtures with small carrier particles, the content variability is often higher than predicted by available models despite the significant degree of interaction visualized with Scanning Electron Microscopy (SEM). The present work details how pair-correlation functions can be used to reveal information about the spatial distribution of mixture constituents and their interactions. SEM pictures of a 2,% w/w oxazepam/sodium starch glycolate (SSG) mixture were recorded (n = 14). The constituent coordinates were extracted and pair-correlation functions as well as the cross-correlation function were calculated. A significant degree of interaction was observed between the constituents in the experimental mixture, compared to a randomized control system. In particular, the probability of finding an oxazepam particle was especially high inside the perimeter of the carrier particle and along its edges. The observed cross-correlation between oxazepam and SSG particles was periodic and repeated at distances corresponding to 1,1.5 carrier diameters. It was concluded that interactive mixtures of powders can be compared to disordered/amorphous solids since both exhibit short-range order, whilst lacking long-range translational periodicity. [source] | ||||||||||||||||