$x ray diffraction pattern of polymers$

Cryogenic grinding of indomethacin polymorphs and solvates : assessment of amorphous phase formation and amorphous phase stability. Criteria for vitrification and predictions of our model. Two-order-parameter description of liquids. A general model of glass transition covering its strong to fragile limit. A thermodynamic theory of supercooled liquids. Generalized Landau Peierls instability: a novel perspective on the nature of glasses? Philos. Total scattering studies of silica polymorphs: similarities in glass and disordered crystalline local structures. Characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites. A classification of molecules, phases, and transitions as recognized by thermal analysis. Local Structure from Diffraction, Plenum, New York, 1998. Metastable Liquids : Concepts and Principles, Princeton University Press, Princeton, New Jersey, 1996. Characteristics and significance of amorphous solids in pharmaceutical systems. The pharmaceutical implications with respect to the stability of the solid are discussed.ī. Treating X-ray amorphous powder patterns with different solid-state models, ranging from disordered nanocrystalline to glassy and amorphous, resulted in the assignment of structures in each of the systems examined. This initial disordered phase was maintained to a critical point when a transition to a completely amorphous RCP structure occurred. The initial disordered phase is consistent with continuous random network (CRN) glass material. However, grinding of Form II of piroxicam initially produced a disordered phase that maintained the local packing of Form II but over a very short nanometer length scale. The same pattern of transformation was detected for the Form I polymorph of piroxicam. For all three polymorphs, with increased grinding time, a two-phase system, consisting of amorphous and crystalline material, continually transformed to a completely random close packed (RCP) amorphous structure. Total scattering modeling of ground samples of α, γ, and δ crystal forms of indomethacin in combination with analysis of the PDFs provided a quantitative picture of the local structure during various stages of grinding. The average crystallite size of the disordered nanocrystalline cellulose was determined to be 10.9 nm.

$x ray diffraction pattern of polymers$

Rietveld modeling of microcrystalline cellulose (Avicel® PH102) indicates that it is predominantly disordered crystalline cellulose Form Iβ with some amorphous contribution. The observation of X-ray amorphous powder patterns may indicate the presence of amorphous, glassy or disordered nanocrystalline material in the sample. Analysis of the data were carried out using a combination of direct methods, such as pair distribution functions (PDF), and indirect material modeling techniques including Rietveld, total scattering, and amorphous packing. The X-ray amorphous powder diffraction patterns of microcrystalline cellulose, indomethacin, and piroxicam were measured with laboratory XRPD instrumentation. Techniques to elucidate structural differences in pharmaceutical solids exhibiting characteristic X-ray amorphous powder patterns are also presented. The purpose of this paper is to provide a physical description of the amorphous state for pharmaceutical materials and to investigate the pharmaceutical implications.

$x ray diffraction pattern of polymers$

X ray diffraction pattern of polymers