Search results for "scanning"
showing 10 items of 1808 documents
COMPARATIVE-STUDY ON INCLUSION-COMPOUNDS OF 4-BIPHENYLACETIC ACID WITH BETA-CYCLODEXTRIN, HYDROXYPROPYLATED-BETA-CYCLODEXTRINS, AND METHYLATED-BETA-C…
1994
AbstractThe inclusion behavior of Hydroxypropyl-β-Cyclodextrin (HP-β-Cyd) and of methylated-β-Cyclodextrins, heptakis-(2,6-di-O-methyl)-β-Cyclodextrin (DM-β-Cyd) and heptakis-(2,3,6-tri-O-methyl)-β-Cyclodextrin (TM-β-Cyd), in solution and solid state was compared with that of natural β-Cyclodextrin (β-Cyd) using an anti-inflammatory drug, 4-biphenylacetic acid (BPAA), as a guest molecule. The solubility of BPAA with β-Cyd and β-Cyd derivatives in aqueous solution were determined. Stability constants were calculated by phase solubility method at various pH values and temperatures. The formation of inclusion complexes with β-Cyd and β-Cyd derivatives in the solid slate were confirmed by infra…
Simulataneous application of charge coupled device array-detected Raman spectroscopy and differential scanning calorimetry to in situ investigation o…
1992
The combination of differential scanning calorimetry (DSC) with charge coupled device (CCD) array-detected Raman spectroscopy for the in situ investigation of phase transition is illustrated using ammonium nitrate as an example. This method aids unambiguous characterization of different phases by providing a simultaneous probe of thermodynamic and vibrational data. The availability of real-time vibrational data, including both the internal and external mode regions, is unique to array-detected Raman spectroscopy. The intensity changes of the symmetric stretching mode ν1 of the nitrate ions and the lattice vibrations, that accompany the phase transition IV → II of ammonium nitrate, are ratio…
Solid-State Transition Mechanisms of Ammonium Nitrate Phases IV, III, and II Investigated by Simultaneous Raman Spectrometry and Differential Scannin…
1993
The solid-state transition mechanisms of ammonium nitrate IV, III, and II were studied by measuring samples simultaneously by Raman spectrometry and differential scanning calorimetry (DSC). The Raman instruments were a Fourier transform Raman spectrophotometer and triple monochromator Raman spectrophotometer with charge-coupled-device (CCD) detector. The spectral data of the transitions were collected simultaneously with the calorimetric data in the temperature-scanning mode of the calorimeter and then isothermally between transitions. The phase transition from phase IV to phase III occurred through an intermediate phase II*, whose lifetime was seven minutes maximum when the onset temperat…
On structural phase transitions in piperidinium halogenoantimonates(III) and bismuthates(III): X-ray, calorimetric, dilatometric, dielectric and Rama…
2000
Abstract Three piperidinium analogues: (C5H10NH2)2BiCl5, (C5H10NH2)2BiBr5 and (C5H10NH2)2SbBr5 have been studied by means of differential scanning calorimetry, thermal expansion, dielectric and Raman scattering techniques. Each piperidinium salt undergoes one high-temperature structural phase transition, which has been classified as an “order–disorder” type. All transitions are connected with onset of reorientational motion of the organic cations. The X-ray studies on (C5H10NH2)2BiCl5 show that it crystallises in orthorhombic Pna21 space group. The structure has been refined to R=0.0336. It consists of one-dimensional (BiCl52−)n polyanionic chains and two non-equivalent piperidinium cations…
On structural phase transitions in the (C 5 H 12 N) 2 SbCl 5 crystals
2000
Abstract The results of the X-ray (at 295 and 355 K), dilatometric, differential scanning calorimetry and dielectric studies on a new piperidinium crystal, (C5H12N)2SbCl5, are presented. The anionic sublattice of the crystal is built up of infinite (SbCl52−)n chains composed of SbCl63− distorted octahedra connected with each other by corners. In voids of anionic sublattice two crystallographically independent piperidinium cations are located. At 295 K they are both in chair conformation. The compound undergoes three first-order phase transitions at 378.5 K (I→II), 339.5 K (II→III) and 205 K (III→IV). The mechanism of the (II→III) transition (Pna21→P212121) was proposed based on the X-ray da…
Crystal structure, phase transitions and ferroelastic properties of [(CH3)2NH2]3[Bi2Cl9]
2003
Abstract A sequence of structural phase transitions in [(CH3)2NH2]3[Bi2Cl9] (DMACB) is established on the basis of differential scanning calorimetry (DSC) and dilatometric studies. Four phase transitions are found: at 367/369, 340/341, 323/325 and 285/292 K (on cooling/heating). The crystal structure of DMACB is determined at 350 K. It crystallizes in monoclinic space group P21/n: a=8.062(2), b=21.810(4), c=14.072(3) A, β=92.63(3)°, Z=4, R1=0.0575, wR2=0.1486. The crystal is built of the double chain anions (“pleated ribbon structure”) and the dimethylammonium cations. Dielectric studies in the frequency range 75 kHz–900 MHz indicate relatively fast reorientation of the dimethylammonium cat…
Pectin biopolymer mechanics and microstructure associated with polysaccharide phase transitions.
2019
Polysaccharide polymers like pectin can demonstrate striking and reversible changes in their physical properties depending upon relatively small changes in water content. Recent interest in using pectin polysaccharides as mesothelial sealants suggests that water content, rather than nonphysiologic changes in temperature, may be a practical approach to optimize the physical properties of the pectin biopolymers. Here, we used humidified environments to manipulate the water content of dispersed solution of pectins with a high degree of methyl esterification (high-methoxyl pectin; HMP). The gel phase transition was identified by a nonlinear increase in compression resistance at a water content …
Transition paths between phases IV, III and II of ammonium nitrate predicted from X-ray powder diffractometer and differential scanning calorimeter d…
1994
Abstract Ammonium nitrate solid phase transition paths between phases IV, III and II were explained and predicted on the basis of X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) data by applying partial least-squares regression (PLS) and principal component analysis (PCA). The samples were clustered according to their different transition paths with the PLS and PCA models, and the transition paths were predicted with PLS component clusters. The best PLS clusters were formed by a few first components. Prediction of the transition path with the PLS clusters made a semiquantitative prediction of the transition energy possible. In PCA, principal components 6 and 11, w…
Crystal structure and dielectric properties of the [(CH3)2NH2]3Sb2(1-x)Bi2xCl9(DMACAB) mixed crystals
2001
Phase transitions in [(CH3)2NH2]3Sb2(1-x)Bi2xCl9 (DMACAB) mixed salts in the composition range 0≤x≤0.41 have been investigated by the pyroelectric method and dielectric measurements over the frequency range from 75 kHz to 900 MHz. The phase situation is additionally confirmed by the differential scanning calorimetry (DSC) and dilatometric techniques. A transition from the paraelectric (PE) to the ferroelectric (FE) phase is observed for crystals with 0≤x≤0.14. Pyroelectric measurements support the presence of polar phases. The dynamic dielectric behaviour of ferroelectric systems is found to be determined by the existence of two independent relaxators. The low-frequency relaxator reveals a …
Modelling phase transition kinetics of chenodeoxycholic acid with the Runge–Kutta method
2009
Abstract The phase transition kinetics of two chenodeoxycholic acid polymorphic modifications— form I (stable at high temperature), form III (stable at low temperature) and the amorphous phase has been examined under various conditions of temperature and relative humidity. Form III conversion to form I was examined at high temperature conditions and was found to be non-spontaneous, requiring seed crystals for initiation. The formation kinetic model of form I was created incorporating the three-dimensional seed crystal growth, the phase transition rate proportion to the surface area of form I crystals, and the influence of the amorphous phase surface area changes with an empirical stage poin…