Pressure and Temperature Effects on the Raman Spectra of Aqueous Micellar Solutions of Sodium Oleate

1983 ◽  
Vol 22 ◽  
Author(s):  
P.T.T. Wong ◽  
H.H. Mantsch
Keyword(s):  
Phase Transition ◽  
Sodium Oleate ◽  
Temperature Effects ◽  
Micellar Solution ◽  
Room Temperature ◽  
Structural Changes ◽  
Micellar Solutions ◽  
Micellar Phase ◽  
Aqueous Micellar Solutions ◽  
Pressure And Temperature Effects

Sodium oleate is practically insoluble in water at room temperature. Yet, when heated above the critical micellization temperature (cmt), its solubility increases rapidly and an isotropic optically clear micellar solution is formed. Upon cooling below the critical coagelization temperature (cct), the micellar phase transforms to an opaque curd, the coagel phase. The structural changes and the nature of this phase transition are, however, not well characterized.

Pressure and temperature effects on the degree of symmetry and chirality of the molecular building blocks of low quartz

2004 ◽  
Vol 60 (2) ◽  
pp. 163-173 ◽  
Author(s):  
Dina Yogev-Einot ◽  
David Avnir
Keyword(s):  
Temperature Effects ◽  
Structural Changes ◽  
Building Blocks ◽  
Pressure Effects ◽  
Continuous Symmetry ◽  
Tetrahedral Symmetry ◽  
Molecular Building Blocks ◽  
Global Nature ◽  
Pressure And Temperature Effects ◽  
Low Pressures

We establish quantitative correlations between pressure and temperature (PT) changes, and the degree of symmetry and of chirality of the main molecular building blocks of low quartz that these PT changes induce. The distortion from ideal tetrahedral symmetry, from helicity (deviation from C 2 symmetry), and the level of chirality are evaluated quantitatively using the continuous-symmetry and chirality-measures approach. These measures are global and reflect all changes in bond angles and bond lengths. The specific molecular building blocks analyzed are the SiO4 elementary building block (which is found to be chiral!), the Si(OSi)4 unit, the second-shell SiSi4 tetrahedron [composed of the five Si atoms of Si(OSi)4] and the four-tetrahedra helix fragment, —O(SiO3)4—. The temperature and pressure effects on symmetry and chirality were found to mirror each other in all building blocks. By employing this quantitative approach to symmetry and chirality we were able to combine the pressure effects and temperature effects into a unified picture. Furthermore, the global nature of the symmetry measure allows the comparison of the behavior of isostructural materials such as germania and quartz. For these crystals it has been shown that the symmetry/chirality behavior of germania at low pressures is a predictor for the behavior of these structural properties in quartz at higher pressures. Finally, given that the rigid SiO4 unit undergoes only minor structural changes, it has been a useful observation that the symmetry/chirality of the small SiSi4 tetrahedron is a very sensitive probe for the symmetry and chirality changes in quartz as a whole.

Pressure and temperature effects on the phase transition from a dense droplet to a lamellar structure in a ternary microemulsion

2000 ◽  
Vol 112 (23) ◽  
pp. 10608-10614 ◽  
Author(s):  
Hideki Seto ◽  
Daisuke Okuhara ◽  
Youhei Kawabata ◽  
Takayoshi Takeda ◽  
Michihiro Nagao ◽  
...  
Keyword(s):  
Phase Transition ◽  
Temperature Effects ◽  
Lamellar Structure ◽  
Pressure And Temperature Effects

scholarly journals Effect of pressure on the crystal structure of α-glycylglycine to 4.7 GPa; application of Hirshfeld surfaces to analyse contacts on increasing pressure

2006 ◽  
Vol 62 (2) ◽  
pp. 310-320 ◽  
Author(s):  
Stephen A. Moggach ◽  
David R. Allan ◽  
Simon Parsons ◽  
Lindsay Sawyer
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Structural Changes ◽  
Ambient Pressure ◽  
Rapid Assessment ◽  
Strain Tensor ◽  
Hirshfeld Surfaces ◽  
Β Sheet

The crystal structure of α-glycylglycine (α-GLYGLY) has been determined at room temperature at pressures between 1.4 and 4.7 GPa. The structure can be considered to consist of layers. The arrangement of molecules within each layer resembles the antiparallel β-sheet motif observed in proteins, except that in α-GLYGLY the motif is constructed through NH...O hydrogen bonds rather than covalent amide links. Compression of α-GLYGLY proceeds via the reduction in void sizes. Voids close in such a way as to decrease the distances of stabilizing interactions such as hydrogen bonds and dipolar contacts. The largest reductions in interaction distances tend to occur for those contacts which are longest at ambient pressure. These longer interactions are formed between the β-sheet-like layers, and the largest component of the strain tensor lies in the same direction. The N...O distance in one NH...O hydrogen bond measures 2.624 (9) Å at 4.7 GPa. This is very short for this kind of interaction and the crystal begins to break up above 5.4 GPa, presumably as the result of a phase transition. The changes that occur have been analysed using Hirshfeld surfaces. Changes in the appearance of these surfaces enable rapid assessment of the structural changes that occur on compression.

Halogen NQR and the Phase Transition in CH3Hg-Halide Family

2000 ◽  
Vol 55 (1-2) ◽  
pp. 215-218 ◽  
Author(s):  
J. Pirnat ◽  
Z. Trontelj ◽  
J. Lužnik ◽  
D. Kirin
Keyword(s):  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Structural Changes ◽  
Proton Relaxation ◽  
Displacive Phase Transition ◽  
Thermal Vibrations

The temperature dependence of the 35Cl NQR line and its relaxation has been measured from 77 K to room temperature. The known displacive phase transition near 162 K is reflected in the change of the slope of the temperature dependence of the quadrupole line, but not so in the chlorine or proton relaxation. The results are discussed in view of the proposed structural changes and thermal vibrations.

Investigation of the Cs x Rb1−x TiOAsO4 Series. I. Crystal Structure Analysis and Pseudo-symmetry

1998 ◽  
Vol 54 (5) ◽  
pp. 635-644 ◽  
Author(s):  
M. N. Womersley ◽  
P. A. Thomas ◽  
D. L. Corker
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Room Temperature ◽  
Structural Changes ◽  
Crystal Structure Analysis ◽  
Orthorhombic Space Group ◽  
Acta Cryst ◽  
Space Group ◽  
Structural Framework

Refinements of five crystals in the Cs2x Rb2−2x Ti2O2As2O8 series, caesium rubidium titanyl arsenate, with x = 0.07, 0.31, 0.58, 0.71 and 0.86, which are compositional analogues of KTiOPO4 (KTP), have been completed at 293 K and two (x = 0.71, 0.86) at low temperature. All the structures are found to be orthorhombic (space group Pna21) and are isostructural with KTP, although there is evidence of some Cs disorder over additional sites in the framework, particularly at the Cs-rich end of the series, as discussed in Part II [Thomas & Womersley (1998). Acta Cryst. B54, 645–651]. Unusually large U 33 parameters for shared Cs/Rb sites are observed and are shown to be the result of the existence of separate sites for Cs and Rb within the structural framework, although the coordinates of these sites cannot be resolved convincingly. The structural changes in the TiO6/AsO4 framework required to accommodate an increasing fraction of the larger Cs cation across the series and under cooling to 120 K are elucidated. Finally, the deviations of the room-temperature and low-temperature structures from the high-temperature prototypic structure (space group Pnan) are examined and suggest that the phase-transition temperature should increase linearly from CsTiOAsO4 to RbTiOAsO4.

scholarly journals A phase transition caught in mid-course: independent and concomitant analyses of the monoclinic and triclinic structures of ( n Bu4N)[Co(orotate)2(bipy)]·3H2O

2017 ◽  
Vol 73 (9) ◽  
pp. 731-742 ◽  
Author(s):  
Miguel Castro ◽  
Larry R. Falvello ◽  
Elena Forcén-Vázquez ◽  
Pablo Guerra ◽  
Nuha A. Al-Kenany ◽  
...  
Keyword(s):  
Phase Transition ◽  
Single Crystal ◽  
Room Temperature ◽  
Structural Changes ◽  
Energy Content ◽  
Single Crystal Diffraction ◽  
Two Phase ◽  
Reverse Transition ◽  
Crystal Phase Transition

The preparation and characterization of the n Bu4N+ salts of two bis-orotate(2−) complexes of cobalt, namely bis(tetra-n-butylammonium) diaquabis(2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide-6-carboxylato-κ2 N 1,O 6)cobalt(II) 1.8-hydrate, (C16H36N)2[Co(C5H2N2O4)2(H2O)2]·1.8H2O, (1), and tetra-n-butylammonium (2,2′-bipyridine-κ2 N,N′)bis(2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide-6-carboxylato-κ2 N 1,O 6)cobalt(III) trihydrate, (C16H36N)[Co(C5H2N2O4)2(C10H8N2)]·3H2O, (2), are reported. The CoIII complex, (2), which is monoclinic at room temperature, presents a conservative single-crystal-to-single-crystal phase transition below 200 K, producing a triclinic twin. The transition, which involves a conformational change in one of the n Bu groups of the cation, is reversible and can be cycled. Both end phases have been characterized structurally and the system was also characterized structurally in a two-phase intermediate state, using single-crystal diffraction techniques, with both the monoclinic and triclinic phases present. Thermal analysis allows a rough estimate of the small energy content, viz. 0.25 kJ mol−1, for both the monoclinic-to-triclinic transformation and the reverse transition, in agreement with the nature of the structural changes involving only the n Bu4N+ cation.

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