Pressure-induced crystallization

It is, therefore, clearly concluded from Figures 9-11 that in the case of conventional fatty acids such as myristic, palmitic, stearic and so on, the crystalline or amorphous phase of monolayer completely depends on the relative magnitude of Tsp to Tm of the monolayer, being independent of the magnitude of surface pressure. The fatty acid monolayers do not show any pressure-induced crystallization during compression of the monolayer on the water surface. The crystalline and amorphous monolayers are schematically summarized in Figure 12. 

Gogolewski, S. and Pennings, A. J. Crystallization of polyamides under elevated pressure 5 Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon-11, poly(aminoundecaneamide) under pressure, Polymer 18, 660 (1977) Stamhuis, J. E. and Pennings, A. J. Crystallization of polyamides under elevated pressure 6. Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon-12, polylaurolactam under pressure. Polymer 18, 667 (1977)... 

Application of high pressure (600-900 MPa) resulted in lower texture degradation of mushroom as compared to thermal blanching. However, high-pressure-induced crystallization of phospholipids in cell membrane led to permeabilization of the cell membrane. Due to increased permeability, extracellularly located polyphenoloxidase could better react with phenols and resulted in increased browning... 

Gogolewski S, Pennings AJ (1977) Crystallization of polyamides under elevated pressure 5. Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon 11, poly(aminoundecaneamide) under pressure. Polymer 18 660... 

In Fig. 5 the isobaric and isothermal pVT curves of P4SC are shown. Because of the very small changes in specific volume the first phase transition can hardly be seen in the isobaric experiment. The two transitions are resolved only in the heating runs. The phase transition temperature, Td, is shifted to higher values and a decrease in AVsp is observed for both phase transitions. The two transitions are separated by only about 7°C for all pressures investigated. In the isothermal experiment (Fig. 5, right) pressure-induced crystallization can be seen for temperatures above 120°C, concurrently with a decrease in Ksp. Crystallization experiments performed with different pressure cycles show no distinct changes in the phase behavior in particular, the pure J. phase could not be observed. 

Direct optical observation and electrical resistance measurements carried out on amorphous silicon by McMillan and coworkers [28] showed that the HDA is highly reflective and LDA is nonreflective (see Fig. 5). From the electrical resistance measurements, the authors found that there is an abrupt decrease in resistivity across the LDA-HDA transition around P = GPa, indicating transformation to metallic HDA. The sample was verified to be in its amorphous state (using Raman spectroscopy), since pressure-induced crystallization to j8-Sn phase could also lead to a drop in resistivity. 

Complete dispersion curves along symmetry directions in the Brillouin zone are obtained from calculated force constants. Calculations of enharmonic terms and phonon-phonon interaction matrix elements are also presented. In Sec. IIIC, results for solid-solid phase transitions are presented. The stability of group IV covalent materials under pressure is discussed. Also presented is a calculation on the temperature- and pressure-induced crystal phase transitions in Be. In Sec. IV, we discuss the application of pseudopotential calculations to surface studies. Silicon and diamond surfaces will be used as the prototypes for the covalent semiconductor and insulator cases while surfaces of niobium and palladium will serve as representatives of the transition metal cases. In Sec. V, the validity of the local density approximation is examined. The results of a nonlocal density functional calculation for Si and... 

Shigemi, M., Takekiyo, T., Abe, H. and Yoshimura, Y, Pressure-induced crystallization of l-butyl-3-methylimidazoliumhexafluorophosphate. High Pressure Res. 33 (1), 229-233 (2013). 

Relatively speaking the polymer field has not yet reached this stage, to some degree in fibers and films but even here there is much room for improvement. We have many tools to help us produce the optimtim structiire, and optimum properties pressure induced crystallization, shear induced orientation and crystallization, polymer blend composition to control melt rheology as well as the synthesis processes to produce the desired relationship between internal structure and application properties. This is the area of future research that deserves our attention. 

Despite the interest raised by medium ordered structures in the last decades, direct experimental evidence of their presence in supercooled liquids has not been achieved so far by means of diffraction techniques like X-rays, electron or neutron diffraction. In 2010, Zeng and co-workers obtained indirect evidence of large ordered crystalline structures in metallic glasses, [11] whose presence was deduced by the pressure induced crystallization of the entire system. However the detection of the incipient, local cluster was not possible. This was explained by the fact, proved by classical molecular simulations [11], that the structure factor of the glass with or without crystalline structures is virtually undistinguishable. Such result would also explain the previous failures. 

AokI M I and Tsumuraya K 1997 Ab initio molecular-dynamics study of pressure-induced glass-to-crystal transitions In the sodium system Pbys. Rev. B 56 2962-8... 

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

Pure barium is a silvery-white metal, although contamination with nitrogen produces a yellowish color. The metal is relatively soft and ductile and may be worked readily. It is fairly volatile (though less so than magnesium), and this property is used to advantage in commercial production. Barium has a bcc crystal stmcture at atmospheric pressure, but undergoes soHd-state phase transformations at high pressures (2,3). Because of such transformations, barium exhibits pressure-induced superconductivity at sufftciendy low temperatures (4,5). 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

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