Search results for "Phase Transition"

Brewster angle microscopy and X-ray GID studies of morphology and crystal structure in monolayers of N-tetradecyl-γ,δ-dihydroxypentanoic acid amide

1997

First-order phase transitions from the low-density fluidlike phase to the condensed phase of monolayers of N-tetradecyl-γ,δ-dihydroxypentanoic acid amides at the air−water interface have been studied by π−A isotherms, Brewster angle microscopy (BAM), and synchrotron X-ray grazing incidence diffraction (GID). The thermodynamic differences between enantiomeric and racemic monolayers are too small to be measured. However, chiral discrimination is observable in the macroscopic domain morphology by BAM. The domains of the condensed phase grow dendritically. The characteristic shapes of domains of the pure S and R enantiomers are mirror images of each other. The domains of the racemic mixture are…

1991

It is shown that the acceptor polyesters [(CH 2 ) x OCOC(=R) COO(CH 2 ) x ] n (R=9-[2,4,7-trinitrofluorenylidene]) x=3, 6, 8) influence the chain behaviour of the discotic hexapentyloxytriphenylene without changing the phase type (D ho ). The clearing temperature of the complexes has a maximum value when x=G. Both intra- and intercolumnar distance are smaller than in the pure discotic compound and independant of the spacer

1986

Influence des groupes mesogenes sur le polymorphisme de polyphenylene-1,4 terephtalate et differents polyesters a chaine principale semi-flexible

Spectroscopic studies of the stability of monolayers of 2-docosylamino-5-nitropyridine at the air/water interface

1991

Monolayers of 2-docosylamino-5-nitropyridine (DCANP) at the air/water interface were investigated by UV/Vis spectroscopy. The combination of this method with the classic constant-area relaxation technique yields insight into the longtime stability and the collapse behavior of monolayers. We have demonstrated that monolayers of DCANP are certainly stable under standard deposition conditions. At surface pressures above 20 mN/m monolayer instabilities lead to the formation of a three-dimensional head-to-head multilayered structure.

The Storage of Dried Apricots: The Effect of Packaging and Temperature on the Changes of Texture and Moisture

2012

During storage, the packaging material was crucial in the product's moisture variation. The aim of this work was to study the changes of both the moisture content and the texture of dried apricots packaged in two types of containers, namely glass and polypropylene trays, which were thermosealed with two different films and stored at a constant temperature (5, 15, 25 and 35C). The moisture content and texture of the product were analyzed periodically over a period of 12 months. In addition, a differential scanning calorimetry of the product was carried out for a better understanding of the relationship between these parameters. In samples packaged in films, the maximum force value increased …

Phase behaviour of Ag2CrO4 under compression: Structural, vibrational, and optical properties

2013

We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of silver chromate (Ag2CrO4) at ambient temperature and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. When the initial orthorhombic Pnma Ag2CrO4 structure (phase I) is compressed up to 4.5 GPa, a previously undetected phase (phase II) has been observed with a 0.95% volume collapse. The structure of phase II can be indexed to a similar orthorhombic cell as phase I, and the transition can be considered to be an isostructural transition. This collapse is mainly due to the drastic contraction of the a ax…

Preservation of Microbial Strains in the Wine Industry

2011

Publisher Summary This chapter provides a general description of the most commonly used methods for the preservation of microbial strains. Long-term preservation methods are considered the most appropriate option wherever possible, since they involve stopping the growth of the microbial cells and keeping them in a viable state. This guarantees maximum genetic stability by preventing the appearance of successive generations. Nevertheless, the possibility that the preparation method itself leads to changes cannot be ruled out. There are two preservation methods belonging to this group: freezing and lyophilization. In the first long-term preservation method, the cells are frozen suspended in a…

Curvature and Torsion of Protein Main Chain as Local Order Parameters of Protein Unfolding

2020

International audience; Thermal protein unfolding resembles a global (two-state) phase transition. At the local scale, protein unfolding is, however, heterogeneous and probe dependent. Here, we consider local order parameters defined by the local curvature and torsion of the protein main chain. Because chemical shift (CS) measured by NMR spectroscopy is extremely sensitive to the local atomic environment, CS has served as a local probe of thermal unfolding of proteins by varying the position of the atomic isotope along the amino-acid sequence. The variation of the CS of each C(alpha) atom along the sequence as a function of the temperature defines a local heat-induced denaturation curve. We…

Protein Thermal Denaturation and Matrix Glass Transition in Different Protein−Trehalose−Water Systems

2011

Biopreservation by saccharides is a widely studied issue due to its scientific and technological importance; in particular, ternary amorphous protein-saccharide-water systems are extensively exploited to model the characteristics of the in vivo biopreservation process. We present here a differential scanning calorimetry (DSC) study on amorphous trehalose-water systems with embedded different proteins (myoglobin, lysozyme, BSA, hemoglobin), which differ for charge, surface, and volume properties. In our study, the protein/trehalose molar ratio is kept constant at 1/40, while the water/sugar molar ratio is varied between 2 and 300; results are compared with those obtained for binary trehalose…

Self-assembly of biopolymeric structures below the threshold of random cross-link percolation

1996

Self-assembly of extended structures via cross-linking of individual biomolecules often occurs in solutions at concentrations well below the estimated threshold for random cross-link percolation. This requires solute-solute correlations. Here we study bovine serum albumin. Its unfolding causes the appearance of an instability region of the sol, not observed for native bovine serum albumin. As a consequence, spinodal demixing of the sol is observed. The thermodynamic phase transition corresponding to this demixing is the determinative symmetry-breaking step allowing the subsequent occurrence of (correlated) cross-linking and its progress up to the topological phase transition of gelation. Th…