Search results for " Temperature"

Radical cation salts based on BEDT-TTF and the paramagnetic anion [Cr(NCS)6]3−

1999

Abstract A new radical cation salt formulated as (ET)5.5[Cr(NCS)6] (ET = BEDT-TTF = bis(ethylene)dithiotetrathiafulvalene) has been synthesised and characterised by X-ray diffraction and magnetic measurements. The structure shows the presence of alternating layers of the ET units and mixed layers of anions and an isolated ET molecule. The magnetic susceptibility data in the temperature range 2–300 K show a Curie law with C = 1.771 cm3.K.mol−1 and Nα = 1.20.10−5 cm3.mol−1, in agreement with the presence of isolated Cr(III) without any contribution from the organic part.

Effect of ionic liquid organizing ability and amine structure on the rate and mechanism of base induced elimination of 1,1,1-tribromo-2,2-bis(phenyl-…

2006

Abstract The kinetics of the elimination reaction of 1,1,1-tribromo-2,2-bis(phenyl-substituted)ethanes into the corresponding 1,1-dibromo-2,2-bis(phenyl-substituted)ethenes induced by amines were studied in three room temperature ionic liquids ([BMIM][BF 4 ], [BMIM][PF 6 ], [BdMIM][BF 4 ]). In order to have information about reagent–ionic liquid interactions, the reaction was carried out over the temperature range (293.1–313.1 K). To study the effect of the amine on the rate and occurrence of the elimination reaction, several primary, secondary and tertiary amines with different structure (cyclic and acyclic), basicity and steric requirements were used. The data collected show that the reac…

Relaxations Below Glass Transition Temperature in Bread and Its Components

1999

ABSTRACT Dry glassy bread, cooked gluten, and gelatinized wheat starch-sucrose mixtures were prepared. Dielectric properties were studied as a function of temperature at different frequencies ranging from 100 to 1,000 kHz. Both bread and starch samples exhibited a tan δ peak at -53°C at 10 kHz, which is associated with a secondary relaxation characterized by an activation energy of 50 kJ/mol. The gluten sample did not show any relaxation in the temperature range studied. The magnitude of the relaxation peak was sensitive to the sucrose concentration of the starch sample. The higher the sucrose content, the greater the amplitude of the peak. Such an effect is attributed to a greater β-relaxa…

A magnetic self-contained thermochromic system with convenient temperature range

2019

A new ionic liquid with sugar-based ligand has been prepared and used to coordinate cobalt(II), at low loading, in an ionic liquid solution. The system obtained reveals magnetic switching and marked thermochromism in solution/polymer films over a convenient temperature range (20–60 °C). This system is self-contained, devoid of any volatile substances, and reproducible over multiple thermal cycles. The colour change can be attributed to a change in the coordination geometry from octahedral (pink) at room temperature to tetrahedral (blue) on warming, monitored by 59Co NMR spectroscopy, which was used for the first time to study the change. This material may find applications in stimuli-respon…

Computer simulations of undercooled fluids and the glass transition

2000

Abstract Two model studies are presented that attempt to describe the static and dynamic properties of glass-forming fluids via molecular dynamics simulations: The first model is an atomistically realistic model of SiO 2 , the second model provides a coarse-grained description of polymer liquids, i.e., typical `fragile' glassformers, while SiO 2 is the prototype of a `strong glassformer'. For both models, attention is given to the questions as to which range of temperatures are properties in equilibrium, and whether such simulations can help to interpret experiments and/or check theoretical predictions. While in the simulation of SiO 2 using the potential of van Beest, Kramer and van Santen…

Biocompatible Poly(N-isopropylacrylamide)-halloysite Nanotubes for Thermoresponsive Curcumin Release

2015

The grafting of poly(N-isopropylacrylamide) (PNIPAAM) onto the halloysite external surface is proposed in order to obtain a novel thermoresponsive drug carrier for curcumin delivery. The new nanomaterial is characterized by means of FT-IR spectroscopy, thermogravimetric analysis, and SEM investigations. A high density of polymer chain was achieved at the nanoparticle surface. The PNIPAAM dehydration phenomenon was observed in water above 32 °C that is nearly coincident with the lower critical solution temperature for the polymer. The colloidal stability as well as the wettability of the obtained nanomaterial may be triggered by temperature stimuli. In vitro tests simulating the gastro-intes…

1,2,4-Triazoles. Improved synthesis of 5-substituted 4-amino-3-mer-cato-(4H)-1,2,4-triazoles and a facile route to 3,6-disubstituted 1,2,4-triazolo[3…

1997

The reaction of thiocarbohydrazide with carboxylic acids at the melting temperature allows an improved preparation of the S-substituted 4-amino-3-mercapto-1,2,4-triazole heterocycles. The crude 4-amino-5-mercapto-1,2,4-triazoles react easily with carboxylic acids or carboxylic acid chlorides to afford the 1,2,4-triazolo[3,4-fc][1,3,4]thiadiazole ring system.

Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization

2001

Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed b…

Studies on the diurnal courses of the contents of abscisic acid, 1-aminocyclopropane carboxylic acid and its malonyl conjugate in needles of damaged …

1993

Summary The diurnal courses of the contents of 1-aminocyclopropane carboxylic acid (ACC), its malonyl conjugate (MACC) and abscisic acid (ABA) in the two-year-old needles of damaged and undamaged spruce trees (Picea abies L.) were investigated. The contents of ACC and MACC were significantly higher in the needles of the damaged trees as compared with the undamaged ones. In the needles of the damaged spruce trees, the ACC and MACC contents, and ABA contents as well, fluctuated to a greater extent than those in the undamaged spruce trees during the day. The relationships between ACC-ABA and MACC-ACC contents as well are also discussed.

1984

An apparatus is presented for the precise measurement of vapour pressures. It is tested with diethyl ether and applied to the system tert-butyle acetate/polystyrene (weight-average molecular weight Mw = 110000) up to polymer concentrations of ca. 60 wt.-% in the temperature range from 10 to 90°C; by means of the Redlich-Kister equation the results can well be described analytically. The data are evaluated to yield the Flory-Huggins parameter in the subsequent article in conjunction with other experimental information.