Search results for "Stability"

Spin-crossover nanocrystals with magnetic, optical, and structural bistability near room temperature.

2008

Synthesis and mesomorphism of related series of triphilic ionic liquid crystals based on 1,2,4-triazolium cations

2021

Abstract The synthesis, liquid crystal and conductivity properties of a series of 27 salts based on the 5-(4-(alkyloxy)phenyl)-1,2,4-triazol-4-ium cation bearing a perfluoroalkyl chain with triflate, tetrafluoroborate and bistriflimide anion are reported. The cations are regarded as triphilic on account of their three distinct regions – hydrocarbon, fluorocarbon and ionic. The mesophases were characterised by a combination of polarised optical microscopy, calorimetry and small-angle scattering experiments using both X-rays and neutrons, while thermal stability was probed using thermogravimetric analysis. The liquid crystal properties are found to be dependent on the anion and the length of …

Complex formation of hypoxanthine and 6-mercaptopurine with Cd(II) ion

1984

Reaction of Cd(II) ion with hypoxanthine (H2 Y) and with 6-mercaptopurine (H2 MP) in dioxane-water (50%) leads to the formation of CdY·2H2O and Cd(HMP)2·2H2O, respectively. In methanolic medium Cd(II) and H2 MP give Cd(MP)·H2O. These compounds have been characterized by chemical analysis, IR spectra and thermogravimetric analysis. The stability constant of CdY complex at 25±0.1 °C and 1M ionic strength with NaClO4 in dioxane-water medium is log β=10.25±0.05.

Synthesis and thermal behavior of Janus dendrimers, part 1

2010

Abstract Eight Janus-type dendrimers up to the second generation were synthesized, and their thermal properties were evaluated. Compounds consist of the dendritic bisMPA based polyester moieties, and either 3,4-dihexyloxybenzoic acid or 3,4-dihexadecyloxybenzoic acid moieties, attached to opposite sides of the pentaerythritol core. The structures of the molecules were verified with 1 H NMR, 13 C NMR, ESI TOF mass spectrometry and elemental analysis. The thermal stability was evaluated by thermogravimetric analysis, displaying onset decomposition temperatures ( T d ) ranging from 241 to 308 °C. Phase transitions were studied by differential scanning calorimetry. Based on the performed studie…

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decompositon kinetics

2010

[EN] The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolutio…

Reprocessed polylactide: Studies of thermo-oxidative decomposition

2012

The combustion process of virgin and reprocessed polylactide (PLA) was simulated by multi-rate linear non-isothermal thermogravimetric experiments under O2. A complete methodology that accounted on the thermal stability and emission of gases was thoroughly developed. A new model, Thermal Decomposition Behavior, and novel parameters, the Zero-Decomposition Temperatures, were used to test the thermal stability of the materials under any linear heating rate. The release of gases was monitored by Evolved Gas Analysis with in-line FT-IR analysis. In addition, a kinetic analysis methodology that accounted for variable activation parameters showed that the decomposition process could be driven by …

Adsorption isotherms and thermal behavior of hybrids based on quercetin and inorganic fillers

2019

We investigated the adsorption process of quercetin onto several inorganic fillers, such as kaolinite, calcium carbonate and alumina. Firstly, we performed equilibrium adsorption studies in order to determine the quercetin/filler adsorption isotherms, which were successfully fitted through the Langmuir model. Based on the adsorption data analysis, we estimated the maximum adsorption capacity of each filler as well as the Langmuir constant, which is related to the affinity between quercetin and the surfaces of the inorganic particles. Then, we prepared hybrids formed by fillers saturated with quercetin. The obtained composites were characterized by thermogravimetric analysis with the aim of …

Surface modification of luminescent lanthanide phosphate nanorods with cationic "Quat-primer" polymers.

2011

"Quat-primer" polymers bearing cationic groups were investigated as a surface modifier for Tb-doped cerium phosphate green-emitting fluorescent nanorods (NRs). The NRs were synthesized by a microwave process without using any complex agents or ligands and were characterized with different analytical tools such as X-ray diffraction, transmission electron microscopy, and fluorescence spectroscopy. Poly(ethyleneimine) partially quarternized with glycidyltrimethylammonium chloride was synthesized separately and characterized in detail. (1)H and (13)C NMR spectroscopic studies revealed that the quaternary ammonium group was covalently attached to the polymer. UV-vis spectroscopy was used to exam…

Characterization of thermoelectric and thermogravimetric properties of conductive PEDOT:PSS films blended with SWCNTs and PVA

2019

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was blended with polyvinyl alcohol (PVA) and single-walled carbon nanotube (SWCNT) filler to form composites with thermoelectric properties. Studied samples were obtained by drop coating and solution casting methods. Thermoelectric measurements of PEDOT:PSS demonstrated that the addition of 5 wt. % SWCNTs increased the Seebeck coefficient value from 8.0 μV/K to 23.6 μV/K, while in the case of PEDOT:PSS/PVA blended with 5 wt. % SWCNT Seebeck coefficient value of 20.3 μV/K was achieved. Thermogravimetric analysis showed slight SWCNT effect on thermal stability of the investigated systems.

A Maze of Solid Solutions of Pimobendan Enantiomers: An Extraordinary Case of Polymorph and Solvate Diversity

2017

Over 10 polymorphs and solvatomorphs of the chiral pharmaceutically active ingredient pimobendan were found to lack enantioselectivity in the solid state, accordingly, forming solid solutions of enantiomers, which is reported to be a rare phenomenon. Solid form screening was performed on different enantiomeric composition samples to analyze obtained phases with powder X-ray diffraction and thermogravimetric differential scanning calorimetry. For nonsolvated forms, a melt phase diagram has been constructed convincingly showing the existence of stable and metastable solid solutions near the pure enantiomer and around the racemic composition regions. A crystal structure study combined with sol…