A series of silicon containing poly(ester imide)s [PEIs] were synthesized using novel vinyl silane diester anhydride (VSEA)
and various aromatic and aliphatic dimines by two-step process includes ring-opening polyaddition reaction to form poly(amic
acid) and thermal cyclo-dehydration process to obtain poly(ester imide)s. VSEA was synthesized by using dichloro methylvinylsilane
and trimellitic anhydride in the presence of K2CO3 by nucleophilic substitution reaction. The PEIs were characterized by FTIR spectroscopy. The thermal properties of PEIs were
investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The prepared PEIs
showed glass transition temperatures in the range of 320–350°C and their 5% mass loss was recorded in the temperature range
of 500–520°C in nitrogen atmosphere. These had char yield in the range of 45–55% at 800°C.
The reinforcement of nano-barium titanate in ferrite filled poly-ether-ether-ketone (PEEK) composites caused a shift in the
decomposition temperature, at which maximum mass loss occurred, to higher side and enhancement in char yield in thermogravimetric
analysis. Loss tangent and glass transition temperature of ferrite filled PEEK composites were also found to be increased
with the reinforcement of nano barium titanate. The effect of nano barium titanate on the melting behaviour of ferrite filled
PEEK composites was negligible.
A nanostructured mesoporous MCM-41 supported N-heterocyclic carbene–Pd (NHC–Pd) complex was prepared through the reaction of an ionic liquid immobilized onto MCM-41 with palladium acetate. The MCM-41-supported NHC–Pd complex could serve as a highly effective catalyst for the Suzuki cross-coupling reaction under aqueous conditions. Furthermore, the Pd(II) catalyst was recovered by a simple filtration from the reaction mixture and reused without a significant loss of its catalytic activity. The heterogeneous catalyst was also air-stable and thermally stable to allow its easy use.
The concentration of radioactive226Ra,232Th and40K in building and ceramic materials of Bangladesh was investigated by γ-spectrometry with two HPGe detectors. Radium equivalent
activities, representative level index values, criterion formula, emanation coefficients and222Rn mass exhalation rates were estimated for the radiation hazard of the natural radioactivity in the materials. The activity
concentrations of the natural radionuclides, radium equivalent activities, emanation coefficients and222Rn mass exhalation rates are compared with the corresponding values for building and ceramic materials of different countries.
The radium equivalent activities in the samples varied between 30.9 (mosaic stone) and 328.0 Bq·kg−1 (gypsum). The emanation coefficient of the materials ranged from 7.83 (cement) to 33.0% (soil) and the222Rn mass exhalation rate ranged from 2.31 (stone chips) to 118.0 μBq·kg−1·s−1 (gypsum).
This work concerns the study of Al–Ni bimetallic nanoparticles synthesized by gamma-radiolysis of aqueous solution containing
aluminium chloride hexahydrate, nickel chloride hexahydrate, polyvinyl alcohol for capping colloidal nanoparticles, and isopropanol
as radical scavenger. While the Al/Ni molar ratio is kept constant, size of the nanoparticles can be well controlled by varying
the radiation dose. The products were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive
X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD). Observations of UV–vis absorption spectra and TEM images showed
that as the radiation dose increases from 50 to 100 kGy the particle size decreases and the number particles distribution
increases. It may be explained due to the competition between nucleation and aggregation processes in the formation of metallic
nanoparticles under irradiation. The EDX and XRD analysis confirmed directly the formation of Al–Ni bimetallic nanoparticles
in form of alloy nanoparticles.
In this paper we present our recent positron annihilation study of the liquid»solid phase boundary for CO2 confined in nanometer pores of VYCOR glass. We find that CO2 remains liquid in the pores far below the bulk freezing temperature and there is pronounced hysteresis between freezing and melting compared to that seen at the gas-liquid boundary in the pores. On freezing we see evidence of open space created in the pores. This leads to complex melting behaviour possibly involving the formation of gas-liquid interfaces. We see that frezing in the pores is totally irreversible, so that any solid which forms (no matter how small) remains stable up to the higher melting temperature. In contrast melting is more reversible (possibly indicating nucleation centres which permit immediate re-freezing). Finally, the pre-frozen state in the pores is different to the post-melted state.
In confined (nanometer-scale) geometry, the effects of substrate forces and finite size produce a shift of the gas liquid phase boundary from that found in corresponding bulk. The pore transitions also show marked hysteresis. The phase behaviour of a binary gas mixture in confined geometry is likely to depend on the miscibility of the system and the interaction between the substrate and the individual fluid molecules/atoms. Here, we present the results of a pilot positronium annihilation study of the condensation and evaporation of argon-nitrogen mixtures confined in 4 nm diameter cylindrical pores in VYCOR glass.
A densitometric HPTLC method for analysis of cordifolioside A both in 60% methanolic extract of Tinospora cordifolia and in a commercial formulation has been established and validated. Cordifolioside A was separated on aluminum-backed silica gel 60 F254 plates with chloroform-methanol 85:15 (%, v/v) as mobile phase. A compact band was obtained for cordifolioside A at RF 0.52 ± 0.03. The limits of detection (LOD) and quantification (LOQ) were 20.12 and 60.36 ng per band, respectively. The highly precise and accurate method was used for analysis of cordifolioside A.
Polyimides have aromatic moieties in the backbone structure which are responsible for their increased thermal stability. If
phosphorus is introduced in the main chain structure of polyimides, there is further improvement in the thermal stability.
This has been proved by the work carried out in our group. The polyimide having amine termination can be used for crosslinking
of epoxy resins.
In the present study amine terminated phosphorus containing nadicimide were taken as curing agent for DGEBA resins. The curing
characteristics of DGEBA resin were studied by DSC using different amounts of nadic endcapped phosphorylated amines. DSC thermogram
showed the heat of polymerization was lower as compared to system cured with aromatic amines.
In this paper we present a brief review of the current state of positron annihilation research into the phase behaviour of fluids confined within restricted boundaries. We summarise, in the form of selected examples, the work done so far on: (1) fluids confined in the nanometer-size pores of VYCOR glass, with particular emphasis on the confined phase diagram and the mechanisms behind phase transitions compared to bulk. (2) The adsorption/physisorption of gases on internal surfaces of grafoil and the potential of positron technique for revealing physical properties, such as the intricate molecular arrangements during phase transitions of the layered fluid.