Synthesis and characterization of some new dimesogenic compounds

We have synthesized four different types of dimesogenic compounds involving the cholesteryl moiety as one of the mesogenic constituents, and have investigated their liquid crystalline properties. The molecular structures of these dimesogens have been confirmed by spectral analyses; they exhibit a rich polymorphism, as revealed by optical microscopic and differential scanning calorimetric observations. The studies show that the mesomorphic behaviour is sensitive to the nature of the terminal alkyl chains, and to the structure of the 'second mesogen' that is attached to the cholesteryl unit through a polymethylene spacer.

The melting and solidification of nanoscale Bi particles embedded in a glassy and crystalline matrix

We report the formation of an amorphous phase in nanosized Pi particles embedded in an Al-based glassy alloy matrix. High-resolution electron microscopy (HREM) has been used to show that the particles contain crystalline and amorphous portions. A depression of the melting point by more than 100 K of the crystalline portion of the Pi particles was found by differential scanning calorimetric studies and by in-situ electron microscopy using a heating stage. The same techniques established the absence of an amorphous phase in the particles when the matrix is crystallized. It is shown that the formation of the amorphous phase and the depression of the melting point cannot be explained by the pressure developed by the volume change during solidification in this constrained system.

Synthesis and Degradation of Sorbitol-Based Polymers

A new class of biodegradable copolyesters was synthesized by the catalyst-free melt condensation of sorbitol with citric acid, tartaric acid, and sebacic acid. The resulting polymers were designated as poly(sorbitol citric sebacate) p(SCS)] and poly(sorbitol tartaric sebacate) p(STS)]. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, H-1-NMR spectroscopy, and differential scanning calorimetry analysis. Porous spongelike scaffolds were prepared with a salt-leaching technique and characterized with scanning electron microscopy. Tensile testing of the p(SCS) and p(STS) polymers showed that they exhibited a wide range of mechanical properties. The Young's modulus and tensile strengths of the polymers ranged from 1.06 +/- 0.12 to 462.65 +/- 34.21 MPa and from 0.45 +/- 0.04 to 20.32 +/- 2.54 MPa, respectively. In vitro degradation studies were performed on disc-shaped polymer samples. The half-life of the polymers ranged from 0.54 to 38.52 days. The percentage hydration of the polymers was in the range 9.36 +/- 1.26 to 78.25 +/- 1.91, with sol contents of 2-14%. At any given polymer composition, the Young's modulus and tensile strength of p(SCS) was higher than that of p(STS), whereas the degradation rates of p(SCS) was lower than that of p(STS). This was attributed to the structural difference between the citric and tartaric monomers and to the degree of crosslinking. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2861-2869, 2011

Synthesis and characterization of novel cationic lipid and cholesterol-coated gold nanoparticles and their interactions with dipalmitoylphosphatidylcholine membranes

Novel gold nanoparticles bearing cationic single-chain, double-chain, and cholesterol based amphiphilic units have been synthesized. These nanoparticles represent size-stable entities in which various cationic lipids have been immobilized through their thiol group onto the gold nanoparticle core. The resulting colloids have been characterized by UV-vis, (1)H NMR, FT-IR spectroscopy, and transmission electron microscopy. The average size of the resultant nanoparticles could be controlled by the relative bulkiness of the capping agent. Thus, the average diameters of the nanoparticles formed from the cationic single-chain, double-chain, and cholesterol based thiolate-coated materials were 5.9,2.9, and 2.04 nm, respectively. We also examined the interaction of these cationic gold nanoparticles with vesicular membranes generated from dipalmitoylphosphatidylcholine (DPPC) lipid suspensions. Nanoparticle doped DPPC vesicular suspensions displayed a characteristic surface plasmon band in their UV-vis spectra. Inclusion of nanoparticles in vesicular suspensions led to increases in the aggregate diameters, as evidenced from dynamic light scattering. Differential scanning calorimetric examination indicated that incorporation of single-chain, double-chain, and cholesteryl-linked cationic nanoparticles exert variable effects on the DPPC melting transitions. While increased doping of single-chain nanoparticles in DPPC resulted in the phases that melt at higher temperatures, inclusion of an incremental amount of double-chain nanoparticles caused the lowering of the melting temperature of DPPC. On the other hand, the cationic cholesteryl nanoparticle interacted with DPPC in membranes in a manner somewhat analogous to that of cholesterol itself and caused broadening of the DPPC melting transition.

Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85-xAgx (0≤x≤0.20) glasses

Temperature modulated alternating differential scanning calorimetric studies show that Se rich Ge0.15Se0.85−xAgx (0 x 0.20) glasses are microscopically phase separated, containing Ag2Se phases embedded in a Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase percolates in the Ge–Se matrix, with a well-defined percolation threshold at x = 0.10. A signature of this percolation transition is shown up in the thermal behavior, as the appearance of two exothermic crystallization peaks. Density, molar volume, and microhardness measurements, undertaken in the present study, also strongly support this view of percolation transition. The superionic conduction observed earlier in these glasses at higher silver proportions is likely to be connected with the silver phase percolation.

Physical ageing in Se-Te-Sb glasses

Bulk Se60-xTe40Sbx glasses in the composition range 0 <= x <= 14 were prepared by the melt quenching method. Differential Scanning Calorimetric (DSC) and thermal crystallization studies were performed to understand the thermodynamic property like glass transition and structural transformations. These glasses exhibit sharp endothermic peak at the glass transition (T-g). Disappearance of the endothermic peak at T-g in the rejuvenated samples clearly indicates the ageing effect in these glasses. Addition of Sb to Se-Te increases the connectivity of the structural network which is evidenced from the increase in T-g. A distinct change in the slope of the T-g at x=6, indicates a major change in the way the network is connected. The glass forming ability and the thermal stability also exhibit a maximum at x=6. T-g increases with the ageing time and the corresponding fictive temperature (T-f) calculated from the specific heat curves shows a decreasing trend. The molecular movements along the polymeric Se chains might cause the structural relaxation and the physical ageing. The physical ageing effect has been understood on the basis of the Bond Free Solid Angle (BFSA) model proposed by Kastner. Thermally crystallized samples show the formation of rhombohedral Sb2Te3, rhombohedral Sb2Se3 and hexagonal Te phases.

Evidence of an intermediate phase in a quaternary Ag bearing telluride glass system using alternating DSC

Alternating Differential Scanning Calorimetric (ADSC) studies on quaternary Ge15Te80-xIn5Agx glasses show the non-reversing enthalpy (Delta H-NR) at T-g to exhibit a broad global minimum in the 8% <= x <= 16% range of Ag, an observation that is taken evidence for existence of an Intermediate Phase (IP) in that range. Glasses at x < 8% are in the flexible phase while those at x > 16% in the stressed-rigid phase. The nature of crystalline phases formed upon crystallization of bulk glasses are elucidated by XRD studies, and reveal presence of Te, GeTe, Ag8GeTe6, AgTe, In2Te3 and In4Te3 phases. These experiments also reveal that the fraction of Ag- bearing phases increases while those of Te- bearing ones decreases with increasing x, suggesting progressive replacement of Te-Te bonds by Ag-Te bonds. (C) 2013 Elsevier Ltd. All rights reserved.

New columnar liquid crystal materials based on luminescent 2-methoxy-3-cyanopyridines

A new series of donor-acceptor-donor (D-A-D) type luminescent mesogens carrying 2-methoxy-3-cyanopyridine as a central core linked with variable alkoxy chain lengths (m = 6 and 8) as terminal substituents was synthesized and characterized using spectral methods. The newly synthesized molecules were subjected to single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), differential scanning calorimetric (DSC), polarizing optical microscopy (POM), and fluorescence emission studies in order to ascertain their mesogenic and photophysical properties. The SCXRD data on 4a and 4b reveal that the presence of short intermolecular contacts, viz. C-H center dot center dot center dot N, C-H center dot center dot center dot O, C-H center dot center dot center dot pi, and pi center dot center dot center dot pi interactions, is responsible for their crystal packing. The measured torsion angle values indicate that molecules possess distorted non-planar structure. The DSC, POM, and PXRD studies confirm that all the molecules show thermotropic liquid crystalline behaviour and exhibit rectangular columnar phase. Further, their UV-visible and fluorescence spectral studies reveal that the target molecules are luminescent displaying a strong absorption band in the range of 335-340 nm and a blue fluorescence emission band in the range of 395-425 nm (both in solution and film state) with good fluorescence quantum yields (10-49 %).

Calorimetric studies on 2TeO(2)-V2O5 glasses

Glasses of the composition 2TeO(2)-V2O5 were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The glass transition and crystallization parameters were evaluated under non-isothermal conditions using DSC. X-ray diffraction studies confirmed the presence of partially oriented crystallites in the heat-treated glasses. Kauzmann temperature (lower bound for the kinetically observed glass transition) was deduced from the heating rate dependent glass transition and crystallization temperatures.

Equal channel angular pressing processing routes and associated structure modification: a differential scanning calorimetry and X-ray line profile analysis

The effectiveness of different routes of equal channel angular pressing (A, B-c, and C) is studied for commercially pure copper. The stored energy and the activation energy of recrystallization for the deformed samples were quantified using differential scanning calorimetry and X-ray diffraction line profile analysis. Results of the study revealed that the dislocation density and the stored energy are higher in the case of route B-c deformed sample. The activation energy for recrystallization is lower for route B-c. (C) 2012 International Centre for Diffraction Data doi:10.1017/S0885715612000310]

Nucleation parameters for polymer crystallization from non-isothermal thermal analysis

Differential scanning calorimetry (DSC) has been used to obtain kinetic and nucleation parameters for polymer crystallization under a non-isothermal mode of operation. The available isothermal nucleation growth-rate equation has been modified for non-isothermal kinetic analysis. The values of the nucleation constant (K g ) and surface free energies (sgr, sgr e ) have been obtained for i-polybutene-1, i-polypropylene, poly(L-lactic acid), and polyoxymethylene and are compared with those obtained from isothermal kinetic analysis; a good agreement in both is seen.

Analysis of microstructure and texture evolution in pure magnesium during symmetric and asymmetric rolling

Asymmetric rolling of commercially pure magnesium was carried out at three different temperatures: room temperature, 200 degrees C and 350 degrees C. Systematic analysis of microstructures, grain size distributions, texture and misorientation distributions were performed using electron backscattered diffraction in a field emission gun scanning electron microscope. The results were compared with conventional (symmetric) rolling carried out under the same conditions of temperature and strain rate. Simulations of deformation texture evolution were performed using the viscoplastic self-consistent polycrystal plasticity model. The main trends of texture evolution are faithfully reproduced by the simulations for the tests at room temperature. The deviations that appear for the textures obtained at high temperature can be explained by the occurrence of dynamic recrystallization. Finally, the mechanisms of texture evolution in magnesium during asymmetric and symmetric rolling are explained with the help of ideal orientations, grain velocity fields and divergence maps displayed in orientation space.

Thermodynamics of the binding of galactopyranoside derivatives to the basic lectin from winged bean (Psophocarpus tetrogonolobus)

The thermodynamics of the binding of D-galactopyranoside (Gal), 2-acetamido-2-deoxygalactopyranoside (GalNAc), methyl-alpha-D-galactopyranoside, and methyl-beta-D-galactopyranoside to the basic agglutinin from winged bean (WBAI) in 0.02 M sodium phosphate and 0.15 M sodium chloride buffer have been investigated from 298.15 to 333.15 K by titration calorimetry and at the denaturation temperature by differential scanning calorimetry (DSC). WBAI is a dimer with two binding sites. The titration calorimetry yielded single-site binding constants ranging from 0.56 +/- 0.14 x 10(3) M-1 for Gal at 323.15 K to 7.2 +/- 0.5 x 10(3) M-1 for GalNAc at 298.15 K and binding enthalpies ranging from -28.0 +/- 2.0 kJ mol-1 for GalNAc at 298.15 K to -14.3 +/- 0.1 kJ mol-1 for methyl-beta-D-galactopyranoside at 322.65 K. The denaturation transition consisted of two overlapping peaks over the pH range 5.6-7.4. Fits of the differential scanning calorimetry data to a two-state transition model showed that the low temperature transition (341.6 +/- 0.4 K at pH 7.4) consisted of two domains unfolding as a single entity while the higher temperature transition (347.8 +/- 0.6 K at pH 7.4) is of the remaining WBAI dimer unfolding into two monomers. Both transitions shift to higher temperatures and higher calorimetric enthalpies with increase in added ligand concentration at pH 7.4. Analysis of the temperature increase as a function of added ligand concentration suggests that one ligand binds to the two domains unfolding at 341.6 +/- 0.6 K and one ligand binds to the domain unfolding at 347.8 +/- 0.6 K.

Experimental analysis of thermo-physical processes in acoustically levitated heated droplets

An experimental setup using radiative heating has been used to understand the thermo-physical phenomena and chemical transformations inside acoustically levitated cerium nitrate precursor droplets. In this transformation process, through infrared thermography and high speed imaging, events such as vaporization, precipitation and chemical reaction have been recorded at high temporal resolution, leading to nanoceria formation with a porous morphology. The cerium nitrate droplet undergoes phase and shape changes throughout the vaporization process. Four distinct stages were delineated during the entire vaporization process namely pure evaporation, evaporation with precipitate formation, chemical reaction with phase change and formation of final porous precipitate. The composition was examined using scanning and transmission electron microscopy that revealed nanostructures and confirmed highly porous morphology with trapped gas pockets. Transmission electron microscopy (TEM) and high speed imaging of the final precipitate revealed the presence of trapped gases in the form of bubbles. TEM also showed the presence of nanoceria crystalline structures at 70 degrees C. The current study also looked into the effect of different heating powers on the process. At higher power, each phase is sustained for smaller duration and higher maximum temperature. In addition, the porosity of the final precipitate increased with power. A non-dimensional time scale is proposed to correlate the effect of laser intensity and vaporization rate of the solvent (water). The effect of acoustic levitation was also studied. Due to acoustic streaming, the solute selectively gets transported to the bottom portion of the droplet due to strong circulation, providing it rigidity and allows it become bowl shaped. (C) 2010 Elsevier Ltd. All rights reserved.

Reactivities of aluminium and aluminium-magnesium alloy powders in polymeric composites

Polymeric compositions containing Al-Mg alloys show higher reactivities, in comparison with similar compositions containing aluminium. This is observed irrespective of the amount of oxidizer, type of oxidizer used, type of polymeric binder, and over a range of the particle sizes of the metal additive. This is evident from the higher calorimetric values obtained for compositions containing the alloy, in comparison to samples containing aluminium. Analysis of the combustion residue shows the increase in calorimetric value to be due to the greater extent of oxidation of the alloy. The interaction between the polymeric binder and the alloy was studied by coating the metal particles with the polymer by a coacervation technique. On ageing in the presence of ammonium perchlorate, cracking of the polymer coating on the alloy was noticed. This was deduced from differential thermal analysis experiments, and confirmed by scanning electron microscopic observations. The increase in stiffness of the coating, leading to cracking, has been traced to the cross-linking of the polymer by magnesium.