Small angle X-ray and neutron scattering Research Papers (original) (raw)
Using small angle x-ray scattering, we find that the correlation length of bulk liquid water shows a steep increase as temperature decreases at subzero temperatures (supercooling) and that it can, similar to the thermodynamic response... more
Using small angle x-ray scattering, we find that the correlation length of bulk liquid water shows a steep increase as temperature decreases at subzero temperatures (supercooling) and that it can, similar to the thermodynamic response functions, be fitted to a power law. This indicates that the anomalous properties of water are attributable to fluctuations between low- and high-density regions with rapidly growing average size upon supercooling. The substitution of H2O with D2O, as well as the addition of NaCl salt, leads to substantial changes of the power law behavior of the correlation length. Our results are consistent with the proposed existence of a liquid-liquid critical point in the deeply supercooled region but do not exclude a singularity-free model.
The aggregation behaviour of alkyl triphenylphosphonium bromide (CnTPPBr, n = 10,12,14,16) in presence of non-ionic Triton X-100 in aqueous solutions is investigated by different analytical techniques viz. surface tensiometry (ST), dye... more
The aggregation behaviour of alkyl triphenylphosphonium bromide (CnTPPBr, n = 10,12,14,16) in presence of non-ionic Triton X-100 in aqueous solutions is investigated by different analytical techniques viz. surface tensiometry (ST), dye solubilization (DS), cloud point (CP), dynamic light scattering (DLS), zeta potential, small-angle neutron scattering (SANS), contact angle, wettability and foamability measurements. The calculated critical micelle concentration (CMC) for aqueous solutions of mixed surfactants is lower than the individual pure surfactants, which confirms the synergistic interactions among the monomers in the formed mixed micelles. On gradual addition of CnTPPBr, the cloud points of TX-100 are shifted to higher temperatures and size of the formed mixed micelles decreases as observed by CP and DLS, respectively. Zeta potential of mixed micelles increases with corresponding increase in the concentration of CnTPPBr. Morphological and clouding behaviour of mixed micelles is found to be independent of chainlength for added cationic surfactant, but initial ellipsoidal shape micelles transform to extended ellipsoids in presence of sodium bromide depicting significant increase in the axial ratio.
Nematic liquid-crystalline elastomers (LCEs) are weakly cross-linked polymeric networks that exhibit rubber elasticity and liquid-crystalline orientational order due to the presence of mesogenic groups. Three end-on side-chain nematic... more
Nematic liquid-crystalline elastomers (LCEs) are weakly cross-linked polymeric networks that exhibit rubber elasticity and liquid-crystalline orientational order due to the presence of mesogenic groups. Three end-on side-chain nematic LCEs were investigated using real-time synchrotron wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and thermogravimetry (TG) to correlate the thermal behaviour with structural and chemical differences among them. The elastomers differed in cross-linking density and mesogen composition. Thermally reversible glass transition temperature, Tg, and nematic-to-isotropic transition temperature, Tni, were observed upon heating and cooling. By varying the heating rate, Tg 0 and Tni 0 were determined at zero heating rate. The temperature dependence of the orientational order parameter was determined from the anisotropic azimuthal angular distribution of equatorial reflections seen during real-time WAXS. Results show that the choice of cross-linking unit, its shape, density, and structure of co-monomers, all influence the temperature range over which the thermal transitions take place. Including multi-ring aromatic groups as cross-linkers increased the effective stiffness of the cross-linking, resulting in a higher glass transition temperature. The
nematic-to-isotropic transition temperature increased in the presence of multi-ring aromatic structures, as either cross-linkers or mesogens, particularly when the multi-ring structures were larger than the low-molar-mass mesogen common to all three samples.
Understanding Neutron Radiography Reading VII-NRHB Part 1 of 2
Effect of ionic liquids (ILs) viz. pyridinium, picolinium and imidazolium halide on the micellization and the structure of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer, F127 in aqueous... more
Effect of ionic liquids (ILs) viz. pyridinium, picolinium and imidazolium halide on the micellization and the structure of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer, F127 in aqueous solution has been studied by small angle neutron scattering (SANS) and dynamic light scattering (DLS) measurements. The interaction information between ILs and PEO/PPO has been explored by using 1H NMR and viscosity measurements. The micellar structural parameters are obtained as a function of variation in alkyl chain length, cationic head group and concentrations of ILs by fitting the SANS data with model composed of core–shell form factor and a hard sphere structure factor of interaction. Addition of ILs is found to decrease the micellar core radius, aggregation number and hard sphere radius of F127 micelles. The effect of concentration, chain length and head groups of ILs also have been studied.
In this manuscript we report pH induced micellar transition in aqueous solution of cetyltrimethylammonium bromide (CTAB) in the presence of three weakly polar aromatic additives viz. p-toluic acid, p-cresol and p-toluidine scrutinized by... more
In this manuscript we report pH induced micellar transition in aqueous solution of cetyltrimethylammonium bromide (CTAB) in the presence of three weakly polar aromatic additives viz. p-toluic acid, p-cresol and p-toluidine scrutinized by viscosity, nuclear magnetic resonance (NMR), dynamic light scattering (DLS) and small-angle neutron scattering (SANS) measurements. Interaction between these additives and CTAB micelles changes the size and shape of the micelles. Variation in pH alters the charge on the polar group and leads to protonation/deprotonation of acidic/basic group of the additives. Depending upon the pH of solution additives interact with CTAB micelles and accordingly change the solution behavior/aggregation characteristics. Morphological changes of surfactant aggregates as a function of additive concentration and pH were monitored by SANS measurements. NMR studies reveal a pH dependent location of the additive molecules in the micelles.
Troponin is a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle by participating in a series of conformational events within the actin-based thin filament. Troponin is a heterotrimeric complex consisting... more
Troponin is a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle by participating in a series of conformational events within the actin-based thin filament. Troponin is a heterotrimeric complex consisting of a Ca2+-binding subunit (TnC), an inhibitory subunit (TnI), and a tropomyosin-binding subunit (TnT). Ternary troponin complexes have been produced by assembling recombinant chicken skeletal muscle TnC, TnI and the C-terminal portion of TnT known as TnT2. A full set of small-angle neutron scattering data has been collected from TnC-TnI-TnT2 ternary complexes, in which all possible combinations of the subunits have been deuterated, in both the +Ca2+ and -Ca2+ states. Small-angle X-ray scattering data were also collected from the same troponin TnC-TnI-TnT2 complex. Guinier analysis shows that the complex is monomeric in solution and that there is a large change in the radius of gyration of TnI when it goes from the +Ca2+ to the -Ca2+ state. Starting w...
The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of... more
The rheology of water-soluble polyelectrolytes at intermediate and high concentrations is controlled by entanglement, hydrophobic, and electrostatic interactions, whose influences are difficult to isolate. We investigate the rheology of semidilute solutions of sodium carboxymethyl cellulose (NaCMC) with molecular weight M w ≃ 2.5 × 10 5 g/ mol and varying degree of substitution (DS) as a function of polymer concentration in various solvent media: salt-free water (long-ranged electrostatic interactions), 0.5 M aqueous NaCl (screened electrostatics), and 0.5 M aqueous NaOH (screened electrostatics, diminished hydrophobic interactions) in order to selectively examine the role played by these different interactions. Decreasing DS is found to decrease solubility and induce partial aggregation and eventual gelation. In salt-free and 0.5 M NaCl solution, NaCMC with DS ≃ 1.2 exhibits hydrophilic polyelectrolyte and neutral polymer in good solvent behavior, respectively. Decreasing DS to ≃0.7−0.8 leads to hydrophobic behavior in both media, becoming weak gels at high concentrations. In 0.5 M NaOH (pH = 13.5) the viscosities of solutions with different DS become identical when plotted against the overlap parameter, which we interpret as resulting from the solubilization of unsubstituted cellulose blocks. Small-angle neutron scattering (SANS) data indicate that the polymer conformation is not strongly affected by hydrophobic interactions. By varying DS, ionic strength, and pH, we demonstrate the tuning of NaCMC−solvent interactions, controlling separately the electrostatic and hydrophobic effects on the solution rheology.