Small-angle neutron scattering studies of nonionic surfactant: Effect of sugars

Micellar solution of nonionic surfactantn-dodecyloligo ethyleneoxide surfactant, decaoxyethylene monododecyl ether [CH₃(CH₂)₁₁(OCH₂CH₂)₁₀OH], C₁₂E₁₀ in D₂O solution have been analysed by small-angle neutron scattering (SANS) at different temperatures (30, 45 and 60° C) both in the presence and absence of sugars. The structural parameters like micelle shape and size, aggregation number and micellar density have been determined. It is found that the micellar structure significantly depends on the temperature and concentration of sugars. The micelles are found to be prolate ellipsoids at 30° C and the axial ratio of the micelle increases with the increase in temperature. The presence of lower concentration of sugar reduces the size of micelles and it grows at higher concentration of sugar. The structure of micelles is almost independent of the different types of sugars used.     

Effect of grain boundaries on paraconductivity of YBa2Cu3Ox

To investigate the effect of grain boundaries on paraconductivity of YBa₂Cu₃O_x, melt-textured and c-axis oriented thin films with controlled grain boundaries (superconducting transition width, ΔT, varying between 0.54 and 2.85 K) were prepared, and dc-conductivity has been measured as a function of temperature. In the logarithmic plots of excess-conductivity (Δσ) and reduced temperature (?), starting from low values of ?, we have observed three different regions namely critical region, mean field region and short wave fluctuation region. A correlation is observed between the range of critical region and ΔT, which is found to increase with ΔT. While for ΔT values smaller than 2.5 K only static critical region is observed, for higher ΔTs both static and dynamic critical regions are observed. In the mean field region a crossover from 3D to 2D was observed for all the samples. At ? values larger than 0.24, the excess-conductivity decreased sharply as ?⁻³, which suggested the existence of the short wave fluctuations.     

Cloaking and imaging effects in plasmonic checkerboards of negative and and dielectric photonic crystal checkerboards

Negative refractive index materials are known to be able to support a host of surface plasmon states for both polarizations of light. This makes possible unique effects such as a perfect lens. Checkerboards consisting of alternating cells of positive and negative refractive index represent a very singular situation in which the density of modes diverges at the corners. This raises the question as to whether such effects will still be observed in a real dissipative system of finite size. We have considered several aspects of such structures including these and symmetry aspects (rectangular against triangular checkerboards). We have also studied silver checkerboards whose transverse extent is finite. Negative refractive index checkerboards bring new electromagnetic paradigms both through the intriguing possibilities they appear to offer, and the challenges they present to our understanding of the diffraction process. Most intriguing of all is the possibility of a triangular checkerboard lens whose resolution is limited not by wavelength, but only by the losses in the constituent materials, while a ray picture suggests it behaves as a perfect mirror. The resolution of this lens increases without limit as the losses tend to zero as shown by the generalized lens theorem. We finally show that light confinement can be achieved to certain extent using dielectric triangular photonic crystal (PC) checkerboards displaying the all-angle-negative-refraction (AANR) within the Bragg regime in p polarization. Effectively even a single rectangular or triangular PC can act as an open resonator that confines light in its neighborhood. This cloaking effect has been previously observed in PC slabs displaying the AANR effect. We show that the cloaking is enhanced for three triangular PC wedges sharing a vertex and further improved for 12 triangular PC wedges arranged in a checkerboard fashion.     

Effect of substitution on aniline in inducing growth of anionic micelles

Small-angle neutron scattering (SANS) measurements were carried out on sodium dodecyl sulfate (SDS) micelles in the presence of three different hydrophobic salts, i.e. aniline hydrochloride,o-toluidine hydrochloride andm-toluidine hydrochloride. All these salts induce a uniaxial growth of micelles to form prolate ellipsoidal structures. A progressive decrease in the surface charge of the micelles was observed with the addition of salts followed by a rapid growth of the micelles. The presence of a methyl substitution at the ortho position of aniline does not alter the growth behavior significantly. However, when the substitution is at meta position micellar growth is favored at lower salt concentration than that is observed for aniline. This can be explained in terms of the difference in the chemical environments of the substituents at the ortho and meta positions.     

Epidemic model of COVID-19 outbreak by inducing behavioural response in population

Nonlinear Dynamics - COVID-19 has spread around the world since December 2019, creating one of the greatest pandemics ever witnessed. According to the current reports, this is a situation when...     

A UNIQUE SUPRAMOLECULAR STRUCTURE OF POLY [μ-OXO -BIS(1,1,2,3,4,5-HEXAHYDRO-1-NITRATOTELLUROPHENE)] [(C4H8TENO3)2O]N WITH—0-TE-0-TE-0—CROSS LINKED CHAINS

Abstract

Poly [μ-oxo bis(1,1,2,3,4.5-hexahydro- 1-nitratotellurophene)] 1, is prepared by the room temperature reaction of 1,1,2,3,4,5-hexahydro- 1.1 -diiodotellurophene with silver nitrate in deionised water. Crystals of 1 are monoclinic. space group CUc with a=13.930(2) Å, b =11.665(2) Å, c=10.0682(11) Å, β=116.264(8)^O and Z=A. The monomeric unit of the title compound is centrosymmetric, with an angular TeOTe skeleton containing bridging O atom at the centre of symmetry. These monomeric units are linked together through —O-Te-O-Te-O—cross linked chains and the nitrate groups are asymmetrically bidentate with a primary Te-ONO₂ and a secondary Te—O semibonding interaction. Each nitrate group further participates in another Te–O semibonding interaction forming another asymmetric Te(NO₃)₂Te bridge. The structural characteristics of 1 are compared with related complexes.     

Rheological response and small-angle neutron-scattering study of diester-bonded cationic biodegradable gemini surfactants in presence of different additives

Morphological changes and internal packing arrangements of planar dicationic-ester-bonded biodegradable gemini surfactants ethane-1, 2-diyl-bis(N,N-dimethyl-N-alkylammonium acetoxy) dichlorides (m-E2-m) have been explored by exploiting small-angle neutron-scattering (SANS) measurements. The data have been analyzed on the basis of Hayter and Penfold model for macroion solutions to obtain information about the aggregation behavior at the molecular level. The extent of micellar growth and structural changes of the micelles formed by these surfactants have been found to depend on the number of methylene units in their tail length. The growth and variation of micellar shape are more pronounced for the surfactant with longer tail length (m?=?16), whereas the surfactants with shorter tail length showed less variation of these properties in aqueous solution. Semi-major axes of the micelles show flexibility while varying the concentration and temperature of the systems; however, semi-minor axes remain rigid. Changes in the structural parameters of the micelles with addition of different salts were also inferred from SANS measurements. The intensity of scattered neutrons at the low Q region was found to increase while varying the nature of salt from monovalent to trivalent. On the basis of rheological responses, the rich aggregation behavior resulting from the addition of sodium salicylate (NaSal) is attributed to the special molecular structure of the gemini surfactant and the appropriate interaction between the surfactant and NaSal. This is inferred on the basis of behavior observed by varying the chain length (m) of the gemini surfactant that resulted in the formation of different types of microstructures.     

Tuning Phenols with Intra‐Molecular Bond Shifted HYdrogens (IM‐SHY) as diaCEST MRI Contrast Agents

The optimal exchange properties for chemical exchange saturation transfer (CEST) contrast agents on 3 T clinical scanners were characterized using continuous wave saturation transfer, and it was demonstrated that the exchangeable protons in phenols can be tuned to reach these criteria through proper ring substitution. Systematic modification allows the chemical shift of the exchangeable protons to be positioned between 4.8 to 12 ppm from water and enables adjustment of the proton exchange rate to maximize CEST contrast at these shifts. In particular, 44 hydrogen‐bonded phenols are investigated for their potential as CEST MRI contrast agents and the stereoelectronic effects on their CEST properties are summarized. Furthermore, a pair of compounds, 2,5‐dihydroxyterephthalic acid and 4,6‐dihydroxyisophthalic acid, were identified which produce the highest sensitivity through incorporating two exchangeable protons per ring.