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In this article, an iterative method for estimating the size distribution of noninteracting polydisperse spherical particles from small-angle scattering data is presented. It utilizes the iterative addition of relevant contributions to an instantaneous size distribution, as obtained from the fractional difference between the experimental data and the simulated profile. An inverse relation between scattering vector and real space is assumed. This method does not demand the consideration of any basis function set together with an imposed constraint such as a Lagrange multiplier, nor does it depend on the Titchmarsh transform. It is demonstrated that the method works quite well in extracting several forms of distribution. The robustness of the present method is examined through the successful retrieval of several forms of distribution, namely monomodal, bimodal, trimodal, triangular and bitriangular distributions. Finally, the method has also been employed to extract the particle size distribution from experimental small-angle X-ray scattering data obtained from colloidal dispersions of silica. [ABSTRACT FROM AUTHOR]

Zinc sulphide quantum dots chemically capped with thioglycerol having two different sizes have been synthesized. The particles have a disordered sphalerite structure and are slightly contracted by 1% against the bulk. Small angle X-ray scattering investigations reveal that powders of these nanocrystallites are mass fractals that aggregate via a reaction-limited process to form irregular but rather dense networks with a fractal dimensionality of Df = 2.7 and 2.1, respectively. [ABSTRACT FROM AUTHOR]

The morphological changes in lignite coal at two different pressures, using small angle x-ray scattering, have been investigated. All the scattering profiles are interpreted in terms of surface fractal morphology. It is observed that the surface fractal dimension does not change appreciably under the experimental pressure range, while the volume of micro-cracks and inter-particle pore space is reduced with increasing pressure. By and large, the constant value of the surface fractal dimension of all the specimens, as calculated from the scattering profiles, indicates that the roughness on the pore coal interface remains almost unaffected under the experimental pressure range. The validity of single scattering approximation for this experiment has also been confirmed by the observation of the identical nature of the small angle scattering profiles with respect to change of wave lengths, namely, 0.154 nm. (Cu Kα) and 0.072 nm (Mo Kα), of the probing radiation. [ABSTRACT FROM AUTHOR]

The evaporation-induced self-assembly of mixed colloidshas beenemployed to synthesize microspheres of TiO2/SiO2nanocomposites. Small-angle neutron/X-ray scattering and scanningelectron microscopy experiments reveal the hierarchical morphologyof the microspheres. Although the internal structure of the microspheres,consisting of solely silica nanoparticles, gets significantly modifiedwith time because of the reduction in the high specific surface areaby internal coalescence, the same for the composite microspheres remainsstable over an aging time of 1 year. Such temporal stability of thecomposite microspheres is attributed to the inhibition of coalescenceof the silica nanoparticles in the presence of titania nanoparticles.X-ray diffraction and thermogravimetric results show the improvedthermal stability of the composite grains against the anatase-to-rutilephase transition. Such thermal stability is attributed to the suppressionof the growth of titania nanoparticles in the presence of silica nanoparticles.The UV–vis results indicate the confinement effect of the TiO2nanoparticles in the silica matrix. A plausible mechanismhas been elucidated for the formation of microspheres with differentmorphology during self-assembly. [ABSTRACT FROM AUTHOR]

The interphase structure of poly(vinyl alcohol) (PVA)-SiC nanofiber polymer nanocomposites has been investigated using positron annihilation lifetime spectroscopy (PALS) and small-angle X-ray scattering (SAXS). The interphase region in polymer nanocomposites extends from nanofillers' surface to bulk polymer matrix. PVA-SiC nanocomposite films with varying concentration of SiC nanofiber (0.1, 0.2, 0.5, and 1.0 wt %) were prepared using solvent casting method. PALS studies indicated the rearrangement of hydrogen bonded structure of PVA and the creation of an interphase layer with larger size nanoholes. SAXS measurements also confirmed the modification of semicrystalline structure of PVA through lamellae structure parameters. The crystallinity of the nanocomposite films have been determined using X-ray diffraction. The observed changes in the polymer nanocomposite structure are resultant of weak interaction between hydrophilic PVA and hydrophobic SiC nanofiber. The mechanical properties of the nanocomposites measured, using tensile testing method, have been explained in view of the changes in structure at interphase. [ABSTRACT FROM AUTHOR]

Guar gum based nano-composite films were prepared using organically modified (cloisite 20A) and unmodified (nanofil 116) nanoclays. Effect of nanoclay incorporation on mechanical strength, water vapor barrier property, chromatic characteristics and opacity of films was evaluated. Nano-composites were characterized using X-ray scattering, FTIR and scanning electron microscopy. A nanoclay concentration dependent increase in mechanical strength and reduction in water vapor transmission rate was observed. Films containing nanofil 116 (2.5% w/w guar gum) and closite 20A (10% w/w guar gum) demonstrated a 102% and 41% higher tensile strength, respectively, as compared to the control. Lower tensile strength of cloisite 20A films as compared to nanofil 116 films was due to its incompatibility with guar gum. X-ray scattering analysis revealed that interstitial spacing between nanofil 116 and cloisite 20A sheets increased due to intercalation by guar gum polymer. This resulted in improved mechanical and barrier properties of nano-composites compared to control. [ABSTRACT FROM AUTHOR]

Assembleddiglycolamides (DGAs) have a strong affinity toward f-elementions at high nitric acid concentrations. Small angle X-ray scatteringstudies revealed that nitric acid concentration dependent changesoccur in the geometrical arrangement of the DGA units of monomericmethacryloyl-DGA and the corresponding polymeric DGA. Cylindricalaggregates of methacryloyl-DGA were formed in 10:1 n-dodecane:1-decanol (added for solubility reasons) upon equilibrationwith nitric acid. The lengths and diameters of the cylindrical methacryloyl-DGAaggregates increased on varying the nitric acid concentration from3 to 4 mol L–1. This resulted in an increase ofthe distribution coefficient (D) of Eu3+ions from 72 to 197. The physical structure of cross-linked (10mol %) poly(methacryloyl-DGA) reorganized distinctly upon equilibrationwith nitric acid. In this case, also the DEu3+values increased significantly from 147 mL g–1at 1 mol L–1HNO3to ∼4000 mLg–1at 4 mol L–1HNO3. Hydrogen bonds between the outer sphere of Eu3+/Am3+/Pu4+nitrate and DGA units provide stabilizationin the hydrophobic environment. This results in enhancement of theirextraction upon increasing nitric acid concentration both in the organicphase as well as in the polymer matrix. Though monomeric and polymericmethacryloyl-DGA are different in their physical assembling, the normalized DIvalues for a same f-elemention upon varying HNO3concentrations show remarkably similarpatterns in both forms. In addition, the unusual stoichiometry deducedfrom the slopes of the log Dvs log[HNO3] curves at fixed nitrate concentration seems to suggest thatthe normal extraction mechanism may not be operating in the hydrogenbonded DGA assemblies. [ABSTRACT FROM AUTHOR]

Thispaper describes the utility of mesoporous alumina (MA), a high capacitynanomaterial based sorbent, for the development of a clinical grade 99Mo/99mTc generator using (n,γ)99Mo. Synthesis of MA was performed using a glucose template in anaqueous system. Structural characterization of the nanosorbent wascarried out by analytical techniques such as X-ray diffraction (XRD),small-angle X-ray scattering (SAXS), atomic force microscopy (AFM),scanning electron miscroscopy (SEM), transmission electron microscopy(TEM), thermogravimetry-differential thermal analysis (TG-DTA), Fouriertransform infrared (FTIR) spectroscopy, and Brunauer–Emmett–Teller(BET) surface area analysis. The material synthesized was mesoporousand nanocrystalline, with average crystallite size of 2–3 nmwith a large surface area of 230 ± 10 m2g–1. In order to evaluate the surface charge of MA in aqueous solution,the zeta potential was determined at different pH environments. Adsorptioncharacteristics of the sorbent such as time course of the adsorption,distribution ratios of 99Mo and 99mTc ions,Mo sorption capacity under static and dynamic conditions, 99Mo adsorption pattern and 99mTc elution pattern were determinedto assess its effectiveness in the preparation of 99Mo/99mTc generator. The measured distribution ratio values indicatethat 99Mo is both strongly and selectively retained byMA at acidic pH and 99mTc could be readily eluted fromit, using 0.9% NaCl solution. The static sorption capacity and practicalsorption capacity under dynamic conditions of MA was determined tobe 225 ± 20 and 168 ± 12 mg Mo per gram of sorbent, respectively.With a view to realize the scope of developing clinical scale generator,a novel tandem column generator concept was used in which two 99Mo loaded columns were connected in series. In this method 99mTc eluted from the first column was fed to the second columnto achieve higher radioactive concentration (RAC) as well as purityof 99mTc. A 26 GBq (700 mCi) 99Mo/99mTc generator was developed using (n,γ)99Mo havingspecific activity of ∼18.5 GBq (500 mCi)/g of Mo. The 99mTc eluted from the generator possessed high radionuclidic,radiochemical, and chemical purity and was amenable for the preparationof 99mTc-labeled radiopharmaceuticals. The technology canbe adapted by those countries having research reactors with flux >1× 1014n·cm–2·s–1to produce 99Mo by (n,γ) route. The capacity ofthe generator can be scaled up to 260 GBq (7 Ci) using (n,γ)99Mo produced from a reactor with flux >1 × 1015n·cm–2·s–1. [ABSTRACT FROM AUTHOR]

Abstract: Pore structure in polypropylene membranes has been investigated using slow positron beam and small-angle X-ray scattering (SAXS) studies. The pore structure has been modified by chemically grafting methylmethacrylate in polypropylene. Depth-resolved Doppler lineshape S-parameter and positronium (Ps) fraction (3γ/2γ ratio) measurements have been carried out using a variable low energy positron beam. Lineshape S-parameter and Ps fraction are found to decrease with the extent of grafting. The deduced positron diffusion length is also seen to decrease with the extent of pore grafting. The power law dependence of SAXS intensity over a wide range of the wave vector transfer reveals the fractal nature of the pore–membrane surface and, the surface fractal dimensions are seen to increase with amount of pore grafting. The value of the negative exponent of the power law size distribution of the pores has been found to be increasing with increase in grafting revealing reduction in the pore size and narrower pore size distribution. The deduced pore size from SAXS measurements is correlated with positron diffusion length and S-parameter from the positron beam measurements. [Copyright &y& Elsevier]

Highly crosslinked/hyperbranched anion-exchange membranes have been prepared by anchoring poly(vinylbenzyl chloride) (PVBCl) within the pores of poly(propylene) microporous base membranes by in situ crosslinking of PVBCl with a diamine 1,4-diazabicyclo[2.2.2]octane (DABCO). The resulting PVBCl-filled precursor membranes were converted to anion-exchange membranes by reacting these with (i) excess of DABCO followed by alkylation with α,α′-dibromo-p-xylene (DBX) (membrane A), and (ii) with excess of tetraethylenepentamine (TEPA) (membrane B). A third membrane C was synthesized by alkylating membrane B with DBX. The chemical analyses indicated that these anion-exchange membranes consist of highly crosslinked/hyperbranched anionic gels within the pores of host microporous membranes. These anion-exchange membranes were characterized in terms of water-uptake capacities, ion-exchange capacities and thermal stability. The physical structures of the membranes were examined by small angle X-rays scattering (SAXS) analysis. The study of SAXS profiles of the dry and water equilibrated membrane A samples indicated that microstructure of anionic gel within the pores of membrane was changed significantly on water equilibration. However, no significant change in the SAXS profile was observed in wet samples of membranes B and C with respect to their dry samples. Thus, the crosslinking generated in membrane A was flexible and very rigid in membranes B and C. The self-diffusion coefficient of I− ions and transport numbers of Cl− ions were measured to examine the effects of crosslinking on transport properties of the membranes. [Copyright &y& Elsevier]