Abstract: The main aim of this study is to synthesize calcium silicate ceramics that exhibit suitable properties to be used for biomedical applications. In the present work, attention was paid to the understanding of processing-structure relationships. A particular effort was made to clarify the identification of Ca-O-Si bonds by means of spectroscopy. The calcium silicate systems were prepared via a sol-gel route, varying the chemical compositions, the catalyst concentration, and the temperature and time of aging and heat treatment. The processes and the phases evolved during the sol-gel procedure were determined. The bond systems were investigated by Fourier transform infrared (FTIR) and (29)Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and the aggregate structures by scanning electron microscopy (SEM), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and X-ray diffraction (XRD) measurements.
Abstract: The parameters of fullerene C(60) dissolved in carbon disulfide CS(2) are analyzed by small-angle neutron scattering (SANS) in a wide interval of momentum transfer. To exclude the influence of nonequilibrium conditions, the solutions are prepared without applying shaking, stirring or ultrasound. No indication of the equilibrium cluster state of C(60) (with the cluster size below 60 nm) in the final solutions is revealed. Molecular dynamic simulations are complementary used to find out the partial volume of C(60) in CS(2) and the scattering contribution of the solvent organization at the interface with the fullerene molecule, which is shown to be small. Among several approaches for describing SANS data the preference is given to the model, which takes into account the presence of stable C(60) dimers (comprising 10% of the total particle number density) in the solution.
Abstract: We report on the phase transitions, solution structure, and consequent effect on the photophysical properties of poly[3-(6-trimethylammoniumhexyl)thiophene] bromide (P3TMAHT) in aqueous sodium dodecylsulfate (SDS). Polythiophene was mixed with SDS or deuterated SDS to form P3TMAHT(SDS)(x) complex (x = the molar ratio of surfactant over monomer units) in D(2)O and studied by small-angle neutron and X-ray scattering (SANS/SAXS) and optical spectroscopy. At room temperature, P3TMAHT forms charged aggregates with interparticle order. The addition of SDS eliminates the interparticle order and leads to rod-like (x = 1/5) or sheet-like polymer-SDS aggregates (x = 1/2 to 1) containing rod-like (x = 1/5 to 1/2) or sheet-like (x = 1/2 to 1) polymer associations. Partial precipitation occurs at the charge compensation point (x = 1). Ellipsoidal particles without interparticle order, reminiscent of SDS micelles modified by separated polymer chains, occur for x = 2 to 5. Free SDS micelles dominate for x = 20. Structural transitions lead to a concomitant variation in the solution color from red (P3TMAHT) to violet (x = 1/5 to 1) to yellow (x > 2). The photoluminescence fingerprint changes progressively from a broad featureless band (x = 0) through the band narrowing and appearance of vibronic structure (x = 1/5 to 1) to the return to a blue-shifted broad emission band (x = 5). The polymer stiffness reaches a maximum for x = 1, which leads to minimization of the Stokes shift (0.08 eV). This work gives fundamental information upon how surfactant complexation can influence both the solution structure and photophysical properties of a water-soluble polythiophene.
Abstract: Purpose â The purpose of this paper is to determine the nano-sized characteristics of SU-8 polymer micro-electromechanical systems airflow metrology turbines samples. These microturbines were made to be the first using axial airflow for low air pressure response. This polymer may be affected during curing by UV and heat baking, as well as confined heat from laser ablation. Defects in the resin matrix may influence the material quality and hence the final turbine performance.
Design/methodology/approach â Small angle neutron scattering investigations were performed using the instrumentation of the Budapest Research Reactor.
Findings â The average sizes of the voids/cracks in the resin matrix of the turbines were determined and allowed the viability of making smaller even thinner rotor blades for higher spin and electrical output capability to be considered.
Originality/value â The obtained results have advanced the industrial applicability of the adopted technique in the considered sector of polymer analysis.
Abstract: Three nonionic classic surfactants C10E7 (heptaethylene glycol monodecyl ether) and C12E7 (heptaethylene glycol monododecyl ether) and C14E7 (heptaethylene glycol monotetradecyl ether) in water solutions were investigated for concentration c = 0.5% (dilute regime) at temperatures t = 6°, 10°, 15°, 20°, 25°, 30° and 35° C with two methodsâtensiometric and small-angle neutron scattering ( SANS ) on SANS diffractometer âYellow Submarineâ at Budapest Neutron Center, Budapest ( Hungary ) and SANS spectrometer (âYuMOâ) of the IBR-2 on pulsed neutron source at FLNP, JINR in Dubna ( Russia ). Measurements have covered Q range from 8 10â3 to 0.4 Aâ1. The micellar solutions were prepared in D2O since the contrast between the micelles and the solvent in neutron experiments is better with D2O than with H2O. It was obtained as the result that the shape of micelles changes depending on surfactant concentration and temperature. At lower concentrations and temperatures micelles are ellipsoids but at higher concentrations and temperature are rather cylinders. For calculation and approximation results from SANS experiments was used program PCG 2.0 of Glatter O. and co-workers from University of Graz (Austria).
Abstract: A hydrophilic non-stoichiometric epoxy network was prepared by end-linking reaction of α,Ï-diamino terminated poly(oxypropylene)-b-poly(oxyethylene)-b-poly(oxypropylene) (POPâPOEâPOP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA) at the excess of amino groups. Series of epoxy hydrogels swollen to various degrees was prepared by swelling of the epoxy network in D2O and solutions of inorganic salt (KNO3) in D2O, respectively, and investigated by small-angle neutron scattering (SANS). Degree of swelling was controlled in two ways: by partial evaporation of the solvent and by KNO3 concentration in the swelling solution. Nanophase separated structure of all hydrogels was confirmed by SANS. Scattering data were fitted to the TeubnerâStrey model assuming bicontinuous locally lamellar structure of the hydrogels. Changes in SANS profiles induced by the presence of KNO3 in swelling solutions reflect a refinement of the nanophase separated structure of hydrogels caused by improvement of POEâD2O interaction by means of breakage of deuterium-bonded structure of D2O by nitrate anions.
Abstract: The spatial structure and dynamics of hen egg white lysozyme have been investigated by small-angle and inelastic neutron scattering. Analysis of the results was carried using the fractal approach, which allowed determination of the fractal and fracton dimensions of lysozyme, i.e., consideration of the protein structure and dynamics by using a unified approach. Small-angle neutron scattering studies of thermal denaturation of lysozyme have revealed changes in the fractal dimension in the vicinity of the thermal denaturation temperature that reflect changes in the spatial organization of protein.
Abstract: The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids.
Abstract: Small-angle neutron scattering experiments and density measurements were performed on dilute solutions of N,N'-dimethylpropyleneurea (DMPU) in heavy water in the mole fraction range 0.005(0.0025)-0.05 at 288.15, 298.15 and 313.15 K. From the experimental results values of the radius of gyration, second osmotic as well as second and third molal volume virial coefficients, and Kirkwood-Buff integrals were calculated. The results led to the conclusions that DMPU has a structure-making effect on water and the pairwise solute-solute interactions exhibit no temperature dependence and are less attractive in DMPU solutions than in N,N'-dimethylethyleneurea and tetramethylurea solutions.
Abstract: Higher plant thylakoid membranes contain a protein kinase that phosphorylates certain threonine residues of light-harvesting complex II (LHCII), the main light-harvesting antenna complexes of photosystem II (PSII) and some other phosphoproteins (Allen, Biochim Biophys Acta 1098:275, 1992). While it has been established that phosphorylation induces a conformational change of LHCII and also brings about changes in the lateral organization of the thylakoid membrane, it is not clear how phosphorylation affects the dynamic architecture of the thylakoid membranes. In order to contribute to the elucidation of this complex question, we have investigated the effect of duroquinol-induced phosphorylation on the membrane ultrastructure and the thermal and light stability of the chiral macrodomains and of the trimeric organization of LHCII. As shown by small angle neutron scattering on thylakoid membranes, duroquinol treatment induced a moderate (~10%) increase in the repeat distance of stroma membranes, and phosphorylation caused an additional loss of the scattering intensity, which is probably associated with the partial unstacking of the granum membranes. Circular dichroism (CD) measurements also revealed only minor changes in the chiral macro-organization of the complexes and in the oligomerization state of LHCII. However, temperature dependences of characteristic CD bands showed that phosphorylation significantly decreased the thermal stability of the chiral macrodomains in phosphorylated compared to the non-phosphorylated samples (in leaves and isolated thylakoid membranes, from 48.3 degrees C to 42.6 degrees C and from 47.5 degrees C to 44.3 degrees C, respectively). As shown by non-denaturing PAGE of thylakoid membranes and CD spectroscopy on EDTA washed membranes, phosphorylation decreased by about 5 degrees C, the trimer-to-monomer transition temperature of LHCII. It also enhanced the light-induced disassembly of the chiral macrodomains and the monomerization of the LHCII trimers at 25 degrees C. These data strongly suggest that phosphorylation of the membranes considerably facilitates the heat- and light-inducible reorganizations in the thylakoid membranes and thus enhances the structural flexibility of the membrane architecture.
Abstract: Two classic nonionic surfactants â C14E7 (heptaethylene glycol monotetradecyl
ether) and C10E7 (heptaethylene glycol monodecyl ether) were investigated in heavy
water solution for concentration c = 0.17% (dilute regime) at different temperatures in
the range t = 10â35â¦C by small angle neutron scattering (SANS) method. In the case
of C14E7 surfactant â for all temperatures at c = 0.17% there are two axial ellipsoidal
micelles with longer axis 15 nm at 10â¦C and 49.5 nm at 35 â¦C in investigated solutions.For C10E7 surfactant at the same concentration of solution and temperature â two axialellipsoidal micelles were observed, too. The longer axis is equal to 7.5 nm at 10â¦C, 9 nm at 20â¦C and at 35⦠C this axis is equal to 12 nm. Micelles of C10E7 nonionic surfactant are smaller than those of C14E7 surfactant in the same experimental conditions.
Abstract: Model fitting to small-angle scattering patterns from a series of dilute sodium- and cesium alkyl sulfate micellar solutions results in two significantly different sets of best-fit parameters for each solution. One of the sets defines nearly monodisperse prolate ellipsoids; the other defines slightly, but significantly, polydisperse oblate ellipsoids. In the prolate and oblate minimum locations, the mean form and structure factors as well as the mean core volumes are equal within the experimental error such that the axial ratios are approximately the reciprocals of each other. The experimental finding is numerically generalized: it is demonstrated that, in a Q range, the upper limit of which depends on the axial ratio, the squared mean and the mean square of the scattering amplitude from homogeneous ellipsoids with equatorial radii and axial ratios, respectively (r,eta) and (reta2/3,1/eta), are indistinguishable in practice. In dilute solutions without added salt, neither the best-fit values of the model parameters nor the available thermodynamic models provide direct evidence for the conformation, although the prolate ellipsoidal shape is indirectly supported by experiment. The elongated conformation of ionic micelles in dense and/or salinated systems seems realistic.
Abstract: Gamma-irradiation from a 60Co source was used to prepare hybrid materials from a mixture of polydimethylsiloxane with tetraethylortosilicate and zirconium propoxide.
The obtained materials are monolithic and transparent after drying in air. They had been previously characterized by thermal analysis, X-ray diffraction, Rutherford backscattering and elemental analysis. The present work reports a small angle neutron scattering study on a few samples of these materials to investigate their microstructure at the nanoscale. This study showed the presence of inorganic oxide regions with mass fractal structure, their size and fractal density increasing with the tetraethylortosilicate content. Although the presence of zirconium propoxide is required to obtain a stable hybrid material yet the increase in its content leads to less dense mass fractal oxide units. It was found that the structure of the oxide regions developed through a reaction-limited aggregation mechanism. The further addition of isopropanol in the sample preparation stage causes the inorganic fractal structure to extend over the whole sample.
Abstract: We report on the aggregate structure of a symmetrical A-B-A 9,9-dialkylfluorene/2-alkylaniline "coil-rod-coil" triblock copolymer (or PF/PANI11112-b-PANI11)--consisting of 2-dodecylanilines as A blocks and 9,9-di(3,7,11-trimethyldodecyl)fluorene)s as B blocks--mixed in deuterated toluene, chloroform, and methylcyclohexane. These mixtures contain micrometer scale aggregates. Small-angle neutron scattering data indicate that the interface between the aggregates and solvents manifests surface fractal-like structure. The upper and lower limit length scales which show fractal character are of the order of > 100 and 15 nm. The surface fractal dimension D(s) varies from 2.2 to 2.8. The data show that stiff polyfluorene (PF) segments (persistence length > or = 9.5 nm, diameter approximately 2 nm) of PF/PANI11112-b-PANI11 are dissolved down to the molecular level. Photoluminescence data indicate that most PF units are isolated from both polyaniline (PANi) units and each others. Together with the scattering data, this implies that the disordered interface consists of stiff isolated PF blocks linked together via domains of associated PANi blocks.
Abstract: The structure of aqueous solutions of a prototype ionic liquid, the short alkyl chain 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) has been investigated by small-angle neutron scattering. Concentration fluctuations and Kirkwood-Buff integrals have been calculated, and the results are in good agreement with corresponding data calculated herein from vapor pressure measurements. The large concentration fluctuations and Kirkwood-Buff integral values indicate that the system is in the vicinity of phase separation, which is known to occur some 20 K below room temperature, at a salt mole fraction of around 0.075.
Abstract: Fullerene solutions in carbon disulfide are studied by small-angle neutron scattering (SANS). In addition to earlier experiments on the given system, the range of measured transmitted impulses is extended and the influence of solution preparation methods on C60 cluster formation in these solutions is studied. It is shown that the formation of large C60 clusters (with a size of about 10 nm) is due to nonequilibrium methods of solution preparation. For nonequilibrium dissolution, there is a 10% excess of the observed fullerene size in the solution over the calculated value. It has been established by simulation of the C60/CS2 interface by molecular dymanics methods that inclusion of how solvent molecules are organized on the C60 surface leads to a decrease in the fullerene size in the solution, observed by using SANS. In this paper, the effect of excess R g is explained by the presence of small clusters in the solution (approximately 10% of dissolved C60 molecules). It is discovered that there is a time variation in the concentration of the saturated solution. The explanation of this effect using a model of formation and sedimentation of large clusters (with a size of 100 nm or more) is proposed.
Abstract: Despite the inability of fullerenes to be directly dissolved in water, there are methods for preparing
stable dispersions of fullerenes in water without any particular modifications of the fullerene or addition of stabilizers.
The colloidal properties of such systems prepared by replacing the solvent and structural changes in
them during coagulation have been studied. The coagulation dynamics has been investigated by spectroscopy
and small-angle neutron scattering. The results obtained confirm the colloidal nature of such systems. During
coagulation, particles retain a large volume of water around them, an indication of interaction between fullerene
and water during solution stabilization.
Abstract: Small angle neutron scattering (SANS) is considered as a nondestructive technique adoptable for the microstructural characterization of polymeric materials. The possibility to substitute hydrogen for deuterium makes SANS an exclusive technique for investigating macromolecular structures in synthetic and biological polymers. The same method allows a visualization of polymer chains, because of a local contrast between small size ordered domains and amorphous matrix around. In this article, some theoretical bases are reported, and industrial applications of SANS in the polymers field are shown. In particular, SANS investigations of either monoethylene glycol-based polyurethanes, or heat cured and laser machined organic resin microturbines as used for airflow sensing are described. Other examples are mentioned, moreover, showing the usefulness of SANS in characterizing polymers and confirming the improvement of this tool to a level of industrial applicability.
Abstract: Fullerene clusters in the C60/N-methyl-2-pyrrolidone (NMP)/water system have been investigated by small-angle neutron scattering. It is shown that the scattering cross section corresponding to the size range 10â100 nm depends on the water content in the mixture. Addition of water to a C60/NMP solution in an amount exceeding 40% leads to a sharp increase in the average scattering cross section. This effect depends on the interval between the times of preparation of a C60/NMP solution and its dilution with water: the size of the clusters formed as a result of adding water increases with increasing the age of the initial solution. The reasons for this effect are discussed.
Abstract: Aqueous solutions of tetramethylurea (TMU) were studied by small-angle neutron and X-ray scattering at temperatures 10, 25 and 40 °C in the TMU mole fraction range of 0.0125â0.025. The scattering data indicate preferential attractive interaction between the solute molecules, which becomes stronger as the temperature increases. From SANS data, concentration fluctuations and KirkwoodâBuff integrals have been calculated. The experimental data reveal a considerable soluteâsolute attraction above 0.01 mole fraction of TMU. These findings indicate that in addition to the usually assumed solute caging by water molecules, solute clustering of hydrophobic nature should also be considered for this system.
Abstract: We report on the solubilization, phase behavior, and self-organized colloidal structure of a ternary water-polyfluorene-surfactant (amphiphile) system comprised of polyelectrolytic poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) in nonionic pentaethylene glycol monododecyl ether (C12E5) at 20 degrees C. We show in particular how a high amount (milligrams per milliliter) of polyfluorene can be solubilized by aqueous C12E5 via aggregate formation. The PBS-PFP and C12E5 concentrations of 0.31 x 10(-4)-5 x 10(-4) M and 2.5 x 10(-4)-75 x 10(-4) M, respectively, were used. Under the studied conditions, the photoluminescence (PL), surface tension, static contact angle, and (pi-A) isotherm measurements imply that D2O-PBS-PFP(C12E5)x realizes three phase regimes with an increasing molar ratio of surfactant over monomer unit (x). First, for x < or = 0.5, the mixture is cloudy. In this regime polymer is only partially dissolved. Second, for 1 < or = x < or = 2, the solution is homogeneous. In this regime polymer is dissolved down to the colloidal level. Small-angle neutron scattering (SANS) patterns indicate rigid elongated (polymer-surfactant) aggregates with a diameter of 30 A and mean length of approximately 900 A. The ratio between contour length and persistence length is less than 3. Third, for x > or = 4, the solution is homogeneous and there is cooperative binding between polymer and surfactant. Surface tension, contact angle, and surface pressure remain essentially constant with increasing x. A PL spectrum characteristic of single separated polyfluorene molecules is observed. SANS curves show an interference maximum at q approximately 0.015 A(-1), indicating an ordered phase. This ordering is suggested to be due to the electrostatic repulsion between polymer molecules adsorbed on or incorporated into the C12E5 aggregates (micelles). On dilution the distance between micelles increases via 3-dimensional packing. In this regime the polymer is potentially dissolved down to the molecular level. We show further that the aggregates (x = 2) form a floating layer at the air-water interface and can be transferred onto hydrophilic substrates.
Abstract: In the conventional setup of a small-angle neutron scattering instrument a nearly monochromatic neutron beam is formed by means of a mechanical velocity selector. We studied the influence of the wavelength distribution in the incident beam on the wavelength of the neutrons reaching the sample. The assumption that the wavelength spectrum behind the selector equals to the product of the incident spectrum of the thermalized neutrons and the transmission window of the selector predicts satisfactorily the wavelength measured at sample position. An approximate relation is given between the effective wavelength and the selector rotation speed. The described method of wavelength calibration can improve the precision of size determination in SANS experiment.
Abstract: The Kirkwood-Buff integrals of some binary aqueous alcohol mixtures are computed from the available vapor pressure measurements and compared with previous results as well as small angle neutron scattering experiments. The emphasis of the present report is on accuracy of the results that can be achieved by these two different types of measurements. This seems to be needed, mainly in view of the discrepancies between the various published results, as shown herein. It is argued that agreement in peak positions is more important than that in magnitude. In general, very good agreement is obtained by both methods, and sources of disagreements are discussed. The issue of the computer simulations of aqueous systems and the problematics related to correlations, microheterogeneity, and consequently the Kirkwood-Buff integrals are equally discussed herein.
Abstract: The small-angle neutron scattering (SANS) data of 12 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) dispersions at low lipid concentration (1 mg per 100-mg heavy water) prepared by 5, 9 and 29 extrusions through filters of pores with 50, 100, 200 and 400 nm diameter are presented. They were analyzed within a theory that permits the determination of both structural and hydration parameters of the bilayers as well as the portions of multilamellar vesicles in dispersions with negligible long-range order between the vesicles. The scattering length density profile across the bilayers is approximated by assuming a central hydrocarbon core surrounded by a water-accessible coat. It is modeled by two different forms of functions. In the boat model, the scattering length density of the coat changes linearly from core to water, whereas in the strip model it is constant across the water-accessible coat. It was found that the boat model reflects the reality better than the strip model. The decrease of the multilamellar vesicle portions, either with increasing the number of extrusions at same filter size and with decreasing the filter size, was characterized quantitatively.
Abstract: Results of experiments on small-angle neutron scattering from ferrofluids on polar carriers (pentanol, water, methyl-ethyl-ketone), with double-layer sterical stabilization of magnetic nanoparticles, are reported. Several types of spatial structural organization are observed. The structure of highly stable pentanol-based samples is similar to that of stable ferrofluids based on organic non-polar carriers (e.g., benzene) with mono-layer covered magnetic nanoparticles. At the same time, the effect of the interparticle interaction on the scattering is stronger in polar ferrofluids because of the structural difference in the surfactant shell. The structure of the studied methyl-ethyl-ketone- and water-based ferrofluids essentially different from the previous case. The formation of large (>100 nm in size) elongated or fractal aggregates, respectively, is detected even in the absence of external magnetic field, which corresponds to weaker stability of these types of ferrofluids. The structure of the fractal aggregates in water-based ferrofluids does not depend on the particle concentration, but it is sensitive to temperature. A temperature increase results in a decrease in their fractal dimension reflecting destruction of the aggregates. In addition, in water-based ferrofluids these aggregates consist of small (radius approximately 10 nm) and temperature-stable primary aggregates.
Abstract: We report results of small-angle neutron scattering (SANS) measurements on aqueous solutions of 1,7-heptanediol in the molarity range 0.11â1.5 mol dmâ3 at room temperature. The experimental data show aggregation of the diol molecules within the whole studied concentration range. The scattering curves could be accurately described by the structural model of random concentration fluctuations. The results suggest that 1,7-heptanediol molecules in aqueous solution aggregate in a rather loose way.
Abstract: The Kirkwood-Buff integrals of acetone-water mixtures are determined using two experimental techniques: small-angle neutron scattering and vapor pressure measurements, in order to test the precision and reliability that can be achieved. The data are then compared with those previously reported by different authors, which tend to show considerable variation between them. The various possible sources of inaccuracies are pointed out, both from experimental origins and from the numerical treatment of the data. Comparison with recent simulation results allows to critically compare different models and provide some information about the microstructure of the aqueous mixture.
Abstract: We report on an experimental study of the self-organization and phase behavior of hairy-rod pi -conjugated branched side-chain polyfluorene, poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl]-i.e., poly[2,7-(9,9-bis(2-ethylhexyl)fluorene] (PF2/6) -as a function of molecular weight (M(n)) . The results have been compared to those of phenomenological theory. Samples for which M(n) =3-147 kg/mol were used. First, the stiffness of PF2/6 , the assumption of the theory, has been probed by small-angle neutron scattering in solution. Thermogravimetry has been used to show that PF2/6 is thermally stable over the conditions studied. Second, the existence of nematic and hexagonal phases has been phenomenologically identified for lower and higher M(n) (LMW, M(n) < M(*)(n) and HMW, M(n) > M(*)(n) ) regimes, respectively, based on free-energy argument of nematic and hexagonal hairy rods and found to correspond to the experimental x-ray diffraction (XRD) results for PF2/6 . By using the lattice parameters of PF2/6 as an experimental input, the nematic-hexagonal transition has been predicted in the vicinity of glassification temperature (T(g)) of PF2/6 . Then, by taking the orientation parts of the free energies into account the nematic-hexagonal transition has been calculated as a function of temperature and M(n) and a phase diagram has been formed. Below T(g) of 80 degrees C only (frozen) nematic phase is observed for M(n)< M(*)(n) = 10(4) g/mol and crystalline hexagonal phase for M(n) > M(*)(n) . The nematic-hexagonal transition upon heating is observed for the HMW regime depending weakly on M(n) , being at 140-165 degrees C for M(n) > M(*)(n). Third, the phase behavior and structure formation as a function of M(n) have been probed using powder and fiber XRD and differential scanning calorimetry and reasonable semiquantitative agreement with theory has been found for M(n) >or=3 kg/mol. Fourth, structural characteristics are widely discussed. The nematic phase of LMW materials has been observed to be denser than high-temperature nematic phase of HMW compounds. The hexagonal phase has been found to be paracrystalline in the (ab0) plane but a genuine crystal meridionally. We also find that all these materials including the shortest 10-mer possess the formerly observed rigid five-helix hairy-rod molecular structure.
Abstract: Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.
Abstract: Highly stable and reproducible molecular-colloidal water solutions of C60 fullerenes (FWS) obtained by transferring fullerenes from an organic solution into an aqueous phase with the help of ultrasonic treatment are investigated by means of small-angle neutron scattering (SANS). A polydispersity in the size of detected particles up to 84 nm is revealed. These particles are slightly anisotropic and have a characteristic size of approximately 70 nm. Along with it, there are some indications that a significant part of fullerenes composes particles with the size of the order of 1 nm. The contrast variation based on mixtures of light and heavy water shows that the mean scattering length density of the particles is close to that of the packed fullerene associates as well as that the characteristic size of possible fluctuations of the scattering length density within the particles does not exceed 2 nm. A smooth surface resulting in the Porod law for the scattering is detected. A number of models discussed in the literature are considered with respect to the SANS data.
Abstract: Neutron radiation and high working temperatures induce important changes in the microstructure of metallic components of nuclear reactors. These changes result in weakening of the mechanical properties, which is the primary interest in the safety and lifetime management of nuclear installations. In order to follow up the microstructural changes, separately due to radiation and high temperature, first we measured thermally aged steel samples. The observed anisotropic scattering was fitted by a 2D model. We found that the microstructure of aged metals shows a strong dependence on the industrial treatment quality and also on the sampling.
Abstract: Critical behaviour of a quasi-binary liquid mixture is investigated by small-angle neutron scattering. Analysis of the changes of the critical parameters, caused by addition of a small amount of electrolyte into the binary mixture 3-methylpyridine-heavy water, shows that the third component does not change the 3D Ising-type behaviour of the system; a crossover towards the mean-field behaviour is not observed.
Abstract: According to the theoretical expectations, the potassium content in bubbles of sintered tungsten covers the internal surface, forming a solid or liquid shell. Depending on the temperature, this coverage becomes thinner and thinner by raising the temperature, as more and more potassium from the shell evaporates into the gas phase in the center of the bubble. Small angle neutron scattering investigations were made on annealed samples, varying the temperature between 300 K and 1023 K. The scattering intensity at 1020 K has been chosen as a reference state and the differences of the scattering intensities, in comparison with this reference state, were analysed by using the model of a hollow sphere. The results of the experiment correspond to the theoretical expectations.
Abstract: The aim of this study was to investigate the influence of three chlorhexidine species, chlorhexidine base and its salts (diacetate and digluconate), on the physico-chemical features of liquid crystalline systems and on drug transport through lipophilic membranes. Nonionic surfactant, Synperonic A7 (PEG(7)-C(13--15)) was selected for the preparation of the liquid crystalline systems. Mixtures of different ratios of Synperonic A7 and water were prepared. The liquid crystalline systems were characterized using polarizing microscopy, small-angle neutron scattering and transmission electron microscopy. Membrane transport was also examined. The addition of chlorhexidine species to the liquid crystalline system modified the structure of the liquid crystalline system. As a result of liquid crystal--drug interaction, the solubility of chlorhexidine base and its diffusion through lipophilic membranes increased in comparison with those of the chlorhexidine salts.
