Small-angle X-ray Diffraction Measurements Research Articles

Smectic A: cholesteric phase transition investigated by small angle X-ray diffraction and viscosity measurements

We have studied the in influence of the mean molecular length on the nature of the cholesteric (N*) – smectic A (A) liquid crystal phase transition for thermotropic compounds of cholesteryl myristate (C14), cholesteryl nonanoate (C9), and binary mixtures of C14 – C9 and cholesteryl caproate (C6) phase (dA), the mean molecular length () in the N* domain, and the correlation length (e), as well as changes along the N* – A phase transition, were determined from the X-ray diffraction data. The results show a decrease in A phase domain and an expansion of the N* – domain as the mean molecular length is diminished. Such effect induces a second order A – N* phase transition for a particular mixture of 63.1 mol% of C9 and 36.9 mol% of C6, evidenced by viscosity measurements in good agreement with previous density data.

Local anaesthetic block copolymer system undergoing phase transition on dilution with water

The possibility of formulating a local anaesthetic system displaying in situ gelation on dilution with water, as well as its dependence on concentration of active ingredients and pH was investigated. For this purpose Lutrol ® F68, water, a eutectic mixture of lidocaine and prilocaine and Akoline MCM were mixed in different ratios and investigated using crossed polarisers, small-angle X-ray diffraction, rheology, conductivity and NMR self-diffusion measurements. In particular, an isotropic phase of low viscosity turning into a high viscous hexagonal phase upon dilution with water was found. The increase in viscosity is only weakly dependent on temperature in the temperature range of 20–37°C. The rheology and in vitro drug release of these systems were studied and the elastic modulus was found to be fairly independent of concentration of active ingredients and pH in the investigated region. The in vitro release of lidocaine and prilocaine was found to increase with increasing concentration of the active ingredients and with decreasing pH, the latter as a consequence of the pH-dependent ionisation of these substances. The behaviour of the system is promising from a pharmaceutical point of view, since the isotropic low-viscous phase can be injected into, e.g. a periodontal pocket where the presence of saliva will cause a temporal transition into a rigid hexagonal phase thus making the formulation stay at the application site. At even higher water content, either as a result of longer application time or rinsing with water, the hexagonal phase is effectively dissolved through transformation to a water-rich micellar phase.

Interactions of cyclic AMP and its dibutyryl analogue with model membrane: X-ray diffraction and Raman spectroscopic study using cubic liquid–crystalline phases of monoolein

Interactions of adenosine 3′:5′-cyclic monophosphate (cAMP) and its dibutyryl analogue, N 6,2′- O-dibutyryladenosine 3′:5′-cyclic monophosphate (dbcAMP), with a lipid bilayer were studied by small-angle X-ray diffraction (SAXD) and Raman spectroscopy. The cubic Pn3m phase of monoolein (MO) served as a bilayer-based model system. SAXD measurements have indicated that incorporation of approximately 3 wt.% cAMP leaves the phase parameters practically unaltered, whereas the same content of dbcAMP induces the intercubic Pn3m→ Ia3d transition. By applying the concepts of lipid shape parameter and infinite periodic minimal surface to these MO phases, we have suggested that, as opposed to cAMP, dbcAMP associates with the MO bilayer. This conclusion has been supported by the different effects of phase matrix on the Raman shifts of the adenine and phosphate vibrational modes of these two nucleotides. Moreover, Raman spectra have indicated that dbcAMP inserts into the bilayer through the butyryladenine group, positioning dbcAMP preferentially at the polar/apolar interface.

Hydrotrope Action of Vitamin C (VC) and Its Application in a Sunscreen

The solubility regions of the sunscreen 2-ethyIhexyl p-methoxycinnamate (E557) in the CTAB/ n-CsHnOH/ H2 O system with and without the hydrotrope agent vitamin C (VC) are determined. E357 was only sohibilized in the bicontinuous microemulsion (BI), the W/ O microemulsion area and the lamellar liquid crystal region (LLC). The addition of VC in the system greatly enlarged the solubility amount of E557in the bicontinuous region, but reduced h in the lamellar liquid crystal area. Small angle X-ray diffraction measurement was used to determine the location of E557 in the lamellar liquid crystal showing the suncreen molecule penetrating between the hydrocarbon chains in the liquid crystal structure.The UV absorption spectra of E557 in various media was measured, surprisingly showing a dependence on the colloidal structure.

Dehydration of acetic acid by pervaporation with charged membranes

Modified Nafion membranes were prepared by charging Nafion 117 membrane with different long-chained counter ions and used for pervaporation of acetic acid–water mixture. It was observed, that the selectivity of Nafion membrane was enhanced by charging with long-chained counter ions. However, it led to a decrease in permeate flux because of decreasing solubility and diffusivity of the membranes. The results of small angle X-Ray diffraction (XRD) measurement of wet Nafion and modified Nafion samples showed that the cluster dimension of the membranes decreased after charging the membrane with long-chained counter ions. The estimation of the pore diameter of the membranes by Kozeny–Carman equation resulted in a similar tendency. Among the modified Nafion membranes, Nafion (C 8H 17) 4N + is concluded to be the most suitable membrane with a flux of 0.18 kg/m 2 h and a selectivity of 243 for the feed concentration of 90 wt.% acetic acid.

Time-resolved X-ray diffraction from tendon collagen during creep using synchrotron radiation

In order to understand the molecular mechanism of relaxation phenomena in collagenous tissue, time-resolved, small-angle X-ray diffraction measurements were performed on bovine Achilles tendon collagen under creep. A tension-induced increase in the 67 nm period ( D-period) was observed, and the strain in the D-period, ε D , was found to be almost proportional to the external force per unit cross-sectional area (average stress) of the specimen. With an increase in ε D , a change in the ratio of intensities of the third-order reflection peak of the D-period to that of the second-order peak was also observed. The increase in ε D was decomposed into three elementary processes of D-period deformation, which are presented on the basis of the Hodge–Petruska model: (1) molecular elongation, (2) increase in gap region, and (3) relative slippage of lateral adjoining molecules. Up to 8 MPa of average stress, the contribution to ε D originated mostly from only mode (1). At more than 10 MPa of average stress, modes (2) and (3) also contributed to fibril elongation. For ε D by molecular elongation (mode (1)), the time dependence of the D-period change in the immediate response region is a sharply shaped step function, while the contribution to ε D by molecular rearranging modes gives a slight creep nature at the immediate response region in the time dependence of ε D . Because this creep nature is observed at the immediate response, it is related qualitatively to the KWW function in a stress-relaxation modulus of collagenous tissue observed in an immediate response region (Sasaki et al. (1993) Journal of Biomechanics 26, 1369–1376). The elementary process of KWW-type relaxation is concluded to be related to the tension-induced molecular rearrangement within a D-period.

Fabrication and characterization of high quality organic multiple quantum well structures

High quality organic multiple quantum well (MQW) structures consisting of alternating layers of tris(8-hydroxyquinoline) aluminum (Alq 3) and 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) have been prepared by a multisource-type high-vacuum organic molecular beam deposition (OMBD) system which we have designed specially to improve the large-area uniformity and abrupt interfaces. Small angle X-ray diffraction, optical absorption and photoluminescence measurement results indicate that the MQW structures have a very uniform layered structure throughout the entire stack, and interfacial roughness is smaller than 1.0 nm. Exciton energy shift to a high energy region with decreasing Alq 3 layer thickness has been observed.

Exciton confinement in organic multiple quantum well structures

High-quality organic multiple quantum well (MQW) structures based on tris(8-hydroxyquinoline) aluminium and 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) have been prepared by use of a multisource-type high-vacuum organic molecular beam deposition system. Small-angle x-ray diffraction measurements indicate that the MQW structures have a very uniform layered structure throughout the entire stack. Both optical absorption and photoluminescence (PL) measurements reveal the evidence for exciton confinement in the /PBD MQW structures. The thickness-dependent blue shift of the PL peak observed upon decreasing the well width is attributed to the change of exciton energy as a result of quantum confinement. Theoretical calculations have been performed and the results agree with the experimental results. Light-emitting diodes (LEDs) based on the /PBD MQW structure with greater efficiency, a narrower electroluminescence spectrum and less of a blue shift than the single heterostructure LEDs have also been fabricated.

Effect of sodium on the electronic properties of Pd/silica-alumina catalysts

The effect of the alkali ion content on the electronic properties of palladium, supported on natural pumice and on synthetic aluminosilicates, was studied by X-ray photoelectron spectroscopy (XPS) measurements. To this aim a series of catalysts of palladium supported on aluminosilicates with various amounts of sodium and potassium in the bulk structure were prepared and analysed. The Pd 3d 5/2 binding energy shifts of the different catalysts with respect to pure metal Pd 3d 5/2 binding energy were followed as a function of the Na/Pd atomic ratio. For reasons of comparison, a silica supported Pd catalyst whose surface had been doped with sodium was also studied. A correlation of the Pd 3d binding energy with the sodium content was found, regardless on whether sodium was present in the bulk structure or just at the surface of the catalyst. The effect was independent of the catalyst preparation procedure. The analysis of the intensity of the photoelectron peaks of Pd 3d and Si 2p of the lower surface area catalysts, using the Kerkhof-Moulijn model, yielded particle sizes in agreement with values obtained from small angle X-ray diffraction measurements (SAXS). For the large surface area supported catalysts a monolayer type of metal distribution was found. The intensity ratios of the Na 1s and Si 2p photoelectron peaks are in accordance with those estimated from the bulk Na/Si atomic ratios of the synthetic and natural pumice support. Therefore any segregation of the alkali ions on the palladium particle of the corresponding catalysts are ruled out. The electronic effect is thus discussed in terms of the formation of an electron donor composite formed by the metal, the oxygen and the alkali ion.

Mechanical Stability of Pure Silica Mesoporous MCM-41 by Nitrogen Adsorption and Small-Angle X-ray Diffraction Measurements

We report experimental data on the mechanical stability of the silica mesoporous material MCM-41. Using X-ray diffraction and nitrogen adsorption we show that the ordered mesoporous structure of MCM-41 can be affected considerably by mechanical compression at pressures as low as 86 MPa and essentially destroyed at 224 MPa.

Structural and Optical Nonlinear Characterizations of Langmuir−Blodgett Films of 1-Benzyl-9-hydrofullerene-60

The structural and optical nonlinear features of the condensed layers at the air-water interface and Langmuir-Blodgett (LB) films of the substituted fullerene 1-benzyl-9-hydrofullerene-60 (C{sub 60}-Be) were investigated by {pi}-A isotherm, small angle X-ray diffraction (SAXD), and optical measurements. Pure C{sub 60}-Be molecules existed at the air-water interface in a bulk phase. A new type of two-chain amphiphilic molecule, 1, 10-bistearyl-4, 6, 13, 15-tetraene-18-nitrogen-crown-6 (NC), was used as an inert material to construct mixed C{sub 60}-Be/NC LB films of much better quality than the pure C{sub 60}-Be LB films. Our {pi}-A, UV-visible absorption, and SAXD measurements show that the structural improvement in the mixed C{sub 60}-Be/NC LB films was realized by insertion of the C{sub 60}-Be molecules between the two hydrophobic chains of the NC molecules. The relatively large third-order nonlinear susceptibility {Chi}{sup (3)}{sub {chi}{chi}{chi}{chi}}(-3{omega}; {omega},{omega},{omega}) = 2.1 x 10{sup -11} esu was deduced by measuring third-harmonic generation in the mixed C{sub 60}-Be/NC LB films. 13 refs., 7 figs.

Structure and phase behaviour of dimyristoylphosphatidic acid/poly(L-lysine) systems.

Differential scanning calorimetry (DSC) and X-ray diffraction studies on (DMPA)/poly(L-lysine) systems are reported. DSC studies revealed that addition of poly(L-lysine) to DMPA bilayers raises the gel to liquid-crystalline phase transition of the systems, and that this effect depends on the molecular weight of the poly(L-lysine). Small-angle X-ray diffraction measurements showed that, in the liquid-crystalline phase, the lamellar spacing of a DMPA/short-poly(L-lysine) (approximately 4000 mol. wt.) system is shorter than that of a DMPA/long-poly(L-lysine) (approximately 22000 mol. wt.). In this connection wide-angle X-ray diffraction measurements indicate that the long-poly(L-lysine) adopts a beta-sheet conformation on the DMPA bilayers in both the gel and the liquid-crystalline phases, but the short-poly(L-lysine) adopts this conformation only on gel phase DMPA bilayers. We found that the spacings of the hydrocarbon chain packing in a DMPA bilayer in the gel phase increases with temperature, while the spacing between neighbouring polypeptide chains in long-poly(L-lysine) in the beta-sheet conformation remains almost constant. These observations indicate that the positively charged lysine residues are structurally independent of the negatively charged head groups of the phospholipid. On the basis of the present results we propose a model to explain the elementary behaviour of extrinsic membrane proteins in biomembranes.

Morphology and crystal structure of an a axis oriented, highly crystalline poly(ethylene terephthalate)

The morphological structure of an extremely highly crystalline poly(ethylene terephthalate) (PET) which was obtained by very long term annealing after direct esterification was characterized by small angle and wide angle X-ray diffraction, infra-red spectroscopy, and density and fusion measurements. The specimen has a high melting point of 302.5°C, an observed density of 1.468 g cm −3 and a calculated density of 1.501 g cm −3. From these results, together with small angle X-ray scattering data and the dependence of the fusion curves on the heating rate, this highly crystalline material is proposed to consist of molecules which are either fully extended or which contain only a few folds. Moreover, the specimen has a good double orientation: the crystallites not only have their a axes parallel, but also have their (001) planes approximately parallel to the main plane of the specimen. The structure determined from the X-ray diffraction intensity data is basically consistent with that obtained by Daubeny et al.

Structures and optical properties of organic/inorganic superlattices

A new class of superlattice materials consisting of alternating layers of organic and inorganic materials has been prepared from 8-hydroxyquinoline aluminum (Alq) and MgF2 by vacuum deposition. The Alq layer thickness in the superlattices was varied from 10 to 50 Å. Small-angle x-ray diffraction measurements indicate that the superlattices have very uniform layered structure throughout the entire stack, and the interfacial roughness is much smaller than 10 Å. From the optical absorption and photoluminescence measurements, it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness. The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.

Preparation and characterization of amorphous SeTe/CdSe superlattices and their constituent thin layers

A method for the preparation of amorphous Se 0.85Te 0.15/CdSe chalcogenide superlattices by means of vacuum evaporation under 1.33 × 10 -4 Pa is described. The small and large angle X-ray diffraction measurements, Raman spectroscopy, electron microscopy and diffraction are used for their characterization. The constituent layers are well defined with interfaces about two atomic layers thick. It is shown for the first time that the thermally evaporated CdSe layer converts into amorphous when two critera—for the layer to be sufficiently thin and to be enclosed between two amorphous Se 0.85Te 0.15 layers—are satisfied.

Ion beam-induced and thermal reactions at Fe:GaAs interface

Ion beam-induced and thermal reactions at Fe:GaAs interface are studied by using conversion electron Mössbauer spectroscopy and small angle X-ray diffraction measurements. A thin film of Fe (enriched to 30% in57Fe Mössbauer isotope) was deposited in UHV environment on 〈100 〉 oriented semi-insulating GaAs substrates. Some of the samples were ion-mixed by 130 keV Ar+ ions at dose values of 3 × 1015 and 1016 ions/cm2. The asdeposited and ion-mixed samples were annealed at different temperatures up to a maximum of 500° C. It was observed that ion mixing led to precipitation of disordered and/or defective binary phase along with ferromagnetic Fe3GaAs ternary phase which upon vacuum annealing at 500°C for 1 h leads to a mixture of structurally well-defined Fe3Ga, FeAs and FeAs2 phases. The combined analysis of Mössbauer and X-ray data is shown to reveal the location of the phases below the sample surface. The mechanism for phase formation and associated reaction kinetics at Fe/GaAs interface is discussed in the light of the experimental results.

Electrical and electrophotographic properties of CdSe/SeTe and CdSe/Se multilayers

Novel amorphous superlattices CdSe/SeTe and CdSe/Se are obtained. Small-angle x-ray diffraction measurements of these structures revealed that high quality super-lattices with smooth interfaces were deposited. Parallel and perpendicular dark currents are measured. The changes of the activation energy and photoconductivity at small sublayer thicknesses are explained with quantum-size effect. The expansion of the spectral sensitivity toward the near-infrared region and fast photo-discharge suggest that a-Se monolayer/superlattice structures would be perspective for electrophotographic and laser printer photoreceptors.

Characterization of long-periodic layered structures by X-ray diffraction I: A system for small angle and intermediate angle X-ray diffraction using a reflection kratky camera

A high resolution camera has been developed for the small angle X-ray diffraction measurement of long-periodic layered structures such as Langmuir-Blodgett multilayers, superlattices and liquid crystals. A block collimation system known as a Kratky camera is used to produce a very narrow incident beam. The camera is mounted on a computer-controlled goniometer whose sample holder is rotated around a vertical Θ axis by a pulse motor. Measurements can be carried out in a θ-2θ scan, and also in θ or 2θ scans. Processing of the collected data includes smoothing, and correction for absorption, polarization factor and instrumental broadening. The performance of the present system has been demonstrated by observation of diffraction patterns of a Langmuir-Blodgett film of cadmium arachidate and a GaAs/AlAs superlattice.

Pulsed laser treatment of Fe2O3 film on Al2O3

Fe2O3 film (∼110 Å) on crystalline Al2O3 substrate is treated by ruby laser pulses at different energy densities up to a maximum of ∼7.5 J/cm2, and the transformations are examined by conversion electron Mössbauer spectroscopy and small-angle x-ray diffraction measurements. It is observed that transformations begin to appear in the sample at an energy density of ∼3.0 J/cm2 although significant modifications are observed only at energy densities higher than about 7.0 J/cm2. The values of hyperfine interaction parameters reveal that the laser treated samples contain FeAlO3 and FeAl2O4 phases, along with the residual α-Fe2O3 phase. The laser-mixed state undergoes structural modifications upon thermal annealing, leading to formation of the Fe3O4 phase and complete disappearance of the FeAlO3 phase.

Miscibility, crystallization and melting behaviour, and morphology of binary blends of polycaprolactone with styrene- co-maleic anhydride copolymers

Blends of polycaprolactone (PCL) and random copolymers of styrene and maleic anhydride (SMA) with different maleic anhydride contents were prepared by the coprecipitation technique. The miscibility of both polymers in the melt and in the solid state was studied by means of optical microscopy, light transmission measurements and dynamic mechanical analysis. The crystallization behaviour of PCL in the miscible blends was examined using optical microscopy and the morphology of the semicrystalline PCL/SMA blends was investigated by means of small-angle X-ray diffraction measurements. Their melting behaviour was studied by differential scanning calorimetry. SMA containing 14 and 25 wt% MA was found to be miscible with PCL over the entire composition and temperature range (up to 200°C). SMA appears to segregate interlamellarly during the isothermal crystallization of PCL. The double melting behaviour of PCL in the blends was attributed to a secondary crystallization process and not to a partial melting-recrystallization-remelting process.