Small-angle X-ray Diffraction Measurements Research Articles

Preparation of a-SiC:H/a-GeC:H superlattices by dual magnetron sputtering

Amorphous semiconductor superlattices composed of hydrogenated amorphous silicon carbon alloys and germanium carbon alloys have been prepared by a dual magnetron sputtering method. A small-angle x-ray diffraction measurement has indicated that the superlattices consist of well-defined smooth layers. Optical band gap has been examined for a series of samples; the thickness of the germanium carbon layer was changed from 20 to 130 Å, while the thickness of the silicon carbon layer was kept constant at 60 Å. The optical band gap increases upon decreasing the thickness of the germanium carbon layer, indicating quantum size effects due to the formation of superlattice structures.

Vermiculite gelation: structural and textural evolution

AbstractMillimetre-sized flakes of a homogeneous, high layer charge vermiculite from S. Olalla (Spain) saturated with l'ornithine cations were made to swell in l'ornithine hydrochloride solutions of various concentrations, and the gel-like structures formed were subjected to uniaxial loads up to 150 g/cm2. Small-angle X-ray diffraction measurements from the swollen flakes show well-modulated intensity patterns from which the equilibrium interlayer distances were obtained for the various swelling conditions. The interlayer spacings can be adequately expressed as normal-logarithmic distribution functions of probability density. The gel texture is described in terms of the average number of elementary layers, all in parallel orientation, constituting independent coherent domains within the swollen flake. Changes in structure and in texture taking place as the gel volume increases, or as water is expelled from the interlayer volume under mechanical compression, are followed by the variation of the corresponding parameters of order.

Deposition of zinc ferrite (ZnxFe3−xO4) films by pulsed laser evaporation process

Zinc ferrite (ZnxFe3−xO4) films have been deposited on a single-crystal Al2O3 substrate by pulsed ruby laser-induced vaporization from a sintered ZnFe2O4 pellet. The film structure has been determined by small-angle x-ray diffraction measurements, and the film morphology by scanning electron microscopy. The microstructural features have been brought out by conversion electron Mössbauer spectroscopy. The dependence of the film properties on the oxygen partial pressure and substrate temperature during deposition is studied to explore optimized conditions for deposition of near single-phase stoichiometric films.

The liquid-crystal structure of adsorbed layers and the stability of dispersed systems in organic liquids

The adsorption of methanol—benzene and ethanol—cyclohexane mixtures has been studied on hydrophobic layer silicates made hydrophobic by cationic surfactants (C 12–C 18). X-ray diffraction measurements of these expanded systems gave the interlayer spacing and interlayer volumes. From the adsorption measurements and from the interlayer volumes the composition of the interlayer phases was determined. It was established that for a known concentration range of surfactant—alcohol—benzene (or cyclohexane) composition the adsorption layer had a smectic or nematic structure in the interlayer space. This layer can be produced without silicate lamellae for a specific concentration range with a small amount of water. A liquid-crystalline structure was shown to be present from polarization microscopy and small-angle X-ray diffraction measurements. At higher alcohol concentrations the adsorption layer was thinner and the lyotropic liquid-crystalline phase no longer existed. The well oriented adsorption layer broke down and the interlayer spacing became smaller.

Characterization of cholesterol hemisuccinate and α-tocopherol hemisucccinate vesicles

Cholesterol hemisuccinate (CHS) and α-tocopherol hemisuccinate (α-THS) were found to be capable of forming liposomes of multi- or single lamellar character. Such veiscles formed spontaneously, did not require the use of organic solvents and yielded high trapping efficiencies and captured volumes. Both CHS and α-THS systems greatly restricted the motion of intercalated spin labelled fatty acids, yet were more osmotically responsive than similar vesicle types comprised of phosphatidylcholine. Small angle X-ray diffraction measurements were consistent with veiscles possessing extremely weak interlamellar forces. CHS vesicles were found to remain intact in vivo, yet followed a pattern of distribution dissimilar to phosphatidylcholine vesicles.

Penetration Enhancer Incorporation in Bilayers

AbstractA preliminary study has been made of the interaction and location of the penetration enhancing agent dodecyl-1-aza-cycloheptane-2-one (Azone) in a system which models certain elements of the lipid arrangements found in the stratum corneum. The model host comprises a nonionic surfactant which forms associated multimolecular structures through hydration interactions with the aqueous component of the system.Azone incorporation into the lamellar bilayer phase leads to a marked increase in ability of the phase to take up water. Small-angle X-ray diffraction and Deuterium NMR measurements indicate the degree of water and azone penetration into the bilayers to be inter-dependent. Similar behaviour is observed for oleyl alcohol but not by hydrotropic materials such as isopropyl alcohol or propylene glycol.The mechanism by which azone promotes the penetration of hydrophilic drugs is indicated to be related to its ability to increase the water capacity of the lipid matrix of the stratum corneum.

Nitridation of iron by pulsed excimer laser treatment under liquid ammonia: Mössbauer spectroscopic study

Iron is nitrided by pulsed excimer laser treatment under liquid ammonia. Conversion electron Mössbauer spectroscopy and small-angle x-ray diffraction measurements reveal formation of γ-austenite in the as-treated sample and its transformation to γ′-Fe4N upon thermal annealing.

Phase separation and hexagonal H II phase formation by gramicidins A, B and C in dioleoylphosphatidylcholine model membranes. A study on the role of the tryptophan residues

The role of the tryptophan-residues in gramicidin-induced H II phase formation was investigated in dioleoylphosphatidylcholine (DOPC) model membranes. 31P-NMR and small angle X-ray diffraction measurements showed, that gramicidin A and C (in which tryptophan-11 is replaced by tyrosine) induce a similar extent of H II phase formation, whereas for gramicidin B and synthetic analogs in which one tryptophan, either at position 9 or 11 is replaced by phenylalanine, a dramatic decrease of the H II phase inducing activity can be observed. Modification of all four tryptophans by means of formylation of the indole NH group leads to a complete block of H II phase formation. Sucrose density centrifugation experiments on the various peptide/lipid samples showed a quantitative incorporation of the peptide into the lipid. For all samples in a 1 10 molar ratio of peptide to lipid distinct bands were found, indicative of a phase separation. For the gramicidin A′/DOPC mixture these bands were analyzed and the macroscopic organization was determined by 31P-NMR and small-angle X-ray diffraction. The results demonstrate that a quantitative phase separation had occurred between a lamellar phase with a gramicidin/lipid ratio of 1 15 and a hexagonal H II phase, which is highly enriched in gramicidin. A study on the hydration properties of tryptophan- N-formylated gramicidin in mixtures with DOPC showed that this analog has a similar dehydrating effect on the lipid headgroup as the unmodified gramicidin. In addition both the hydration study and sucrose density centrifugation experiments showed that, like gramicidin also its analogs have a tendency to aggregate, but with differences in aggregation behaviour which seemed related to their H II phase inducing activity. It is proposed (i) that the main driving force for H II phase formation is the tendency of gramicidin molecules to self-associate and organize into tubular structures such as found in the H II phase and (ii) that whether gramicidin (analogs) form these or other types of aggregates depends on their tertiary structure, which is determined by intra- as well as intermolecular aromatic-aromatic stacking interactions.

SAXD studies on bulk crystallization of nylon 6.I. Changes in crystal structure, heat of fusion, and surface free energy of lamellar crystals with crystallization temperature

Abstract Measurements of small-angle x-ray diffraction (SAXD) were performed for nylon 6 samples quenched from the melt at various crystallization temperatures T (°K). The spacing estimated from the position of maximum intensity in a SAXD diagram, which is assumed to be equal to the thickness of lamellar crystals l, decreases with the decrease of T. The behavior was analyzed in terms of nucleation theory. In applying the theory. the contribution of γ-form crystals for the samples crystallized at lower T was considered. For this purpose wide-angle x-ray diffraction and infrared data obtained for the same samples used in SAXD measurements were used. It was shown that the relation of l versus T deviates remarkably from the theoretical prediction under the premise that the surface free energy σe (ergs/square centimeter) is constant with T. We present an approach to the analysis of the data from the standpoint that σe is a parameter changing with T, where σe should be interpreted as related to the degree of ir...

Study of a magnetically oriented lyotropic mesophase

A study of a magnetically oriented lyomesophase formed by a quaternary system (Na decyl sulfate/water/decanol/Na sulfate) is reported. Small angle x-ray diffraction measurements have been performed on unoriented samples and samples previously subjected to the action of magnetic fields (H). Diffraction patterns show a diffuse inner halo at 80–140 Å and a sharp outer ring at 38 Å. They reduce to spots in the equator for oriented samples with the x-ray beam parallel to H; no diffraction figure is produced for the x-ray beam perpendicular to H. NMR spectra indicate that the director of the phase orients perpendicular to H. These results show that this lyomesophase has a structure not previously encountered. A model of finite planar micelles surrounded by water is proposed. In this model the micelles consist of a bilayer in the form of platelets, probably disk shaped. These platelets align in presence of magnetic fields, with their plane parallel to H, and further orientational restrictions are imposed by the container; they tend to be parallel and some periodicity appears in the director of the direction of the phase, perpendicular to the plane of polar heads. The mesophase satisfies the definition for nematics taking into account periodicities induced in nematic phases by magnetic fields.

Some small‐angle x‐ray diffraction measurements on blown polyethylene films

Journal of Applied Polymer ScienceVolume 22, Issue 10 p. 3027-3029 NoteFree Access Some small-angle x-ray diffraction measurements on blown polyethylene films W. F. Maddams, W. F. Maddams Group Research and Development Department The British Petroleum Company Limited Chertsey Road Sunbury-on-Thames Middlesex, TW16 7LN EnglandSearch for more papers by this authorJ. E. Preedy, J. E. Preedy Group Research and Development Department The British Petroleum Company Limited Chertsey Road Sunbury-on-Thames Middlesex, TW16 7LN EnglandSearch for more papers by this author W. F. Maddams, W. F. Maddams Group Research and Development Department The British Petroleum Company Limited Chertsey Road Sunbury-on-Thames Middlesex, TW16 7LN EnglandSearch for more papers by this authorJ. E. Preedy, J. E. Preedy Group Research and Development Department The British Petroleum Company Limited Chertsey Road Sunbury-on-Thames Middlesex, TW16 7LN EnglandSearch for more papers by this author First published: October 1978 https://doi.org/10.1002/app.1978.070221028Citations: 12AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References 1 W. F. Maddams and J. E. Preedy, J. Appl. Polym. Sci., 22, 2721 (1978). 2 W. F. Maddams and J. E. Preedy, J. Appl. Polym. Sci., 22, 2739 (1978). 3 W. F. Maddams and J. E. Preedy, J. Appl. Polym. Sci., 22, 2751 (1978). 4 A. Keller and M. J. Machin, J. Macromol. Sci., Rev. Macromol. Phys., 1, 41 (1967). 5 W. Glenz and A. Peterlin, J. Macromol. Sci., Rev. Macromol. Phys., 4, 473 (1970). 6 M. A. McRae and W. F. Maddams, Makromol. Chem., 177, 473 (1976). 7 J. R. Dees and J. E. Spruiell, J. Appl. Polym. Sci., 18, 1053 (1974). 8 A. Peterlin, J. Mater. Sci., 6, 490 (1971). 9 M. A. McRae, W. F. Maddams, and J. E. Preedy, J. Mater. Sci., 11, 2036 (1976). 10 D. S. Brown, K. U. Fulcher, and R. E. Wetton, Polymer, 14, 379 (1973). 11 G. C. Vonk, J. Appl. Crystallogr., 6, 81 (1973). 12 W. O. Statton and P. H. Geil, J. Appl. Polym. Sci., 3, 357 (1960). 13 S. Kavesh and J. M. Schultz, J. Polym. Sci., A-2, 9, 85 (1971). 14 M. A. McRae and W. F. Maddams, J. Appl. Polym. Sci., 22, 2761 (1978). Citing Literature Volume22, Issue10October 1978Pages 3027-3029 ReferencesRelatedInformation

Conformation of the high molecular weight form ofDunaliella salina phosphofructokinase in solution by means of small-angle X-ray diffraction and viscosity measurements

The intrinsic viscosity of phosphofructokinase fromDunaliella salina in different states of aggregation was determined. The instrinsic viscosity [η], of the biologically active tetramer, with a molecular weight of 320,000, was found to be 6.5 ml·g−1 at 4°C. Moreover, for the inactive dimer, with a molecular weight of 160,000, a value of [η]=8.0 ml·g−1 was determined. The high molecular weight aggregate of phosphofructokinase fromDunaliella salina, that shows little activity, has an intrinsic viscosity of 23.2 ml·g−1, which is significantly higher than that found for the active tetramer and the inactive dimer.

An infra-red spectroscopic and X-ray diffraction study of cold-drawn high density polyethylene samples

Three samples of high-density polyethylene, one linear, the second with one ethyl branch per thousand carbon atoms and the third with a comparable concentration of butyl branches, cold drawn at 60° C to elongations of 300, 800 and 1600%, have been examined by infra-red spectroscopy and wide- and small-angle X-ray diffraction. The results are consistent with, and give additional information about, the Peterlin model of plastic deformation. The change in crystallinity with draw ratio has been measured by infra-red spectroscopy and a wide-angle transmission X-ray diffraction method that minimizes the effect of the uniaxial orientation of the drawn specimens. Wide-angle measurements by reflection proved to be unreliable. Changes in the relative concentrations of methylene groups in crystalline regions, in gauche conformations and in tie chains in amorphous regions, and the alignment of tie molecules, have been followed by unpolarized and polarized infra-red spectroscopy. Small-angle X-ray diffraction measurements show that microvoids, with average dimensions of 250 and 80 A parallel to and perpendicular to the draw direction respectively, are formed during the transition from the lamellar to the fibrillar structure.