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Abstract: Due to the availability of high-brilliance X-rays at synchrotron radiation facilities, small angle X-ray scattering (SAXS) measurements have become feasible for new sample environments, like microfluidics or aerosol systems. The combination of continuous flow methods and SAXS with spatial scanning enables in situ measurements of time-resolved structures at the nanoscale important for reactions kinetics and material synthesis and processing. In this review we present the latest achievements in terms of scanning SAXS along continuous flow mixing devices reducing the limit of time resolution at the microsecond range. This led to the determination of early stages of biological reactions like protein folding, and to gain insight into chemical reaction kinetics like nanoparticles formation. We also describe the coupling of scanning SAXS with aerosol generators, which is the only way to study the mechanisms for the self-assembly and aggregation of nanomaterials via the aerosol route. We finally give a brief outlook, as the potentiality of these techniques has not been fully exploited, leaving the possibility for further improvements in time resolution and sample consumption, for example with the new X-ray sources like Free Electron Lasers.

Dynamic Light Scattering and Small-Angle X-ray Scattering measurements, at different temperatures on a commercial polynaphthalene sulfonate dispersant (Daxad) dissolved in water, show the occurrence of poly-disperse domains with size between 10 and 20 nm. After addition of silver nitrate to Daxad aqueous solutions, the formation of new larger domains, coexisting with the smaller ones, takes place. Their growth is promoted by Ag+ions that reduce the particle negative surface charge possibly also linking sulfonic groups of different small particles. Further on, upon addition of ascorbic acid as reducing agent, silver platelets, strips, and tabular hexagonal particles covered by the polynaphthalene sulfonate are formed at 5, 10, and 40 °C, respectively. The capacity of the polymer to cooperate with silver has been discussed and ascribed to the strong coordination of its sulfonic groups toward Ag+ions and to a significant adsorption and stability on the resulting Ag0crystallites. The crystallite size, about 20 nm, is comparable with the size of Daxad domains observed by Small Angle X-ray Scattering and Dynamic Light Scattering measurements. This may indicate that crystallite size is determined by the size of Daxad domains constituting a sort of nanoreactor for the silver crystallite growth. Moreover, probably induced by the polymer coordination along preferential silver crystalline planes, silver crystallites assemble forming tabular hexagonal particles of about 200 nm, which, in turn, assemble building two-dimensional micrometer sized strips and platelets.

As the main difference between bacterial and mammalian cell membranes is their net charge, the focal point of consideration in many model membrane experiments with antimicrobial peptides is lipid headgroup charge. We studied the interaction of the human multifunctional peptide LL-37 with single phospholipid monolayers, bilayers, and bilayers composed of binary mixtures of the four phospholipid species predominantly used in model membrane experiments (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine). We found that 1), the effects on single lipid monolayers are not comparable to those on the corresponding bilayers; 2), there are four different effects of LL-37 on bilayers of the four lipids; 3), the preference of LL-37 for the specific lipids is roughly inversely related to chain packing density; and 4), in the binary lipid mixtures, one lipid—and not necessarily the charged one—generally governs the mode of lipid/peptide interaction. Thus, our results show that lipid net charge is not the decisive factor determining the membrane-perturbing mechanism of LL-37, but only one of several parameters, among them packing density, the ability to form intermolecular H-bonds, and lipid molecular shape, which emphasizes how profoundly the choice of the model system can influence the outcome of a study of lipid/peptide interaction.

Mesoporous thin films are prepared using a simple sol–gel technique. Using lithographically patterned (100)‐orientated substrates and a dip‐coating method reproducible alignment of the pores across the substrate surface can be obtained. The pores preferentially align parallel to the long side of the channels etched into the surface. The channels within the aligned films are subsequently filled with cobalt (to form nanowire‐type structures) using a supercritical fluid inclusion technique, to allow high‐resolution imaging of the pore by using secondary electron microscopy. The channel structure imposes a strain on the mesoporous arrangement resulting in some variation in d‐spacings compared to simple films. The results indicate that the topographic structure can be used to engineer the placement and directionality of the pore structure and the potential of the aligned mesostructures are discussed.

The effect of the surfactant content and hydration conditions in the phases of dioleoyl phosphatidylcoline (DOPC)/ sodium dodecyl sulfate (SDS) mixtures was studied. To this end, surface X-ray diffraction experiments have been performed on bilayers of the mixtures deposited on hydrophobic silicon wafers by dip coating. To investigate the effect of relative humidity (RH) on bilayer organization, a humidity chamber with dry−wet air control was used, and RH values were fixed between 1 and 65%. Our results showed, in addition to the lamellar phase, a rhombohedral phase in mixtures at low hydration conditions (RH < 30%). The dspacing between lamellae increased with the RH and SDS content. This fact could be associated with a swelling effect that is probably due to the localization of water molecules between the polar headgroups of the DOPC and SDS forming the bilayers. The electron-density profiles calculated by Fourier reconstruction of the lamellar stacking for the different samples also confirmed this fact. In addition, the increase in dspacing could be related to the increase in the hydrophilic character of the mixture when the SDS content increases. The rhombohedral phase was more clearly observed in mixtures with high SDS content. Thus, the stalk structure of the rhombohedral phase could be facilitated because of the SDS contribution to inverse structures.

Effects of the number of actin-bound S1 and of axial tension on x-ray patterns from tetanized, intact skeletal muscle fibers were investigated. The muscle relaxant, BDM, reduced tetanic M3 meridional x-ray reflection intensity (IM3), M3 spacing (dM3), and the equatorial I11/I10ratio in a manner consistent with a reduction in the fraction of S1 bound to actin rather than by generation of low-force S1-actin isomers. At complete force suppression, IM3was 78% of its relaxed value. BDM distorted dynamic IM3responses to sinusoidal length oscillations in a manner consistent with an increased cross-bridge contribution to total sarcomere compliance, rather than a changed S1 lever orientation in BDM. When the number of actin-bound S1 was varied by altering myofilament overlap, tetanic IM3at low overlap was similar to that in high [BDM] (79% of relaxed IM3). Tetanic dM3dependence on active tension in overlap experiments differed from that observed with BDM. At high BDM, tetanic dM3approached its relaxed value (14.34nm), whereas tetanic dM3at low overlap was 14.50nm, close to its value at full overlap (14.56nm). This difference in tetanic dM3behavior was explicable by a nonlinear thick filament compliance which is extended by both active and passive tension.

Multicomponent cationic lipid−DNA complexes (lipoplexes) were prepared by adding linear DNA to mixed lipid dispersions containing two populations of binary cationic liposomes and characterized by means of small angle X-ray scattering (SAXS). Four kinds of cationic liposomes were used. The first binary lipid mixture was made of the cationic lipid (3‘[N-(N‘,N‘-dimethylaminoethane)-carbamoyl]cholesterol (DC−Chol) and the neutral helper lipid dioleoylphosphocholine (DOPC) (DC−Chol/DOPC liposomes), the second one of the cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and the neutral dioleoylphosphatidylethanolamine (DOPE) (DOTAP/DOPE liposomes), the third one of DC−Chol and DOPE (DC−Chol/DOPE liposomes), and the fourth one of DOTAP and DOPC (DOTAP/DOPC liposomes). Upon DNA-induced fusion of liposomes, large lipid mixing at the molecular level occurs. As a result, highly organized mixed lipoplexes spontaneously form with membrane properties intermediate between those of starting liposomes. By varying the composition of lipid dispersions, different DNA packing density regimes can also be achieved. Furthermore, occurring lipid mixing was found to induce hexagonal to lamellar phase transition in DOTAP/DOPE membranes. Molecular mechanisms underlying experimental findings are discussed.

Mesostructured silica films have been doped with lead sulfide (PbS) nanocrystals by a two-step impregnation, using the mesopores as nanoreactors for PbS growth. Secondary ion mass spectrometry and transmission electron microscopy characterizations demonstrated nanocrystals growth inside the pores and throughout the film thickness, pointing out the feasibility of an impregnation-based synthesis made possible by the porous properties of mesoporous silica films. The mean particles diameter is 5 nm, which is compatible with the pore dimensions. The mesostructure order was retained after the growth of the nanocrystals, as pointed out by small-angle X-ray scattering measurements. Optical absorption and Z-scan measurements indicated that PbS nanoparticles show a quantum confinement effect, while the films are characterized by high nonlinearities of the optical response. The optical properties of this material can be usefully exploited in several nonlinear optical applications.

The mechanism of formation of two different cubic mesoporous silica materials formed with Pluronic triblock copolymers is investigated with in situ time-resolved small-angle synchrotron X-ray scattering, in situ time-resolved ¹H nuclear magnetic resonance, and time-resolved transmission electron microscopy. The materials studied are the micellar cubic (Im&thremacr;m) SBA-16 formed with Pluronic F108 and the bicontinuous cubic (Ia&thremacr;d) silica material formed with Pluronic P103 and NaI. The formation mechanisms of the two cubic structures are shown to be dissimilar. For the Im&thremacr;m material, in the early stages of the synthesis, flocs of unordered micelles are observed, but areas where the micelles have started to order are also present. With time, there is an increase in order; however, there is a coexistence of unordered micelles and ordered material all through this study. The bicontinuous cubic silica is formed via a different path. The system is phase-separated already before the addition of the silica source, which implies that a concentrated phase is present, acting as the structure director of the Ia&thremacr;d structure. The results are compared with earlier reports on the formation of the hexagonal SBA-15 material.

We report a combined use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to the study of counterion condensation in ionic micelles. Small-angle neutron and X-ray scattering measurements have been carried out on two surfactants cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl), which are similar but having different counterions. SANS measurements show that CTABr surfactant forms much larger micelles than CTACl. This is explained in terms of higher condensation of Br−counterions than Cl−counterions. SAXS data on these systems suggest that the Br−counterions are condensed around the micelles over smaller thickness than those of Cl−counterions.

The initial stages of the formation of SBA-15 have been studied by in situ SAXS/XRD using synchrotron radiation. Modeling of both the diffuse scattering and the X-ray diffraction patterns obtained at different stages of the reaction results in a detailed description of the different reaction steps. The first step in the formation is the liquid−liquid phase separation of spherical P123−silicate hybrid micelles after which nucleation and growth of the 2D hexagonal phase occurs. Two-dimensional electron density maps calculated on the basis of the intensities of the Bragg reflections suggest that changes in the degree of intermicellar condensation are responsible for the time-dependent observations. The silica source (alkoxysilanes) may be partially unhydrolyzed long after formation of the hexagonal structure, since the kinetics of the mesophase evolution is notably slower when TEOS is used as the silica precursor as compared to TMOS. The results obtained for SBA-15 are compared with other published data on the formation of SBA-15 and of the smaller pore MCM-41 materials.

The influence of LiCl solutions on liposomal and surface-supported phosphatidylcholine/water systems (dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), respectively) has been studied by small-angle X-ray techniques. In liposomal dispersions of DPPC, an osmotically stressed liquid-crystalline phase, denoted as Lα osm, forms readily after rapid mixing with salt solutions. The transition from Lα → Lα osm proceeds in two steps. The first step takes place within seconds and is due to water diffusion from the liposome into the bulk solution. The second, slower process (minutes) can be attributed to the relaxation of initially deformed intermediate liposomes into spherical ones. In experiments with aligned lipid bilayers supported on silicon wafers, it was possible to reproducibly exchange different concentrations of LiCl solutions on a single sample and to determine the lattice changes by time-resolved X-ray scattering at grazing incidence. Independently of the deposition technique (spray- or spin-coating, respectively), none of the investigated POPC samples displayed an osmotically stressed liquid-crystalline phase. While liposomes can be considered nearly defect-free, supported bilayer stacks show a high abundance of defects, such as oily streaks typical of the Lα phase. Thus, the alkali ions are free to diffuse into the interbilayer water regions and to cause a slight increase of the bilayer separation (about 1 Å). It is concluded that low to medium concentrations of Li⁺ ions partially screen the attractive van der Waals force between adjacent membrane layers. However, upon annealing the defect regions or regions of high curvature in the oriented lipid matrix, e.g. by low amounts of oleyl alcohol (OA), the system is able to sense osmotic stress upon addition of a salt solution.

This article gives an overall view of the mechanisms involved in the mesostructuring that takes place during the formation of surfactant‐templated inorganic materials by evaporation. Since such a method of preparation is well suited to fabricating thin films by dip coating, spin coating, casting, or spraying, it is of paramount interest to draw a general description of the processes occurring during the formation of self‐assembled hybrid organic/inorganic materials, taking into account all critical parameters. The following study is based on very recent works on the meso‐organization of thin silica films using tetraethylorthosilicate (TEOS) as the inorganic source and cetyltrimethylammonium bromide (CTAB) as the structuring agent, but we will show that the method can also be extended to other systems based on non‐silica oxides and block copolymer surfactants. We demonstrate that the organization depends mainly on the chemical composition of the film when it reaches the modulable steady state (MSS), where the inorganic framework is still flexible and the composition is stable after reaching an equilibrium in the diffusion of volatile species. This MSS state is generally attained seconds after the drying line, and the film's composition depends on various parameters: the relative vapor pressures in the environment, the evaporation conditions, and the chemical conditions in the initial solution. Diagrams of textures, in which the stabilized structures are controlled by local minima, are proposed to explain the complex phenomena associated with mesostructuring induced by evaporation.

The anionic surfactant sodium dodecyl sulfate (SDS) was used to induce the initial steps of the solubilization of liposomes. The structural transformations as well as the kinetics associated with this initial period were studied by means of time-resolved small-angle X-ray scattering (SAXS) using a synchrotron radiation source. Neutral and electrically charged (anionic and cationic) liposomes were used to investigate the effect of the electrostatic charges on the kinetics of these initial steps. The mechanism that induces the solubilization process consisted of adsorption of surfactant on the bilayers and desorption of mixed micelles from the liposomes surface to the aqueous medium. In all cases the time needed for desorption of the first mixed micelles was shorter than that for complete adsorption of the surfactant on the liposomes surface. The present work demonstrates that adsorption of the SDS molecules on negatively charged liposomes was slower and release of mixed micelles from the surface of these liposomes was faster than for neutral liposomes. In contrast, in the case of positively charged liposomes, the adsorption and release processes were, respectively, faster and slower than those for neutral vesicles.

TiO2 optical thin films stable to 700 °C, exhibiting 35% volume porosity, more than 100 m²·g^-1 in surface area, fully nanocrystalline anatase framework, and organized mesostructure (cubic Im3m derived), have been stabilized by careful delayed rapid crystallization (DRC) thermal treatments. In-situ time-resolved SAXS and WAXS investigations were simultaneously performed during such treatments. They revealed that a slow and progressive heating to a temperature just below that of the formation of anatase (Tc ≈ 400 °C), followed by a long pretreatment at this temperature, stabilizes the amorphous network. A following rapid increase of temperature up to temperatures as high as typically 700 °C, followed by a short residence time at this high temperature, provokes the homogeneous formation of crystalline small nanoparticles and the total elimination of organic residues. The crystallization is accompanied by matter migration through diffusing sintering and pore merging along the [111] directions of the cubic structure, leading to a novel grid-like mesostructure with open porosity. This DRC treatment allows the preparation of highly porous and crystalline anatase films, with thermal stability 200 °C higher than previously reported, that are ideal for energy transfer applications. This emphasizes the role of the treatment method to stabilize transition metal oxide mesoporous materials over extended crystallization at high temperatures. These films exhibit excellent long time stability below 500 °C.

Using SAXD and NMR techniques as well as visual observations, a detailed study of the extension of the phase regions and their structures has been performed for the ternary system 1-monooleoyl-rac-glycerol (MO)/n-octyl-β-d-glucopyranoside (OG)/²H2O at 25 °C. OG in water forms a large region of a micellar solution phase, in which substantial amounts of MO can be dissolved. Increasing the MO concentration at constant water content results in the formation of two- and three-phase areas, consisting of liquid, lamellar, or cubic phases in equilibrium with a very dilute water/OG solution. Besides the different phases previously reported for the binary systems, an additional hexagonal phase occurs at high OG contents. Addition of minor amounts (≈1.5 wt %) of OG converts the cubic phases present in the MO/²H2O system to an Lα phase, while the cubic phase in the OG/²H2O system is able to dissolve as much as 15 wt % MO. Since a major part of the phase diagram consists of planar bilayers, it is concluded that for most MO/OG ratios the spontaneous curvature is close to zero. The reason for this is discussed in terms of the molecular packing of MO and OG.

Since mesoporous materials can be prepared by combining the sol-gel chemistry and the structuring effect of surfactants, they have attracted attention for application in various high technology fields. The present work deals with the analyses of the mechanisms involved in the formation of SiO2and TiO2highly organised 2D-hexagonal meso-structured films using Brij 58 as surfactant. The preparation of such films by dip-coating involves rapid evaporation which makes the different steps difficult to control. Simultaneous in-situ SAXS (synchrotron) and interferometry analyses have been performed to get a first understanding of the self-assembly process. SiO2and TiO2materials have a different chemical reactivity (kinetics and coordination aspects). However, we show that the mechanisms involved during dip-coating are quite similar : the self-assembly leading to the organised phase takes place at a final stage of the drying process, involves the formation of a disorganised intermediate phase and depends also on the presence of micellar interfaces in addition to film/air and film/substrate interfaces.

The formation of mesoscopically ordered silica/surfactant composites under acidic synthesis conditions is studied by time-resolved in-situ small-angle X-ray scattering (SAXS) using synchrotron radiation. Benzene is used a an additive which acts as a weak swelling agent although most of the benzene molecules are found to reside near the surfactant/silicate interface region rather than in the micelle cores. With increasing relative amounts of benzene, the curvature of the micellar aggregates decreases, which finally leads to a transition from (hexagonally) rodlike to lamellar; a mechanism for this change in curvature is suggested.

Mesostructured vanadium-oxo-based hybrid thin films have been prepared by evaporation-induced self-assembly. Anhydrous metal chlorides (VOCl3 or VCl4) were used as the vanadium source, and the nonionic surfactant Brij 56 or 58 was used as the structure-directing agent in ethanol/water solutions. Mesostructured films were obtained from solutions having V(IV)/Vtotal ratios higher than 0.7, evidencing the role of V(IV) in the formation of a curved inorganic VOx-based (2 ≤ x ≤ 2.15) framework. The hybrids obtained are fragile and water-sensitive, so that deposition and all of the processing leading to stabilization of the mesostructure must be performed at low relative humidity. A combination of synchrotron-SAXS and interferometry was applied to evaluate the structural evolution related to the evaporation process during dip-coating. The SAXS data clearly showed a 2D hexagonal structure (P6m space group, a = 65−80 Å) that is converted to a 2D centered rectangular (C2m space group) through preferential contraction in the direction normal to the substrate. The structure of the hybrid films is stable up to 250 °C in inert atmosphere.

Abstract:: Synchrotron Small-Angle X-Ray scattering (SAXS) measurements on aggregate formation of a Polyvinyl acetate-b-Perfluoro octyl acrylate (PVAc-b-PFOA) block copolymer in supercritical CO2 are here reported. Experiments were carried out for a series of different thermodynamic conditions, changing the solvent density by profiling both the pressure at constant temperature and the temperature at constant pressure. This block copolymer and in general fluorocarbon-hydrocarbon di-blocks form aggregates depending on the value of CO2 density. A sharp transition between monomers dissolved as random coils and micelles characterized by a solvophilic shell and a solvophobic core occurs when the CO2 density reaches a critical value. Results of critical micellization density (CMD) derived from pressure and temperature ramps experiment along with the comparison with previous SANS results are here reported to give additional experimental support to the solvent density-driven aggregation process.

Mesoscopically ordered silicate−surfactant composite materials of the M41S type synthesized in the presence of a swollen agent have been characterized by in situ and ex situ X-ray diffraction analysis. The key feature of the room-temperature synthesis is the use of a mixture of cationic and anionic surfactants as structure-directing agents. The lower interfacial charge density of the mixed surfactant aggregates stabilizes structures of lower interfacial curvature and therefore facilitates a more controlled solubilization of organic swelling agents. An increased solubilization capacity of the catanionic surfactant−silicate mesophase was observed close to an anionic/cationic surfactant ratio corresponding to a transition to the lamellar phase in the absence of toluene. In the presence of toluene, the catanionic template stabilizes microemulsion droplets that serve as building blocks for the final material. However, a fair amount of organic compound is solubilized in the silica−catanionic surfactant composite after the mesophase is formed. Although the present communication concerns mesoporous silica, the concept is a general one and may allow the synthesis of non-siliceous large-pore materials.

Silica thin films with ordered porosity can be prepared by dip coating, combining polycondensation of silicate species and organization of amphiphilic mesophases. This paper reports on the preparation of templated films using cetyltrimethylammonium bromide (CTAB) as the surfactant and tetraethoxysilane (TEOS) as the inorganic precursor. Depending on the CTAB/Si molar ratio, films with different porous networks&sbd;3D hexagonal (P63/mmc), cubic (Pm3n), and columnar hexagonal (p6m)&sbd;were obtained. Identification of the structures was accomplished by coupling two-dimensional X-ray diffraction at grazing incidence and TEM investigations on film cross sections. Other experimental parameters (e.g., deposition rate and composition of the starting sol, including its aging time) appeared also to influence the degree of organization of the final films greatly. To obtain a better understanding of the self-assembly mechanism, the structural formation of the films was followed in real time by in situ SAXS. Because of the very fast self-assembly process (&lt;30 s), high-flux synchrotron radiation was used, which allows to record good quality X-ray patterns in 100 ms. For the first time, interferometry measurements were also combined with the SAXS experiments to correlate the organization steps detected during dip coating with the thickness profiles. A model has thus been proposed for the film formation: organization at the mesoscale (i) takes place at the final stage of liquid-phase evaporation; (ii) involves the formation of micelles at the film/air interface in the early stage of deposition and, in some cases, the formation of intermediate phases; and (iii) is influenced by the condensation degree of inorganic intermediates, the surfactant concentration, and the deposition external conditions.

Silica thin films with a two-dimensional (2D) hexagonal structure were produced from TEOS and the F127 triblock copolymer PEO106PPO70PEO106. The structure of the films was deduced from transmission electron microscopy (TEM) performed on microtomed sections and from a 2D X-ray scattering technique adapted for film characterization. Both methods are complementary and allow for a detailed characterization of the film structure. The pore channels within the coatings are organized in domains, which spin and curve inside the film, but align with the surface plan at the air/film and film/substrate interfaces. The formation of the film was monitored by in situ time-resolved SAXS experiments to follow the structural evolution during the first minutes after deposition. Cylindrical micelles, which gives rise to a wormlike structure, form first at the air/film interface and extend toward the film/substrate interface via solvent evaporation. When most of the liquid phase is evaporated, the well-aligned domains located at both interfaces are obtained by a self-arrangement of the micelles parallel to the interfaces. This rearrangement occurs when the film is considered to be dry. The atom content profiles in the as-prepared films were obtained by Rutherford backscattering (RBS) and show homogeneous distribution of atoms throughout the film thickness. To stiffen the network and remove the surfactant, various postsynthesis treatments were applied to the coatings, that is, thermal treatment, base-catalyzed condensation, and solvent extraction. Each method induces shrinkage, leading to 2D-centered rectangular films through a contraction of the initial 2D hexagonal structure. As-prepared and treated films exhibit excellent optical transparency and high degree of organization. Ellipsometry measurements and N2 adsorption/desorption isotherms were thus used to estimate the refractive index and the porosity of the films. Refractive index down to 1.2 was obtained in the film that was pretreated under a NH3 atmosphere before solvent extraction of the surfactant. This shows the efficiency of this treatment to minimize the network shrinkage. N2 adsorption−desorption measurement performed on films calcined at 350 °C gives a surface area of 800 m² g^-1 and a porosity of 63%.

The main goal of the work was to examine the structural changes induced by water (D2O and H2O) in the dense cellulose film, Tomophan I, using temperature time-resolved SAXS and WAX measurements. We found that dry cellulose and water-saturated cellulose contains hydrophobic microregions at room temperature. At increasing temperature microphase separation was observed, as a formation of a broad peak on the SAXS curves, with Tcof about 55 and 60°C, depending on the kind of water. Further heating, up to 85°C, causes an appearance of a set of very small peaks, generated by the cubic structure, in SAXS. The structural changes of the system are typical for the thermo-associative process, observed in the copolymer–water systems.

The response kinetics of liquid crystalline phosphatidylcholine bilayer stacks to rapid, IR-laser-induced temperature jumps has been studied by millisecond-time-resolved X-ray diffraction. The system reacts on the fast temperature change by a discrete bilayer compression normal to its surface and a lateral bilayer expansion. Since water cannot diffuse from the excess phase into the interbilayer water region within the 2 ms duration of the laser pulse, the water layer has to follow the bilayer expansion, by an anomalous thinning. Structural analysis of a 20 ms diffraction pattern from the intermediate phase indicates that the bilayer thickness remains within the limits of equilibrium values. Both, the intermediate structure and its relaxation into the original equilibrium Lα phase, depend on the viscoelastic properties of the bilayer/water system. We present an analysis of the relaxation process by an overdamped one-dimensional oscillation model revealing the concepts of Hooke's law for phospholipid bilayers on a supramolecular basis. The results yield a constant bilayer repulsion and viscosity within Hooke's regime suggesting that the hydrocarbon chains act as a buffer for the supplied thermal energy. The bilayer compression is a function of the initial temperature and the temperature amplitude but is independent of the chain length.

The influence of added short-chain amines, n-butylamine, BA, and n-octylamine, OA, on the mesophase formation of surfactant−silicate composite structures in a room-temperature synthesis has been investigated in situ by synchrotron small-angle X-ray scattering. For BA a marked decrease in the d spacing of the hexagonal phase was observed with increasing amine concentration, while a slight increase in d spacing was initially observed for OA. However, the d spacing of the hexagonal phase went through a maximum with increasing concentration. Furthermore, two coexisting hexagonal phases or a purely lamellar phase was observed if the concentration of OA was increased further. The results are discussed in terms of two competing mechanisms of amine incorporation:  solubilization within the CTAB−silicate mesophase and competitive adsorption of the amine to the silicate.

1The nature of the force (T) response during and after steady lengthening has been investigated in tetanized single muscle fibres from Rana temporaria(4 °C; 2.15 μm sarcomere length) by determining both the intensity of the third order myosin meridional X‐ray reflection (IM3) and the stiffness (e) of a selected population of sarcomeres within the fibre.2With respect to the value at the isometric tetanus plateau (T0), IM3was depressed to 0.67 ± 0.04 during steady lengthening at ≈160 nm s−1(T≈ 1.7) and recovered to 0.86 ± 0.05 during the 250 ms period of after‐stretch potentiation following the rapid decay of force at the end of lengthening (T≈ 1.3); under the same conditions stiffness increased to 1.25 ± 0.02 and to 1.12 ± 0.03, respectively.3After subtraction of the contribution of myofilaments to the half‐sarcomere compliance, stiffness measurements indicated that (1) during lengthening the cross‐bridge number rises to 1.8 times the original isometric value and the average degree of cross‐bridge strain is similar to that induced by the force‐generating process in isometric conditions (2.3 nm), and (2) after‐stretch potentiation is explained by a residual larger cross‐bridge number.4Structural data are compatible with mechanical data if the axial dispersion of attached heads is doubled during steady lengthening and recovers half‐way towards the original isometric value during after‐stretch potentiation.

The solubilization of n-hexane and toluene by silicate−surfactant hexagonal mesophases has been studied by time-resolved in situ synchrotron small-angle X-ray scattering. It is suggested that the extent of solubilization is mainly governed by the oil solubility in the continuous phase. The availability of the oil will largely influence the phase behavior and the long-range order of the silicatropic mesophase. While the addition of n-hexane to the synthesis results in a loss of order, a substantial amount of toluene can be solubilized without affecting the long-range order. Many of the observed effects can be rationalized based on time-dependent changes in the properties of the system due to silicate hydrolysis and condensation reactions, in addition to the water solubility of the solubilizate. The results are compared with those obtained for corresponding systems in the absence of silica.

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The modifications induced in single-crystal silicon by implanted helium have been investigated by grazing incidence small angle X-ray scattering technique. The samples prepared by implanting 2×1016cm−2helium ions at 20 keV in silicon wafers held at 77 K were thermally treated for 2 h in the 100–800°C temperature range. It is shown that implantation produced a film with slightly lower density than that of undamaged single crystal silicon. Further thermal treatment caused shrinking of the film leaving well ordered subsurface layer and damaged film below. Upon annealing at 600°C this structure apparently disappear, to be formed again upon annealing at 800°C.

Dislocation densities, arrangements and long-range internal stresses in cold worked polycrystalline nickel were determined by X-ray diffraction profile analysis using synchrotron radiation. Torsionally deformed samples were scanned across the diameter of the specimens with a focal spot of 300 μm providing strain dependent results in good correlation with residual electrical resistivity data. On cold rolled specimens with different deformations, scanning measurements across single grains with a focal spot of less than 50 μm were carried out, in order to inform on the features of the deformation induced substructure. At small deformations including stage III, the dislocation densities and internal stresses are uniform within single grains while at higher deformations in stages IV and V, the dislocation density and internal stresses exhibit correlated fluctuations. In analogy to Cu, in stage IV these fluctuations could be identified as polarized tilt walls (PTW) formed from polarized dipole walls (PDW) whereas in stage V, as a difference to Cu, only PDWs and pile-ups of dislocations at the grain boundaries were found. It is suggested that the differences to Cu arise from the enhanced presence of deformation induced vacancies in Ni, enabling stronger effects of static recovery through dislocation climb to take place in between single passes of rolling deformation.

We investigated the liquid crystalline phase structures and their temperature-dependent dynamics in the ternary system composed of Brij-35 [poly(oxyethylene(~23))lauryl ether, C12OE~23], dibutyl ether (DBE) and 10 mM Na/K buffer. A sequence of schematic ternary phase diagrams at 10, 20, 30, 40, and 60 °C, derived from temperature-scanning small- and wide-angle X-ray scattering (SWAX), has been established. In the binary Brij-35/H2O system, the amphiphilic component Brij-35, being totally miscible with water, self-assembles as a function of its concentration into a normal micellar solution L1, a normal packed micellar cubic I1-phase region, and an extended region of various lamellar structures. The cubic I1 phases show diffraction patterns with Im3m (unit cell parameter aIm3m = 85−94 Å) and Ia3d (aIa3d = 162−167 Å) symmetry. Increasing temperature destabilizes the cubic phases between 15 and 55 °C, depending on the weight ratio of the used components. The lamellar phases show unit cell dimensions of a = 179−181 Å. A phase transition from Lc (crystalline lamellar phase), Lβ (gel lamellar phase), to a isotropic micellar phase, here denoted as L2, occurs at temperatures from 15 to 35 °C, as a function of the water content. The DBE uptake of these structures is limited to 20−50%(w/w), which generates biphasic regions at higher DBE amounts, where a DBE excess phase containing approximately 2% (w/w) H2O and 0.02% (w/w) Brij-35 is formed. Increasing amounts of DBE lead&sbd;with exception of the Lc phase&sbd;to enhanced phase temperature stabilities in the water-lean region and induce normal hexagonal H1 (a = 68−135 Å) and various cubic structures. We found the cubic space groups Im3m and Ia3d with unit cell dimensions aIm3m = 83−112 Å and aIa3d = 162−195 Å in the cubic I1 region and Pn3m (aPn3m = 164 Å) and Ia3d (aIa3d = 187−214 Å) as well as Fd3m (aFd3m = 218−275 Å) in the cubic region with low water contents.

The kinetics of structure development during isothermal melt crystallization in blends containing low-molecular-weight fractions of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) has been investigated as a function of composition. Time-resolved synchrotron small-angle X-ray scattering, static wide-angle X-ray scattering and differential scanning calorimetry has been used. It has been found that in early stages of crystallization, PEO lamellae of the transient nonintegral folding (NIF) type in a wide range of compositions were formed. Subsequent transformation of NIF lamellae into the crystals with one-folded (1F) or extended chains (EC) has occurred through isothermal thinning or thickening. The amorphous PMMA diluent has played a decisive role in structure development. With increasing PMMA content, the induction time prior to crystal formation increased and the rates of NIF, 1F and EC crystallization decreased. Furthermore the recrystallization of the NIF crystals into either 1F or EC crystals was retarded. The addition of PMMA meant that the crystals were growing slowly in a more viscous medium and the retardation effect of the amorphous diluent on the kinetics of these processes resulted in the tendency to create stable and more perfectly ordered structures

The formation of hexagonal and lamellar surfactant−silicate mesophases at room temperature has been investigated by in situ synchrotron small angle X-ray scattering. Emphasis was given to the influence of butanol and hexanol on the surfactant−silicate phase behavior. The experimental setup included a continuous flow reactor allowing a resolution in time as high as 0.3 s. Depending on the reaction composition, one, two, or three coexisting phases were observed. The results are discussed in terms of time-dependent changes in the concentration of cosurfactant not incorporated into the composite aggregates. Although many of the observed effects are paralleled by well-known properties of aqueous surfactant solutions, important dissimilarities exist. Furthermore, the relative intensity of the high-order reflections are suggested to correspond to the degree of interaggregate condensation in the composite mesophase.