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International audience; A series of nickel-cerium-promoted mesoporous silica (SBA-15) catalysts modified with different loadings of yttrium were synthesized by cetyltrimethylammonium bromide (CTAB)-assisted impregnation. The catalysts were tested in CO2 methanation reaction and characterized by N2 sorption, X-ray fluorescence (XRF), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (XRD), H2 chemisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), CO2 temperature-programmed desorption (CO2-TPD), and thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The best catalytic performance in CO2 methanation was found for Y-modified NiCe/SBA-15 catalysts compared to the unpromoted sample. The modification with 10 wt% of yttrium gave the highest CO2 conversion of 61% ± 2% at 350 °C. We attribute this increase to an improved dispersion of Ni, increased reducibility of Ni species, higher ratio of Ce3+/(Ce3+ + Ce4+), and increased moderate basicity found for 15Ni10Ce10Y/SBA-15. This paper shows that 10 wt% of Y loading not only improves the catalytic activity in CO2 methanation, but also gives stable performance. The tested 15Ni10Ce10Y/SBA-15 catalyst did not exhibit activity loss during 26 h of time-on-stream (TOS) experiment at 350 °C. Moreover, carbon deposits and sintered nickel particles could hardly be found in 15Ni10Ce10Y/SBA-15 catalyst used for 7 h.

Cement degradation caused by CO2 exposure is an increasingly important environmental challenge that must be understood, for example, if former oil reservoirs are to be used for CO2 storage. When exposed to CO2-saturated brine, cement undergoes a chemically complex carbonation process that influences all the physicochemical properties of the cement. It is known that under favorable conditions, fractures and voids in cement can be occluded, or self-sealed, by precipitation of calcium carbonate. Here, we report a detailed X-ray microcomputed tomography (μ-CT) study on the carbonation of gas pores (macropores) of diameter ∼1 mm in cement. Specifically, cured class G Portland cement with sub-millimeter spherical disconnected macropores was exposed to CO2-saturated brine at high pressure (280 bar) and high temperature (90 °C) for 1 week. High-resolution synchrotron-based μ-CT enabled visualizing the morphology of the precipitates inside the macropores within both unreacted and carbonated regions. Quantitative analysis of the type and amount of material deposited in the macropores during carbonation suggests that the filling of the disconnected macropores involves transport of calcium ions from the cement bulk to the macropore interior. A detailed model describing the chemical processes involved is provided. The present study gives a deeper understanding of cement carbonation by literally shedding light on the complex precipitate structures within the macropores., Crystal Growth & Design, 19 (10), ISSN:1528-7483, ISSN:1528-7505

The simplest route to synthesize porous calcium carbonate in large quantity is to mix concentrated aqueous solutions containing Ca2+ and CO32– ions. The formed vaterite microspheres have a porous structure, but are not thermodynamically stable. Heating above 350 °C induces a solid-state transformation of vaterite into the most stable phase, calcite, while maintaining an unusual spheroidal morphology. Here, by using three-dimensional coherent X-ray diffraction imaging, the morphological evolution associated with the thermally induced phase transition is studied. We observe that despite an overall similar pore volume, the pore geometry differs markedly before and after annealing. Before annealing, the microspheres display elongated and nanometer sized pores, while after annealing they exhibit large and open pores. During transition, the specific surface area decreases from 7 m2/g for vaterite to 3 m2/g for calcite. The general trend resulting from 3D observations is that the solid state phase transition is ...

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core., Using SiGe in the core of optical fibres extends the wavelength range and potential optical functionality, but fabrication challenges exist. Here, Coucheron et al. report the fabrication and tailoring of SiGe-core optical fibres using CO2 laser irradiation to heat the glass cladding and recrystallize the core.

Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications.We measure the thermoelectric properties of various poly(3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics. Refereed/Peer-reviewed

This research was supported in part with computational resources at NTNU provided by NOTUR (project nn9331k). NP and DWB acknowledge The Research Council of Norway for the financial support through M-ERA.NET project RADESOL under the European Union's seventh framework programme (FP/2007-2013), grant agreement no. 234648/O70. The degradation of the chemotherapy drug 5-Fluorouracil by a non-pristine metal surfaces is studied. Using Density Functional Theory, X-ray Photoelectron Spectroscopy and X-ray Absorption Spectroscopy we show that the drug is entirely degraded by medical-grade silver surfaces, already at body temperature, and that all of the fluorine has left the molecule, presumably as HF. Remarkably, this degradation is even more severe than that reported previously for 5-Fluorouracil on a pristine monocrystalline silver surface (in which case 80% of the drug reacted at body temperature) Mazzola et al. (2015). We conclude that the observed reaction is due to a reaction pathway, driven by H to F attraction between molecules on the surface, which results in the direct formation of HF; a pathway which is favoured when competing pathways involving reactive Ag surface sites are made unavailable by environmental contamination. Our measurements indicate that realistically cleaned, non-pristine silver alloys, which are typically used in medical applications, can result in severe degradation of 5-Fluorouracil, with the release of HF – a finding which may have important implications for the handling of chemotherapy drugs. Postprint

A nickel/spinel (Ni/MgAl_2O_4) catalyst, w(Ni) = 22 wt %, was investigated in situ during reduction with wide-angle X-ray scattering (WAXS) in a laboratory setup and with anomalous small-angle X-ray scattering (ASAXS) at a synchrotron source. Complementary high-resolution transmission electron microscopy (HRTEM) was performed on the fresh catalyst sample. The Ni particles in the fresh catalyst sample were observed to exhibit a Ni/NiO core-shell structure. A decrease of the Ni lattice parameter is observed during the reduction in a temperature interval from 413 to 453 K, which can be related to the reduction of the NiO shell, whereby stress due to the lattice mismatch of Ni and NiO is relieved.

A major limitation to the use of coherent X-ray diffraction imaging (CXDI) for imaging soft materials like polymers and biological tissue is that the radiation can cause extensive damage to the sample under investigation. In this study, CXDI has been used to monitor radiation-induced structural changes in metal-coated poly(methyl methacrylate) microspheres. Using a coherent undulator X-ray beam with 8.10 keV photon energy, 14 tomograms at a resolution of ∼30 nm were measured consecutively, which resulted in an accumulated dose of 30 GGy. The three-dimensional images confirmed that the polymer core was strongly affected by the absorbed dose, giving pronounced mass loss. Specifically, as the metal–polymer composite was exposed to the X-ray beam, a bubble-like region of reduced density grew within the composite, almost filling the entire volume within the thin metallic shell in the last tomogram. The bubble seemed to have its initiation point at a hole in the metal coating, emphasizing that the free polymer surface plays an important role in the degradation process. The irradiation of an uncoated polystyrene microsphere gave further evidence for mass loss at the free surface as the radius decreased with increased dose. The CXDI study was complemented by X-ray photon correlation spectroscopy, which proved efficient in establishing exposure dose limits. Our results demonstrate that radiation-induced structural changes at the tens of nanometer scale in soft materials can be followed as a function of dose, which is important for the further development of soft-matter technology.

Long-lasting cement plugging of wells is crucial for successful CO2 storage in underground reservoirs. It requires a profoundly improved understanding of the behavior of fractured cement under realistic subsurface conditions including elevated temperature, high pressure and the presence of CO2 saturated brine. Here we report computed X-ray tomography studies on the effects of CO2 on cement. More specifically, we have exposed cured Portland G cement samples with pre-made microchannels mimicking fractures to CO2 saturated brine at elevated pressure (100 bars) and room temperature. The microchannels were observed to get filled with calcite (CaCO3) during the CO2 exposure. The extent of this self-healing was dependent on the diameter of the leakage path, with narrower channels more readily getting clogged. Chemical simulations taking into account the cement composition, CO2 availability, pH, pressure and temperature gave results consistent with our conceptual understanding of how the differences in dissolution/precipitation profiles in the cement may result from the availability of CO2. In particular, the modelling provides an explanation why calcite precipitates preferentially in the channels rather than on the external cement sample surfaces. We conclude that the localized precipitation can be ascribed to higher pH inside the cavities compared to near the external surfaces, owing to long diffusion distances giving a locally limited CO2 supply within the voids. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Charge-carrier transport in thin-film organic field-effect transistors takes place within the first (few) molecular layer(s) of the active organic material in contact with the gate dielectric. Here, we use atomistic molecular dynamics simulations to evaluate how interactions with bare amorphous silica surfaces that vary in terms of surface potential influence the molecular packing and dynamics of a monolayer pentacene film. The results indicate that the long axis of the pentacene molecules has a non-negligible tilt angle away from the surface normal. Grazing-incidence X-ray diffraction patterns for these models are calculated, and we discuss notable differences in the shapes of the Bragg rods as a function of the molecular packing, also in relation to previously published experimental reports. Intermolecular electronic couplings (transfer integrals) evaluated for the monolayers show marked differences compared to bulk crystal calculations, a result that points to the importance of fully considering the molecular packing environment in charge-carrier mobility models for organic electronic materials.

Using raster-scanning wide-angle X-ray scattering, we investigate oriented fibres of the low bandgap conjugated polymer, poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (F8TBT), that was developed in particular for polymer solar cells. For the first time, structural data are provided for F8TBT. Our results demonstrate that the nano-scale structure of this polymer is closely related to the externally observable features of the fibre, and thus emphasise the importance of having full control over the local molecular conformation. Liquid-crystalline phases are observed at elevated temperatures, and the molecular alignment in the drawn fibres yields scattering patterns that are dominated by broad peaks of equatorial diffuse scattering. The significant degree of preferred orientation facilitates the analysis, leading to estimates of (average) nearest-neighbour packing distances and coherence length of this macromolecule. In particular, we observe a pronounced broad signal assigned to packing of the conjugated backbone with an approximate spacing of 4.00–4.39 A that is coherent over 5-6 polymer segments.

We show that charge-transporting polymer chains in the brush conformation can be synthesized from a variety of substrates of interest, displaying a high degree of stretching and showing up to a 3 orders of magnitude increase in current density normal to the substrate as compared with a spin-coated film. These nanostructured polymeric films may prove to be suitable for electronic devices based on molecular semiconductors as current fabrication techniques often provide little control over film structure.

Optimizing the morphology of bulk heterojunctions is known to significantly improve the photovoltaic performance of organic solar cells, but available quantitative imaging techniques are few and have severe limitations. We demonstrate X-ray ptychographic coherent diffractive imaging applied to all-organic blends. Specifically, the phase-separated morphology in bulk heterojunction photoactive layers for organic solar cells, prepared from a 50:50 blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) and thermally treated for different annealing times is imaged to high resolution. Moreover, using a fast-scanning calorimetry chip setup, the nano-morphological changes caused by repeated thermal annealing applied to the same sample could be monitored. X-ray ptychography resolves to better than 100 nm the phase-segregated domains of electron donor and electron acceptor materials over a large field of view within the active layers. The quantitative phase contrast images further allow us to estimate the local volume fraction of PCBM across the photovoltaically active layers. The volume fraction gradient for different regions provides insight on the PCBM diffusion across the depletion zone surrounding PCBM aggregates. Phase contrast X-ray microscopy is under rapid development, and the results presented here are promising for future studies of organic-organic blends, also under in situ conditions, e.g., for monitoring the structural stability during UV-Vis irradiation. © 2016 Patil et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT-C(14)) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C(12) to C(14) and C(16) are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films.

Langmuir 25, 10970-10974 (2009). doi:10.1021/la9011795, The shape, structure, and orientation of rubbing-aligned cadmium selenide (CdSe) nanorods on polymer coated glass substrates have been studied using transmission electron microscopy (TEM) and grazing incidence X-ray scattering combined with computer simulations. The nanorods are found to be of wurtzite structure and highly monodisperse, and have an essentially ellipsoidal shape with short axes of approximately 8 nm and long axis of approximately 22 nm. The nanorods exhibit preferred biaxial orientation with the hexagonal a-c-plane parallel to the sample surface and the c-axis oriented along the rubbing direction of the sample. Some tendency of smectic-A ordering is observed. A quantitative model incorporating atomic structure, rod shape, and preferred orientation was developed for numerically simulating the diffraction peak positions, widths, and intensities, giving good correlation with the experimental observations., Published by ACS Publ., Washington, DC

We investigate the growth and field-effect transistor performance of aligned pentacene thin films deposited by zone-casting from a solution of unsubstituted pentacene molecules in a chlorinated solvent. Polarized optical microscopy shows that solution processed pentacene films grow as large crystalline domains with pronounced anisotropy in the substrate plane, in contrast to vacuum sublimed pentacene films, which consist of small crystalline grains with random in-plane orientation. The high structural alignment is confirmed by in-plane and out-of-plane X-ray diffraction analysis, with out-of-plane 00n reflections up to at least the seventh order, and a pronounced in-plane anisotropy with the a-axis of the triclinic unit cell predominantly aligned parallel to the zone-casting direction and the ab-plane parallel to the substrate. The average charge carrier mobility of the zone-cast pentacene devices depends strongly on the underlying dielectric. Divinylsiloxane-bis-benzocyclobutene (BCB) resin is found to b...

Using grazing incidence X-ray diffraction, perylene crystallites grown on thin highly oriented poly(tetrafluoroethylene) (PTFE) films on silicon substrates have been investigated. All the perylene crystallites are found to orient with the ab plane of the monoclinic unit cell parallel to the substrate. The scattering data is interpreted as a trimodal texture of oriented perylene crystallites, induced by interactions between the perylene molecules and the oriented PTFE substrate. Three families of biaxial orientations are seen, with the 〈h10〉 axes (h = 1, 2, or 3) parallel to the PTFE alignment, all having the ab-plane parallel to the substrate. About 92% of the scattered intensity corresponds to a population with 〈110〉 highly parallel to 〈001〉PTFE.

Semiconducting diblock copolymers of polyethylene (PE) and regioregular poly(3-hexylthiophene) (P3HT) are demonstrated to exhibit a rich phase behaviour, judicious use of which permitted us to fabricate field-effect transistors that show saturated charge carrier mobilities, ?FET, as high as 2 × 10-2 cm2V-1 s-1 and ON-OFF ratios, Ion/Ioff ?105 at contents of the insulating PE moiety as high as 90 wt %. In addition, the diblock copolymers display outstanding flexibility and toughness with elongations at break exceeding 600 % and true tensile strengths around 70 MPa, opening the path towards robust and truly flexible electronic components. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA

Organic electronics technology, in which at least the semiconducting component of the integrated circuit is an organic material, offers the potential for fabrication of electronic products by low-cost printing technologies, such as ink jet, gravure offset lithography and flexography. The products will typically be of lower performance than those using the present state of the art single crystal or polysilicon transistors, but comparable to amorphous silicon. A range of prototypes are under development, including rollable electrophoretic displays, active matrix liquid crystal (LC) displays, flexible organic light emitting diode displays, low frequency radio frequency identification tag and other low performance electronics. Organic semiconductors that offer both electrical performance and stability with respect to storage and operation under ambient conditions are required. This work describes the development of reactive mesogen semiconductors, which form large crosslinked LC domains on polymerization within mesophases. These crosslinked domains offer mechanical stability and are inert to solvent exposure in further processing steps. Reactive mesogens containing conjugated aromatic cores, designed to facilitate charge transport and provide good oxidative stability, were prepared and their liquid crystalline properties evaluated. The organization and alignment of the mesogens, both before and after crosslinking, were probed by grazing incidence wide-angle X-ray scattering of thin films. Both time-of-flight and field effect transistor devices were prepared and their electrical characterization reported.

Very high conductivities (>1000 S/cm) were obtained in poly(3,4-ethylenedioxythiophene) films oxidized with Fe(III)tosylate when the acidity during the polymerization process was controlled using a basic inhibitor. The best results were obtained with pyridine as inhibitor. The films could either be polymerized from a solution of 3,4-ethylenedioxythiophene (EDT), Fe(III)tosylate and pyridine or by vapor phase polymerization (VPP) of EDT on a surface coated with Fe(III)tosylate and pyridine. By incorporating non-conducting adhesive (up to 75% vol.) in the vapor phase polymerized PEDT system, films with activation energy of 1/3 the value of pure PEDT, were obtained. The reason for this phenomenon could not be explained by changes in the PEDT structure investigated with grazing incidence X-ray diffraction.

The influence of a commercial grade and a pure anionic surfactant (dodecylbenzenesulfonic acid sodium salt, DBS) in aqueous solutions on the environmental stress cracking (ESC) of high-density polyethylene (HDPE) has been investigated. Injection moulded HDPE samples in ‘‘dog-bone’’ shape were exposed to the aqueous solutions of surfactant (0.14 M) at 80 C under strain (3 Z 1.2%) for 5 days. Both the commercial and pure surfactants caused cracks under the experimental conditions. The change in surface chemistry of the HDPE was followed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectroscopy. The thermogravimetric analysis (TGA) did not show any significant differences in thermal stability of the samples studied. Differential scanning calorimetry (DSC) analysis, however, revealed an increase in crystallinity of the exposed samples. Wide Angle X-ray Scattering (WAXS) indicated that the HDPE sample has a boundary of both preferred and random (isotropic) crystallite orientations close and far away from the injection moulding inlet, respectively. The structure of the surfactants in solution was investigated by light scattering (LS). This showed that the commercial grade surfactant forms large aggregates (e.g., 500 nm) both at room temperature and at the exposure temperature of 80 C, whereas the pure surfactant has a critical micelle temperature (CMT) of around 45 C. Below the CMT aggregates are formed, and above the CMT the surfactants are unimeric. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) analysis revealed that the commercial surfactant has a wide distribution of hydrocarbon chains from C-10 to C-13, whereas the pure one contains predominantly hydrocarbon dodecyl (chain of C-12). 2005 Elsevier Ltd. All rights reserved.

The structure of a thin zone-cast film of the hexa-n-dodecyl-substituted hexa-peri-benzocoronene (HBC) has been investigated using grazing incidence X-ray diffraction. A model with an orthorhombic unit cell containing two molecules accounts well for the observations. The molecules are arranged in a "herringbone" structure resembling the packing observed for unsubstituted HBC. The molecular disk planes are oriented perpendicularly to the substrate, rotated by approximately 39 degrees about the film normal. The relatively long side chains of dodecyl were found to be in an ordered interdigitated state. The aliphatic side chains and the aromatic HBC-cores segregate to form regular vertical domains spanning the film thickness. For in-plane rocking scans a discrete orientation distribution is observed with peaks at regular angle intervals. We interpret this as a grain boundary effect induced by alkyl chain stacking faults.

Thin films of poly(tetrafluoroethylene) (PTFE) produced by friction deposition were studied using grazing incidence X-ray diffraction as the principal tool. The structure of the deposited thin films was compared with that of the surface of the PTFE bar used for depositing the films. Both exhibited the 15/7 helix conformation characteristic of crystal PTFE phase IV. A high degree of biaxial orientation was found for the highly crystalline thin films. Whereas the unit cell of the bar surface material appeared to be single-stem hexagonal, the film displayed diffraction characteristics consistent with a larger multistem unit cell. The origin of this increase of the unit cell is attributed to a higher degree of regular packing, possibly related to alternating right- and left-handed PTFE helicessa structure which has never been verified experimentally for PTFE in the 15/7 configuration. We discuss the possibility of a continuous transition between the low-order single-stem hexagonal and the multistem high-order unit cell. The degree of chain orientation was much lower at the surface of the bar than in the thin film. A modification of the commonly accepted mechanism for the transfer of material from the bar to the substrate is proposed.

X-band electron spin resonance was employed to study the structural anisotropy in several polythiophene derivatives. Because of the dominating homoge- neous width, the obtained absorption spectra were Lorentzian-shaped. Information about the structural anisotropy was obtained from the position and width of the absorption peak. Qualitatively, the anisotropy was in full agreement with earlier results from X-ray diffraction, including a flip in molecular orientation with respect to the film substrate between solution-cast and spin-cast films. With the Monte Carlo technique, the spectra were fitted with a biaxial g tensor, an anisotropy parameter S, and an intrinsic width . The simulations showed that g could be treated as pseudo- uniaxial, with the unique axis along the side chains rather than along the ring normal. Closed-form analytical expressions relating g to the anisotropy were obtained and used for a quantitative assessment of the molecular anisotropy. Because the molecular g tensor for these materials was not known, a known value of S for one of the samples obtained by X-ray diffraction was used for normalization. Fairly consistent values were obtained for both g and S. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3011-3025, 2003

The drying process of poly(octyl-thiophene) (POT) from chloroform and tetrahydrofuran (THF) solutions has been studied using grazing incidence diffraction (GID). Concentrated solutions combined with high ventilation rates in the sample cell promote the formation of a solid skin at the solution–air interface. This skin has a swollen unit cell and restricted correlation length compared with the dry films. The early skin formation could be reversed by switching off the ventilation. Conversely, dilute concentrations and low ventilation rates tend to give drying from the edges, i.e. solidification directly onto the substrate. It appears that the anisotropy of the films produced by low ventilation rates, especially those resulting from ‘edge drying’, is slightly higher than for the other films. A three-stage model of drying is appropriate for most of the cases studied. After an initial period of constant rate volume loss, the thickness reduction obeys exponential decay in a falling rate period. In the final third stage, the minute residual amounts of solvent leave the sample accompanied with an increasing internal order in the sample. However, both the ‘edge drying’ for dilute solutions and the skin formation for concentrated solutions modify this three-stage description.

Sub-micrometer layers of electrochemically prepared methyl- and decylsubstituted poly(3,4-ethylenedioxythiophene) (PEDOT) carrying perchlorate counterions have been examined with grazing incidence X-ray diffraction with synchrotron radiation. The materials were found to be partially crystalline, and the data could be ascribed to a model of sheets of π-π stacked polymer chains with a smectic ordering of these sheets. An unsubstituted PEDOT sample with the polymeric polystyrenesulfonic acid as a counterion was also investigated and turned out to be essentially amorphous.

Cobalt nanoparticles play an important role as catalysts for the Fischer–Tropsch synthesis, which is an attractive route for production of synthetic fuels. It is of particular interest to understand the varying conversion rate during the first hours after introducing synthesis gas (H2 and CO) to the system. To this end, several in situ characterization studies have previously been done on both idealized model systems and commercially relevant catalyst nanoparticles, using bulk techniques, such as X-ray powder diffraction and X-ray absorption spectroscopy. Since catalysis takes place at the surface of the cobalt particles, it is important to develop methods to gain surface-specific structural information under realistic processing conditions. We addressed this challenge using small-angle X-ray scattering (SAXS), a technique exploiting the penetrating nature of X-rays to provide information about particle morphology during in situ experiments. Simultaneous wide-angle X-ray scattering was used for monitoring the reduction from oxide to catalytically active metal cobalt, and anomalous SAXS was used for distinguishing the cobalt particles from the other phases present. After introducing the synthesis gas, we found that the slope of the scattered intensity in the Porod region increased significantly, while the scattering invariant remained essentially constant, indicating a change in the shape or surface structure of the particles. Shape- and surface change models are discussed in light of the experimental results, leading to an improved understanding of catalytic nanoparticles.

The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed in situ by grazing incidence diffraction of synchrotron X-rays from the solution surface, with the solvent evaporation rate being controlled by a flow of dry nitrogen gas. It was found that a solid, partially crystalline film is formed on the upper surface while the interior is still fluid. The initially formed film is swollen and of restricted correlation length, but the swelling disappears gradually on further drying. A considerable fraction (>20%) of the polymer within the effective beam volume near the surface is transformed from the disordered to the ordered state only during the removal of the last 5% of the solvent.

Discotic hydrazone molecules are of particular interest as they form discotic phases where the discs are rigidified by intramolecular hydrogen bonds. Here, we investigate the thermotropic behavior and solid-state organizations of three discotic hydrazone derivatives with dendritic groups attached to their outer peripheries, containing six, eight, and ten carbons of linear alkoxy chains. On the basis of two-dimensional wide angle X-ray scattering (2DWAXS), the elevated temperature liquid crystalline (LC) phases were assigned to a hexagonal columnar (Colh) organization with nontilted hydrazone discs for all three compounds. With WAXS, advanced solid-state nuclear magnetic resonance (SSNMR) techniques, and ab initio computations, the compounds with six and ten carbons of achiral alkoxy side chains were further subjected to studies at 25 °C, revealing complex crystalline phases with rigid columns and flexible side chains. This combined approach led to models of coexisting helical columnar stacking morphologies for both systems with two different tilt/pitch angles between successive hydrazone molecules. The differences in tilt/pitch angles between the two compounds illustrate that the columns with short alkoxy chains (six carbons) are more influenced by the presence of other stacks in their vicinity, while those with long side chains are less tilted due to a larger alkoxy (ten carbons) buffer zone. The formation of different packing morphologies in the crystalline phase of a columnar LC has rarely been reported so far, which suggests the possibility of complex stacking structures of similar organic LC systems, utilizing small molecules as potential materials for applications in organic electronics.

Discotic mesophases are known for their ability to self-assemble into columnar structures and can serve as semiconducting molecular wires. Charge carrier mobility along these wires strongly depends on molecular packing, which is controlled by intermolecular interactions. By combining wide-angle X-ray scattering experiments with molecular dynamics simulations, we elucidate packing motifs of a perylene tetracarboxdiimide derivative, a task which is hard to achieve by using a single experimental or theoretical technique. We then relate the charge mobility to the molecular arrangement, both by pulse-radiolysis time-resolved microwave conductivity experiments and simulations based on the non-adiabatic Marcus charge transfer theory. Our results indicate that the helical molecular arrangement with the 45 degrees twist angle between the neighboring molecules favors hole transport in a compound normally considered as an n-type semiconductor. Statistical analysis shows that the transport is strongly suppressed by structural defects. By linking molecular packing and mobility, we eventually provide a pathway to the rational design of perylenediimide derivatives with high charge mobilities.

We report a simple synthetic route to novel symmetrical alkylated and acylated amphiphilic 4,4'-diaminoazobenzene dyes, with their optical axis perpendicular to the amphiphilic direction of the molecule. Three different substitution patterns are reported, two of which are highly amphiphilic. At the air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing synchrotron radiation. Compression beyond the collapse point does not change the XR data, showing that the film is unchanged at the molecular level, even at areas less than half of that of the collapse. This leads to the conclusion that few macroscopic collapse sites are responsible for reversibly removing large amounts of material from the interface.

The inorganic (or ‘organometallic’) polymers poly(dibutylstannane), poly(dioctylstannane), and poly(didodecylstannane) have been oriented by shear forces, the tensile drawing of blends with polyethylene, and deposition from solution onto glass slides coated with an oriented, friction-deposited poly(tetrafluoroethylene) (PTFE) layer. Orientation of the polystannanes has been examined by polarization microscopy, UV-vis spectroscopy with polarized light, and X-ray diffraction and their direction is found to depend on the length of the alkyl side groups and the method of orientation. Remarkably, in some cases the polystannane backbones are oriented parallel and in other instances perpendicular to the direction of the external orientation stimuli. The latter structural arrangement is most conspicuous for polymers substituted with dodecyl side groups, which are found to align parallel to the applied orientation direction, which forces the polymer backbone into a perpendicular position. Finally, UV-vis spectra indicate that changes in the backbone conformation of certain polystannanes might be induced by applying mechanical stress.

Blends and other multicomponent systems are used in various polymer applications to meet multiple requirements that cannot be fulfilled by a single material. In polymer optoelectronic devices it is often desirable to combine the semiconducting properties of the conjugated species with the excellent mechanical properties of certain commodity polymers. Here we investigate bicomponent blends comprising semicrystalline regioregular poly(3-hexylthiophene) and selected semicrystalline commodity polymers, and show that, owing to a highly favourable, crystallization-induced phase segregation of the two components, during which the semiconductor is predominantly expelled to the surfaces of cast films, we can obtain vertically stratified structures in a one-step process. Incorporating these as active layers in polymer field-effect transistors, we find that the concentration of the semiconductor can be reduced to values as low as 3 wt% without any degradation in device performance. This is in stark contrast to blends containing an amorphous insulating polymer, for which significant reduction in electrical performance was reported. Crystalline-crystalline/semiconducting-insulating multicomponent systems offer expanded flexibility for realizing high-performance semiconducting architectures at drastically reduced materials cost with improved mechanical properties and environmental stability, without the need to design all performance requirements into the active semiconducting polymer itself.

Interchain interactions have a profound effect on the optical as well as charge transport properties of conjugated polymer thin films. In contrast to oligomeric model systems in solution-deposited polymer thin films the study of such effects is complicated by the complex microstructure. We present here a detailed study of interchain interaction effects on both charged polarons as well as neutral excitons in highly crystalline, high-mobility poly-3-hexylthiophene (P3HT) as a function of molecular weight. We find experimental evidence for reduced exciton bandwidth and increased polaron delocalization with increasing conjugation length and crystalline quality. From comparative studies of field-effect transistor characteristics, film morphology, and optical properties our study provides a microscopic understanding of the factors which limit the charge transport in P3HT to field-effect mobilities around $0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$, and which will need to be addressed to improve mobility further.

X-ray waveguides are successfully produced employing standard silicon technology of UV photolithography and wafer bonding. Contrary to theoretical expectations for similar systems even 100 mu m broad guides of less than 80 nm height do not collapse and can be used as one dimensional waveguides to excite single guided modes at typical x-ray energies.

Charge transport properties in organic semiconductors depend strongly on molecular order. Here we demonstrate field-effect transistors where drain current flows through a precisely defined array of nanostripes made of crystalline and highly ordered molecules. The molecular stripes are fabricated across the channel of the transistor by a stamp-assisted deposition of the molecular semiconductors from a solution. As the solvent evaporates, the capillary forces drive the solution to form menisci under the stamp protrusions. The solute precipitates only in the regions where the solution is confined by the menisci once the critical concentration is reached and self-organizes into molecularly ordered stripes 100-200 nm wide and a few monolayers high. The charge mobility measured along the stripes is 2 orders of magnitude larger than the values measured for spin-coated thin films.

The crystalline to liquid crystalline (Cr-LC) phase transition in thin films of zone-cast hexa-peri-hexabenzocoronene sixfold substituted with dodecyl side chains (HBC-C12H25) has been studied in detail using grazing incidence X-ray diffraction (GID), electron diffraction (ED), and variable angle spectroscopic ellipsometry (VASE), When heating the material, a first minor transition is observed around 42 degrees C. This change is attributed to alterations of the crystalline alkyl chain packing, which only slightly changes the electronic properties of the material. At higher temperatures of about 90 degrees C, but still significantly below the previously reported transition temperature in bulk, the Cr-LC transition is observed. An accompanying large increase in optical anisotropy is compatible with the X-ray data, showing a transition from the as-cast herringbone-like crystalline state to a highly ordered discotic hexagonal columnar LC phase. The structural transition has the macroscopic effect of increasing the film thickness. The high structural order of the as-cast low-temperature phase is only partly recovered after cooling, and the phase transition exhibits a large hysteresis. From the ellipsometry data, the dielectric tensor of HBC-C12H25 was refined to unprecedented detail.

Nature Materials 13, 190–194 (2014); published online 8 December 2013; corrected after print 16 April 2014. In the version of this Article originally published, the grazing incidence wide-angle X-ray scattering (GIWAXS) pattern shown in Fig. 2c was obtained for a contaminated thin-film sample. The correct scattering pattern and caption is given here.

Block copolymers of regioregular poly(3-hexylthiophene) (P3HT) and polyethylene (PE) were synthesized through the chain transfer of olefin-terminated P3HT in the presence of cyclooctene via ring-opening metathesis polymerization (ROMP). Subsequent hydrogenation of the poly(cyclooctene) block yielded high molecular weight, crystalline-crystalline P3HT-PE block copolymers, which are thermally stable and resistant to solvents under ambient conditions. These copolymers were characterized by 1H NMR, DSC, and WAXS and represent the first materials of a class of crystalline-crystalline semiconducting-insulating block copolymers.

Ultra-thin layers (10 - 50nm) of poly(alkyl)thiophenes (PATs) spread on water from diluted chloroform solutions were studied by means of synchrotron radiation. The molecular orientation in the films was obtained using grazing incidence diffraction (GID) and reflectometry, for both doped and pristine samples. Despite alkanes being hydrophobic, the side chains tend to orient perpendicularly to the water subphase. The study reveals the presence of crystalline order with a high degree of preferred orientation. A smectic model for the polymeric layers is in good agreement with the experimental data.

Using grazing incidence diffraction (GID), the drying of concentrated solutions of the conjugated polymer poly(octylthiophene) (POT) was followed in situ. The influence of the initial concentration of polymer in the solution and the ventilation rate of the closed sample cell was studied. For most of the samples, studied, the drying behaviour adheres to a two-stage model; an initial stage with a constant evaporation rate. and a finalising state with only minor evaporation, but with convergence of the crystallinily and spatial correlation to their final values. Concentrated solutions and high ventilation rates promote early formation of a dry skin at the polymer-air interface, effectively acting as a barrier to the solvent flow, thereby slowing down further evaporation from the sample. In this case, the distinction between the two drying stages vanishes. For both extremes, the unit cell of the initially formed solid phase is swollen and has a correlation length substantially shorter than for dry samples.

We investigated the crystalline nanostructures and film morphologies of pentacene films deposited onto a polymer brush organic interlayer in high performance organic field-effect transistors (OFETs). Polymer brushes were grafted onto the oxide substrates by spin-coating and thermal annealing. Pentacene FETs fabricated on top of the polymer brushes showed excellent device performance, with a field-effect mobility of 0.82 cm2 V−1s−1 and an on/off current ratio of 107. These properties were superior to those of devices using typical surface modification techniques, such as octadecyltrichlorosilane (ODTS) and hexamethyldisilazane (HMDS). The improvements in OFET performance appeared to be due to the pentacene layer's crystalline nanostructure and grain interconnectivity, which formed during the submonolayer stage of film growth. This stage of growth is strongly correlated with the surface energy, morphology, and viscoelastic properties of the resulting gate dielectrics. The inclusion of a polymer brush dielectric surface modification is a significant step toward optimizing the nanostructures of organic semiconductors, which are directly linked to device performance enhancement, by engineering the interfaces in OFETs.

Polyaniline (PANI) protonated with camphorsulfonic acid (CSA) receives high interest but its molecular and crystalline structure is still unclear. We undertook detailed studies of thin films cast from m-cresol, dichlorometane and trifluoroacetic acid (TFAA) solutions. Such samples were subjected to diffraction measurements by use of the grazing incident beam technique, applying the z-axis diffractometer installed at the beamline BW2 at HASYLAB. We obtained very important information concerning an anisotropy of the crystalline reflections for all samples investigated. These results demonstrate the significance of the solvents on the structural ordering, and the observed anisotropy plays an important role in new modelling attempts for the crystalline structure.

Conjugated polymers and small molecules based on alternating electron-donating (D) and electronaccepting (A) building blocks have led to state-of-the-art organic solar cell materials governing efficiencies beyond 10%. Unfortunately, the connection of D and A building blocks via cross-coupling reactions does not always proceed as planned, which can result in the generation of side products containing D-D or A-A homocoupling motifs. Previous studies have reported a reduced performance in polymer and small molecule solar cells when such defect structures are present. A general consensus on the impact of homocouplings on device performance is, however, still lacking as is a profound understanding of the underlying causes of the device deterioration. For differentiating the combined effect of molecular weight and homocouplings in polymer solar cells, a systematic study on a small molecule system (DTS(FBBTh2)2) is presented. The impact of homocouplings on nanomorphology, thermal, and electro-optical properties is investigated. It is demonstrated that small quantities of homocouplings (

Differences in drug kinetics between supine rest and ambulation have been reported, but the relative contribution of postural changes and changes in the level of physical activity has not been evaluated. Ampicillin pharmacokinetics, glomerular filtration rate (GFR) and renal plasma flow (RPF) were studied in six male volunteers at rest in the sitting and lying position with an interval of 1 week. After intravenous administration ampicillin kinetics, analyzed according to a two-compartment open model, demonstrated significant changes in drug distribution when the position was changed from lying to sitting: alpha-increased by 50%, V1 and V beta increased by 19% and 22% respectively. Ampicillin clearance, the fraction of dose recovered from urine, GFR and RPF were, however, not influenced by the change in posture. Our data on effects of posture in resting subjects suggest that previously reported differences in drug elimination and RPF between lying and ambulatory subjects are largely due to differences in the level of physical activity.