Publications by authors named "Oskar Paris"

40 Publications

A Facile One-Pot Synthesis of Hierarchically Organized Carbon/TiO Monoliths with Ordered Mesopores.

Chempluschem 2021 Feb;86(2):275-283

Dept. of Chemistry and Physics of Materials, Paris-Lodron-University of Salzburg, Jakob-Haringer-Straße 2a, 5020, Salzburg, Austria.

Sol-gel processing combined with soft templating and gelation-induced phase separation is very sensitive to the precursor sol composition. In this work we present a straightforward synthesis towards hierarchically structured, macroporous carbon/titania monoliths with ordered mesopores derived from resorcinol/formaldehyde monoliths and a glycolated titanium precursor. We demonstrate the influence of various reaction solvents, where diol-based media and the proportion of the catalyst seem to be essential in controlling spinodal decomposition, obtaining similar monolithic structures under different synthesis conditions. Based on these observations, we further homogeneously incorporated TiO into the carbon structure by an in situ synthesis approach, obtaining structural features similar to pure carbon materials with surface areas of about 400 m  g , periodically arranged mesopores with a mean distance of 10-11 nm and cellular macroporosity.
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http://dx.doi.org/10.1002/cplu.202000740DOI Listing
February 2021

Hierarchically organized materials with ordered mesopores: adsorption isotherm and adsorption-induced deformation from small-angle scattering.

Phys Chem Chem Phys 2020 Jun;22(22):12713-12723

Institute of Physics, Montanuniversität Leoben, Franz-Josef Strasse 18, 8700, Leoben, Austria.

In situ small angle scattering is used to study the pore filling mechanism and the adsorption induced deformation of a silica sample with hierarchical porosity upon water adsorption. The high structural order of the cylindrical mesopores on a 2D hexagonal lattice allows obtaining adsorption induced strains from the shift of the corresponding Bragg peaks measured by in situ small-angle X-ray scattering (SAXS). However, apparent strains due to scattering contrast induced changes of the Bragg peak shapes emerge in SAXS. In contrast, small-angle neutron scattering (SANS) allows determining the real adsorption induced strains by employing a H2O/D2O adsorbate with net coherent scattering length density of zero. This allows separating the apparent strains from the real strains experimentally and comparing them with strains obtained from model calculations of the SAXS intensity. It is shown that the apparent strains cannot be described at all by a simple mesopore model of film growth and capillary condensation. A hierarchical model taking the scattering of the micropores and the outer surface of the mesoporous struts in the hierarchically porous sample properly into account, together with a modified mesopore filling mechanism based on a corona model, leads to satisfactory description of both, the adsorption isotherm and the measured apparent strains as derived by SAXS.
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http://dx.doi.org/10.1039/d0cp01026jDOI Listing
June 2020

Hierarchically Organized and Anisotropic Porous Carbon Monoliths.

Chem Mater 2020 May 20;32(9):3944-3951. Epub 2020 Apr 20.

Materials Chemistry, Paris Lodron University Salzburg, Jakob-Haringer Str. 2a, Salzburg 5020, Austria.

Anisotropy is a key factor regarding mechanical or transport properties and thus the functionality of porous materials. However, the ability to deliberately design the pore structure of hierarchically organized porous networks toward anisotropic features is limited. Here, we report two straightforward routes toward hierarchically structured porous carbon monoliths with an anisotropic alignment of the microstructure on the level of macro- and mesopores. One approach is based on nanocasting (NC) of carbon precursors into hierarchical and anisotropic silica hard templates. The second route, a direct synthesis approach based on soft templating (ST), makes use of the flexibility of hierarchically structured resorcinol-formaldehyde gels, which are compressed and simultaneously carbonized in the deformed state. We present structural data of both types of carbon monoliths obtained by electron microscopy, nitrogen adsorption analysis, and SAXS measurements. In addition, we demonstrate how the degree of anisotropy can easily be controlled via the ST route.
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http://dx.doi.org/10.1021/acs.chemmater.0c00302DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7222333PMC
May 2020

Towards Real-Time Ion-Specific Structural Sensitivity in Nanoporous Carbon Electrodes Using In Situ Anomalous Small-Angle X-ray Scattering.

ACS Appl Mater Interfaces 2019 Nov 4;11(45):42214-42220. Epub 2019 Nov 4.

Institute of Physics , Montanuniversitaet Leoben , Franz-Josef Straße 18 , 8700 Leoben , Austria.

Current in situ techniques to study ion charge storage and electrical double-layer formation in nanoporous electrodes are either chemically sensitive to element-specific concentration changes or structurally sensitive to rearrangements of ions and solvent molecules; but rarely can they cover both. Here we introduce in situ anomalous small-angle X-ray scattering (ASAXS) as a unique method to extract both real-time structural and ion-specific chemical information from one single experiment. Using a 1 M RbBr aqueous electrolyte and a hierarchical micro- and mesoporous carbon electrode, we identify different charging mechanisms for positive and negative applied potentials. We are able not only to track the global concentration change of each ion species individually, but also to observe their individual local rearrangement within the pore space.
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http://dx.doi.org/10.1021/acsami.9b14242DOI Listing
November 2019

In Situ Small-Angle Neutron Scattering Investigation of Adsorption-Induced Deformation in Silica with Hierarchical Porosity.

Langmuir 2019 Sep 22;35(35):11590-11600. Epub 2019 Aug 22.

Institute of Physics , Montanuniversitaet Leoben , Franz-Josef-Str. 18 , 8700 Leoben , Austria.

Adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in situ small-angle neutron scattering (SANS) and in situ dilatometry. Monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally ordered cylindrical mesopores and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A HO/DO adsorbate with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in situ dilatometry result from a combination of axial and radial mesopore deformation together with micropore deformation. Strain data were quantitatively analyzed with a theoretical model for micro-/mesopore deformation by combining information from nitrogen and water adsorption isotherms to estimate the water-silica interaction. It was shown that in situ SANS provides complementary information to dilatometry and allows for a quantitative estimate of the elastic properties of the mesopore walls from water adsorption.
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http://dx.doi.org/10.1021/acs.langmuir.9b01375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6733155PMC
September 2019

Mechanical Characterization of Hierarchical Structured Porous Silica by in Situ Dilatometry Measurements during Gas Adsorption.

Langmuir 2019 Feb 12;35(8):2948-2956. Epub 2019 Feb 12.

Bavarian Center for Applied Energy Research , Magdalene-Schoch-Str. 3 , 97074 Würzburg , Germany.

Mechanical properties of hierarchically structured nanoporous materials are determined by the solid phase stiffness and the pore network morphology. We analyze the mechanical stiffness of hierarchically structured silica monoliths synthesized via a sol-gel process, which possess a macroporous scaffold built of interconnected struts with hexagonally ordered cylindrical mesopores. We consider samples with and without microporosity within the mesopore walls and analyze them on the macroscopic level as well as on the microscopic level of the mesopores. Untreated as-prepared samples still containing some organic components and the respective calcined and sintered counterparts of varying microporosity are investigated. To determine Young's moduli on the level of the macroscopic monoliths, we apply ultrasonic run time measurements, while Young's moduli of the mesopore walls are obtained by analysis of the in situ strain isotherms during N adsorption at 77 K. For the latter, we extended our previously reported theoretical approach for this type of materials by incorporating the micropore effects, which are clearly not negligible in the calcined and most of the sintered samples. The comparison of the macro- and microscopic Young's moduli reveals that both properties follow essentially the same trends, that is, calcination and sintering increase the mechanical stiffness on both levels. Consequently, stiffening of the monolithic samples can be primarily attributed to stiffening of the backbone material which is consistent with the fact that the morphology on the mesopore level is mainly preserved with the post-treatments applied.
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http://dx.doi.org/10.1021/acs.langmuir.8b03242DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6393851PMC
February 2019

A new device for high-temperature in situ GISAXS measurements.

Rev Sci Instrum 2018 Mar;89(3):035103

Institute of Physics, Montanuniversität Leoben, Franz-Josef-Str. 18, 8700 Leoben, Austria.

A heating stage originally designed for diffraction experiments is implemented into a Bruker NANOSTAR instrument for in situ grazing incidence small-angle x-ray scattering experiments. A controlled atmosphere is provided by a dome separating the sample environment from the evacuated scattering instrument. This dome is double shelled in order to enable cooling water to flow through it. A mesoporous silica film templated by a self-assembled block copolymer system is investigated in situ during step-wise heating in air. The GISAXS pattern shows the structural development of the ordered lattice of parallel cylindrical pores. The deformation of the elliptical pore-cross section perpendicular to the film surface was studied with increasing temperature. Moreover, the performance of the setup was tested by controlled in situ heating of a copper surface under controlled oxygen containing atmosphere.
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http://dx.doi.org/10.1063/1.5005879DOI Listing
March 2018

Quantifying adsorption-induced deformation of nanoporous materials on different length scales.

J Appl Crystallogr 2017 Oct 14;50(Pt 5):1404-1410. Epub 2017 Sep 14.

Institute of Physics, Montanuniversität Leoben, Franz-Josef Strasse 18, Leoben, 8700, Austria.

A new setup combining small-angle neutron scattering (SANS) and dilatometry was used to measure water-adsorption-induced deformation of a monolithic silica sample with hierarchical porosity. The sample exhibits a disordered framework consisting of macropores and struts containing two-dimensional hexagonally ordered cylindrical mesopores. The use of an HO/DO water mixture with zero scattering length density as an adsorptive allows a quantitative determination of the pore lattice strain from the shift of the corresponding diffraction peak. This radial strut deformation is compared with the simultaneously measured macroscopic length change of the sample with dilatometry, and differences between the two quantities are discussed on the basis of the deformation mechanisms effective at the different length scales. It is demonstrated that the SANS data also provide a facile way to quantitatively determine the adsorption isotherm of the material by evaluating the incoherent scattering contribution of HO at large scattering vectors.
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http://dx.doi.org/10.1107/S1600576717012274DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627682PMC
October 2017

Setting Directions: Anisotropy in Hierarchically Organized Porous Silica.

Chem Mater 2017 Sep 31;29(18):7969-7975. Epub 2017 Aug 31.

Chemistry and Physics of Materials, Paris Lodron University Salzburg, 5020 Salzburg, Austria.

Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of sol-gel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the material's macroporosity is also reflected in its mechanical properties; i.e., the Young's modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy.
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http://dx.doi.org/10.1021/acs.chemmater.7b03032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627989PMC
September 2017

Biological fabrication of cellulose fibers with tailored properties.

Science 2017 09;357(6356):1118-1122

Max Planck Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany.

Cotton is a promising basis for wearable smart textiles. Current approaches that rely on fiber coatings suffer from function loss during wear. We present an approach that allows biological incorporation of exogenous molecules into cotton fibers to tailor the material's functionality. In vitro model cultures of upland cotton () are incubated with 6-carboxyfluorescein-glucose and dysprosium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-glucose, where the glucose moiety acts as a carrier capable of traveling from the vascular connection to the outermost cell layer of the ovule epidermis, becoming incorporated into the cellulose fibers. This yields fibers with unnatural properties such as fluorescence or magnetism. Combining biological systems with the appropriate molecular design offers numerous possibilities to grow functional composite materials and implements a material-farming concept.
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http://dx.doi.org/10.1126/science.aan5830DOI Listing
September 2017

In Situ Measurement of Electrosorption-Induced Deformation Reveals the Importance of Micropores in Hierarchical Carbons.

ACS Appl Mater Interfaces 2017 Jul 3;9(28):23319-23324. Epub 2017 Jul 3.

Institute of Physics, Montanuniversitaet Leoben , Franz-Josef Straße 18, 8700 Leoben, Austria.

Dimensional changes in carbon-based supercapacitor electrodes were investigated using a combination of electrochemical dilatometry and in situ small-angle X-ray scattering. A novel hierarchical carbon material with ordered mesoporosity was synthesized, providing the unique possibility to track electrode expansion and shrinkage on the nanometer scale and the macroscopic scale simultaneously. Two carbons with similar mesopore structure but different amounts of micropores were investigated, employing two different aqueous electrolytes. The strain of the electrodes was always positive, but asymmetric with respect to positive and negative applied voltages. The asymmetry strongly increased with increasing microporosity, giving hints to the possible physical origin of electrosorption induced pore swelling.
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http://dx.doi.org/10.1021/acsami.7b07058DOI Listing
July 2017

Adsorption-Induced Deformation of Hierarchically Structured Mesoporous Silica-Effect of Pore-Level Anisotropy.

Langmuir 2017 06 26;33(22):5592-5602. Epub 2017 May 26.

Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey , 98 Brett Road, Piscataway, New Jersey 08854, United States.

The goal of this work is to understand adsorption-induced deformation of hierarchically structured porous silica exhibiting well-defined cylindrical mesopores. For this purpose, we performed an in situ dilatometry measurement on a calcined and sintered monolithic silica sample during the adsorption of N at 77 K. To analyze the experimental data, we extended the adsorption stress model to account for the anisotropy of cylindrical mesopores, i.e., we explicitly derived the adsorption stress tensor components in the axial and radial direction of the pore. For quantitative predictions of stresses and strains, we applied the theoretical framework of Derjaguin, Broekhoff, and de Boer for adsorption in mesopores and two mechanical models of silica rods with axially aligned pore channels: an idealized cylindrical tube model, which can be described analytically, and an ordered hexagonal array of cylindrical mesopores, whose mechanical response to adsorption stress was evaluated by 3D finite element calculations. The adsorption-induced strains predicted by both mechanical models are in good quantitative agreement making the cylindrical tube the preferable model for adsorption-induced strains due to its simple analytical nature. The theoretical results are compared with the in situ dilatometry data on a hierarchically structured silica monolith composed by a network of mesoporous struts of MCM-41 type morphology. Analyzing the experimental adsorption and strain data with the proposed theoretical framework, we find the adsorption-induced deformation of the monolithic sample being reasonably described by a superposition of axial and radial strains calculated on the mesopore level. The structural and mechanical parameters obtained from the model are in good agreement with expectations from independent measurements and literature, respectively.
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http://dx.doi.org/10.1021/acs.langmuir.7b00468DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5484557PMC
June 2017

Pore shape and sorption behaviour in mesoporous ordered silica films.

J Appl Crystallogr 2016 Oct 23;49(Pt 5):1713-1720. Epub 2016 Sep 23.

Institute of Physics, Montanuniversität Leoben, Franz-Josef-Strasse 18, 8700 Leoben, Austria.

Mesoporous silica films templated by pluronic P123 were prepared using spin and dip coating. The ordered cylindrical structure within the films deforms due to shrinkage during calcination. Grazing-incidence small-angle X-ray scattering (GISAXS) measurements reveal that both the unit cell and the cross section of the pores decrease in size, mainly normal to the surface of the substrate, leading to elliptical cross sections of the pores with axis ratios of about 1:2. Water take-up by the pores upon changing the relative humidity can be monitored quantitatively by the shift in the critical angle of X-ray reflection as seen by the Yoneda peak.
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http://dx.doi.org/10.1107/S1600576716013698DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5045732PMC
October 2016

Passive and active mechanical properties of biotemplated ceramics revisited.

Bioinspir Biomim 2016 10 13;11(6):065001. Epub 2016 Oct 13.

Chair for Biogenic Polymers, Technical University of Munich, Schulgasse 16, D-94315 Straubing, Germany. Straubing Center of Science for Renewable Resources, Schulgasse 16, D-94315 Straubing, Germany.

Living nature and human technology apply different principles to create hard, strong and tough materials. In this review, we compare and discuss prominent aspects of these alternative strategies, and demonstrate for selected examples that nanoscale-precision biotemplating is able to produce uncommon mechanical properties as well as actuating behavior, resembling to some extent the properties of the original natural templates. We present and discuss mechanical testing data showing for the first time that nanometer-precision biotemplating can lead to porous ceramic materials with deformation characteristics commonly associated with either biological or highly advanced technical materials. We also review recent findings on the relation between hierarchical structuring and humidity-induced directional motion. Finally, we discuss to which extent the observed behavior is in agreement with previous results and theories on the mechanical properties of multiscale hierarchical materials, as well as studies of highly disperse technical materials, together with an outlook for further lines of investigation.
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http://dx.doi.org/10.1088/1748-3190/11/6/065001DOI Listing
October 2016

Cantilever bending based on humidity-actuated mesoporous silica/silicon bilayers.

Beilstein J Nanotechnol 2016 28;7:637-44. Epub 2016 Apr 28.

Institute of Physics, Montanuniversitaet Leoben, Austria.

We use a soft templating approach in combination with evaporation induced self-assembly to prepare mesoporous films containing cylindrical pores with elliptical cross-section on an ordered pore lattice. The film is deposited on silicon-based commercial atomic force microscope (AFM) cantilevers using dip coating. This bilayer cantilever is mounted in a humidity controlled AFM, and its deflection is measured as a function of relative humidity. We also investigate a similar film on bulk silicon substrate using grazing-incidence small-angle X-ray scattering (GISAXS), in order to determine nanostructural parameters of the film as well as the water-sorption-induced deformation of the ordered mesopore lattice. The strain of the mesoporous layer is related to the cantilever deflection using simple bilayer bending theory. We also develop a simple quantitative model for cantilever deflection which only requires cantilever geometry and nanostructural parameters of the porous layer as input parameters.
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http://dx.doi.org/10.3762/bjnano.7.56DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4902073PMC
June 2016

Moisture-Driven Ceramic Bilayer Actuators from a Biotemplating Approach.

Adv Mater 2016 Jul 6;28(26):5235-40. Epub 2016 May 6.

Professur für Biogene Polymere, Technische Universität München, Straubing Center of Science for Renewable Resources, Schulgasse 16, D-94315, Straubing, Germany.

The former ovuliferous scales of biotemplated cones of Pinus nigra show moisture-driven actuation similar to their biological templates, demonstrating a facile route to obtain ceramic moisture-sensitive bilayer actuators. Based on comparative analysis of their hierarchical nanometer-precision replica structures, using, e.g., spatially resolved small-angle X-ray scattering, the origin of the actuation is explained.
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http://dx.doi.org/10.1002/adma.201600117DOI Listing
July 2016

Structural analysis of Gossypium hirsutum fibers grown under greenhouse and hydroponic conditions.

J Struct Biol 2016 06 7;194(3):292-302. Epub 2016 Mar 7.

Martin-Luther-Universität Halle-Wittenberg, Biozentrum, Weinbergweg 22, 06120 Halle, Germany; Institut für Chemie - Organische Chemie, Naturwissenschaftliche Fakultät II-Chemie, Physik und Mathematik, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Straße 2, Halle 06120, Germany.

Cotton is the one of the world's most important crops. Like any other crop, cotton growth/development and fiber quality is highly dependent on environmental factors. Increasing global weather instability has been negatively impacting its economy. Cotton is a crop that exerts an intensive pressure over natural resources (land and water) and demands an overuse of pesticides. Thus, the search for alternative cotton culture methods that are pesticide-free (biocotton) and enable customized standard fiber quality should be encouraged. Here we describe a culture of Gossypium hirsutum ("Upland" Cotton) utilizing a greenhouse and hydroponics in which the fibers are morphological similar to conventional cultures and structurally fit into the classical two-phase cellulose I model with 4.19nm crystalline domains surrounded by amorphous regions. These fibers exhibit a single crystalline form of cellulose I-Iß, monoclinic unit cell. Fiber quality bulk analysis shows an improved length, strength, whiteness when compared with soil-based cultures. Finally, we show that our fibers can be spun, used for production of non-woven fabrics and indigo-vat stained demonstrating its potential in industrial and commercial applications.
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http://dx.doi.org/10.1016/j.jsb.2016.03.005DOI Listing
June 2016

Crystal Phase Transitions in the Shell of PbS/CdS Core/Shell Nanocrystals Influences Photoluminescence Intensity.

Chem Mater 2014 Oct 29;26(20):5914-5922. Epub 2014 Sep 29.

Institute of Physics, Montanuniversitaet Leoben , 8700 Leoben, Austria.

We reveal the existence of two different crystalline phases, i.e., the metastable and the equilibrium phase within the CdS-shell of PbS/CdS core/shell nanocrystals formed by cationic exchange. The chemical composition profile of the core/shell nanocrystals with different dimensions is determined by means of anomalous small-angle X-ray scattering with subnanometer resolution and is compared to X-ray diffraction analysis. We demonstrate that the photoluminescence emission of PbS nanocrystals can be drastically enhanced by the formation of a CdS shell. Especially, the ratio of the two crystalline phases in the shell significantly influences the photoluminescence enhancement. The highest emission was achieved for chemically pure CdS shells below 1 nm thickness with a dominant metastable phase fraction matching the crystal structure of the PbS core. The metastable phase fraction decreases with increasing shell thickness and increasing exchange times. The photoluminescence intensity depicts a constant decrease with decreasing metastable phase fraction but shows an abrupt drop for shells above 1.3 nm thickness. We relate this effect to two different transition mechanisms for changing from the metastable phase to the equilibrium phase depending on the shell thickness.
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http://dx.doi.org/10.1021/cm502521qDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4311954PMC
October 2014

A customizable software for fast reduction and analysis of large X-ray scattering data sets: applications of the new package to small-angle X-ray scattering and grazing-incidence small-angle X-ray scattering.

J Appl Crystallogr 2014 Oct 30;47(Pt 5):1797-1803. Epub 2014 Sep 30.

Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, Potsdam, Brandenbug 14476, Germany.

X-ray scattering experiments at synchrotron sources are characterized by large and constantly increasing amounts of data. The great number of files generated during a synchrotron experiment is often a limiting factor in the analysis of the data, since appropriate software is rarely available to perform fast and tailored data processing. Furthermore, it is often necessary to perform online data reduction and analysis during the experiment in order to interactively optimize experimental design. This article presents an open-source software package developed to process large amounts of data from synchrotron scattering experiments. These data reduction processes involve calibration and correction of raw data, one- or two-dimensional integration, as well as fitting and further analysis of the data, including the extraction of certain parameters. The software, (directly programmable data analysis kit), is based on a plug-in structure and allows individual extension in accordance with the requirements of the user. The article demonstrates the use of for on- and offline analysis of scanning small-angle X-ray scattering (SAXS) data on biological samples and microfluidic systems, as well as for a comprehensive analysis of grazing-incidence SAXS data. In addition to a comparison with existing software packages, the structure of and the possibilities and limitations are discussed.
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http://dx.doi.org/10.1107/S1600576714019773DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4180741PMC
October 2014

Adsorption of n-pentane on mesoporous silica and adsorbent deformation.

Langmuir 2013 Jul 26;29(27):8601-8. Epub 2013 Jun 26.

Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey 08544, USA.

Development of quantitative theory of adsorption-induced deformation is important, e.g., for enhanced coalbed methane recovery by CO2 injection. It is also promising for the interpretation of experimental measurements of elastic properties of porous solids. We study deformation of mesoporous silica by n-pentane adsorption. The shape of experimental strain isotherms for this system differs from the shape predicted by thermodynamic theory of adsorption-induced deformation. We show that this difference can be attributed to the difference of disjoining pressure isotherm, responsible for the solid-fluid interactions. We suggest the disjoining pressure isotherm suitable for n-pentane adsorption on silica and derive the parameters for this isotherm from experimental data of n-pentane adsorption on nonporous silica. We use this isotherm in the formalism of macroscopic theory of adsorption-induced deformation of mesoporous materials, thus extending this theory for the case of weak solid-fluid interactions. We employ the extended theory to calculate solvation pressure and strain isotherms for SBA-15 and MCM-41 silica and compare it with experimental data obtained from small-angle X-ray scattering. Theoretical predictions for MCM-41 are in good agreement with the experiment, but for SBA-15 they are only qualitative. This deviation suggests that the elastic modulus of SBA-15 may change during pore filling.
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http://dx.doi.org/10.1021/la401513nDOI Listing
July 2013

Infrared emitting and photoconducting colloidal silver chalcogenide nanocrystal quantum dots from a silylamide-promoted synthesis.

ACS Nano 2011 May 22;5(5):3758-65. Epub 2011 Apr 22.

Institute for Semiconductor and Solid State Physics, University Linz , Altenbergerstr. 69, Linz 4040, Austria.

Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region, making these materials promising as environmentally benign alternatives to established infrared active nanocrystals containing toxic metals such as Hg, Cd, and Pb. We present Ag(2)Se nanocrystals in detail, giving size-tunable luminescence with quantum yields above 1.7%. The luminescence, with a decay time on the order of 130 ns, was shown to improve due to the growth of a monolayer thick ZnSe shell. Photoconductivity with a quantum efficiency of 27% was achieved by blending the Ag(2)Se nanocrystals with a soluble fullerene derivative. The co-injection of lithium silylamide was found to be crucial to the synthesis of Ag chalcogenide nanocrystals, which drastically increased their nucleation rate even at relatively low growth temperatures. Because the same observation was made for the nucleation of Cd chalcogenide nanocrystals, we conclude that the addition of lithium silylamide might generally promote wet-chemical synthesis of metal chalcogenide nanocrystals, including in as-yet unexplored materials.
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http://dx.doi.org/10.1021/nn2001118DOI Listing
May 2011

Structural characterization of surfactant aggregates adsorbed in cylindrical silica nanopores.

Langmuir 2011 May 8;27(9):5252-63. Epub 2011 Apr 8.

Institute of Chemistry, Stranski Laboratory, Technical University Berlin, Strasse des 17. Juni 124, 10623 Berlin, Germany.

The self-assembly of nonionic surfactants in the cylindrical pores of SBA-15 silica with a pore diameter of 8 nm was studied by small-angle neutron scattering (SANS) at different solvent contrasts. The alkyl ethoxylate surfactants C(10)E(5) and C(12)E(5) exhibit strong aggregative adsorption in the pores as indicated by the sigmoidal shape of the adsorption isotherms. The SANS intensity profiles can be represented by a sum of two terms, one accounting for diffuse scattering from surfactant aggregates in the pores and the other for Bragg scattering from the pore lattice of the silica matrix. The Bragg reflections are analyzed with a form factor model in which the radial density profile of the surfactant in the pore is approximated by a two-step function. Diffuse scattering is represented by a Teubner-Strey-type scattering function which indicates a preferred distance between adsorbed surface aggregates in the pores. Our results suggest that adsorption starts with formation of discrete surface aggregates which increase in number and eventually merge to interconnected patches as the plateau value of the adsorption isotherm is approached. A grossly different behavior, viz. formation of micelles as in solution, is found for the maltoside surfactant C(10)G(2), in agreement with the observed weak adsorption of this surfactant in SBA-15.
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http://dx.doi.org/10.1021/la200333qDOI Listing
May 2011

Pore-lattice deformations in ordered mesoporous matrices: experimental studies and theoretical analysis.

Phys Chem Chem Phys 2010 Oct 29;12(37):11267-79. Epub 2010 Jul 29.

Stranski-Laboratorium für Physikalische und Theoretische Chemie, Fakultät für Mathematik und Naturwissenschaften, Technische Universität Berlin, Berlin, Germany.

The sorption of fluids in mesoporous silica is an important physical phenomenon with a wide range of applications. Traditionally, mesoporous materials have been considered as inert scaffolds for the sorption and condensation reaction of the fluid. Here we present in situ small angle X-ray diffraction experiments providing evidence for a sorption strain induced in the solid that manifests itself as a change in the lattice parameter of the ordered mesopore array as the pores gradually adsorb fluid material. The experimental data are analyzed by means of Monte Carlo simulations carried out in a grand canonical ensemble describing a fluid confined by deformable substrates. We show that-in agreement with experimental data-sorption of a nonpolar fluid causes the pores to expand initially, to shrink abruptly when capillary condensation sets in, and to expand again as more liquid-like fluid is adsorbed subsequently. We show that the pore pressure can be extracted from a thermodynamic analysis of sorption isotherms in the liquid-like regime and that this information can be used for an estimation of the Young's modulus of the porous silica material. In addition, our Monte Carlo simulations indicate that the phase behavior of confined fluids is considerably changed by the deformability of the confining solid. This is reflected by a change of the location of phase boundaries at sufficiently subcritical temperatures.
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http://dx.doi.org/10.1039/c000782jDOI Listing
October 2010

Fluid adsorption in ordered mesoporous solids determined by in situ small-angle X-ray scattering.

Phys Chem Chem Phys 2010 Jul 20;12(26):7211-20. Epub 2010 May 20.

Institute of Chemistry, Stranski Laboratory, Technical University Berlin, D-10623 Berlin, Germany.

The adsorption of two organic fluids (n-pentane and perfluoropentane) in a periodic mesoporous silica material (SBA-15) is investigated by in situ small-angle X-ray scattering (SAXS) using synchrotron radiation. Structural changes are monitored as the ordered and disordered pores in the silica matrix are gradually filled with the fluids. The experiments yield integrated peak intensities from up to ten Bragg reflections from the 2D hexagonal pore lattice, and additionally diffuse scattering contributions arising from disordered (mostly intrawall) porosity. The analysis of the scattering data is based on a separation of these two contributions. Bragg scattering is described by adopting a form factor model for ordered pores of cylindrical symmetry which accounts for the filling of the microporous corona, the formation of a fluid film at the pore walls, and condensation of the fluid in the core. The filling fraction of the disordered intrawall pores is extracted from the diffuse scattering intensity and its dependence on the fluid pressure is analyzed on the basis of a three-phase model. The data analysis introduced here provides an important generalisation of a formalism presented recently (J. Phys. Chem. C, 2009, 13, 15201), which was applicable to contrast-matching fluids only. In this way, the adsorption behaviour of fluids into ordered and disordered pores in periodic mesoporous materials can be analyzed quantitatively irrespective of the fluid density.
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http://dx.doi.org/10.1039/c001541pDOI Listing
July 2010

On the mineral in collagen of human crown dentine.

Biomaterials 2010 Jul 18;31(20):5479-90. Epub 2010 Apr 18.

Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany.

Dentine, the main material of mammalian teeth, contains mineral platelets that are embedded in a collagen fiber mesh. These particles entail stiffness and longevity, which is important for human teeth because these organs do not remodel. By means of small angle X-ray scattering, we mapped 2D and 3D variations in mineral particle characteristics in molar crowns. Our results show that the mean mineral-platelet thickness of 3.2 nm decreases to 2.6 nm within the shallow 300 microm beneath the dentin-enamel junction (DEJ), and that these platelets become still thinner albeit moderately in deep dentine surrounding the pulp. The mineral volume fraction in crown dentine is mostly 50% except for a 250 microm layer beneath the DEJ. Most of the mineral particles are randomly orientated, with about 20% having a preferred orientation that is parallel to the plane of the DEJ. Beneath the cusps and close to the margins of enamel, higher co-alignment is found: 40% of the particles reveal orientations that match expected load trajectories that are imposed on teeth during mastication in the general cusp-root direction. This suggests that variations in mineral platelet arrangements help to locally tune dentine anisotropy and stiffness. The serendipitous finding of incipient caries suggests that at least in early stages of pathological destruction, mineral particle thickness and orientation resemble those of the intact tissue.
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http://dx.doi.org/10.1016/j.biomaterials.2010.03.030DOI Listing
July 2010

Mapping amorphous calcium phosphate transformation into crystalline mineral from the cell to the bone in zebrafish fin rays.

Proc Natl Acad Sci U S A 2010 Apr 22;107(14):6316-21. Epub 2010 Mar 22.

Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel.

The continuously forming fin bony rays of zebrafish represent a simple bone model system in which mineralization is temporally and spatially resolved. The mineralized collagen fibrils of the fin bones are identical in structure to those found in all known bone materials. We study the continuous mineralization process within the tissue by using synchrotron microbeam x-ray diffraction and small-angle scattering, combined with cryo-scanning electron microscopy. The former provides information on the mineral phase and the mineral particles size and shape, whereas the latter allows high-resolution imaging of native hydrated tissues. The integration of the two techniques demonstrates that new mineral is delivered and deposited as packages of amorphous calcium phosphate nanospheres, which transform into platelets of crystalline apatite within the collagen matrix.
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http://dx.doi.org/10.1073/pnas.0914218107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851957PMC
April 2010

Strontium is incorporated into mineral crystals only in newly formed bone during strontium ranelate treatment.

J Bone Miner Res 2010 May;25(5):968-75

Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, Research Campus Golm, Potsdam, Germany.

Strontium ranelate has been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk. The aim of this study was to investigate the potential influence of strontium ranelate (Protelos) treatment on human bone tissue characteristics and quality at the micro- and nanostructural levels. We investigated transiliac biopsies from patients treated for 36 months with strontium ranelate or placebo (n = 5 per group) using synchrotron radiation with a microbeam combining scanning small-angle scattering, X-ray diffraction, and fluorescence spectroscopy (SAXS/XRD/XRF) for a detailed characterization of the mineral crystals within the collagenous bone matrix. A scanning procedure allowed the simultaneous determination of maps of the chemical composition together with thickness, length, and lattice spacing of these mineral crystals within each of the 15- or 25-microm-wide pixels in a thin bone section. The fluorescence results show that only bone packets or osteons formed during the strontium ranelate treatment contain significant amounts of strontium and that up to 0.5 of 10 calcium atoms in the mineral crystals are replaced by strontium, as revealed by a corresponding shift in apatite lattice spacing. The thickness and length of the plate-shaped bone mineral crystals were not affected by the strontium ranelate treatment. As a consequence, there was no indication for a change in human bone tissue quality at the nanoscale after a 36-month treatment of postmenopausal osteoporotic women with strontium ranelate, except for a partial replacement of calcium by strontium ions in the hydroxyapatite crystals, only in newly formed bone.
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http://dx.doi.org/10.1359/jbmr.091038DOI Listing
May 2010

The two plastidial starch-related dikinases sequentially phosphorylate glucosyl residues at the surface of both the A- and B-type allomorphs of crystallized maltodextrins but the mode of action differs.

Plant Physiol 2009 Jun 24;150(2):962-76. Epub 2009 Apr 24.

Institute of Biochemistry and Biology, Department of Plant Physiology, University of Potsdam, 14476 Potsdam-Golm, Germany.

In this study, two crystallized maltodextrins were generated that consist of the same oligoglucan pattern but differ strikingly in the physical order of double helices. As revealed by x-ray diffraction, they represent the highly ordered A- and B-type allomorphs. Both crystallized maltodextrins were similar in size distribution and birefringence. They were used as model substrates to study the consecutive action of the two starch-related dikinases, the glucan, water dikinase and the phosphoglucan, water dikinase. The glucan, water dikinase and the phosphoglucan, water dikinase selectively esterify glucosyl residues in the C6 and C3 positions, respectively. Recombinant glucan, water dikinase phosphorylated both allomorphs with similar rates and caused complete glucan solubilization. Soluble neutral maltodextrins inhibited the glucan, water dikinase-mediated phosphorylation of crystalline particles. Recombinant phosphoglucan, water dikinase phosphorylated both the A- and B-type allomorphs only following a prephosphorylation by the glucan, water dikinase, and the activity increased with the extent of prephosphorylation. The action of the phosphoglucan, water dikinase on the prephosphorylated A- and B-type allomorphs differed. When acting on the B-type allomorph, by far more phosphoglucans were solubilized as compared with the A type. However, with both allomorphs, the phosphoglucan, water dikinase formed significant amounts of monophosphorylated phosphoglucans. Thus, the enzyme is capable of acting on neutral maltodextrins. It is concluded that the actual carbohydrate substrate of the phosphoglucan, water dikinase is defined by physical rather than by chemical parameters. A model is proposed that explains, at the molecular level, the consecutive action of the two starch-related dikinases.
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http://dx.doi.org/10.1104/pp.109.138750DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689988PMC
June 2009

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution.

Proc Natl Acad Sci U S A 2009 Apr 30;106(15):6048-53. Epub 2009 Mar 30.

Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel.

The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools.
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http://dx.doi.org/10.1073/pnas.0810300106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662956PMC
April 2009

Novel insights into nanopore deformation caused by capillary condensation.

Phys Rev Lett 2008 Aug 22;101(8):086104. Epub 2008 Aug 22.

Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Strasse des 17. Juni 135, 10623 Berlin.

By means of in situ small-angle x-ray diffraction experiments and semi-grand-canonical ensemble Monte Carlo simulations we demonstrate that sorption and condensation of a fluid confined within nanopores is capable of deforming the pore walls. At low pressures the pore is widened due to a repulsive interaction caused by collisions of the fluid molecules with the walls. At capillary condensation the pores contract abruptly on account of attractive fluid-wall interactions whereas for larger pressures they expand again. These features cannot solely be accounted for by effects related to pore-wall curvature but have to be attributed to fluid-wall dispersion forces instead.
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http://dx.doi.org/10.1103/PhysRevLett.101.086104DOI Listing
August 2008