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Small-angle scattering (SAS) has long been used to study nucleation and growth of particles in solid or liquid matrices. In some special cases, nucleation of particles occurs on interfaces, e. g., grain boundaries in crystalline solids or membranes in a solvent. Clearly, the position of the particles is constrained in this case to a narrow region close to the interface, which leads to correlations between the particles. In the present paper, we derive simple expressions for the analysis of SAS data from particles located on planar interfaces, and compare the analytical approximations with computer simulations.

Small-angle scattering (SAS) has long been used to study nucleation and growth of particles in solid or liquid matrices. In some special cases, nucleation of particles occurs on interfaces, e. g., grain boundaries in crystalline solids or membranes in a solvent. Clearly, the position of the particles is constrained in this case to a narrow region close to the interface, which leads to correlations between the particles. In the present paper, we derive simple expressions for the analysis of SAS data from particles located on planar interfaces, and compare the analytical approximations with computer simulations.

Deformation of superhydrophobic cylindrical mesopores is studied during a cycle of forced water filling and spontaneous drying by in situ small-angle neutron scattering. A high-pressure setup is put forward to characterize the deformation of ordered mesoporous silanized silica up to 80 MPa. Strain isotherms of individual pores are deduced from the shift of the Bragg spectrum associated with the deformation of the hexagonal pore lattice. Due to their superhydrophobic nature, pore walls are not covered with a prewetting film. This peculiarity gives the ability to use a simple mechanical model to describe both filled and empty pore states without the pitfall of disjoining pressure effects. By fitting our experimental data with this model, we measure both the Young’s modulus and the Poisson ratio of the nanometric silica wall. The measurement of this latter parameter constitutes a specificity offered by superhydrophobic nanopores with respect to hydrophilic ones.

Small-angle scattering (SAS) has long been used to study nucleation and growth of particles in solid or liquid matrices. In some special cases, nucleation of particles occurs on interfaces, e.g., grain boundaries in crystalline solids or membranes in a solvent. Clearly, the position of the particles is constrained in this case to a narrow region close to the interface, which leads to correlations between the particles. In the present paper, we derive simple expressions for the analysis of SAS data from particles located on planar interfaces, and compare the analytical approximations with computer simulations.

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.

One of the most fascinating topics currently being discussed in the field of biomineralization is the occlusion of organic macromolecules within mineral crystals. It is already known that intracrystalline organic inclusions in biogenic calcite improve the fracture behavior and anisotropically distort the calcite lattice. However, the detailed structure of the crystals and the underlying processes leading to the incorporation of the organic molecules are poorly understood. In this work, we investigate calcite prisms extracted from the shell of Pinna nobilisby means of three-dimensional synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS). Organic–inorganic interfaces within the single crystals give rise to a strong, anisotropic SAXS signal. The results are shown as a stereographic projection of the integrated SAXS intensity (gray scale) together with the wide-angle spots (colored) of different calcite lattice planes. A comparison of native (left) and annealed (right) prisms, where the contrast for the latter is enhanced due to the removal of organics, shows a preferential orientation along the highly charged (001) lattice planes, which strongly interact with negatively charged aspartate groups of intracrystalline proteins. Our findings on the nanostructure help to understand how biogenic calcite crystals achieve their remarkable properties and thereby open up ways for the development of bioinspired hybrid materials.

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.

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 H2O/D2O 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.

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 N2adsorption 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.

The efficient storage of energy combined with a minimum carbon footprint is still considered one of the major challenges towards the transition to a progressive, sustainable and environmental friendly society on a global scale. The energy storage in pure chemical form using gas carriers with high heating values, including H2and CH4, as well as via electrochemical means using state-of-the-art devices, such as batteries or supercapacitors, are two of the most attractive alternatives for the combustion of finite, carbon-rich and environmentally harmful fossil fuels, such as diesel and gasoline. A few-step, reproducible and scalable method is presented in this study for the preparation of an ultra-microporous (average pore size around 0.6nm) activated carbon cloth (ACC) with large specific area (> 1200m2/g) and pore volume (~ 0.5cm3/g) upon combining chemical impregnation, carbonization and CO2activation of a low-cost cellulose-based polymeric fabric. The ACC material shows a versatile character towards three different applications, including H2storage via cryo-adsorption, separation of energy-dense CO2/CH4mixtures via selective adsorption and electrochemical energy storage using supercapacitor technology. Fully reversible H2uptake capacities in excess of 3.1wt% at 77K and ~ 72bar along with a significant heat of adsorption value of up to 8.4kJ/mol for low surface coverage have been found. Upon incorporation of low-pressure sorption data in the ideal adsorbed solution theory model, the ACC is predicted to selectively adsorb about 4.5 times more CO2than CH4in ambient conditions and thus represents an appealing adsorbent for the purification of such gaseous mixtures. Finally, an electric double-layer capacitor device was assembled and tested for its electrochemical performance, constructed of binder-free and flexible ACC electrodes and aqueous CsCl electrolyte. The full-cell exhibits a gravimetric capacitance of ~ 121F/g for a specific current of 0.02A/g, which relative to the ACC's specific area, is superior to commercially available activated carbons. A capacitance retention of more than 97% was observed after 10,000 charging/discharging cycles, thus indicating the ACC's suitability for demanding and high-performance energy storage on a commercial scale. The enhanced performance in all tested applications seems to be attributed to the mean ultra-micropore size of the ACC material instead of the available specific area and/or pore volume.

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.

Experimental results on sorption-induced deformation during n-pentane desorption were obtained by in-situ dilatometry and in-situ small angle X-ray scattering (SAXS). The sample investigated was a silica-based monolith with hierarchical pore structure comprising a macroporous network of struts, each strut containing well-defined cylindrical mesopores ordered on a 2D hexagonal lattice. In-situ dilatometry and in-situ SAXS measurements revealed strain isotherms of similar shape, which are qualitatively in good agreement with recent theoretical predictions. From the relative pressure range of the liquid filled mesopores a pore load modulus of 1.5 GPa is determined. The relative pressure region of mono- and multilayer formation, however, reveals differences between the two independent methods. In particular, the net strain at saturation pressure is considerably larger for in-situ dilatometry. We attribute this observation to the different sensitivity of the two methods to anisotropic deformation in the hierarchical solid framework. While in-situ SAXS measures the mesopore lattice strain and is therefore exclusively sensitive to radial deformation of the struts, dilatometry measures the linear deformation of the isotropic macroscopic sample, being sensitive to the volumetric strain of the whole network.

The pore characteristics and the mechanical properties of silica samples templated by wood were investigated. The wood samples had been either solely extracted with solvent, delignified or delignified and functionalized with maleic acid anhydride prior to infiltration with tetraethyl orthosilicate and subsequent calcination. All three samples show similar mesopore characteristics, while the one based on maleic acid anhydride functionalized wood exhibited also a large volume of micropores. These micropores are only partly accessible as shown by a combination of in situsmall angle x-ray scattering and sorption experiments with n-pentane. Nanoindentation experiments reveal that the presence of the micropores decreases the indentation hardness of the material, while the reduced elastic modulus is similar for all three samples when taking mesoporosity properly into account. In addition, the micropores enhance the ductility index of the material. The microporosity introduced by this biotemplating approach proves to be advantageous for increasing the toughness of silica, as the material can dissipate more energy by irreversible collapse of the pores.

The mechanical response of two ordered mesoporous silica films on silicon substrates was investigated by in situgrazing-incidence small-angle X-ray scattering during change of relative humidity. Films were prepared by using well known approaches of evaporation-induced self-assembly (EISA) of block-copolymer templated silica precursor sols. A thick film (≈500 nm) was prepared by dip coating and a thin film (≈100 nm) was prepared by spin coating. Both films exhibited a distorted 2D-hexagonal arrangement of cylindrical mesopores. While for the thin film these pores were highly oriented within the film plane, the thick film was much more disordered with respect to the in-plane orientation. The evaluation of the pore lattice strain as a consequence of changing relative humidity reveals a similar magnitude of deformation and similar elastic properties in the out-of-plane direction for the two samples. However, the in-plane strains are completely different. While the thin film is essentially unstrained within the plane of the film as expected for a thin film on a rigid substrate, there seems to be a considerable in-plane strain for the thick film. This result underlines the importance of film thickness and film quality when aiming at using such systems for bioinspired bilayer actuators.

Biominerals are complex inorganic‐organic structures that often show excellent mechanical properties. Here a bio‐inspired study of a remarkably simple synthetic system is presented in which only one charged polymer additive (poly(sodium 4‐styrenesulfonate)) is able to induce hierarchical structuring of calcite similar to biominerals. The interaction of the negatively charged polymer with the nucleation and growth of the mineral, in particular via selective adsorption to internal and external (001) facets of the calcite lattice, implies structural features from the micrometer down to the nanometer level. The crystals exhibit a distinct rounded morphology and a controlled orientation. Moreover, the polymer molecules are occluded within the crystals with different concentrations in well‐defined regions. This leads to the induction of a mesoscale structure based on 100 nm sized mineral building blocks with granular substructure and rough surface, as well as small modifications of the crystallographic structure. Such a combination of hierarchically organized structural features has previously only been reported for biogenic calcite, which is typically grown in a complex process involving multiple organic additives. It is also shown that the organic occlusions in the calcite‐PSS hybrid crystals strongly affect the mechanical performance, as known for some biominerals.

In this work, the three-dimensional (3D) structure and replication of pomelo (Citrus maxima) peel as silica on several hierarchical levels is reported. The native peel as well as mineralized and calcined replica were assessed by their dimensional changes and their structures investigated by scanning electron microscopy. Computed x-ray microtomography yielded a detailed 3D model of the gradient foam structure, demonstrating the true replication of the entire structure on the millimeter and micrometer scales. SAXS evidenced the replication of the single cellulose fibrils on the nanometer scale. This work therefore demonstrates the possibility of transforming complex low-density polysaccharide templates into silica with nanometer precision, yielding inorganic, temperature-resistant gradient foam structures.

Many biological materials and in particular biomineralized tissues exhibit structural and compositional gradients at several length scales. Nanostructural features varying at the micrometer scale can be imaged by employing synchrotron radiation based small‐ and wide‐angle X‐ray scattering combined with microbeam scanning. In particular, the lattice distortions caused by a substituted atoms within a crystal structure can be mapped by evaluating the corresponding shifts of Bragg reflections. As we demonstrate here by reviewing three examples of mineralized biological tissues, this approach delivers valuable complementary information to chemical imaging (e.g., X‐ray fluorescence imaging). Specifically, we show that strontium is incorporated in the hydroxyapatite crystal structure of human bone after osteoporosis treatment with Sr ranelate. Moreover, we discuss how local magnesium gradients within two different calcite phases in the tip of the sea urchin tooth may relate to the excellent mechanical properties and the self sharpening ability of this exceptional grinding tool. Finally, we show how this method allows drawing conclusions about the stability of the amorphous calcium carbonate in the cuticle of the American Lobster by determining the magnesium concentration after crystallization induced by an in situ heat treatment.

Abstract

Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag2Se, Ag2Te, and Ag2S) 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 Ag2Se 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 Ag2Se 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.

Ordered and disordered pores in SBA-15 silica and the gradual filling of these pores by an adsorbed fluid (dibromomethane, CH2Br2) are investigated by in situsmall-angle X-ray scattering. Adsorption into the microporous corona and film formation at the corrugated surface of the ordered cylindrical pores is described by two different geometrical models. The analytical form factor resulting from these models is used to fit the integrated intensities of up to 10 Bragg diffraction peaks from the mesopore lattice. Model fits for the evacuated sample yield the porosity caused by the ordered pores. From these results and the total porosity obtained by nitrogen sorption, we determine the contribution of the disordered porosity, which is nearly 20% for the present sample. The model fits also provide new insight into the adsorbate structure in the ordered pores at different stages of pore filling, while the analysis of diffuse scattering provides information about fluid adsorption in the disordered pores in the walls. It is shown that the filling of the wall porosity affects the evaluation of the adsorbed amount in the ordered pores and leads to a distinction between relative and absolute adsorbed amounts. Using absolute adsorbed amounts, the filling isotherm of the ordered pores and the overall pore filling isotherm can be derived and compared with direct adsorption measurements. On the basis of the results of the present study, a quantitative modeling of the pore morphology and fluid sorption in the ordered and disordered pore regions of SBA-15 is presented in a subsequent paper (part II, DOI 10.1021/jp810040k).

The nanostructure of SBA-15 ordered mesoporous silica is modeled by considering a full crystallite about 500 nm in size. The lattice sites of a 2D hexagonal lattice are occupied by circular mesopores that exhibit a size distribution and a rough pore wall. In addition, the walls of the ordered pores contain randomly distributed disordered pores. This model is introduced to quantitatively reproduce the experimental X-ray scattering profile from an evacuated SBA-15 sample considering both Bragg diffraction from the ordered pore lattice and the diffuse small-angle scattering from the disordered pores. In contrast to a previous form factor model which analyzed the Bragg diffraction peaks only, the present model reproduces correctly the total porosity of the material in good agreement with nitrogen sorption. The adsorption behavior of the model crystallite is studied by introducing simple filling rules for the ordered and the disordered porosity. The filling of the disordered pores as well as film formation and capillary condensation in the ordered pores are reproduced by the model. Good agreement between the calculated and measured scattering profiles along the adsorption isotherm of a contrast-matching fluid is found. In particular, the change of the integral diffuse scattering intensity with increasing vapor pressure of the fluid is quantitatively reproduced by the model. The integrated intensities from the Bragg reflections show however some quantitative discrepancies. Comparing the density profiles derived from the present lattice model with the one obtained from direct form factor fitting of the experimental data, we conclude that the experimental system is also subjected to fluctuations of the fluid density on the pore walls.

The exoskeleton of the American lobster Homarus americanusis a hierarchical nanocomposite consisting of chitin–protein fibers, reinforced with amorphous calcium carbonate (ACC) and a small amount of crystalline calcite. Crystallographic pole‐figure analysis reveals two texture components of the crystalline α‐chitin in the exoskeleton. One component represents the well‐known twisted plywood structure of chitin–protein fibers within the cuticle plane, and the second component represents fibers oriented roughly perpendicular to the cuticle surface. These perpendicular fibers interpenetrate the open canals of the planar honeycomblike structure originating from the well‐developed pore‐canal system present in this material. The calcite crystallites reveal fiber texture with the crystallographic c‐axis oriented perpendicular to the cuticle surface, suggesting an orientation relationship between calcite and the organic chitin–protein fibers. Local orientation analysis using X‐ray microdiffraction reveals that the crystalline calcium carbonate fraction is associated with the chitin–protein fibers oriented perpendicular to the surface. Calcite is exclusively found in the exocuticle and is mostly restricted to a thin layer in the outermost region, while the major part of the exocuticle and the whole endocuticle contain ACC exclusively. It is therefore speculated that the most likely function of calcite in the exoskeleton of the American lobster is related to impact‐ and wear‐resistance.