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Understanding and controlling nucleation is important for many crystallization applications. Calcium carbonate (CaCO3) is often used as a model system to investigate nucleation mechanisms. Despite its great importance in geology, biology, and many industrial applications, CaCO3 nucleation is still a topic of intense discussion, with new pathways for its growth from ions in solution proposed in recent years. These new pathways include the so-called nonclassical nucleation mechanism via the assembly of thermodynamically stable prenucleation clusters, as well as the formation of a dense liquid precursor phase via liquid-liquid phase separation. Here, we present results from a combined experimental and computational investigation on the precipitation of CaCO3 in dilute aqueous solutions. We propose that a dense liquid phase (containing 4-7 H2O per CaCO3 unit) forms in supersaturated solutions through the association of ions and ion pairs without significant participation of larger ion clusters. This liquid acts as the precursor for the formation of solid CaCO3 in the form of vaterite, which grows via a net transfer of ions from solution according to z Ca2+ + z CO32- → z CaCO3. The results show that all steps in this process can be explained according to classical concepts of crystal nucleation and growth, and that long-standing physical concepts of nucleation can describe multistep, multiphase growth mechanisms. [ABSTRACT FROM AUTHOR]

Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17 kDa and hydrophilic weight fractions of ≤0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460 nm. Significantly, altering the block copolymer hydrophilic-hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19 nm. [ABSTRACT FROM AUTHOR]

Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17 kDa and hydrophilic weight fractions of ≤0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460 nm. Significantly, altering the block copolymer hydrophilic-hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19 nm. [ABSTRACT FROM AUTHOR]

The phase behavior of block copolymer based supramolecular complexes polystyrene- block-poly(4-vinylpyridine) (PS- b-P4VP) and amphiphilic pentadecylphenol (PDP) molecules resembles the phase behavior of conventional block copolymers. Several PS- b-P4VP(PDP) complexes are found to self-assemble into gyroid nanostructures. Typically, the grains are randomly oriented with a maximal size of several micrometers. Here, the orientation of a gyroid PS- b-P4VP(PDP) complex upon shearing is reported. It is found that the (111) gyroid lattice direction orients parallel to the shear direction after only several seconds of large amplitude oscillatory shearing. Oriented gyroid complexes can be used as templates for the preparation of metal nanofoams with improved ordering with potentially superior properties. [ABSTRACT FROM AUTHOR]

Abstract: Electron tomography is a unique technique for imaging the microstructure of materials with a nanometer resolution. The signal-to-noise ratio of electron tomograms is, however, often too low for a reliable segmentation-based image analysis. We derive a general relation between the grey-tone correlation function of the tomograms and the 2-point correlation function of the morphology, which enables us to analyse quantitatively the grey-tone correlation function with a morphological model of the material. The methodology is applied to SBA-15 ordered mesoporous silica. The three-dimensional grey-tone correlation function obtained from electron tomography is analysed in terms of a hexagonal array of Gaussian independent pores. The model enables us to relate the morphology obtained from the 2-point correlation function to macroscopic characterization data of the material, notably small-angle X-ray scattering and nitrogen adsorption. [Copyright &y& Elsevier]

Binary nanocrystal superlattices, that is, ordered structures of two sorts of nanocolloids, hold promise for a series of functional materials with novel collective properties. Here we show that based on electron tomography a comprehensive, quantitative, three-dimensional characterization of these systems down to the single nanocrystal level can be achieved, which is key in understanding the emerging materials properties. On four binary lattices composed of PbSe, CdSe, and Au nanocrystals, we illustrate that ambiguous interpretations based on two-dimensional transmission electron microscopy can be prevented, nanocrystal sizes and superlattice parameters accurately determined, individual crystallographic point and plane defects studied, and the order/disorder at the top and bottom surfaces imaged. Furthermore, our results suggest that superlattice nucleation and growth occurred at the suspension/air interface and that the unit cells of some lattices are anisotropically deformed upon drying. [ABSTRACT FROM AUTHOR]

The article discusses the research about electron tomography for heterogeneous catalyst and nanostructure materials. The study highlights the importance of electron tomography (TM) in the field of catalysis and notes that knowledge in using the three-dimensional (3D) morphology significantly aids when studying about hierarchical materials such as mesoporous zeolites. It stresses that using image can be consider when obtaining unbiased quantitative information from the study.

Abstract: An explanation is put forward for the beneficial effect of thermal decomposition of supported Ni3(NO3)2(OH)4 in NO/He flow (0.1–1 vol%) that enables preparation of well-dispersed (3–5 nm particles) 24 wt% Ni-catalysts via impregnation and drying using aqueous [Ni(OH2)6](NO3)2 precursor solution. Moreover, combining electron tomography, XRD and N2-physisorption with SBA-15 support yielded a clear picture of the impact of air, He and NO/He gas atmospheres on NiO shape and distribution. TGA/MS indicated that NO2, N2O, H2O products evolved more gradually in NO/He. In situ XRD and DSC revealed that NO lowers the nitrate decomposition rate and appears less endothermic than in air supposedly due to exothermic scavenging of oxygen by NO, which is supported by MS results. The Ni/SiO2 catalyst prepared via the NO-method displayed a higher activity in the hydrogenation of soybean oil as the required hydrogenation time decreased by 30% compared to the traditionally air calcined catalyst. [Copyright &y& Elsevier]

Postsynthesis ammonium treatment induces a substantial increase in the catalytic activity of Au/Ti-SBA-15 catalysts for the direct vapor-phase epoxidation of propylene using hydrogen and oxygen. The PO formation rate of a calcined Au/Ti-SBA-15 catalyst prepared by this method increased from 4.3 mgPO h−1 g−1 cat to 37.2 mgPO h−1 g−1 cat at 200 °C compared with a catalyst prepared in an identical manner without this treatment. The catalysts were characterized by XRD, N2-sorption, UV–vis–NIR DRS, 29Si MAS NMR, FT-IR spectroscopy, and TEM to gain insight into the relationship between ammonia treatment and catalyst activity. 29Si MAS NMR measurements proved that the ammonium nitrate solution caused hydrolysis of ph name="sbnd" />Oph name="tbnd" /> or ph name="sbnd" />Oph name="tbnd" /> bonds, resulting in a Ti-SBA-15 surface with a greater amount of surface hydroxyl groups. FT-IR measurements indicated the presence of amine species that favor the homogeneous deposition of Au nanoparticles. This was confirmed by TEM measurements showing greater metal dispersion for NH4NO3-treated Au/Ti-SBA-15 materials. [Copyright &y& Elsevier]

Abstract: Increased computer speed has helped to proliferate tomography throughout the geosciences. Although best known from the medical CATscan, tomography is also a powerful tool for geological problems. Whereas qualitative tomography is widely used, quantitative data from tomograms are not so commonly available. Presented here are two programs, Electron Tomography Segmentation, surface Area, and Volume (ETSAV) and Electron Tomography CUTter (ETCut), that were written to obtain quantitative volume and surface-area data from tomograms. Based on a specified threshold value, ETSAV distinguishes objects within a tomogram and then returns volume and surface-area data for each object. If object separation is unsatisfactory using a single threshold, ETCut is called to digitally separate objects that appear connected in the tomogram, allowing ETSAV to perform its functions. By knowing the nature of the object of interest, error can be corrected to, on average, less than 5% for a single object; combined volumes of many particles of different sizes may result in lesser errors. A section of the Brenham pallasite meteorite was examined using the programs. Olivine comprises 67.2% of the volume (50.4%wt%), followed by FeNi metal at 23.1% (39.3%wt%), troilite at 4.4% (4.8%wt%), and schreibersite at 3.4% (5.5%wt%). In all, 56.1% and 44.7% of the troilite and schreibersite surface areas, respectively, border olivine, suggesting that they wet olivine. Since the programs can be applied to any tomogram, from any field, there are many potential applications. [Copyright &y& Elsevier]

By the combination of electron tomography with image segmentation, the properties of 299 NiO crystallites contained in 6 SBA-15 pores were studied. A statistical analysis of the particle size showed that crystallites between 2 and 6 nm were present with a distribution maximum at 3 and 4 nm, for the number-weighted and volume-weighted curves, respectively. Interparticle distances between nearest neighbors were 1-3 nm with very few isolated crystallites. In the examined pores, a local loading twice the applied average of 24 wt % NiO was found. This suggests that a very high local loading combined with a high dispersion is achievable. [ABSTRACT FROM AUTHOR]

Collagen type I, the main component of the extracellular matrix in vertebrates, is widely used in tissue engineering applications. This is on account that collagen molecules can self‐assemble under certain conditions into 3D fibrillar hydrogels. Although there is an extensive body of literature studying collagen self‐assembly, there is a lack of systematic understanding on how different experimental factors, such as pH and temperature, and their cumulative effects guide the self‐assembly process. In this work, a comprehensive workflow to study the interactive effects of several assembly parameters on the collagen self‐assembly process is implemented. This workflow consists of: 1) efficient statistical sampling based on Design of Experiments, 2) high‐throughput and automated data collection and 3) automated data analysis. This approach enables to screen several parameters simultaneously and derive a set of mathematical equations that link parameters with the kinetics and morphological aspects of collagen self‐assembly, and can be used to design collagen constructs with predefined characteristics. [ABSTRACT FROM AUTHOR]

In a recent letter to the editor Prof Khosravi-Darani responded to our paper ''Unravelling mechanisms of protein and lipid oxidation in mayonnaise at multiple length scales". In our work, we observed liposomes in the continuous phase of mayonnaise. In the letter the objection was made that liposomes cannot be formed in a non-aqueous phase which, however, was not argued in our publication. As mayonnaise is an oil-in-water (O/W) emulsion and its continuous phase is aqueous, liposomes may be observed in this phase. Therefore, the objection from Prof Khosravi-Darani does not apply to our work. [ABSTRACT FROM AUTHOR]

The mineralization of collagen in vitro has been extensively investigated for hydroxyapatite, silica, calcium carbonate and lepidocrocite (γ-FeOOH). Henceforth, it is interesting to investigate whether collagen also could serve as a generic mineralization template for other minerals, like magnetite. To this end, and inspired by the partial oxidation approach, first a ferrous hydroxide (Fe(OH)2) intermediate is synthesized via the titration of base to a solution of Fe2+. Subsequently, the Fe(OH)2 is mixed with collagen fibrils and poly(aspartic acid) is added to promote the formation of intrafibrillar crystals. Platelet-shaped lepidocrocite crystals being present throughout the entire thickness of the collagen fibrils can be realized, as was confirmed with electron tomography. The formation of lepidocrocite, which is an Fe3+ compound, is hypothesized to be induced via oxidation of the Fe2+ species and, therefore, the oxygen concentration during titration, TEM sample preparation and drying of TEM samples are investigated. Although the reaction is sensitive to small changes in experimental conditions, highly mineralized collagen fibers can be realized. [ABSTRACT FROM AUTHOR]

Hexamethylenetetramine (HMTA) is commonly used as a base releasing agent for the synthesis of ZnO under mild aqueous conditions. HMTA hydrolysis leads to gradual formation of a base during the reaction. Use of HMTA, however, does have limitations: HMTA hydrolysis yields both formaldehyde and ammonia, it provides no direct control over the ammonia addition rate or the total amount of ammonia added during the reaction, it results in a limited applicable pH range and it dictates the accessible reaction temperatures. To overcome these restrictions, this work presents a direct base titration strategy for ZnO synthesis in which a continuous base addition rate is maintained. Using this highly flexible strategy, wurtzite ZnO can be synthesized at a pH >5.5 using either KOH or ammonia as a base source at various addition rates and reaction pH values. In situ pH measurements suggest a similar reaction mechanism to HMTA-based synthesis, independent of the varied conditions. The type and concentration of the base used for titration affect the reaction product, with ammonia showing evidence of capping behaviour. Optimizing this strategy, we are able to influence and direct the crystal shape and significantly increase the product yield to 74% compared to the ∼13% obtained by the reference HMTA reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] The shelf life of multiphase systems, e.g. oil-in-water (O/W) emulsions, is severely limited by physical and/or chemical instabilities, which degrade their texture, macroscopic appearance, sensory and (for edible systems) nutritional quality. One prominent chemical instability is lipid oxidation, which is notoriously complex. The complexity arises from the involvement of many physical structures present at several scales (1–10,000 nm), of which the smallest ones are often overlooked during characterization. We used cryogenic transmission electron microscopy (cryo-TEM) to characterize the coexisting colloidal structures at the nanoscale (10–200 nm) in rapeseed oil-based model emulsions stabilized by different concentrations of a nonionic surfactant. We assessed whether the oxidative and physical instabilities of the smallest colloidal structures in such emulsions may be different from those of larger colloidal structures. By deploying cryo-TEM, we analyzed the size of very small oil droplets and of surfactant micelles, which are typically overlooked by dynamic light scattering when larger structures are concomitantly present. Their size and oil content were shown to be stable over incubation, but lipid oxidation products were overrepresented in these very small droplets. These insights highlight the importance of the fraction of "tiny droplets" for the oxidative stability of O/W emulsions. [ABSTRACT FROM AUTHOR]

The cover page of the journal "Angewandte Chemie International Edition" is presented.

By using wet-chemical methods, cubic, tetrahedral, and randomly shaped Rh nanoparticles (NPs) with different surface terminations were synthesized and subsequently deposited on ZrO2 supports. To guide the NP shape, three capping agents were used during the synthesis: polyvinylpyrrolidone (PVP), trimethyl(tetradecyl)ammonium bromide (TTAB), and oleylamine (OAm). TTAB and PVP could not be completely removed from the final catalyst, leaving a capping residue as confirmed by X-ray photoelectron spectroscopy (XPS). In contrast, OAm could be fully removed. The influence of the NP shape and the influence of the capping agents were evaluated under CO hydrogenation conditions. Both the PVP and TTAB residues blocked parts of the Rh surface and dominated catalytic activity beyond the effects from NP shape and surface termination. OAm could be successfully removed. The extent of metal surface blocking by the capping residue, probed by chemisorption, is larger than the observed reduction in CO hydrogenation activity. This suggests that a majority of less-active sites are being blocked by the capping residue and that successful removal of the residue from the most active sites is possible. [ABSTRACT FROM AUTHOR]

• LDL particles engage in multi-scale aggregation in the continuous phase of mayonnaise. • Micronscale localisation of protein free radicals with a fluorescent spintrap. • Local protein oxidation induced by local lipid oxidation • At the droplet interface dispersed proteins undergo lipid-radical induced oxidation. • Protein oxidation also occurs in LDL particles in the continuous phase. In mayonnaise, lipid and protein oxidation are closely related and the interplay between them is critical for understanding the chemical shelf-life stability of mayonnaise. This is in particular the case for comprehending the role of low-density lipoprotein (LDL) particles acting as a main emulsifier. Here, we monitored oxidation and the concomitant aggregation of LDLs by bright-field light microscopy and cryogenic transmission electron microscopy. We further probed the formation of protein radicals and protein oxidation by imaging the accumulation of a water-soluble fluorescent spin trap and protein autofluorescence. The effect of variation of pH and addition of EDTA on the accumulation of the spin trap validated that protein radicals were induced by lipid radicals. Our data suggests two main pathways of oxidative protein radical formation in LDL particles: (1) at the droplet interface, induced by lipid free radicals formed in oil droplets, and (2) in the continuous phase induced by an independent LDL-specific mechanism. [ABSTRACT FROM AUTHOR]

Core-corona supracolloids can be assembled in aqueous dispersions by controlling the physical interactions between the corona and core colloidal particles. A raspberry corona configuration with full surface coverage of the core can be reached by inducing strong attractive interactions between the individual particles. A controlled partial surface coverage of the core, i.e. strawberry configuration, is however, more difficult to achieve. Supracolloids with different surface coverage ratio exhibit unique and multifunctional surface properties. By counterbalancing the multiple physical interactions playing a role during the assembly, the configuration and stability of the assemblies could be fine-tuned over a wide range of concentrations. Supracolloids consisting of polyethylene glycol (PEO)-grafted polymer particles covered by silica nanoparticles were assembled with different configurations, by adjusting the pH and ionic strength of the dispersion, the PEO grafting density and the particles concentration. The self-assembly process and resulting configurations were monitored via cryogenic transmission electron microscopy (Cryo-TEM) and light scattering. The suitable conditions to assemble supracolloids with partial corona coverage have been established. Stable strawberry supracolloids could be prepared, both for diluted (1 wt%) and concentrated (12 wt%) dispersions. These hybrid supracolloids with well-defined configuration are highly relevant to developing advanced water-borne paints and inks, food dispersions, cosmetic and healthcare products. [ABSTRACT FROM AUTHOR]

Many food emulsions, such as mayonnaise or infant formula, are stabilized by combinations of proteins and phospholipids that are concomitantly present at the oil-water interface. It is expected that the physical, as well as the oxidative stability of emulsions are affected by the interfacial composition. Controlling the interfacial composition can therefore be a means to improve emulsion stability, and in particular lipid oxidation. In this work, we varied the ratio of pea protein and sunflower phosphatidylcholine and investigated the resulting interfacial composition and oxidative stability of oil-in-water (O/W) emulsions prepared at fixed pea protein concentration. Increasing the phospholipid concentration led to a monotonic decrease in the adsorbed proteins and to an increase in the adsorbed phospholipids. Cryo-transmission electron microscopy revealed a slight decrease in interfacial thickness, measuring 2.8 nm for pea protein alone, compared to 2.3 nm at the highest phosphatidylcholine-to-pea protein ratio (PC/sPPI) of 0.8 (w/w), and a slight decrease in interfacial roughness, albeit that the differences are small. The oxidative stability of the emulsions globally increased with increasing the PC/sPPI ratio, with the exception of the system with a PC/sPPI ratio of 0.6, which was more sensitive to oxidation than all the other PC-containing emulsions. This peculiar behavior is discussed in the context of model interfacial films of comparable mixed compositions, which exhibit discrete spherical structures and strands. Our results suggest that the PC/sPPI ratio determines the specific interfacial structure that is formed (i.e., packing and patchiness), and it can be expected that thereby the oxidative stability of O/W emulsions stabilized by proteins and phospholipids is modulated. [Display omitted] • For all emulsifier ratios, the emulsions were stable to coalescence. • Phosphatidylcholine (PC)-containing emulsions resisted flocculation. • Interfacial heterogeneity decreased with increasing PC/pea protein (PP) ratio. • At high PC/PP ratio, PC became dominant at the oil-water interface. • This ratio non-monotonically affects oxidative stability and interfacial structure. [ABSTRACT FROM AUTHOR]

Investigating and understanding the intrinsic material properties of biogenic materials, which have evolved over millions of years into admirable structures with difficult to mimic hierarchical levels, holds the potential of replacing trial-and-error-based materials optimization in our efforts to make synthetic materials of similarly advanced complexity and properties. An excellent example is biogenic silica which is found in the exoskeleton of unicellular photosynthetic algae termed diatoms. Because of the complex micro- and nanostructures found in their exoskeleton, determining the intrinsic mechanical properties of biosilica in diatoms has only partly been accomplished. Here, a general method is presented in which a combination of in situ deformation tests inside an SEM with a realistic 3D model of the frustule of diatom Craspedostauros sp. (C. sp.) obtained by electron tomography, alongside finite element method (FEM) simulations, enables quantification of the Young's modulus (E = 2.3 ± 0.1 GPa) of this biogenic hierarchical silica. The workflow presented can be readily extended to other diatom species, biominerals, or even synthetic hierarchical materials. [ABSTRACT FROM AUTHOR]

Poly(3-hexylthiophene)(P3HT) assemblies in vitrified organic solventswere visualized at nanometer scale resolution by cryo-transmissionelectron microscopy, low dose electron diffraction, and cryo-tomographyrevealing a three-dimensional lamellar structure formed by the stackingof the conjugated backbones of P3HT with a distance of 1.7 nm andincreased order in the bulk of the nanowire. This combination of techniquesreveals local structures in dispersion and the condensed state thatplay a crucial role in the performance of organic electronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional materials like graphene and boron nitride find applications in numerous innovations thanks to their high specific surface area and unusual electrical, thermal and optical properties. These materials are often produced via liquid-phase exfoliation, yielding nanoplatelets with a high degree of polydispersity. Unfortunately, methods for the characterization of both lateral dimension and thickness for dispersed polydisperse nanoplatelets are still lacking. In this work, a fast and quantitative method for the characterization of polydisperse nanoplatelets in dispersion is proposed using the example of graphene nanoplatelets (GNPs). The method is benchmarked using well-defined gibbsite nanoplatelets. Synchrotron small-angle X-ray scattering (SAXS) is used to probe the structure of the platelets over a wide range of length scales. The SAXS data are fitted with a polydisperse form factor for discs, which yields size distributions in both thickness and diameter. Benchmarking the procedure with the gibbsite model system shows excellent agreement between the SAXS results and previous transmission electron microscopy and atomic force microscopy data. The method is also successfully applied to GNPs from 1–60 layers in thickness and 20–2000 nm in diameter. We believe that this work brings reliable quantitative in situ characterization, for instance during preparation, of nanoplatelet dispersions within reach. [Display omitted] [ABSTRACT FROM AUTHOR]

Bicontinuousnanospheres have been observed (although rarely) froma variety of block copolymers with architectural and compositionalcomplexity, and often in the presence of additives. Unlocking keyfeatures involved in their formation presents possibilities for bicontinuousaggregates with varied functionality and application. An attractiveprospect is the ability to form them from much simpler polymeric structuresderived from facile syntheses. To that end, we herein report the formationof bicontinuous aggregates from simple amorphous amphiphilic diblockcopolymers of poly(ethylene oxide)-b-poly(n-butyl methacrylate), analogous to our previous reportof the same from a semicrystalline comb-like block copolymer. Moreover,we demonstrate that polymorphism can be achieved by altering the relativeblock proportions and the nonselective cosolvent. We find that thepolymeric structure is not the dominating factor in the formationof bicontinuous nanospheres but that the choice of cosolvent for thehydrophilic block appears to have greater influence on determiningthe end morphology. [ABSTRACT FROM AUTHOR]

Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage/conversion and as catalysts for the sustainable production of fuels and chemicals. However, the tendency of nanoparticles to grow into larger crystallites is an impediment for stable performance. Exemplarily, loss of active surface area by metal particle growth is a major cause of deactivation for supported catalysts. In specific cases particle growth might be mitigated by tuning the properties of individual nanoparticles, such as size, composition and interaction with the support. Here we present an alternative strategy based on control over collective properties, revealing the pronounced impact of the three-dimensional nanospatial distribution of metal particles on catalyst stability. We employ silica-supported copper nanoparticles as catalysts for methanol synthesis as a showcase. Achieving near-maximum interparticle spacings, as accessed quantitatively by electron tomography, slows down deactivation up to an order of magnitude compared with a catalyst with a non-uniform nanoparticle distribution, or a reference Cu/ZnO/Al2O3 catalyst. Our approach paves the way towards the rational design of practically relevant catalysts and other nanomaterials with enhanced stability and functionality, for applications such as sensors, gas storage, batteries and solar fuel production. [ABSTRACT FROM AUTHOR]

Abstract: The structural details of a bifunctional Pt/USY catalyst were studied using electron tomography. As a part of a fundamental study on the synthesis of Pt/USY catalyst, H2PtCl6 precursor was used for the impregnation of USY zeolite support as a source of negatively charged PtCl6 2− ions in order to restrict interaction with acidic sites of USY zeolite. After heat treatments, it was visualized in 3D that some Pt particles were 3–4nm in size, while the majority maintained the size of 1.2–1.5nm which corresponds to the diameter of the zeolite Y micropore cavities (1.2nm). Electron tomography further revealed that 3–4nm Pt particles seem to be entrapped in the zeolite crystal, without preferential location in mesopores or at the surface of the crystals. Quantitative image analysis provided the diameters (compared with EXAFS results) and the nearest neighbor distances of hundreds of imaged Pt particles. [Copyright &y& Elsevier]

Abstract: The role of the cobalt particle size distribution in the Fischer–Tropsch (FT) reaction for supported Co catalysts was investigated. Using TEM histogram analyses and activity measurements of carbon nanofiber-supported catalysts, the TOF of discrete Co particle sizes was calculated. It was found that cobalt particles of 4.7±0.2nm are the most active in the FT reaction (1bar, 220°C), and a narrow Co particle size distribution is clearly essential to arrive at the maximum activity. We have approached this requirement for maximum FT activity with an 18wt.% Co/SiO2 catalyst prepared via impregnation, drying and calcination in NO/He. The more narrow Co particle size distribution (4.6±0.8nm) in Co/SiO2 led to an activity enhancement of ∼40% compared to Co/CNF (5.7±1.4nm), although some promoting effect of silica could not be excluded. [Copyright &y& Elsevier]

Biocomposite structures are difficult to characterize by bulk approaches due to their morphological complexity and compositional heterogeneity. Therefore, a versatile method is required to assess, for example, the mechanical properties of geometrically simple parts of biocomposites at the relevant length scales. Here, it is demonstrated how a combination of Focused Ion Beam Scanning Electron Microscopy (FIB‐SEM) and micromanipulators can be used to isolate, transfer, and determine the mechanical properties of frustule constituents of diatom Thalassiosira pseudonana (T.p.). Specifically, two parts of the diatom frustule, girdle bands and valves, are separated by FIB milling and manipulated using a sharp tungsten tip without compromising their physical or chemical integrity. In situ mechanical studies on isolated girdle bands combined with Finite Element Method (FEM) simulations, enables the quantitative assessment of the Young's modulus of this biosilica; E = 40.0 GPa. In addition, the mechanical strength of isolated valves could be measured by transferring and mounting them on top of premilled holes in the sample support. This approach may be extended to any hierarchical biocomposite material, regardless of its chemical composition, to isolate, transfer, and investigate the mechanical properties of selected constituents or specific regions. [ABSTRACT FROM AUTHOR]

Polyamines play a major role in biosilicification reactions in diatoms and sponges. While the effects of polyamines on silicic acid oligomerization and precipitation are well known, the impact of polyamines chain length on silica particle growth is unclear. We studied the effects of polyamine chain length on silica particle growth and condensation in a known, simple, and salt-free biphasic reaction system; with tetraethyl orthosilicate as organic phase and polyamine dissolved in the aqueous phase. The particles at various growth stages were characterized by Cryo- Transmission Electron Microscopy, Scanning Electron Microscopy, Thermogravimetric Analysis, Zeta Potential, and solid-state NMR analysis. Polyamines were found co-localized within silica particles and the particle diameter increased with an increase in polyamine chain length, whereas silica condensation showed the opposite trend. Particle growth is proposed to progress via a coacervate intermediate while the final particles have a core shell structure with an amine-rich core and silica-rich shell. The results presented in this paper would of interest for researchers working in the field of bioinspired materials. Polyamines play an important role in biogenic silica formation, however, their effects on silica particle size and condensation have not been well described. Here the authors show that bioinspired polyamine length affects silica particle size and extent of condensation. [ABSTRACT FROM AUTHOR]

Biodegradable porous calcium phosphate (CaP) ceramics are widely used as synthetic graft substitutes for bone regeneration, owing to their chemical and structural similarity to bone and associated bioactivity in terms of bone‐bonding, osteoconductive, and even osteoinductive properties. Nevertheless, the intrinsic brittleness and poor processability of porous CaP ceramics strongly impair their clinical applicability. Herein, a biphasic calcium phosphate (BCP) sponge is developed that consists of a self‐supporting network of seamlessly interwoven hydroxyapatite nanowires and β‐tricalcium phosphate nanofibers and possesses a highly interconnected porous structure with open cell geometry and ultrahigh porosity. Owing to its unique properties, the ceramic sponge can be easily processed into various shapes and dimensions, such as cylindrical scaffolds and thin, flexible membranes. Moreover, the BCP sponge can be introduced into a bone defect in a compacted or folded state from a syringe and, upon wetting, expand to its original shape, thereby filling the cavity. The nanofibrous sponge gradually degrades in vitro and rapidly mineralizes when immersed in simulated body fluid. Moreover, it adsorbs significantly more proteins than a conventional porous BCP ceramic. Finally, the nanofibrous sponge supports the attachment, proliferation, and osteogenic differentiation of human mesenchymal stromal cells comparable to the conventional porous BCP ceramic. [ABSTRACT FROM AUTHOR]

Liquid‐Phase (Scanning) Transmission Electron Microscopy (LP‐(S)TEM) has become an essential technique to monitor nanoscale materials processes in liquids in real‐time. Due to the pressure difference between the liquid and the microscope vacuum, bending of the silicon nitride (SiNx) membrane windows generally occurs. This causes a spatially varying liquid layer thickness that makes interpretation of LP‐(S)TEM results difficult due to a locally varying achievable resolution and diffusion limitations. To mediate these difficulties, it is shown: 1) how to quantitatively map liquid layer thickness for any liquid at less than 0.01 e− Å−2 total dose; 2) how to dynamically modulate the liquid thickness by tuning the internal pressure in the liquid cell, co‐determined by the Laplace pressure and the external pressure. It is demonstrated that reproducible inward bulging of the window membranes can be realized, leading to an ultra‐thin liquid layer in the central window area for high‐resolution imaging. Furthermore, it is shown that the liquid thickness can be dynamically altered in a programmed way, thereby potentially overcoming the diffusion limitations towards achieving bulk solution conditions. The presented approaches provide essential ways to measure and dynamically adjust liquid thickness in LP‐(S)TEM experiments, enabling new experiment designs and better control of solution chemistry. [ABSTRACT FROM AUTHOR]

A fundamental understanding of the drying behavior of droplets containing solids or solutes is important for various industrial applications. However, droplets are typically highly polydisperse and time-resolved imaging data of the process dynamics are often lacking, which makes it difficult to interpret the effects of different drying parameters. Here, the controlled drying of monodisperse emulsion droplets containing colloidal silica nanoparticles and their subsequent assembly into mesoporous silica microspheres (MSMs) is investigated using an optical microscope outfitted with a heating and vacuum stage. Quantitative imaging results on droplet shrinkage and observed contrast are compared with a theoretical mass-transfer model that is based on the droplet number density, solvent characteristics and temperature. The results presented here provide key insights in the time-resolved formation of MSMs and will enable an optimized direct synthesis of monodisperse MSMs for separation applications and beyond. [ABSTRACT FROM AUTHOR]

Crystalline materials are often formed via transient phases. Here we focus on ZnO as a widely used and investigated material for technological applications. Although the literature for the wet chemical synthesis of ZnO is extensive, its formation pathway using these strategies has gained limited attention so far and is poorly understood. To gain insight into these pathways, a HMTA-mediated ZnO synthesis protocol with a variety of zinc salts was employed using in situ pH measurements combined with discrete cryoTEM and SEM sampling studies, in addition to more typical pXRD and SEM product analysis. These results indicate a significant counter-ion effect on the reaction product. Using acetate, nitrate, chloride and sulphate as counter-ions all result first in the formation of a layered zinc hydroxy salt (LZHS), the exact composition of which depends on the counter-ion. Rather stable LZHSs are formed using chloride and sulphate, preventing the eventual formation of ZnO. Only acetate and nitrate result in the formation of ZnO. For acetate, ZnO is preferably grown in-dispersion, while for nitrate it is formed on exposed solid interfaces to the reaction medium (on-surfaces). For the latter the nucleation of its LZHS precursor requires an additional incubation time, resulting in heterogeneous nucleation instead. [ABSTRACT FROM AUTHOR]

Colloidal assembly of silica (nano)particles is a powerful method to design functional materials across multiple length scales. Although this method has enabled the fabrication of a wide range of silica‐based materials, attempts to design and synthesize porous materials with a high level of tuneability and control over pore dimensions have remained relatively unsuccessful. Here, the colloidal assembly of silica nanoparticles into mesoporous silica microspheres (MSMs) is reported using a discrete set of silica sols within the confinement of a water‐in‐oil emulsion system. By studying the independent manipulation of different assembly parameters during the sol–gel process, a design strategy is outlined to synthesize MSMs with excellent reproducibility and independent control over pore size and overall porosity, which does not require additional ageing or post‐treatment steps to reach pore sizes as large as 50 nm. The strategy presented here can provide the necessary tools for the microstructural design of the next generation of tailor‐made silica microspheres for use in separation applications and beyond. [ABSTRACT FROM AUTHOR]

In this work, a nanohybrid material based on a freestanding polymeric liquid crystal network capable of postmodification via cation exchange to tune birefringence is proposed. The smectic liquid crystal films can be infiltrated with a variety of cations, thereby changing the refractive indices (ne and no) and the effective birefringence (Δn) of the nanohybrid material, with reversible cation infiltration occurring within minutes. Birefringence could be tuned between values of 0.06 and 0.19, depending on the cation infiltrated into the network. Upon infiltration, a decrease in the smectic layer spacing is found with layer contraction independent of the induced change in birefringence. Potential applications are in the field of specialty optical devices, such as flexible, retunable reflective filters. [ABSTRACT FROM AUTHOR]

Stimuli‐responsive properties of soft materials originate from dynamic structure changes. Layered polydiacetylene (PDA) shows color‐change properties with the application of external stimuli, such as thermal and mechanical stresses. Layered organic materials possessing intercalation capabilities and dynamic properties have potentials for tuning their structures and properties by the intercalated guests. A variety of sensing and imaging devices can be developed by control of the stimuli responsivity. Here, the key structures, processes, and mechanisms for tuning the stimuli‐responsive color‐change properties of layered PDA are studied by in situ analyses with heating and cooling. The in situ analyses indicate that heating initiates thermal motion of the alkyl side chains of the PDA main chain in the host layers around 60 °C, regardless of the type of intercalated guests. Further heating induces torsion of the PDA main chain leading to color changes at different temperatures, depending on the types of the intercalated guest. Then, the layered structure is irreversibly deformed with lowering the crystallinity. The results indicate that the stimuli‐responsive color‐change properties are controlled by the rigidity of the layered structures consisting of the host layers and guests. The control strategy based on rigidity tuning can be applied to a variety of soft materials with stimuli responsivity. The tunable soft and rigid nature of organic layered structures with intercalation control the stimuli‐responsive color‐change properties of layered polydiacetylene, such as color, responsivity, and reversibility. In situ analyses reveal the relationship between the layered structure and stimuli‐responsive color‐change properties. The interlayer guests determine the rigidity of the organic layered materials and their properties. [ABSTRACT FROM AUTHOR]

Graphene as an optoelectronic material displays unique advantages in the modulation of amplitude and phase of millimeter waves attributed to its high carrier mobility and broadband optoelectronic properties. The electronic properties of graphene are precisely controllable with the screen-printing technique. We herein employed the screen-printed graphene to manipulate the transmission of the guided millimeter waves in a metallic waveguide. The effects of the patterns and sizes of screen-printed graphene on the modulation of guided waves are first investigated and found that the rhombus is the optimal pattern shape in terms of linearly broadband modulation and reflection loss. The advanced screen-printing technique enables tuning the sheet resistance of the graphene from 45 Ω/sq. to 205 Ω/sq. Numerical simulation shows that the maximum transmittance modulation depth of the guided wave is about 20 dB related to the tuning range of the graphene sheet resistance. A millimeter-wave metallic waveguide integrated with screen-printed graphene is fabricated and measured to validate the proposed scenario. The broadband transmittance modulation depth of 4 dB is experimentally observed with reflection loss lower than −15 dB in the full frequency band of 60–75 GHz, which is consistent with simulated results. The guided wave modulation with screen-printed graphene exhibits great opportunities in millimeter wave devices and systems. [Display omitted] • Screen-printed graphene manipulates the guided millimeter waves with high modulation depth and low reflection loss. • Rhombus-shaped graphene pattern exhibits optimal modulation performance compared to the rectangle and ellipse. • Transmittance of the guided waves can be linearly modulated by varying the length and sheet resistance of the graphene. • Screen printing technique provides a new solution for low-cost and high-accuracy modulation of guided millimeter waves. [ABSTRACT FROM AUTHOR]

Morphology plays an essential role in chemistry through the segregation of atoms and/or molecules into different phases, delineated by interfaces. This is a general process in materials synthesis and exploited in many fields including colloid chemistry, heterogeneous catalysis, and functional molecular systems. To rationally design complex materials, we must understand and control morphology evolution. Toward this goal, we utilize cryogenic transmission electron microscopy (cryoTEM), which can track the structural evolution of materials in solution with nanometer spatial resolution and a temporal resolution of <1 s. In this Account, we review examples of our own research where direct observations by cryoTEM have been essential to understanding morphology evolution in macromolecular self-assembly, inorganic nucleation and growth, and the cooperative evolution of hybrid materials. These three different research areas are at the heart of our approach to materials chemistry where we take inspiration from the myriad examples of complex materials in Nature. Biological materials are formed using a limited number of chemical components and under ambient conditions, and their formation pathways were refined during biological evolution by enormous trial and error approaches to self-organization and biomineralization. By combining the information on what is possible in nature and by focusing on a limited number of chemical components, we aim to provide an essential insight into the role of structure evolution in materials synthesis. Bone, for example, is a hierarchical and hybrid material which is lightweight, yet strong and hard. It is formed by the hierarchical self-assembly of collagen into a macromolecular template with nano- and microscale structure. This template then directs the nucleation and growth of oriented, nanoscale calcium phosphate crystals to form the composite material. Fundamental insight into controlling these structuring processes will eventually allow us to design such complex materials with predetermined and potentially unique properties. [ABSTRACT FROM AUTHOR]

Despite the great promise of printed flexible electronics from 2D crystals, and especially graphene, few scalable applications have been reported so far that can be termed roll-to-roll compatible. Here we combine screen printed graphene with photonic annealing to realize radio-frequency identification devices with a reading range of up to 4 meters. Most notably our approach leads to fatigue resistant devices showing less than 1% deterioration of electrical properties after 1000 bending cycles. The bending fatigue resistance demonstrated on a variety of technologically relevant plastic and paper substrates renders the material highly suitable for various printable wearable devices, where repeatable dynamic bending stress is expected during usage. All applied printing and post-processing methods are compatible with roll-to-roll manufacturing and temperature sensitive flexible substrates providing a platform for the scalable manufacturing of mechanically stable and environmentally friendly graphene printed electronics. [ABSTRACT FROM AUTHOR]

This paper describes the gelation of highly concentrated graphene/polymer dispersions triggered by mild heating. The gel formation is only dependent on the concentration of graphene with 3.25 mg mL−1 as the minimum value for graphene network formation. The graphene gel is then utilized for the preparation of colloidally stable and highly concentrated (52 mg mL−1) graphene pastes that demonstrate excellent performance in screen printing down to lines of 40 μm in width. Printed patterns dried at 100 °C for only 5 min exhibit sheet resistances of 30 Ω −1 at 25 μm thickness, thus, removing the need for long-time high temperature annealing, doping, or other treatments. Such a low drying temperature, high printing definition, and compatibility with industrially relevant plastic and paper substrates brings high-volume roll-to-roll application in printed flexible electronics within reach. [ABSTRACT FROM AUTHOR]

Sampling limitations in electron microscopy questions whether the analysis of a bulk material is representative, especially while analyzing hierarchical morphologies that extend over multiple length scales. We tackled this problem by automatically acquiring a large series of partially overlapping (S)TEM images with sufficient resolution, subsequently stitched together to generate a large-area map using an in-house developed acquisition toolbox ( TU/e Acquisition ToolBox ) and stitching module ( TU/e Stitcher ). In addition, we show that quantitative image analysis of the large scale maps provides representative information that can be related to the synthesis and process conditions of hierarchical materials, which moves electron microscopy analysis towards becoming a bulk characterization tool. We demonstrate the power of such an analysis by examining two different multi-phase materials that are structured over multiple length scales. [ABSTRACT FROM AUTHOR]

Phosvitins is a key egg yolk protein and can often be found in food emulsions. It is highly phosphorylated and hence phosvitins contain a large number of negatively charged amino acid groups, for pH > pI. Due to the presence of these phophoserines, phosvitins bind to positively charged multivalent ions. Its amphipolar structure makes phosvitin also an efficient emulsion stabilizer. The ion binding and emulsifying abilities of phosvitins are influenced by environmental conditions such as pH and ionic strength. Various physicochemical properties of phosvitins such as size and charge under various conditions, and how they self-assemble via multivalent ions are not well-understood. To gain more insight into these physical characteristics, we performed high brilliance synchrotron small angle X-ray scattering (SAXS) on phosvitin solutions. The structure factor S (q) obtained from the SAXS profiles showed that the double layer interactions between charged phosvitin assemblies are strongly affected by pH and ionic strength of the buffer. The effects of multivalent ions (Mg2+, Fe3+) on the size and structure of phosvitin were also investigated. Our results revealed that the aggregation of phosvitin mediated by metal ions is induced by electrostatic attraction and only occurs beyond a threshold cation concentration, where phosvitin loses long-range electrostatic double layer repulsions. These findings help understanding the effects of metal ions and pH on phosvitin in more complex environments such as food emulsions. [Display omitted] • The physicochemical properties of phosvitins such as size and charge were measured using scattering. • An improved purification method was developed to prepare high-purity phosvitins. • SAXS yielded the structure factor S (q), showing phosvitins behave as charged colloidal spheres. • Adding multivalent cations can induce aggregation of phosvitins. • A threshold cation concentration is needed to initiate phosvitin aggregation. [ABSTRACT FROM AUTHOR]

Biological systems show impressive control over the shape, size and organization of mineral structures, which often leads to advanced physical properties that are tuned to the function of these materials. Such control is also found in magnetotactic bacteria, which produce-in aqueous medium and at room temperature-magnetite nanoparticles with precisely controlled morphologies and sizes that are generally only accessible in synthetic systems with the use of organic solvents and/or the use of high-temperature methods. The synthesis of magnetite under biomimetic conditions, that is, in water and at room temperature and using polymeric additives as control agents, is of interest as a green production method for magnetic nanoparticles. Inspired by the process of magnetite biomineralization, a rational approach is taken by the use of a solid precursor for the synthesis of magnetite nanoparticles. The conversion of a ferrous hydroxide precursor, which we demonstrate with cryo-TEM and low-dose electron diffraction, is used to achieve control over the solution supersaturation such that crystal growth can be regulated through the interaction with poly-(α,β)- dl-aspartic acid, a soluble, negatively charged polymer. In this way, stable suspensions of nanocrystals are achieved that show remanence and coercivity at the size limit of superparamagnetism, and which are able to align their magnetic moments forming strings in solution as is demonstrated by cryo-electron tomography. [ABSTRACT FROM AUTHOR]

Solution-processed conductive, flexible and transparent graphene thin films continue drawing attention from science and technology due to their potential for many electrical applications. Here, an up-scalable method for the solution processing of graphite to graphene and further to self-assembled large-area conductive transparent thin-films is presented. The method proceeds via the graphite intercalation route followed by thermal expansion to obtain expanded graphite. The resulting material is dispersed in a surfactant-free mixture of isopropanol and propylene glycol to obtain a stable colloidal dispersion. A graphene thin film is subsequently formed by self-organization at an oil/water interface followed by lift-up transfer to virtually any substrate of interest. Thermally annealed thin-films exhibit a thickness-tunable sheet resistances of between 10 and 0.8 kΩ/□ with transparencies between 75% and 45% at 500 nm wavelength, respectively. Additional Au-doping decreases the sheet resistance by a factor of 5. Heating doped films to temperatures above 380 K or exposure to ambient conditions significantly increases the sheet resistance as a result of decreasing charge carrier concentration. The presented method is a simple, up-scalable and thus competitive alternative to other techniques for large area graphene film production. [ABSTRACT FROM AUTHOR]

In electron tomography, the fidelity of the 3D reconstruction strongly depends on the employed reconstruction algorithm. In this paper, the properties of SIRT, TVM and DART reconstructions are studied with respect to having only a limited number of electrons available for imaging and applying different angular sampling schemes. A well-defined realistic model is generated, which consists of tubular domains within a matrix having slab-geometry. Subsequently, the electron tomography workflow is simulated from calculated tilt-series over experimental effects to reconstruction. In comparison with the model, the fidelity of each reconstruction method is evaluated qualitatively and quantitatively based on global and local edge profiles and resolvable distance between particles. Results show that the performance of all reconstruction methods declines with the total electron dose. Overall, SIRT algorithm is the most stable method and insensitive to changes in angular sampling. TVM algorithm yields significantly sharper edges in the reconstruction, but the edge positions are strongly influenced by the tilt scheme and the tubular objects become thinned. The DART algorithm markedly suppresses the elongation artifacts along the beam direction and moreover segments the reconstruction which can be considered a significant advantage for quantification. Finally, no advantage of TVM and DART to deal better with fewer projections was observed. [ABSTRACT FROM AUTHOR]

Althoughmonodisperse amorphous silica nanoparticles have beenwidely investigated, their formation mechanism is still a topic ofdebate. Here, we demonstrate the formation of monodisperse nanoparticlesfrom colloidally stabilized primary particles, which at a criticalconcentration undergo a concerted association process, concomitantwith a morphological and structural collapse. The formed assembliesgrow further by addition of primary particles onto their surface.The presented mechanism, consistent with previously reported observations,reconciles the different theories proposed to date. [ABSTRACT FROM AUTHOR]

Highlights: [•] Activity of PtRe/C in APR of glycerol increases with Re. [•] Acetaldehyde decomposition: PtRe more active in C–C bond cleavage than Pt/C. [•] Formation of acid sites (Re-OH) in PtRe: increased C–O cleavage rates. [•] Water activation promoted by Re confirmed by CO stripping voltammetry. [•] High APR activity of PtRe correlates with high WGS activity. [ABSTRACT FROM AUTHOR]