Search

Skin-compatible printed stretchable conductors that combine a low gauge factor with a high durability over many strain cycles are still a great challenge. Here, a graphene nanoplatelet-based colloidal ink utilizing a skin-compatible thermoplastic polyurethane (TPU) binder with adjustable rheology is developed. Stretchable conductors that remain conductive even under 100% strain and demonstrate high fatigue resistance to cyclic strains of 20–50% are realized via printing on TPU. The sheet resistances of these conductors after drying at 120 °C are as low as 34 Ω □–1mil–1. Furthermore, photonic annealing at several energy levels is used to decrease the sheet resistance to <10 Ω □–1mil–1, with stretchability and fatigue resistance being preserved and tunable. The high conductivity, stretchability, and cyclic stability of printed tracks having excellent feature definition in combination with scalable ink production and adjustable rheology bring the high-volume manufacturing of stretchable wearables into scope.

Control over the assembly and morphology of nanoscale functional building blocks is of great importance to hybrid and porous nanomaterials. In this paper, by combining different types of spherical nanoparticles with different size ratios in a hierarchical assembly process which allows us to control the final structure of multi-component assemblies, we discuss self-assembly of an extensive range of supraparticles, labelled as AB particles, and an extension to novel ternary particles, labelled as ABC particles. For supraparticles, the organization of small nanoparticles is known to be inherently related to the size ratio of building blocks. Therefore, we studied the formation of supraparticles prepared by colloidal self-assembly using small silica nanoparticles (SiO2NPs) attached on the surface of large polystyrene latex nanoparticles (PSL NPs) with a wide size ratio range for complete and partial coverage, by controlling the electrostatic interactions between the organic and inorganic nanoparticles and their concentrations. In this way hierarchically ordered, stable supraparticles, either fully covered or partially covered, were realized. The partially covered, stable AB supraparticles offer the option to create ABC supraparticles of which the fully covered shell contains two different types of nanoparticles. This has been experimentally confirmed using iron oxide (Fe3O4) nanoparticles together with silica nanoparticles as shell particles on polystyrene core particles. Cryo-electron tomography was used to visualize the AB binary and ABC ternary supraparticles and to determine the three-dimensional structural characteristics of supraparticles formed under different conditions.

The mineralization of collagen via synthetic procedures has been extensively investigated for hydroxyapatite as well as for silica and calcium carbonate. From a fundamental point of view, it is interesting to investigate whether collagen could serve as a generic mineralization template for other minerals, like iron oxides. Here, bio-inspired coprecipitation reaction, generally leading to the formation of magnetite, is used to mineralize collagen with iron hydroxides. Platelet-shaped green rust crystals form outside the collagen matrix, while inside the collagen, nanoparticles with a size of 2.6 nm are formed, which are hypothesized to be iron (III) hydroxide. Mineralization with nanoparticles inside the collagen solely occurs in the presence of poly(aspartic acid) (pAsp). In the absence of pAsp, magnetite particles are formed around the collagen. Time-resolved cryo-TEM shows that during the coprecipitation reaction, initially a beam-sensitive phase is formed, possibly an Fe3+–pAsp complex. This beam-sensitive phase transforms into nanoparticles. In a later stage, sheet-like crystals are also found. After 48 h of mineralization, ordering of the nanoparticles around one of the collagen sub-bands (the a-band) is observed. This is very similar to the collagen–hydroxyapatite system, indicating that mineralization with iron hydroxides inside collagen is possible and proceeds via a similar mechanism as hydroxyapatite mineralization.

Electron microscopy (EM) of materials undergoing chemical reactions provides knowledge of the underlying mechanisms. However, the mechanisms are often complex and cannot be fully resolved using a single method. Here, we present a distributed electron microscopy method for studying complex reactions. The method combines information from multiple stages of the reaction and from multiple EM methods, including liquid phase EM (LP-EM), cryogenic EM (cryo-EM), and cryo-electron tomography (cryo-ET). We demonstrate this method by studying the desilication mechanism of zeolite crystals. Collectively, our data reveal that the reaction proceeds viaa two-step anisotropic etching process and that the defects in curved surfaces and between the subunits in the crystal control the desilication kinetics by directing mass transport.

The characterization of polymeric materials is key towards the understanding of structure–activity relations and therefore for the rational design of novel and improved materials for a myriad of applications. Many microscopy techniques are currently used, with electron microscopy, fluorescence microscopy, and atomic force microscopy being the most relevant. In this perspective paper, we discuss the use of correlative imaging, that is, the combination of multiple imaging methodologies on the same sample, in the field of polymeric materials. This innovative approach is emerging as a powerful tool to unveil the structure and functional properties of biological and synthetic structures. Here we discuss the possibilities of correlative imaging and highlight their potential to answer open questions in polymer science. In this Perspective, the use of correlative imaging is reviewed in the field of polymeric materials. This innovative approach is emerging as a powerful tool to unveil the structure and functional properties of biological and synthetic structures. The possibilities of correlative imaging and its potential in polymer science are outlined.

Nanoscale chemical analysis of functional polymer systems by electron microscopy, to gain access into degradation processes during the materials life cycle, is still a formidable challenge due to their beam sensitivity. Here a systematic study on the different stages of degradation in a P3HT‐PCBM organic photovoltaic (OPV) model system is presented. To this end pristine samples, samples with (reversibly) physisorbed oxygen and water and samples with (irreversibly) chemisorbed oxygen and water are imaged utilizing the full capabilities of cryogenic STEM‐EELS. It is found that oxygen and water are largely physisorbed in this system leading to significant effects on the band structure, especially for PCBM. Quantification proves that degradation concomitantly decreases the amount of CC bonds and increases the amount of COC bonds in the sample. Finally, it is shown that with a pulsed electron beam utilizing a microwave cavity, beam damage can be significantly reduced which likely extends the possibilities for such studies in future. In this study, different stages of degradation in a P3HT‐PCBM organic photovoltaic (OPV) model system are presented. It is found that oxygen and water are primarily physisorbed in this system leading to significant effects on the band structure, especially PCBM. The techniques employed in this article can be used in the future to analyze chemical changes in beam‐sensitive materials.

Periodic nano- or microscale structures are used to control light, energy and mass transportation. Colloidal organization is the most versatile method used to control nano- and microscale order, and employs either the enthalpy-driven self-assembly of particles at a low concentration or the entropy-driven packing of particles at a high concentration. Nonetheless, it cannot yet provide the spontaneous three-dimensional organization of multicomponent particles at a high concentration. Here we combined these two concepts into a single strategy to achieve hierarchical multicomponent materials. We tuned the electrostatic attraction between polymer and silica nanoparticles to create dynamic supracolloids whose components, on drying, reorganize by entropy into three-dimensional structured materials. Cryogenic electron tomography reveals the kinetic pathways, whereas Monte Carlo simulations combined with a kinetic model provide design rules to form the supracolloids and control the kinetic pathways. This approach may be useful to fabricate hierarchical hybrid materials for distinct technological applications.

Liquid crystal-based actuators are receiving increased attention for their applications in wearables and biomedical or surgical devices, with selective actuation of individual parts/fingers still being in its infancy. This work presents the design and realization of two gripper devices with four individually addressable liquid-crystal network (LCN) actuators thermally driven via printed graphene-based heating elements. The resistive heat causes the all-organic actuator to bend due to anisotropic volume expansions of the splay-aligned sample. A heat transfer model that includes all relevant interfaces is presented and verified via thermal imaging, which provides good estimates of dimensions, power production, and resistance required to reach the desired temperature for actuation while maintaining safe electrical potentials. The LCN films displace up to 11 mm with a bending force of 1.10 mN upon application of 0–15 V potentials. The robustness of the LCN finger is confirmed by repetitive on/off switching for 500 cycles. Actuators are assembled into two prototypes able to grip and lift objects of small weights (70–100 mg) and perform complex actions by individually controlling one of the device’s fingers to grip an additional object. Selective actuation of parts in soft robotic devices will enable more complex motions and actions to be performed.

The adsorption mechanism of small positively charged silica nanoparticles (SiO2NPs) onto larger polystyrene latex nanoparticles (PSL NPs) forming hybrid particles was studied. CryoTEM showed the morphology of these supraparticles to be raspberry-like. After surface modification of the SiO2NPs, the optimum pH regime to initiate the formation of nanoraspberries was determined. Thereafter, their size evolution was evaluated by dynamic light scattering for different surface charge densities. Reversibility of nanoraspberry formation was shown by cycling the pH of the mixture to make interparticle forces either attractive or repulsive, while their stability was confirmed experimentally. The number of SiO2NPs on the PSL NPs as determined with cryoTEM matched the theoretically expected maximum number. Understanding and controlling the relevant parameters, such as size and charge of the individual particles and the Debye length, will pave the way to better control of the formation of nanoraspberries and higher-order assemblies thereof.

Supramolecular fibers in water, micrometers long and several nanometers in width, are among the most studied nanostructures for biomedical applications. These supramolecular polymers are formed through a spontaneous self-assembly process of small amphiphilic molecules by specific secondary interactions. Although many compounds do not possess a stereocenter, recent studies suggest the (co)existence of helical structures, albeit in racemic form. Here, we disclose a series of supramolecular (co)polymers based on water-soluble benzene-1,3,5-tricarboxamides (BTAs) that form double helices, fibers that were long thought to be chains of single molecules stacked in one dimension (1D). Detailed cryogenic transmission electron microscopy (cryo-TEM) studies and subsequent three-dimensional-volume reconstructions unveiled helical repeats, ranging from 15 to 30 nm. Most remarkable, the pitch can be tuned through the composition of the copolymers, where two different monomers with the same core but different peripheries are mixed in various ratios. Like in lipid bilayers, the hydrophobic shielding in the aggregates of these disc-shaped molecules is proposed to be best obtained by dimer formation, promoting supramolecular double helices. It is anticipated that many of the supramolecular polymers in water will have a thermodynamic stable structure, such as a double helix, although small structural changes can yield single stacks as well. Hence, it is essential to perform detailed analyses prior to sketching a molecular picture of these 1D fibers.

Designer particles that are embued with nanomachinery for autonomous motion have great potential for biomedical applications; however, their development is highly demanding with respect to biodegradability/compatibility. Previously, biodegradable propulsive machinery based on enzymes has been presented. However, enzymes are highly susceptible to proteolysis and deactivation in biological milieu. Biodegradable hybrid nanomotors powered by catalytic inorganic nanoparticles provide a proteolytically stable alternative to those based upon enzymes. Herein we describe the assembly of hybrid biodegradable nanomotors capable of transducing chemical energy into motion. Such nanomotors are constructed through a process of compartmentalized synthesis of inorganic MnO2nanoparticles (MnPs) within the cavity of organic stomatocytes. We show that the nanomotors remain active in cellular environments and do not compromise cell viability. Effective tumor penetration of hybrid nanomotors is also demonstrated in proof-of-principle experiments. Overall, this work represents a new prospect for engineering of nanomotors that can retain their functionality within biological contexts.

The nucleation of crystals has long been thought to occur through the stochastic association of ions, atoms or molecules to form critical nuclei, which will later grow out to crystals1. Only in the past decade has the awareness grown that crystallization can also proceed through the assembly of different types of building blocks2,3, including amorphous precursors4, primary particles5, prenucleation species6,7, dense liquid droplets8,9or nanocrystals10. However, the forces that control these alternative pathways are still poorly understood. Here, we investigate the crystallization of magnetite (Fe3O4) through the formation and aggregation of primary particles and show that both the thermodynamics and the kinetics of the process can be described in terms of colloidal assembly. This model allows predicting the average crystal size at a given initial Fe concentration, thereby opening the way to the design of crystals with predefined sizes and properties.

Magnetite (Fe3O4) nanoaggregates with a flower-like morphology are considered promising materials in the field of magnetically induced hyperthermia in cancer therapy due to their good heating efficiency at low applied alternating magnetic fields. Although the structure and the magnetic state of such flower-like aggregates have been investigated previously, the mechanism that leads to the hierarchical morphology is still poorly understood. Here, we study the formation mechanism of Fe3O4aggregates synthesized through the partial oxidation of ferrous hydroxide in the presence of poly(acrylic acid) by using cryogenic electron microscopy. The aggregates are formed through a multistep process involving first the conversion of ferrous hydroxide precursors in ∼5 nm primary particles that aggregate into ∼10 nm primary Fe3O4crystals that finally arrange into the secondary mesocrystal structure. High-resolution electron tomography is used to show that the Fe3O4mesocrystals are composed of ∼10 nm subunits, often showing a uniform crystallographic orientation resulting in single-crystal-like diffraction patterns. Furthermore, electron holography reveals that mesocrystals have a single magnetic domain despite polymeric interfaces between subunits being present throughout the mesocrystal. Our findings could be used to design materials with specific properties by modulating the morphology and/or magnetic state that is suitable for biomedical application.

The self-assembly of amphiphilic molecules in solution is a ubiquitous process in both natural and synthetic systems. The ability to effectively control the structure and properties of these systems is essential for tuning the quality of their functionality, yet the underlying mechanisms governing the transition from molecules to assemblies have not been fully resolved. Here we describe how amphiphilic self-assembly can be preceded by liquid–liquid phase separation. The assembly of a model block co-polymer system into vesicular structures was probed through a combination of liquid-phase electron microscopy, self-consistent field computations and Gibbs free energy calculations. This analysis shows the formation of polymer-rich liquid droplets that act as a precursor in the bottom-up formation of spherical micelles, which then evolve into vesicles. The liquid–liquid phase separation plays a role in determining the resulting vesicles’ structural properties, such as their size and membrane thickness, and the onset of kinetic traps during self-assembly.

Herein we report our efforts to control the size of colloidal Ni nanoparticles (NiNPs) viaa seed-mediated approach and to produce supported Ni catalysts that are sinter-resistant. NiNPs are prepared using a mild capping ligand and an external reducing agent at 90 °C to obtain seeds of 3–4 nm, followed by NiNP growth at 220 °C to vary the final size up to 8 nm. These NiNPs were either introduced onto high surface area silica viadirect deposition in organic solvents, or encapsulated in mesoporous silica. Encapsulation was determined to be the most promising approach to support the particles. A range of such encapsulated NiNP catalysts were evaluated for CO2hydrogenation between 200–400 °C: they were comparably active as catalysts reported in the literature, and thermally stable and sinter-resistant for 70 h at 350 °C. Nevertheless, it was found that the Ni phase was redistributed throughout the mesoporous silica network, resulting in Ni catalysts with nearly identical particle size of 4–5 nm, determined by the size of the support pores, after a combination of oxidative and reductive pretreatments. Our approach provides a route to obtain Ni@SiO2catalysts with a narrow particle size distribution from a range of colloidal NiNP precursors.

In this study, native chemical ligation (NCL) was used as a selective cross-linking method to form core-cross-linked thermosensitive polymeric micelles for drug delivery applications. To this end, two complementary ABA triblock copolymers having polyethylene glycol (PEG) as midblock were synthesized by atom transfer radical polymerization (ATRP). The thermosensitive poly isopropylacrylamide (PNIPAM) outer blocks of the polymers were copolymerized with either N-(2-hydroxypropyl)methacrylamide-cysteine (HPMA-Cys), P(NIPAM-co-HPMA-Cys)-PEG-P(NIPAM-co-HPMA-Cys) (PNC) or N-(2-hydroxypropyl)methacrylamide-ethylthioglycolate succinic acid (HPMA-ETSA), P(NIPAM-co-HPMA-ETSA)-PEG-P(NIPAM-co-HPMA-ETSA) (PNE). Mixing of these polymers in aqueous solution followed by heating to 50 °C resulted in the formation of thermosensitive flower-like micelles. Subsequently, native chemical ligation in the core of micelles resulted in stabilization of the micelles with a Z-average of 65 nm at body temperature. Decreasing the temperature to 10 °C only affected the size of the micelles (increased to 90 nm) but hardly affected the polydispersity index (PDI) and aggregation number (Nagg) confirming covalent stabilization of the micelles by NCL. CryoTEM images showed micelles with an uniform spherical shape and dark patches close to the corona of micelles were observed in the tomographic view. The dark patches represent more dense areas in the micelles which coincide with the higher content of HPMA-Cys/ETSA close to the PEG chain revealed by the polymerization kinetics study. Notably, this cross-linking method provides the possibility for conjugation of functional molecules either by using the thiol moieties still present after NCL or by simply adjusting the molar ratio between the polymers (resulting in excess cysteine or thioester moieties) during micelle formation. Furthermore, in vitro cell experiments demonstrated that fluorescently labeled micelles were successfully taken up by HeLa cells while cell viability remained high even at high micelle concentrations. These results demonstrate the potential of these micelles for drug delivery applications.

The formation of condensed (compacted) protein phases is associated with a wide range of human disorders, such as eye cataracts, amyotrophic lateral sclerosis, sickle cell anaemia and Alzheimer’s disease. However, condensed protein phases have their uses: as crystals, they are harnessed by structural biologists to elucidate protein structures, or are used as delivery vehicles for pharmaceutical applications. The physiochemical properties of crystals can vary substantially between different forms or structures (‘polymorphs’) of the same macromolecule, and dictate their usability in a scientific or industrial context. To gain control over an emerging polymorph, one needs a molecular-level understanding of the pathways that lead to the various macroscopic states and of the mechanisms that govern pathway selection. However, it is still not clear how the embryonic seeds of a macromolecular phase are formed, or how these nuclei affect polymorph selection. Here we use time-resolved cryo-transmission electron microscopy to image the nucleation of crystals of the protein glucose isomerase, and to uncover at molecular resolution the nucleation pathways that lead to two crystalline states and one gelled state. We show that polymorph selection takes place at the earliest stages of structure formation and is based on specific building blocks for each space group. Moreover, we demonstrate control over the system by selectively forming desired polymorphs through site-directed mutagenesis, specifically tuning intermolecular bonding or gel seeding. Our results differ from the present picture of protein nucleation, in that we do not identify a metastable dense liquid as the precursor to the crystalline state. Rather, we observe nucleation events that are driven by oriented attachments between subcritical clusters that already exhibit a degree of crystallinity. These insights suggest ways of controlling macromolecular phase transitions, aiding the development of protein-based drug-delivery systems and macromolecular crystallography.

In transmission electron microscopy (TEM) the interaction of an electron beam with polymers such as P3HT:PCBM photovoltaic nanocomposites results in electron beam damage, which is the most important factor limiting acquisition of structural or chemical data at high spatial resolution. Beam effects can vary depending on parameters such as electron dose rate, temperature during imaging, and the presence of water and oxygen in the sample. Furthermore, beam damage will occur at different length scales. To assess beam damage at the angstrom scale, we followed the intensity of P3HT and PCBM diffraction rings as a function of accumulated electron dose by acquiring dose series and varying the electron dose rate, sample preparation, and the temperature during acquisition. From this, we calculated a critical dose for diffraction experiments. In imaging mode, thin film deformation was assessed using the normalized cross-correlation coefficient, while mass loss was determined via changes in average intensity and standard deviation, also varying electron dose rate, sample preparation, and temperature during acquisition. The understanding of beam damage and the determination of critical electron doses provides a framework for future experiments to maximize the information content during the acquisition of images and diffraction patterns with (cryogenic) transmission electron microscopy.

We demonstrate the construction of pH-responsive bicontinuous nanospheres (BCNs) with nonlinear transient permeability and catalytic activity. The BCNs were assembled from amphiphilic block copolymers comprising pH-responsive groups and were loaded with the enzymes urease and horseradish peroxidase (HRP). A transient membrane permeability switch was introduced by employing the well-known pH-increasing effect of urease upon conversion of urea to ammonia. As expected, the coencapsulated HRP displayed a transiently regulated catalytic output profile upon addition of urea, with no significant product formation after the pH increase. This transient process displayed a nonlinear “dampening” behavior, induced by a decrease in membrane permeability as a result of significant local ammonia production. Furthermore, the catalytic output of HRP could be modulated by addition of different amounts of urea or by altering the buffer capacity of the system. Finally, this nonlinear dampening effect was not observed in spherical polymersomes, even though the membrane permeability could also be inhibited by addition of urea. The specific BCN morphology therefore allows to optimally control catalytic processes by pH changes in the nanoreactor microenvironment compared to bulk conditions due to its unique permeability profile.

Mesoscale networks of multiwalled carbon nanotubes (CNTs) dispersed in 50/50 PS/PPO (polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide)) are studied. Various dispersion states are formed by several processing methods such as solvent casting (SC) and extrusion (EXT) and followed by compression molding (CM), which alters the topology of the conductive CNT network. This in turn affects the measured electrical conductivity up to 9 orders of magnitude. Quantitative large-area STEM imaging of the representative topology revealed the existence of subtle differences in topology for various dispersion states. The analyses also reveal that strong localized CNT interactions during the SC process result in highly conductive inhomogeneous networks consisting of CNT clusters connected by individual CNTs embedded in the polymer matrix. This leads to a low electrical percolation threshold, so that as compared to a random network a higher local volume fraction than the overall volume fraction of CNTs is present. A dispersion state created by the extrusion process (EXT) results in less conductive and close to randomly oriented networks. The electrical conductivity of the mesoscale networks is further enhanced by compression molding (annealing), which increases the effective CNT–CNT contact area per unit volume and hence decreases the contact resistance between CNTs and results in significant improvement in electrical conductivity. This study illustrates how multiscale information can be used to understand and subsequently tailor the macroscopic functional properties of many scientifically and technologically relevant functional materials.

Mesoporous silica nanoparticles (MSNs) have been explored extensively as solid supports for proteins in biological and medical applications. Small (<200 nm) MSNs with ordered large pores (>5 nm), capable of encapsulating therapeutic small molecules suitable for delivery applications in vivo, are rare however. Here we present small, elongated, cuboidal, MSNs with average dimensions of 90 × 43 nm that possess disk-shaped cavities, stacked on top of each other, which run parallel to the short axis of the particle. Amine functionalization was achieved by modifying the MSN surface with 3-aminopropyltriethoxysilane or 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AP-MSNs and AEP-MSNs) and were shown to have similar dimensions to the nonfunctionalized MSNs. The dimensions of these particles, and their large surface areas as measured by nitrogen adsorption–desorption isotherms, make them ideal scaffolds for protein encapsulation and delivery. We therefore investigated the encapsulation and release behavior for seven model proteins (α-lactalbumin, ovalbumin, bovine serum albumin, catalase, hemoglobin, lysozyme, and cytochrome c). It was discovered that all types of MSNs used in this study allow rapid encapsulation, with a high loading capacity, for all proteins studied. Furthermore, the release profiles of the proteins were tunable. The variation in both rate and amount of protein uptake and release was found to be determined by the surface chemistry of the MSNs, together with the isoelectric point (pI), and molecular weight of the proteins, as well as by the ionic strength of the buffer. These MSNs with their large surface area and optimal dimensions provide a scaffold with a high encapsulation efficiency and controllable release profiles for a variety of proteins, enabling potential applications in fields such as drug delivery and protein therapy.

Abstract

An interview with Michael Heizer, a land artist, is presented. Heizer talked about how he created land art in the Mojave desert in California, his "Munich Depression" project that depicted the optical properties of the deprivation of vision and the erasure of landscape and objects, and his photographic installation "Actual Size: Munich Rotary" which offers an exact reproduction of the "Munich Depression."

The formation of different mesoscale networks in multiwalled carbon nanotube (CNT) systems that are realized by the mixing of CNTs of varying lengths and length dispersities is reported. By this mixing process, we introduce competing length scales; hence, we alter the self-organized packing that contributes to the synergistic effects on the functional properties of the networks. The experimental findings show a gradual change of volume fraction and aspect ratio as well as a 2-fold increase in electrical conductivity for such networks at certain specific compositions, hence an average aspect ratio. Quantitative large-area scanning transmission electron microscopy (STEM) imaging indeed revealed the existence of such mesoscale packing distribution variations. These packing observations suggest that these optimized networks of CNTs fit into an electrical conduction model that attributes its behavior to the formation of conduction knots, i.e., high-volume-fraction regions of relatively short CNTs that are connected by relatively long CNTs. If these conduction knots occupied by many short CNTs are distributed evenly with their nearest-neighbor distance being close to the average length of the CNT population, then the total electrical contact resistance in the conduction path will be effectively minimized. This study shows that optimized macroscale functional material properties can be designed into the initial colloidal dispersions by understanding and thus tuning the self-organization behavior of colloidal matter.

Electron tomography is a powerful tool that is widely used in materials science to unravel the 3D morphology of functional nanostructures such as organic solar cells. However, analysis of the 3D information is limited by the data quality which is dominated by the beam sensitivity of specimens. Therefore, it is necessary to develop advanced acquisition schemes to obtain high-quality 3D morphological information. In this work we simulate the electron tomography workflow to study the influence of the electrons dose, tilt range, and tilt scheme on the reconstruction quality. We employ a slab model of rodlike filler particles in a polymer matrix that is directly compared with the simulated 3D reconstruction using statistical means and by characterizing edge intensity profiles. We find that using counterintuitive acquisition schemes, i.e., large tilt increments at low electron doses, the reconstruction quality is preserved or even improved. Furthermore, inaccuracies in determining the position of interfaces between materials are quantified in dependence of the acquisition scheme with implications for volume and connectivity determination. Finally, it is shown that for the chosen specimen geometry at a tilt range of ±75° the resolution becomes isotropic regardless of the total electron dose and the tilt increment, which is a clear advantage for subsequent quantitative analysis.

To develop structure–performance relationships for important catalysts, a detailed characterization of their morphology is essential. Using electron tomography, we determined in three dimensions the structure of Pt/zeolite Y bifunctional catalysts. Optimum experimental conditions enabled for the first time high-resolution 3D imaging of Pt particles as small as 1 nm located inside zeolite micropores. Semiautomated image analysis of 3D reconstructions provided an efficient study of numbers, size distributions, and interparticle distances of thousands of Pt particles within individual zeolite crystals. Upon extending this approach to a number of zeolite crystals of one batch of Pt/zeolite Y catalyst, heterogeneities were revealed. The Pt loading, an important parameter for catalyst performance, varied between zeolite crystals up to a factor of 35. This discovery calls for re-evaluation of catalyst preparation methods and suggests potential for lowering the nominal loading with noble metals.

Quantitativen Einblickin die dreidimensionale Morphologie des komplexen Zeolith‐Y‐Mesoporennetzwerks verschaffte eine Kombination aus Elektronentomographie und Bildbearbeitung, durch die anders nicht untersuchbare Eigenschaften, wie die Größenverteilung der intakten mikroporösen Domänen, zugänglich wurden. Das ist für die Beschreibung der Moleküldiffusion durch Zeolithkristalle und damit die katalytische Aktivität und Selektivität von großer Bedeutung.

The efficiency of filling carbon nanotubes (CNTs) by ultrasound‐assisted wet impregnation is quantified by electron tomography (ET). For image analysis, a method that combines edge detection with single‐value thresholding is proposed and validated. A high proportion (80 wt %) of the ruthenium was deposited inside the tube at an average particle size of 2–4 nm. Particles located on the outer surface of the CNT had a size of 1–3 nm. The local ruthenium loading measured by ET (3.2 wt %) closely matched the value from elemental analysis (3.5 wt %). In addition, a few 1 nm‐sized ruthenium particles were detected inside the carbon wall, which contained pores/cracks. Direct imaging and quantification is a powerful tool to understand and possibly model the unique properties of CNT‐based catalysts.

Working at the Y: Zeolite Y crystals with micropores (ca. 1 nm), small mesopores (ca. 3 nm), and large mesopores (ca. 30 nm) were obtained by base leaching of previously steamed and acid‐leached material. The zeolite Y crystals with trimodal porosity (see electron‐tomographic picture) displayed close to ideal hydrocracking selectivity and enhanced yields of kerosene and diesel.

The investigation of solution‐borne nanostructures by transmission electron microscopy (TEM) is a frequently used analytical method in materials chemistry. In many cases, the preparation of the TEM sample involves drying and staining steps, and the collection of images leads to the interaction of the specimen with the electron beam. Both aspects call for cautious interpretation of the resulting electron micrographs. Alternatively, a near‐native solvated state can be preserved by cryogenic vitrification and subsequent imaging by low‐dose cryogenic TEM. In this Minireview, we provide a critical analysis of sample preparation, and more importantly, of the acquisition and interpretation of electron micrographs. This overview should provide a framework for the application of (cryo)‐TEM as a powerful and reliable tool for the analysis of colloidal and self‐assembled structures with nanoscopic dimensions.

In der Materialchemie werden in Lösung gezüchtete Nanostrukturen oft mithilfe der Transmissionselektronenmikroskopie (TEM) untersucht. Häufig werden die TEM‐Proben bei der Probenvorbereitung getrocknet und kontrastiert, und bei der Bildaufnahme selbst kommt es zur Wechselwirkung zwischen der Probe und dem Elektronenstrahl. Beide Prozesse rufen zur Vorsicht bei der Interpretation der erhaltenen elektronenmikroskopischen Aufnahmen auf. Alternativ dazu kann durch kryogene Probenpräparation und anschließende Abbildung mit kryogener Niederdosis‐TEM ein beinahe nativer solvatisierter Zustand konserviert werden. In unserem Kurzaufsatz geben wir eine kritische Analyse der Probenvorbereitung und, noch wichtiger, der Datenaufnahme und Interpretation von elektronenmikroskopischen Aufnahmen. Die Übersicht soll auch Leitlinien für die Anwendung von (Kryo‐)TEM als leistungsstarkes und zuverlässiges Hilfsmittel für die Analyse kolloidaler und selbstorganisierter Strukturen mit Abmessungen im Nanometerbereich bieten.

A new family of periodic mesoporous organosilicas with 100% E-configured ethenylene-bridges and controllable pore systems is presented. 2D hexagonally ordered hybrid nanocomposites consisting of cylindrical pores are obtained, of which some are filled with solid material. The architectural composition of these hybrid materials can be accurately controlled by fine-tuning the reaction conditions; that is, there is a unique correlation between the reaction mixture acidity and the amount of confined mesopores. This correlation is related to the filling of the pores with solid material whereby the length of the pore channels can be tailored. Hereby the mesophase either shifts toward long-ranged 2D hexagonally ordered open cylinders or toward 3D hexagonally ordered interconnected spheres. The synthesis of these organic−inorganic hybrid composites is straightforward via the direct condensation of E-1,2-bis(triethoxysilyl)ethene, in the presence of pluronic P123. The true nature of these periodic mesoporous organosilicas is disclosed by means of nitrogen gas physisorption, nonlocal density functional theory, SAXS, TEM, and electron-tomography.

Abstract—We used high‐resolution transmission electron microscopy (HRTEM), electron tomography, electron energy‐loss spectroscopy (EELS), and energy‐dispersive spectroscopy (EDS) to investigate the structure and composition of polyhedral serpentine grains that occur in the matrices and fine‐grained rims of the Murchison, Mighei, and Cold Bokkeveld CM chondrites. The structure of these grains is similar to terrestrial polygonal serpentine, but the data show that some have spherical or subspherical, rather than cylindrical morphologies. We therefore propose that the term polyhedral rather than polygonal be used to describe this material. EDS shows that the polyhedral grains are rich in Mg with up to 8 atom% Fe. EELS indicates that 70% of the Fe occurs as Fe3+. Alteration of cronstedtite on the meteorite parent body under relatively oxidizing conditions is one probable pathway by which the polyhedral material formed. The polyhedral grains are the end‐member serpentine in a mineralogic alteration sequence for the CM chondrites.

Many mineral crystallization processes in aqueous solutions involve formation of nanoclusters with short-range order. Their transformation into crystalline products is not well understood. Here we investigate the formation of long-range crystalline order within networks of cobalt-based nanoclusters. High-resolution cryogenic transmission electron microscopy (cryoTEM) together with NMR and FTIR spectroscopies shows the formation of ∼0.8 nm sized (Co)(NH3)5CO3complexes at the initial stage. By ligand exchange, those complexes become bridged by CO32–/OH–ligands and form ∼2 nm sized clusters, which subsequently aggregate into sheetlike networks due to the structural heterogeneity of the clusters. By further ligand change and adjustment in cluster orientations, long-range order is established, which leads to the nucleation of ammonium cobalt kambaldaite nanocrystals. Our observations demonstrate that nanoclusters with short-range order can form crystals via an oriented-attachment pathway, which provides new insights into multistep crystallization processes.

No Abstract

Review: ca. 80 refs.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.