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We study the crystallization of colloidal dispersions under capillary-action-induced shear as the dispersion is drawn into flat walled capillaries. Using confocal microscopy and small angle x-ray scattering, we find that the shear near the capillary walls influences the crystallization to result in large random hexagonal close-packed (RHCP) crystals with long-range orientational order over tens of thousands of colloidal particles. We investigate the crystallization mechanism and find partial crystallization under shear, initiating with hexagonal planes at the capillary walls, where shear is highest, followed by epitaxial crystal growth from these hexagonal layers after the shear is stopped. We then characterize the three-dimensional crystal structure finding that the shear-induced crystallization leads to larger particle separations parallel to the shear and vorticity directions as compared to the equilibrium RHCP structure. Confocal microscopy reveals that competing shear directions, where the capillary walls meet at a corner, create differently oriented hexagonal planes of particles. The single-orientation RHCP colloidal crystals remain stable after formation and are produced without the need of complex shear cell arrangements. [ABSTRACT FROM AUTHOR]

β‐NaYF4 nanocrystals are a popular class of optical materials. They can be doped with optically active lanthanide ions and shaped into core‐multi‐shell geometries with controlled dopant distributions. Here, we follow the synthesis of β‐NaYF4 nanocrystals from α‐NaYF4 precursor particles using in situ small‐angle and wide‐angle X‐ray scattering and ex situ electron microscopy. We observe an evolution from a unimodal particle size distribution to bimodal, and eventually back to unimodal. The final size distribution is narrower in absolute numbers than the initial distribution. These peculiar growth dynamics happen in large part before the α‐to‐β phase transformation. We propose that the splitting of the size distribution is caused by variations in the reactivity of α‐NaYF4 precursor particles, potentially due to inter‐particle differences in stoichiometry. Rate equation modeling confirms that a continuous distribution of reactivities can result in the observed particle growth dynamics. [ABSTRACT FROM AUTHOR]

β‐NaYF4 nanocrystals are a popular class of optical materials. They can be doped with optically active lanthanide ions and shaped into core‐multi‐shell geometries with controlled dopant distributions. Here, we follow the synthesis of β‐NaYF4 nanocrystals from α‐NaYF4 precursor particles using in situ small‐angle and wide‐angle X‐ray scattering and ex situ electron microscopy. We observe an evolution from a unimodal particle size distribution to bimodal, and eventually back to unimodal. The final size distribution is narrower in absolute numbers than the initial distribution. These peculiar growth dynamics happen in large part before the α‐to‐β phase transformation. We propose that the splitting of the size distribution is caused by variations in the reactivity of α‐NaYF4 precursor particles, potentially due to inter‐particle differences in stoichiometry. Rate equation modeling confirms that a continuous distribution of reactivities can result in the observed particle growth dynamics. [ABSTRACT FROM AUTHOR]

The characterization of periodic order in assemblies of colloidal particles can be complicated by the coincidence of Bragg diffraction peaks of the structure and minima in the form factor of the particles. Here, we demonstrate a general strategy to overcome this problem that is applicable to all low-dimensional structures. This approach is demonstrated in the application of small-angle X-ray scattering (SAXS) for the characterization of monolayers of colloidal silica superballs prepared using the unidirectional rubbing method. In this method, the ordering of the colloidal superballs is achieved by mechanically rubbing them onto a polydimethylsiloxane (PDMS)-coated surface. Using three differently shaped superballs, ranging from spherical to almost cubic, we show that certain Bragg peaks may not appear in the diffraction patterns due to the presence of minima in the form factor. We show that these missing Bragg peaks can be visualized by imaging the colloidal monolayers at various orientations. Moreover, we argue that the same strategy can be applied to other techniques, such as neutron scattering. [ABSTRACT FROM AUTHOR]

The adsorption, self-organization and oriented attachment of PbSe nanocrystals (NCs) at liquid-air interfaces has led to remarkable nanocrystal superlattices with atomic order and a superimposed nanoscale geometry. Earlier studies examined the NC self-organization at the suspension/air interface with time-resolved in-situ X-ray scattering. Upon continuous evaporation of the solvent, the NC interfacial layer will finally contact the (ethylene glycol) liquid substrate on which the suspension was casted. In order to obtain structural information on the NC organization at this stage of the process, we examined the ethylene glycol/NC interface in detail for PbSe NCs of different sizes, combining in-situ grazing-incidence small-and-wide-angle X-ray scattering (GISAXS/GIWAXS), X-ray reflectivity (XRR) and analytical calculations of the adsorption geometry of these NCs. Here, we observe in-situ three characteristic adsorption geometries varying with the NC size. Based on the experimental evidence and simulations, we reveal fully three-dimensional arrangements of PbSe nanocrystals at the ethylene glycol-air interface with and without the presence of rest amounts of toluene. To understand the self-assembly of semiconductor nanocrystals, the formation mechanism of two-dimensional superlattices needs to be deciphered. Here the authors observe lead selenide nanocrystal organization at the ethylene glycol-air interface combining in-situ grazing-incidence small -and-wide-angle X-ray scattering, X-ray reflectivity and analytical calculations to obtain a three-dimensional picture of the adsorption geometry of the nanocrystals. [ABSTRACT FROM AUTHOR]

A novel compact small‐angle X‐ray scattering (SAXS) setup with tuneable resolution in both direct and reciprocal space has been designed and tested for the study of nanostructured materials with a hierarchical structure. The setup exploits a set of compound refractive lenses that focus the X‐ray beam at the detector position. Anodic alumina membranes with a self‐ordered porous structure were chosen as test samples. The setup allows patterns to be collected with a minimum scattering vector value of 0.001 nm−1 and gives the possibility for an easy continuous switch between taking high‐resolution statistically averaged diffraction data of macroscopically large sample volumes and lower‐resolution diffraction on a small single domain of the anodic aluminium oxide film. It is revealed that the pores are longitudinal and their ordering within each domain tends towards the ideal hexagonal structure, whereas the in‐plane orientation of the pore arrays changes from domain to domain. The possible advantages and disadvantages of the proposed compact SAXS scheme are discussed. [ABSTRACT FROM AUTHOR]

Anisotropic and binary colloids self-assemble into a variety of novel supracolloidal structures within the thermo-switchable confinement of molecular microtubes, achieving structuring at multiple length scales and dimensionalities. The multistage self-assembly strategy involving hard colloidal particles and a soft supramolecular template is generic for colloids with different geometries and materials as well as their binary mixtures. The colloidal architectures can be controlled by colloid shape, size, and concentration. Colloidal cubes align in chains with face-to-face arrangement, whereas rod-like colloids predominantly self-organize in end-to-end configurations with their long axis parallel with the long axis of the microtubes. The 1D microconfinement imposed on binary mixtures of anisotropic and isotropic colloids further increases the diversity of colloid-in-tube structures. In cube-sphere mixtures, cubes may act as additional confiners, locking in colloidal sphere chains, while a 'colloidal Morse code' is generated where rods and spheres alternate in the case of rod-sphere mixtures. The versatile confined colloidal superstructures including their thermoresponsive assembly and disassembly are relevant for the development of stimulus-responsive materials where controlled release and encapsulation are desired. [ABSTRACT FROM AUTHOR]

Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-assembly of core-shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close-packed (RHCP) one. External field drives the self-assembly toward a body-centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles. [ABSTRACT FROM AUTHOR]

Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-assembly of core-shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close-packed (RHCP) one. External field drives the self-assembly toward a body-centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles. [ABSTRACT FROM AUTHOR]

The crystalline structure assembled out of charge-stabilized asymmetric dumbbell-like colloidal particles in ethyl alcohol by sedimentation has been probed using small-angle X-ray scattering with microradian resolution. The existence of plastic face-centered cubic crystals was inferred from the observed Bragg peaks. The presence of stacking faults and the mosaic structure of the sample lead to the appearance of diffuse scattering, forming Bragg scattering cylinders in the three-dimensional reciprocal space. The quality of the crystalline structure, as ascertained from a detailed analysis of the diffuse scattering intensity distribution, indicates the presence of only 1.5% of stacking faults between the hexagonal close-packed layers. [ABSTRACT FROM AUTHOR]

Die gemeinsame Assemblierung von sphärischen Kolloiden und Mikroröhren bestehend aus Tensiden und Cyclodextrinen führte zu dynamischen Kolloid ‐ in ‐ Röhre ‐ Strukturen, darunter Helices. In ‐ situ ‐ Beobachtungen dieser Strukturen, u. a. ihres thermoreversiblen Auf ‐ und Abbau, demonstrieren das Zusammenspiel von molekularer und kolloidaler Selbstassoziation und zeigen den Weg für eine temperatursensitive Partikelanordnung und ‐ freisetzung auf. [ABSTRACT FROM AUTHOR]

The co‐assembly of spherical colloids and surfactant–cyclodextrin microtubes yields a library of dynamic colloid‐in‐tube structures, including helices. In situ observations of these structures, including their thermo‐reversible assembly and disassembly, demonstrate the potential of the interplay between molecular and colloidal self‐assembly, thereby providing a novel route to temperature‐sensitive particle alignment and release. [ABSTRACT FROM AUTHOR]

Hard sphere crystal growth is a delicate interplay between kinetics and thermodynamics, where the former is commonly thought to favour a random hexagonal close packed structure and the latter leads to a face centered cubic crystal. In this article, we discuss the influence of slanted stacking faults on the growth of sedimentary colloidal crystals from dispersions with high initial volume fraction and particles that sediment relatively fast. We find that the presence of these persisting faults locally induces fcc structure, while defect free regions form rhcp crystals as expected for a system where kinetics dominate. These results are promising for use in epitaxial growth of colloidal crystals, where proper templating could lead to almost perfect fcc crystals with selectively incorporated defects. [ABSTRACT FROM AUTHOR]

Hard sphere crystal growth is a delicate interplay between kinetics and thermodynamics, where the former is commonly thought to favour a random hexagonal close packed structure and the latter leads to a face centered cubic crystal. In this article, we discuss the influence of slanted stacking faults on the growth of sedimentary colloidal crystals from dispersions with high initial volume fraction and particles that sediment relatively fast. We find that the presence of these persisting faults locally induces fcc structure, while defect free regions form rhcp crystals as expected for a system where kinetics dominate. These results are promising for use in epitaxial growth of colloidal crystals, where proper templating could lead to almost perfect fcc crystals with selectively incorporated defects. [ABSTRACT FROM AUTHOR]

Microradian X-ray diffraction from sedimentary colloidal crystals is studied using synchrotron radiation with photon energies of 12.4, 27, and 38 keV. Stacking disorder in these hard-sphere crystals leads to diffuse X-ray scattering along the Bragg scattering rods normal to the randomly stacked layers. We observed the appearance of diffuse scattering, shown to be induced by multiple scattering, along the secondary Bragg rods in between the stacking-independent true Bragg reflections. This effect can be reduced by measuring at higher X-ray energies. [ABSTRACT FROM AUTHOR]

A simple model is presented that allows calculation of the small-angle X-ray diffraction patterns of perfect colloidal crystals. The model is based on the Wentzel–Kramers–Brillouin approximation and permits a straightforward evaluation of multibeam interactions. Results are illustrated by several examples. [ABSTRACT FROM AUTHOR]

This paper describes the characterization of dispersions of oleic-acid-coated magnetic iron particles by small-angle neutron and X-ray scattering (SANS and SAXS). Both oxidized and non-oxidized dilute samples were studied by SANS at different contrasts. The non-oxidized samples are found to consist of non-interacting superparamagnetic single dipolar particles, with a lognormal distribution of iron cores, surrounded by a surfactant shell, which is partially penetrated by solvent. This model is supported by SAXS measurements on the same dispersion. Small iron particles are expected to oxidize upon exposure to air. SANS was used to study the effect of this oxidation, both on single particles, as well as on interparticle interactions. It is found that on exposure to air, a nonmagnetic oxide layer is formed around the iron cores, which causes an increase of particle size. In addition, particles are found to aggregate upon oxidation, presumably because the surfactant density on the particle surfaces is decreased. [ABSTRACT FROM AUTHOR]

Discusses the measurement of the structure of hard-sphere colloidal suspensions at different concentrations. Use of the spin-echo small-angle neutron scattering (SESANS) technique; Attempt to show that SESANS measures real-space correlations ranging from the size of the particle for a dilute suspension to several particle diameters for a concentrated suspension, glass and crystalline state.

In this work, we designed and fabricated a multifunctional nanocomposite system that consists of chitosan, raspberry-like silver nanoparticles, and graphene oxide. The room temperature atmospheric pressure microplasma (RT-APM) process provides a rapid, facile, and environmentally-friendly method for introducing silver nanoparticles into the composite system. Our composite can achieve a pH controlled single and/or dual drug release. Under pH 7.4 for methyl blue loaded on chitosan, the drug release profile features a burst release during the first 10 h, followed by a more stabilized release of 70–80% after 40–50 h. For fluorescein sodium loaded on graphene oxide, the drug release only reached 45% towards the end of 240 h. When the composite acted as a dual drug release system, the interaction of fluorescein sodium and methyl blue slowed down the methyl blue release rate. Under pH 4, both single and dual drug systems showed a much higher release rate. In addition, our composite system demonstrated strong antibacterial abilities against E. coli and S. aureus, as well as an excellent photothermal conversion effect under irradiation of near infrared lasers. The photothermal conversion efficiency can be controlled by the laser power. These unique functionalities of our nanocomposite point to its potential application in multiple areas, such as multimodal therapeutics in healthcare, water treatment, and anti-microbials, among others. [ABSTRACT FROM AUTHOR]

Many low-dimensional nanostructured metal oxides (MOXs) with impressive room-temperature gas-sensing characteristics have been synthesized, yet transforming them into relatively robust bulk materials has been quite neglected. Pt-decorated SnO2 nanoparticles with 0.25–2.5 wt% Pt were prepared, and highly attractive room-temperature hydrogen-sensing characteristics were observed for them all through pressing them into pellets. Some pressed pellets were further sintered over a wide temperature range of 600–1200 °C. Though the room-temperature hydrogen-sensing characteristics were greatly degraded in many samples after sintering, those samples with 0.25 wt% Pt and sintered at 800 °C exhibited impressive room-temperature hydrogen-sensing characteristics comparable to those of their counterparts of as-pressed pellets. The variation of room-temperature hydrogen-sensing characteristics among the samples was explained by the facts that the connectivity between SnO2 grains increases with increasing sintering temperature, and Pt promotes oxidation of SnO2 at high temperatures. These results clearly demonstrate that some low-dimensional MOX nanocrystals can be successfully transformed into bulk MOXs with improved robustness and comparable room-temperature gas-sensing characteristics. [ABSTRACT FROM AUTHOR]

Experimental evidence is presented for the spontaneous formation of chiral configurations in bulk dispersions of magnetized colloids that interact by a combination of anisotropic dipolar interactions and isotropic depletion attractions. The colloids are superparamagnetic silica spheres, magnetized and aligned by a carefully tuned uniform external magnetic field; isotropic attractions are induced by using poly(ethylene oxide) polymers as depleting agents. At specific polymer concentrations, sphere chains wind around each other to form helical structures–of the type that previously have only been observed in simulations on small sets of unconfined dipolar spheres with additional isotropic interactions. [ABSTRACT FROM AUTHOR]

The templating effect of the Keggin polyanion derived from phosphotungstic acid (PTA) during the synthesis of NH2-MIL-101(Al) has been investigated by means of in situSAXS/WAXS. Kinetic analysis and structural observations demonstrate that PTA acts as a nucleation site and that it stabilizes the precursor phase NH2-MOF-235(Al). Surprisingly kinetics of formation are little changed. [ABSTRACT FROM AUTHOR]

Proteins can readily assemble into rigid, crystalline and functional structures such as viral capsids and bacterial compartments. Despite ongoing advances, it is still a fundamental challenge to design and synthesize protein-mimetic molecules to form crystalline structures. Here we report the lattice self-assembly of cyclodextrin complexes into a variety of capsid-like structures such as lamellae, helical tubes and hollow rhombic dodecahedra. The dodecahedral morphology has not hitherto been observed in self-assembly systems. The tubes can spontaneously encapsulate colloidal particles and liposomes. The dodecahedra and tubes are respectively comparable to and much larger than the largest known virus. In particular, the resemblance to protein assemblies is not limited to morphology but extends to structural rigidity and crystallinity-a well-defined, 2D rhombic lattice of molecular arrangement is strikingly universal for all the observed structures. We propose a simple design rule for the current lattice self-assembly, potentially opening doors for new protein-mimetic materials. [ABSTRACT FROM AUTHOR]

Hierarchical, bottom‐up, self‐organization processes of nano‐ and microscale building blocks constitute an important design route for stimulus‐responsive materials. On page 313, Andrei V. Petukhov and co‐workers demonstrate that a rich variety of novel supracolloidal structures emerge from the self‐organization of various shape‐anisotropic colloids and binary mixtures of isotropic and anisotropic colloids in 1D microconfinement. [ABSTRACT FROM AUTHOR]

Hierarchische Selbstorganisation führt oft in der Natur zum Aufbau komplexer funktioneller Einheiten. Ein ähnlicher Ansatz, der die thermoreversible Coassemblierung sphärischer Kolloidpartikel und molekularer Mikroröhren nutzt, ergab dynamische Kolloid ‐ in ‐ Röhre ‐ Strukturen, wie kolloidale Zickzack ‐ Ketten, Doppel ‐ und Tripelhelices. Der Auf ‐ und Abbau dieser Strukturen nahe Körpertemperatur wurde in situ und in Echtzeit untersucht, wie J. Huang, A. V. Petukhov et al. in der Zuschrift auf S. 3448 ff. berichten. [ABSTRACT FROM AUTHOR]

Hierarchical self‐assembly is often exploited by nature to build complex functional entities. A similar approach yielded a library of dynamic colloid‐in‐tube structures, such as colloidal zigzags, double‐ and triple‐helices, by utilizing the thermo‐reversible co‐assembly of colloidal spheres and molecular microtubes, as reported by J. Huang, A. V. Petukhov, et al. in their Communication on page 3364 ff. The assembly and disassembly of these structures near human body temperature was explored in situ and in real time. [ABSTRACT FROM AUTHOR]