Covalent attachment of polymersomes to surfaces.

We show that vesicles made of block copolymers with aldehyde end groups can be covalently attached to aminated and non-aminated, untreated glass surfaces. The attached vesicles were sufficiently stable to allow a detailed investigation of vesicle shapes by confocal laser scanning microscopy (CLSM) and AFM in aqueous solutions allowing reconstruction of 3D images of the vesicle structure. Covalently attached PCL-PEO, PLA-PEO, and PI-PEO block copolymer vesicles have different footprint areas and different shapes due to their differences in bilayer stiffness.

Micelle and vesicle formation of amphiphilic nanoparticles.

Nanoparticle brushes: Complex nanostructures can be formed by self assembly of amphiphilic CdSe/CdS core-shell nanoparticles that bear a brushlike layer of poly(ethylene oxide) chains. This route is based on controlling the volume fractions of hydrophilic and hydrophobic moieties within the particles and allows the formation of micellar, cylindrical, or vesicular nanoobjects (see picture).

Highly ordered nanostructured surfaces obtained with silica-filled diblock-copolymer micelles as templates.

In this work, we present the size-controlled preparation of silica-filled micelle cores and their self-assembly behavior, which is dependent on the block lengths, different coating techniques, and substrates. Furthermore, we present a way to use these structures as templates for highly ordered magnetic nanostructures, revealed by Ar-ion milling. The resulting structures were characterized by different imaging and scattering techniques and model simulations were performed. The characterization of the obtained nanostructured surfaces has be performed with atomic force microscopy, by scanning electron microscopy, grazing-incidence X-ray small-angle scattering, and X-ray reflectivity measurements. The magneto-optical Kerr effect was utilized to investigate magnetic properties.

mu-GISAXS experiment and simulation of a highly ordered model monolayer of PMMA-beads.

Uniform sized PMMA-beads were deposited as a monolayer on silicon substrates using dip-coating techniques. High-resolution grazing incidence X-ray small angle scattering experiments were performed using a micrometer sized beam (mu-GISAXS) to determine the structure of a highly ordered monolayer with two-dimensional hexagonal arrays. A clear and strong interference pattern coming from the reflection and refraction effects of particles on flat surfaces with small uncorrelated roughnesses is shown. The quantitative analysis and simulations of the X-ray scattering pattern have been performed, and a detailed explanation of the analysis is reported. The results were directly compared and verified with atomic force microscopy (AFM) measurements and their resulting FFT spectra.

On the electric conductivity of highly ordered monolayers of monodisperse metal nanoparticles.

Monolayers of colloidally synthesized cobalt-platinum nanoparticles of different diameters characterized by transmission electron microscopy were deposited on structured silicon oxide substrates and characterized by scanning electron microscopy, grazing incidence X-ray scattering, and electric transport measurements. The highly ordered nanoparticle films show a thermally activated electron hopping between spatially adjacent particles at room temperature and Coulomb blockade at low temperatures. We present a novel approach to experimentally determine the particles charging energies giving values of 6.7-25.4 meV dependent on the particles size and independent of the interparticle distance. These observations are supported by finite element method calculations showing the self-capacitance to be the determining value which only depends on the permittivity constant of the surrounding space and the particles radius.

In situ synthesis and alignment of Au nanoparticles within hexagonally packed cylindrical domains of diblock copolymers in bulk.

We present a simple method to prepare hexagonally packed metallic nanocylinders based on gold nanoparticles embedded in a copolymeric matrix. The gold nanoparticles are generated selectively within the P4VP-rich cylindrical domains of a polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) diblock copolymer. In order to achieve this selectivity, a gold precursor (HAuCl4) is coupled to the pyridine blocks of a spherical PS327-b-P4VP27 block copolymer. In consequence, the hybrid block copolymer is able to self-assemble in a hexagonally packed cylinders morphology. The application of mechanical oscillatory shear improved markedly the alignment of these nanocylinders, while simultaneously the gold precursor was reduced in situ into gold nanoparticles. Following rheological characterization in the linear viscoelastic regime, a set of alignment parameters were comprehensively selected and checked with a series of transmission electron microscopy (TEM) micrographs. An optimal temperature of alignment was found after systematic evaluation of samples sheared at different temperatures. The block copolymer exhibited an increase in the domain period as a consequence of chain rearrangements around the newly formed gold nanoparticles. The hexagonally packed morphology was preserved, and under the optimal conditions single grain sizes showed significant improvement to macroscale order in comparison to nonaligned samples. In contrast to current multistep lithographic techniques, the present method constitutes a simple path to produce three-dimensional organic-inorganic conductive nanowires with periodicities at the macroscopic level.

Preparation and electrical properties of cobalt-platinum nanoparticle monolayers deposited by the Langmuir-Blodgett technique.

The Langmuir-Blodgett technique was utilized and optimized to produce closed monolayers of cobalt-platinum nanoparticles over vast areas. It is shown that sample preparation, "dipping angle", and subphase type have a strong impact on the quality of the produced films. The amount of ligands on the nanoparticle's surface must be minimized, the dipping angle must be around 105 degrees , while the glycol subphase is necessary to obtain nanoparticle monolayers. The achieved films were characterized by scanning electron microscopy (SEM) and grazing incidence X-ray scattering (GISAXS). The electrical properties of the deposited films were studied by direct current (DC) measurements, showing a discrepancy to the variable range hopping transport from the granular metal model and favoring the simple thermal activated charge transport. SEM, GISAXS, as well as DC measurements confirm a narrow size distribution and high ordering of the deposited films.

Direct observation of confined acoustic phonons in the photoluminescence spectra of a single CdSe-CdS-ZnS core-shell-shell nanocrystal.

We report on the direct observation of confined acoustic phonons in the photoluminescence spectra of single CdSe-CdS-ZnS nanocrystals, whose ligands were exchanged to poly(ethylene oxide) (PEO) before they were embedded in a PEO matrix. Modeling a nanocrystal as an elastic sphere, the confined acoustic modes can be assigned to purely radial vibrations: the breathing mode and its two first radial harmonics. In addition to acoustic modes, we also observe longitudinal optical modes of the core material and, remarkably, also of both shell materials.

Characteristics of picoliter droplet dried residues as standards for direct analysis techniques.

The characteristics of dried residues of picodroplets of single-, two-, and three-element aqueous solutions, which qualify these as reference materials in the direct analysis of single particles, single cells, and other microscopic objects using, e.g., laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and micro-X-ray fluorescence (MXRF), were evaluated. Different single-, two-, and three-element solutions (0.01-1 g/L) were prepared in picoliter volume (around 130 pL) with a thermal inkjet printing technique. An achievable dosing precision of 4-15% was calculated by total reflection X-ray fluorescence (TXRF) determination of the transferred elemental mass of an array of 100 droplets. The size of the dried residues was determined by optical microscopy to be 5-20 microm in diameter depending on the concentration and the surface material. The elemental distribution of the dried residues was determined with synchrotron micro-X-ray fluorescence (SR-MXRF) analyses. The MXRF results show high uniformity for element deposition of every single droplet with an RSTD of 4-6% depending on the concentration of spotted solution. The shape and height profile of dried residues from picoliter droplets were studied using atomic force microscopy (AFM). It was found that these dry to give symmetrical spherical segments with maximum heights of 1.7 microm. The potential of this technique for direct LA-ICP-TOF-MS analysis is shown.

Order causes secondary Bragg peaks in soft materials.

Highly ordered soft materials exhibit Bragg peaks that cannot be indexed assuming homogeneous crystal structures. Their origin has been attributed to changes in the crystal structure that are induced by the ordering process such as by application of external fields. This would restrict the use for the generation of highly ordered nano- and microstructured materials where a homogeneous crystal structure is a key requirement. Here, we demonstrate that these Bragg peaks are an inherent property of homogeneous ordered soft materials related to the finite coherence of their crystalline lattice. Their consideration allows a detailed and quantitative analysis of the diffraction patterns of seemingly unrelated materials such as lyotropic liquid-crystalline phases, mesoporous materials, colloidal dispersions, block copolymers, electrorheological fluids and photonic crystals. It further enables us to develop a concise picture of order, line density, field-induced orientation and epitaxial relations for soft-material lattices.