Characterization of the dynamics of block copolymer microdomains with local morphological measures.

We investigate the structure formation in thin films of cylinder forming block copolymers. With in situ scanning probe microscopy image sequences can be recorded with high temporal (2 min per frame) and spatial (10 nm) resolution. We compare different image processing methods for quantitative analysis of the large amount of data. Computing local Minkowski functionals yields local geometrical and morphological information about the observed structures and enables us to track their evolution with time. An alternative characterization method is to reduce the gray scale images to their skeleton and to classify and count the branching points of the skeletonized structure. We tracked the temporal evolution of these measures and computed correlation functions.

Visualizing the dynamics of complex spatial networks in structured fluids.

We present a data reduction and visualization approach for the microdomain dynamics in block copolymers and similar structured fluids. Microdomains are reduced to thin smooth lines with colored branching points and visualized with a tool for protein visualization. As a result the temporal evolution of large volume data sets can be perceived within seconds. This approach is demonstrated with simulation results based on the dynamic density functional theory of the ordering of microdomains in a thin film of block copolymers. As an example we discuss the dynamics at the cylinder-to-gyroid grain boundary and compare it to the epitaxial cylinder-to-gyroid phase transition predicted by Matsen [Phys. Rev. Lett. 80, 4470 (1998)].

Automatization of nanotomography.

An approach for automated nanotomography, a layer-by-layer imaging technique based on scanning probe microscopy (SPM), is presented. Stepwise etching and imaging is done in situ in a liquid cell of an SPM. The flow of etching and rinsing solutions after each etching step is controlled with solenoid valves which allow for an automated measuring protocol. The thermal drift and the drift of the piezo scanner is corrected by applying offsets calculated from the cross correlation coefficients between successive images. As an example, we have imaged human bone with approximately 10 nm resolution using tapping mode SPM and successive etching with hydrochloric acid.

Identification of nanoscale dissipation processes by dynamic atomic force microscopy.

Identification of energy-dissipation processes at the nanoscale is demonstrated by using amplitude-modulation atomic force microscopy. The variation of the energy dissipated on a surface by a vibrating tip as a function of its oscillation amplitude has a shape that singles out the dissipative process occurring at the surface. The method is illustrated by calculating the energy-dissipation curves for surface energy hysteresis, long-range interfacial interactions and viscoelasticity. The method remains valid with independency of the amount of dissipated energy per cycle, from 0.1 to 50 eV. The agreement obtained between theory and experiments performed on silicon and polystyrene validates the method.

Direct imaging and mesoscale modelling of phase transitions in a nanostructured fluid.

The kinetics of phase transitions is essential for understanding pattern formation in structured fluids. These fluids play a key role in the morphogenesis of biological cells, and they are very common in pharmaceutical products and plastic materials. Until now, it has not been possible to follow phase transitions in structured fluids experimentally in real time and with high spatial resolution. Previous work has relied on static images and indirect experimental evidence from spatially averaging scattering experiments. Simulating the processes with computer models is a further challenge because of the multiple time and length scales involved. Our movies based on in situ scanning force microscopy show the time sequence of the elementary steps of a phase transition in a fluid film of block copolymer from the cylinder to the perforated lamella phase. The movies validate a versatile simulation model that gives physical insight into the nature of the process. Our approach provides a means of improving the study and understanding of pattern formation processes in nanostructured fluids. We expect a significant impact on nanotechnology where block copolymers serve as self-organized templates for the synthesis of inorganic nanostructured materials.

Phase behavior in thin films of cylinder-forming ABA block copolymers: mesoscale modeling.

The phase behavior of cylinder-forming ABA block copolymers in thin films is modeled in detail using dynamic density functional theory and compared with recent experiments on polystyrene-block-polybutadiene-block-polystyrene triblock copolymers. Deviations from the bulk structure, such as wetting layer, perforated lamella, and lamella, are identified as surface reconstructions. Their stability regions are determined by an interplay between surface fields and confinement effects. Our results give evidence for a general mechanism governing the phase behavior in thin films of modulated phases.

Role of dissimilar interfaces in thin films of cylinder-forming block copolymers.

We study the effect of dissimilar interfaces on the phase behavior of cylinder forming block copolymers in thin films by means of dynamic density-functional theory. In this article, we show that dissimilarity of the interfaces induces hybrid structures. These structures appear when the surface fields at the two interfaces stabilize different surface structures and/or reconstructions. We propose a general classification of hybrid structures and give an unifying description of phase behavior of cylinder forming block copolymer films. Our results are consistent with experimental observations.

Phase behavior in thin films of cylinder-forming block copolymers.

We have experimentally determined a phase diagram for cylinder-forming polystyrene-block-polybutadien-block-polystyrene triblock copolymer in thin films. The phase behavior can be modeled in great detail by dynamic density functional theory. Deviations from the bulk structure, such as wetting layer, perforated lamella, and lamella, are identified as surface reconstructions. Their stability regions are determined by an interplay between surface fields and confinement effects.

Surface reconstruction of an ordered fluid: an analogy with crystal surfaces.

The surface structure of a lamellar polystyrene-block-polybutadiene-block-polymethylmethacrylate (SBM) triblock copolymer forms a complex reconstruction, which breaks the two-dimensional continuous translational symmetry of an ideal (homogeneous) SBM surface. Despite the very different types of matter and order, our findings reveal a remarkable analogy with the well-known phenomenon of surface reconstruction of single crystals, in particular, with the (2x1) "buckling row" reconstruction of the Si(100) surface. Similarities and differences between both classes of materials are discussed on the basis of symmetry considerations.

Nanotomography

Scanning probe microscopy (SPM) can be expanded to volume imaging. As an example, the core of a dislocation within the three-dimensional (3D) spatial microdomain structure of poly(styrene-block-butadiene-block-styrene) was imaged with approximately 10 nm resolution. The specimen was eroded step by step and its chemical composition in layers beneath the original surface was imaged with SPM. Similar to computed tomography, the 3D distribution of polystyrene and polybutadiene was reconstructed from a series of images. This approach might provide a simple means for real-space volume imaging with nanometer and even atomic resolution of various materials and physical properties.

Destabilization of egg lecithin liposomes on the skin after topical application measured by perturbed gamma gamma angular correlation spectroscopy (PAC) with 111In.

Unilamellar and oligolamellar liposomes were topically applied to the skin of porcine ears. Perturbed angular correlation spectroscopy of 111In-DTPA, initially entrapped into the liposomes, was used to study the release kinetics of the hydrophilic probe. After drying of the liposomal suspensions, a decrease of the time-integrated perturbation factor within 30 min indicated destabilization of the liposomes and total marker release in the upper epidermal layers.

[The "white hole" phenomenon--a potential functional parameter in non-gated 201Tl-myocardial scintigraphy]. / Das "white hole"-Phänomen--ein möglicher Funktions-parameter der ungetriggerten 201Tl-Myokardszintigraphie.

In 50 patients with a "white hole" in their scintigram--among them 44 patients with a history of myocardial infarction--the relation between its relative volume and the ventriculographically determined ejection fraction was studied retrospectively. A relative volume of the "white hole" larger than 13.7% showed a specificity of 93% and a sensitivity of 45% for a decreased ejection fraction and had a significant correlation of r = -0.54 (alpha = 0.01) with the ejection fraction. Thus the relative volume of the "white hole" derived automatically from 201Tl-SPECT is an easy-to-determine additional parameter which allows an at least semiquantitative statement about the function of the left ventricle.