Bernd Struth

Layer-by-layer assembled multicomposite films

Three topics in the field of layer-by-layer assembly have made significant progress recently: structural investigations on multilayers composed of strong flexible polyelectrolytes and the development of a model for composition and architecture of films of this kind; the incorporation of enzymes in multilayers for either biosensing or multistep biocatalysis; and the investigation of electroluminescent properties of such films.

Influence of ether linkages on the structure of double-chain phospholipid monolayers

Abstract The structure of phosphatidylcholine monolayers has been studied by Synchrotron X-ray diffraction at the air/water interface varying the ester and ether linkages of the aliphatic tails at the glycerol backbone. All systems investigated exhibit an oblique lattice structure with extremely large tilt angles of the chains from vertical, even at high lateral pressures. Although no large difference is seen in the isotherms, the replacement of ester by ether linkages causes a reduction of the tilt angle and of the area per molecule. These changes also depend on the position of the ether group with respect to the glycerol backbone and can be understood within a model where the carbonyl group of the ester at the C2 position pulls the attached chain towards the water subphase.

Sticking polydisperse hydrophobic magnetite nanoparticles to lipid membranes.

The formation of a layer of hydrophobic magnetite (Fe(3)O(4)) nanoparticles stabilized by lauric acid is analyzed by in situ X-ray reflectivity measurements. The data analysis shows that the nanoparticles partially disperse their hydrophobic coating. Consequently, a Langmuir layer was formed by lauric acid molecules that can be compressed into an untilted condensed phase. A majority of the nanoparticles are attached to the Langmuir film integrating lauric acid residue on their surface into the Langmuir film. Hence, the particles at the liquid-gas interface can be identified as so-called Janus beads, which are amphiphilic solids having two sides with different functionality.

Chemical modification of Topaz surfaces

In chemisorption, one is typically faced with the problem that the two-dimensional structure of the organic layer does not match the structure of the inorganic substrate. This work describes the first steps toward an induced epitaxial correlation of organic compounds on an inorganic surface. The idea of this work was to use a single crystal with a two-dimensional surface structure, Topaz (001), that matches an alkyl chain lattice better than existing substrates. X-ray reflectivity and FTIR experiments prove the surface modification of the Topaz, which is probably an etherification of the reactive OH-groups on the Topaz (001) surface.

Formation of iron containing aggregates at the liquid-air interface.

The early stages of the formation of inorganic aggregates, composed of iron compounds at the solution-air interface, were investigated in situ. The properties of the solution-air interface were changed by using different Langmuir layers. In order to get insight into the evolution of the sample system in situ, the processes were studied by X-ray scattering and spectroscopy techniques. The formation of aggregates was detected under cationic as well as under anionic Langmuir layers. The observed compounds lack long range order which indicates the formation of amorphous structures. This is supported by extended X-ray absorption fine structure measurements showing only minor order in the formed aggregates.