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Decomposition, dewetting, and adhesive-driven patterns and dynamicsExperiments on the dynamics of thin films of binary mixtures of polymers show complex behaviour not known from the dewetting of simple liquids. The dewetting via convective flow caused by effective molecular interactions between substrate and film surface is accompanied by diffusion processes that may lead to phase ordering. These can even change the pathways of dewetting. In cases involving ultrathin films of thicknesses below 100 nm on or between chemically structured substrates the phase ordering (and dewetting) may be strongly influenced by the lateral variation of the substrate properties. In addition to confinement, the pattern formation can be driven by external forces. An alternative mechanism of pattern formation in thin adsorbed layers which will be studied within this sub-project involves cavity nucleation and subsequent crack propagation in adhesive films. We plan to model the dynamics of adsorbed thin films by a mesoscopic continuum description specially adapted to accommodate driven and non-driven thin films adsorbed on/between nanostructured substrates; to develop analytical and numerical bifurcation tools and simulations for coupled 1D and 2D fields; to ascertain the role of the stochastic influence of the microscale on the mesoscale by the inclusion of noise or by hybrid micro-meso models; to determine the physiochemical dynamics underlying pattern formation in adhesive layers and thus establish their role in determining adhesive strength; and to use graph theory to analyse the network properties.
Self-organised criticality in micro- and nanostructured systemsWe will focus on five areas where dynamic critical behaviour is of especial interest: (i) the importance of self-organised criticality in pattern formation; (ii) the emergence of networks in complex systems (nanoparticles, polymers, autocatalysis); (iii) transport properties of nanoparticle assemblies, and (iv) electrical and magnetic (Barkhausen) noise in nanoparticle arrays. We will apply statistical mechanics and graph theory to quantify and predict the evolution of networks and patterns in nanoparticle and polymer systems, carry out experimental measurements of a wide range of nanoparticle, conducting polymer, and nanoparticle-polymer hybrid networks and arrays, compare the measurements against theoretical predictions of network conduction, carry out a combined theory-experiment study of electrical and magnetic noise in nanoscale systems and explore the roles of Barkhausen noise and electromigration-related effects in nanostructured films.
Self-organising chemical systemsChemical systems are comparatively simple to investigate, and have proven to be important models for the exploration and analysis of self-organized pattern formation. Even simple autocatalytic systems like the CO-oxidation on Pt-like metals show all the rich non-linear dynamics phenomena of the more complex systems and are nevertheless environmentally very important. Any enhancement in understanding and in the control of these surface reactions will have a clear fundamental scientific and industrial impact. We plan to study pattern formation in CO oxidation reations under feedback and periodic forcing in order to coerce the pattern forming process to form particular surface morphologies; to extend these investigations to composite materials created by microlithography to establish the impact of multi-component systems on the self-organisation process; to manipulate reaction patterns using focused laser beams on lithographically-modified catalytic surfaces; and to apply mechanical oscillations of ultrathin catalytic crystals to the construction of simple sensors for very low reaction rates in heterogeneous catalysis.
Pattern Formation in Nanoparticle Self-OrganisationInvestigate the roles of spinodal decomposition, hydrodynamics, nanoparticle and/or substrate functionalisation, viscoelasticity, and (de)wetting in the self-organisation of nanoparticles on technologically important substrates. To develop protocols to tune the non-equilibrium self-organisation of metal nanoparticles across multiple length scales by exploiting phase transitions, thermal grating effects, Faraday instabilities, and variations in substrate/nanoparticle chemistry. To use this tuning ability to control the self-organisation process and thus form pre-defined nanostructures. To explore pattern formation in nanoparticle-polymer hybrids. In particular, to exploit and control phase transitions and dewetting in these systems with aim of generating anisotropic structures.
Patterning via field-induced instabilitiesIn addition to the study of fundamental aspects of patterns formation, it is often desirable to interact with the pattern formation process. This can be achieved by, for example, modifying the boundary conditions (e.g. dewetting or demixing on a patterned substrate). In a more robust approach, forces are applied that act thoughout the sample. This was recently demonstrated using electric fields and temperature gradients. These forces can not only trigger pattern formation processes that display a surprising variety of structures, but they can also be used to replicate templates with a lateral resolution down to 100 nm. We plan to gain an understanding of the fundamental processes that lead to pattern formation; to explore the limits in the pattern formation and replications process, with the aim to establish novel lithographic techniques; to investigate the interplay of different pattern forming processes with the aim to develop new strategies for the creation/ replication of hierarchical patterns (i.e. patterns spanning 1mm down to 10nm length-scales); to extend the pattern formation process to new materials, with the aim to manufacture surfaces/ thin films with novel functionalities (e.g. polymeric light emitting materials, organic photovoltaics, nanoparticle-polymer hybrids, optical band-gap materials, (super)conducting thin film structures, self-cleaning surfaces, etc..); to explore (via both experiment and theory) electrophoretic synthesis of nanoparticle networks; to exploit E fields in the fabrication of novel hybrid nanoparticle-polymer nanostructures; to synthesis a variety of novel patterns/ architectures in ferrofluids and mixed nonmagnetic-magnetic NP systems via the application of B fields.
thiele at mpipks-dresden.mpg.de