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B. Hartl:
"Softness- and anisometry-driven self-assembly in colloidal systems";
Poster: DOC award ceremony 2017, Aula der Wissenschaften, Vienna Austria; 09.06.2017.

Colloidal particles (with their size typically ranging from nm to µm) have become very useful, versatile, and highly appreciated building blocks in bottom-up self-assembly processes in many fields of technology, food industry, or pharmaceutics. This remarkable feature is due to the fact that these particles can be synthesized - in contrast to atomic building blocks - with suitable techniques with seemingly unlimited freedom in desired shapes (ellipsoids, cuboids, octapods, etc.), desired surface decorations (created via chemical or physical processes), and tailored interactions.

In order to steer these self-assembly processes as efficient as possible, it is mandatory to understand (i) the complex internal architecture of these marcomolecules (which, in turn, are built up by atomic or molecular entities), (ii) their overall behaviour as "effective" particles (i.e., when the huge number of degrees-of-freedom of the monomeric entities is averaged out) and (iii) - based on this information - their self-assembly strategies. Such a strategy, which covers the range from the monomeric level up to meso- or macroscopic scales requires in theoretical and simulation based approaches to the problem reliable models for the macromolecules that mimic the essential features of these particles (notably their shape, their deformability, and their interactions); based on such a model, suitable theoretical and numerical tools can be applied that allow a faithful description of the self-assembly processes.

In the overwhelming part of investigations dedicated to the self-assembly scenarios of colloids, so far, these particles were considered as soft, spherical (i.e., non-deformable) entities. The notation "soft" reflects the fact that these macromolecules are - due to their often rather loose internal structure - often able to overlap to a considerable amount. As for their shape, these particles are in reality - and confirmed in computer simulations - definitely not spherical and they are deformable; this holds in particular if one considers solutions of colloidal particles at intermediate and high densities.

In my project I want to systematically overcome these limitations imposed by sphericity and rigidity in shape, which were - so far - the result of conceptual and numerical restrictions. My idea is to treat the colloidal particles at any level of resolution as soft, penetrable, and deformable objects: to this end I will first study the particles at a monomeric level, i.e., by explicitly taking into account their internal architecture, formed by atomic or molecular entities.
By suitably tracing out the huge number of degrees-of-freedom of these units, I will then arrive at the second level, i.e., at the level of "effective particles" that interact via effective interactions. These particles will in general be aspherical in their shape; in addition, the interactions will reflect the deviation from the original, spherical symmetry. In order to establish connection to realistic systems I will closely collaborate on a third level with experimental group, investigating in a complementary fashion the self-assembly of colloidal particles with heterogeneously charged surfaces and the deposition of complex organic molecules on a gold surface. The investigations will be carried out with three different, numerical state-of-the-art methods which allow to explicitly include both softness and anisometry (in combination with deformability): the self-assembly scenarios will be studied with optimization tools that are based on ideas of evolutionary algorithm, thermodynamic and structural properties will be investigated by classical density functional theory and different types of computer simulations. To cope with the new challenges of this project, a considerable amount of time will be dedicated to develop and/or to adapt numerical tools that take softness, anisometry, and deformability of colloidal particles faithfully into account. These code developments require high level skills both in computational statistical physics as well as in informatics.

With my project I hope to contribute to a deeper understanding of bottom-up self-assembly processes of colloidal particles and to the structural and thermodynamic properties of the emerging phases.

Softness anisometry-driven self-assembly colloidal systems evolutionary

Projektleitung Benedikt Hartl:
Soft and Anisometric Self-Assembly