Jure Dobnikar   |   Organization of Soft and Biological Matter


Magnetic Membranes

Self-assembly of magnetic colloids

In cooperation with the Experimental Soft Matter Lab in Ljubljana, we recently studied self-assembly of magnetic colloids in external fields. In quasi-2D confinement we explained the clustering mechanism of soft repulsive particles. In time-dependent magnetic driving at the magic-angle geometry the induced pair interactions are isotropic Van der Waals-like, and yet we observed formation of chains, networks and thin colloidal membranes. We have theoretically explained the aggregation pathway by including many-body polarization effects. I am currently studying the elastic properties of the magnetic low-dimensional structures, as well as the magneto-hydrodynamic coupling.

PRL 2009, PRL 2007, JPCM 2009 , Soft Matter 2013

Colloidal interactions at soft surfaces

Soft surfaces mediate complex interactions between colloids or macromolecules, leading to novel aggregation patterns or dynamic behaviour. We have seen that even simple hard spheres immersed into polymer brushes exhibit non-trivial clustering and crystallization patterns [preprint 2012]. I study the inclusion of nanoparticles into polymer brushes and their collective interactions within the brushes by means of Monte Carlo and Molecular Dynamics simulations. I am interested in the effects of direct and surface-induced particle interactions, elastic properties and geometry of the confining surfaces, selective binding and driving by external fields on particle organization and dynamics.

PRE 2012, PNAS 2012, Soft Matter 2013,

Bacterial motility

I am interested in the design aspects of biological systems translating noise on the micro scale into beneficial macroscopic behaviour. We have studied chemotactic response of E. coli to external stimuli and showed that stochastic fluctuations can alter their search strategy from diffusive to super-diffusive (LÚvy walks), which presents an evolutionary advantage in nutrientpoor environments. Recently, I am interested in how the regulation mechanisms and evolution enable the populations to adapt to large environmental variations including emergence of resistance to drugs. I study the pattern formation of bacteria confined to porous substrates and to explore the phenotypic variability of the population within the patterns subject to varying external conditions. I also model the transition from planktonic to surface motility and the initial stages in formation of biofilms, which are one of the most efficient survival strategies of bacterial populations.

Biophysical J. 2009, PLoS One 2011 , Adv. Exp. Med. Biol. 2012, PLoS One 2013

Electrostatic colloidal interactions

My main past work on electrostatics is related tothe many-body interactions in colloidal suspensions. We have directly measured and calculated three- and four-body forces among charged colloids (collaboration with Clemens Bechinger, Stuttgart) and demonstrated that they are of similar order of magnitude and range as the pair interaction terms. In dense suspensions, therefore, the many-body expansion is poorly converging. I designed a multiparticle Poisson-Boltzmann solver and studied the many-body effects on the solid-liquid melting transition in dense colloids. I also discussed the consistency of various coarse-graining approaches from the effective pair interaction description to the microion-based cell or Jellium models. With E. Trizac and S. El Shawish we studied orientational ordering of colloidal molecules on patterned substrates. Recently, I study electrostatics in heterogeneous and disordered media, polarization effects on DNA-DNA interactions, the transition from weak to strong coupling regimes, and the electrokinetic flow under the influence of ac and dc external electric fields.

JCP 2003, CPC 2004, EPL 2003, JPCM 2003

Many-body effects on phase behaviour

PRL 2004, PRE 2004

Direct determination of three-body interactions

Soft Matter 2008, AABC 2010, PRE 2011, JPCM 2012

Orientational ordering of colloidal molecules

Soft Matter 2009, preprint 2002

Weak and strong coupling interactions between DNA molecules

EPL 2006

Strain-induced colloidal clustering

Soft Matter 2008, preprint 2012

Phonons and friction in colloidal crystals

NJP 2006, PRE 2007

Coarse-graining electrostatic interactions ion higly charged colloidal suspensions