We developed, characterized and optimized colloidal particles with DNA-based bonds that allow rearrangements yet are stable against unspecific aggregation and spontaneous rigidification. We used both self-assembly as well as manual assembly by optical tweezers to create flexible chains, rings, colloidal molecules, and lattices of these colloidal particles.
We studied how rearrangements after bonding and other parameters such as size, particle shape and number ratio affect the assembly pathway towards ordered, well-controlled structures, which allowed us to significantly increase the yield and fidelity of the resulting structures. Particle shape and number ratio can be exploited to control the number of bonds per particle as well as their angular range of motion. We exploited the latter to confine particles to specific regions and showed that this confinement can be lifted in situ by an elevation of temperature. We demonstrated these concepts by assembling finite sized clusters, so called “flexible colloidal molecules” and showed that the bond flexibility allowed us to assemble finite-sized clusters of uniform shape in high yield, which has been challenging before. We successfully assembled these “flexible colloidal molecules” in various shapes and quantified their assembly dynamics. We found that bond flexibility is crucial for achieving maximum valence and the degree of flexibility impacts the assembly speed. Using an anisotropic particle shape, control over bond directionality and angular motion range was implemented. We exploited our insights gained from assembling colloidal molecules for assembling larger structures to creating square lattices with floppy reconfiguration modes. We quantified these modes and explored approaches to controllable switch between different conformations.
Finally, we investigated self-propelled elements (so-called active particles) for integration with reconfigurable structures. We employed spheres half-coated with a catalytically active material and found that their velocity is strongly dependent on the material that they are moving on, in particular, it depends on the slip length of the substrate. Since the influence of slip on particle motion hinges on the distance with which particles move from a substrate, we devised a new strategy to extract this crucial information from the diffusive contribution to their motion. We found the striking result that catalytically propelled particles assume a preferred height over the substrate that persist for a wide range of parameters and is in stark contrast to the behavior of passive particles. We discovered that microswimmers synchronize their motion due to a competition between repulsive and attractive interactions. We quantified their velocity distribution, and found remarkable intermittency of the active motion with robust power-law velocity distributions which we could model by an interplay of active force, limited by the velocity dependent fluid gradient, and hydrodynamic drag.
Our results were published in high-quality journals, and presented at over 30 conferences, workshops and seminars. We have engaged with the general public through lectures, school visits, press releases, and twitter.
