Periodic Reporting for period 1 - TOPACT (Topological defects in nematic liquid crystals of active colloidal rods)
Reporting period: 2016-03-08 to 2018-03-07
An important bottleneck in current efforts to unravel these physical effects and to study collective dynamics in active matter is the lack of reliable experimental model systems for dense active matter. To overcome this limitation, we developed a well-defined experimental model system of active colloids and studied this at the single-particle level. The active particles are enclosed in a thin optical cell with electrodes at the top and bottom to control the activity of the particles by means of an oscillating electric field. Analysis of the activity, orientation and interactions of every particle in these active systems will help gain more insight in the physical mechanisms that underlie collective effects in large groups of active objects, such as schools of fish and flocks of birds.
We have mapped out the behaviour of the active colloids as a function of colloidal packing fraction, ion concentration, and amplitude and frequency of the electric field. At low frequency, the electric field acts on the polarised double layer that surrounds the particles, causing a flow of solvent around the particles, which induces active motion. At high frequency other effects come into play, and the direction of motion reverses.
Finally, we have studied the formation of structures as a function of time and their behaviour in dense systems of these model active particles.
Our results have been disseminated within the scientific community on various occasions: several talks at seminars, as well as oral and poster contributions at a conference in a focus session dedicated to Active Matter and a second conference on Soft Matter. In addition, we are preparing publications about our findings to further disseminate the results.
The progress in this project has contributed to the building up of knowledge and expertise in the field of active matter at the forefront of science at the host university, leading to the increased attractiveness of the host group for talented researchers in active matter research from around the world. Finally, the collaborations that were set up during this project have helped strengthen the position of European research in the field of active matter.