Active Matter

Active matter is one of the newest and most attractive topics in the field of soft matter. Studies of biological activity due to different species of bacteria can be found in the late sixties. In the last two decades, thanks to technical improvements to optical micropscopy, it has become possible to detect and track particles of a few micrometers. Moreover, in the same years, activity was found in different contexts: molecular motors, cells, nematic fluids as well as flock of birds and group of mammals. Developments in polymer synthesis allowed also to build active particles like Janus particles. Even though every active system has its own peculiar feature, they all share some type of collective motion due to hydrodynamic or short-range interaction, survival strategies, improved decision making etc. The overall effect is always that the motion of a single unit is dominated by the surrounding ones. This common behaviour can be translated in a scaling theory, in which the order parameter is played by the average normalized velocity φ

and the rule of temperature is played by the "noise" η, which is used to model the activity of the particles. From an experimental point of view, the enhancement of high-speed microscopy techniques and personal computers made possible to track a large number (102 - 103) of particles and to resolve particles dynamics with increasing accuracy.
High precision tracking experiments allowed to probe the flow fields created by active swimmers and hence their connection with evolutionary strategies of microorganisms. Moreover the study of active particles is extremely charming because a novel class of micromechanical devices using non-equilibrium fluctuations generated by bacteria has been developed very recently and opened new scenarios for further application. 
Saturday the 23rd. Web page designed & maintained by: Daniele Filippi & Matteo Pierno
Copyright 2012