Condensed Matter Theory

Abstract:

Meso-scale turbulence is an innate phenomenon, distinct from inertial turbulence, that spontaneously occurs at low-Reynolds number in fluidized biological systems. This spatio-temporal disordered flow radically changes nutrient and molecular transport in living fluids and can strongly affect the collective behaviour in prominent biological processes, including biofilm formation, morphogenesis and cancer invasion. Despite its crucial role in such physiological processes, understanding meso-scale turbulence and any relation to classical inertial turbulence remains obscure. Here, we show how the motion of active matter along a micro-channel transitions to mesoscale turbulence through the evolution of locally disordered patches (active puffs) from an ordered vortex-lattice flow state. We demonstrate that the stationary critical exponents of this transition to meso-scale turbulence in a channel coincide with the directed percolation universality class. This finding bridges our understanding of the onset of low-Reynolds number meso-scale turbulence and traditional scaleinvariant turbulence, therefore generalizing theories on the onset of turbulence in confinement to the distinct classes of incoherent flows observed in biological fluids.

Abstract:

Advances in controlling and exploiting the wetting and adsorption properties of complex fluids, such as liquid crystals, ionic liquids, colloids and active matter, have been fostered by impressive technical achievements allowing the fabrication of tailored surfaces with a well-controlled distribution of micro- or nano-scale features. Such patterned substrates may be used to control the properties of adsorbed fluids in ways relevant to applications including microfluidic devices, surfaces with switchable wettability, new generation liquid crystal displays, or supercapacitors for efficient energy storage. In this special issue we collect together experimental, theoretical and computational papers that showcase recent contributions to understanding complex fluids at structured surfaces. These underline the diversity of phenomena encountered when complex fluids interact with complex surfaces.