ACTIVEDYNAMICS

Dynamics of Active Suspensions

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 Obiettivo del progetto (Objective)

'Collective behaviour is ubiquitous in nature: from crystallization through to animal swarming. Such phenomena are ubiquitous in colloids– 0.1-1micron particles suspended in liquids by Brownian motion – and are responsible for their amazing ability to ‘self assemble’. The self assembly of colloids is now an established route to new materials, e.g. photonic crystals. Recently, active colloidal particles capable of self propulsion have been synthesized. Their collective behaviour is completely unknown. The researcher proposes a research programme into collective phenomena in active suspensions. While synthetic active colloids have only recently been synthesized, ‘natural active colloids’ have existed for billions of years – motile bacteria. Therefore the candidate proposes to investigate both natural motile particles (bacteria) as well as synthetic ones. The bacterial results should have significant biological relevance, although the primary goal is to generate new, fundamental physics insights, which will lead to ‘design principles’ for a completely new type of self-assembled structures based on active colloids. We will use a new method, ‘differential dynamic microscopy’ (DDM), which uses everyday laboratory apparatus (a microscope and a camera) to generate comprehensive dynamical information on the collective motion of suspended particles (in the form of the so-called ‘intermediate scattering function’). Compared to single-particle tracking, the standard tool in active colloids and bacterial motility research to date, DDM yields much better averages and is orders of magnitude quicker to perform. The researcher and co-workers have demonstrated recently the use of DDM for the high-throughput characterisation of the motility of dilute populations of bacteria. A second goal of the proposed work is to develop DDM into a versatile tool for studying active particles of all kinds, at a range of concentrations.'

Introduzione (Teaser)

Collective behaviour is ubiquitous in nature and, in its natural form, has been around for millions of years, motile bacteria being a classic example. EU research is tracking this type of particle using new methods.

Descrizione progetto (Article)

Movement of bacteria in suspensions are so-called active colloids and are crucial in natural systems such as the gut. Recent research has focused on the synthesis of active colloidal particles capable of self-propulsion.

The 'Dynamics of active suspensions' (ACTIVEDYNAMICS) project has completed fascinating research into the movement of both natural active particles (bacteria) as well as synthetic particles. Using differential dynamic microscopy which simply combines a microscope and a camera, the researchers have generated comprehensive dynamical information on the collective motion of suspended particles.

Project researchers investigated the dynamics of suspensions of bacteria as a function of bacterial and suspension concentration. A first, they tracked the movement of non-motile bacteria in a bath of motile bacteria in 3D. To study the movement of bacteria in a complex polymeric environment such as the gut, the impact of hydrodynamic flow fields created by the swimming bacteria was incorporated. The result was a quantitative description of the experimental data.

Applying the methodology from the swimming bacteria, the scientists looked at other motile living structures such as sperm and algae. On the synthetic front, ACTIVEDYNAMICS looked at self-propelled particles such as active Janus particles. Having surfaces with two or more distinct physical properties, Janus particles can exhibit controlled affinity towards human endothelial cells, for example. Another application is under conditions where there are anisotropic conditions influenced by a magnetic field.

One remarkable property of active colloids is dynamic self-assembly where simple building blocks organise into complex functional architectures. Applications range from tunable, self-healing colloidal crystals and membranes to self-assembled microswimmers and robots. The ACTIVEDYNAMICS project has received interest from a wide range of academic science to industrial research institutions.