In contrast to systems passively subjected to thermal fluctuations, active materials take up energy from the medium and convert it into net motion. One class of active materials consists of patchy colloids that produce localized gradients (chemical, thermal or electrical) which in turn lead to directed propulsion.
(Left) Brownian particle. (Right) Phoretic active particle.
(a) Diffusiophoretic active particle driven by the local catalytic decomposition of hydrogen peroxide. (b) Thermophoretic active particle driven by a local temperature gradient under illumination of a light-absorbing coating. (c) Active particle driven by local electro-osmotic flows under an applied AC electric field.
In spite of the growing interest around the physics of active materials, experimental results on self-propelling particles are often limited to systems of swimmers in homogeneous media. I investigate the behaviour of phoretic swimmers under complex environmental conditions. Examples include solid substrates, arrays of obstacles, dense suspensions, liquid interfaces, gravitational fields, and harmonic optical potentials.
Self-propelling particle near a solid wall.
Cluster of self-propelling particles
Self-propelling particle in an array of elliptical obstacles (a vertical force is also applied).
Self-propelling particle in a colloidal crystalline landscape
Active colloid trapped and released by an optical tweezer