Oxford Colloid Group

Department of Chemistry University of Oxford
In contrast to Brownian particles subject to thermal fluctuations, synthetic self-propelling active colloidal particles take up energy from the medium and convert it into net motion (see videos below). Artificial active particles are remarkable models to mimic the food-searching strategies of living microorganisms (e.g., bacteria) and to design tantalizing vehicles for localization, pick-up, and delivery of drugs, biomarkers, etc.

One class of synthetic microswimmers comprises patchy colloids that produce localized gradients (chemical, thermal or electrical, Figure 1) which lead to directed propulsion through self-phoresis. Here, the swimming velocity is typically controlled by the amount of fuel (chemical fuel, illumination power or electric field) in the environment, and their reorientation is driven by thermal fluctuations.

(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.

Complex environments (e.g., obstacles, interfaces, and dense suspensions), shapes and a non-linear response to the tuning field lead to a plethora of unexplored out-of-equilibrium phenomena.

Current Research
Active Crystals

We study the behaviour of two dimensional colloidal crystals made, partly or entirely, by catalytic self-propelling particles. We characterise the mechanical response of these novel 2D materials using laser-based microrheology.

Electrokinetically active colloidal particles

We investigate highly tunable and switchable active systems of colloidal Janus particles in water. Activity is induced by an AC electric field and can be adapted and switched on and off at will. We can control the speed and direction of the particles by changing the amplitude and frequency of the electric field and the ionic strength of the solvent. We study the rich behaviour and dynamics that result from the interplay between activity, dipolar interactions and electrohydrodynamics.

Key People
References
  • G. Volpe, I. Buttinoni, D. Vogt, H. Kümmerer & C. Bechinger, Soft Matter 7, 8810-8815 (2011)
  • I. Buttinoni, G. Volpe, F. Kümmel, G. Volpe & C. Bechinger, J. Phys.: Condens. Matter 24, 284129 (2012)
  • I. Buttinoni, J. Bialké, F. Kümmel, H. Löwen, Clemens Bechinger & T. Speck, Phys. Rev. Lett. 110, 238301 (2013)
  • F. Kümmel, B. ten Hagen, R. Wittkowski, I. Buttinoni, R. Eichhorn, G. Volpe, H. Löwen & C. Bechinger, Phys. Rev. Lett. 110, 198302 (2013)
  • S. Ni, E. Marini, I. Buttinoni, H. Wolf & L. Isa, Soft Matter 13, 4252-4259 (2017)
  • K. Dietrich, D. Renggli, M. Zanini, G. Volpe, I. Buttinoni & L. Isa, New J. Phys. 19, 065008 (2017)
  • L.Isa, I. Buttinoni, M. A. Fernandez-Rodriguez & S. A. Vasudevan, EPL 119, 26001 (2017)