Oxford Colloid Group

 

Driven Systems

Driven systems can broadly be described as systems which are forced out of equilibrium by some external force. This can be imposed in many ways but common examples include applying a driving force, solvent flow or an optical field. At the macro-scale, these systems can lead to earthquakes and complex weather systems. We also see many examples at the microscale which can lead to interesting phenomena such as synchronisation of electron motion seen in superconductors, dispersionless transport, and particle sorting.

We focus on driving systems that are subject to one or more optical traps. We can drive particles through this so-called optical potential energy landscape. By tracking particle motion we can gather information about the forces exerted on the particle by the optical traps and introduce more complex driving motion [1] to model atomic and molecular systems.

A schematic of the experimental system shown. The plot displays the rough energy landscape (U(x)) that the particle is driven across.
 
A colloidal particle is driven from left to right at constant velocity through an optical potential energy landscape. The particle experiences an optical force which leads to the unusual observed motion.
 

We also use a system with feedback to explore the behaviour of an optically driven particle with an associated delay time. We use a dumbbell with two lobes of different refractive indices to form a system where we see oscillatory and persistent motion as one lobe is attracted to the optical trap and the other lobe is repelled by it. 

Key People
References
  • [1] Juniper M.P.N. et al., Nature Communications, 6, 7187 (2015)

Videos

http://dullens.chem.ox.ac.uk/driven-systems-1.aspx