Pattern formation in colloidal explosions

A. V. Straube^1,2, A. A. Louis², J. Baumgartl³, C. Bechinger³ and R. P. A. Dullens⁴

¹ Department of Physics, Humboldt University of Berlin - Newtonstr. 15, D-12489 Berlin, Germany, EU
² Rudolf Peierls Centre for Theoretical Physics, University of Oxford - 1 Keble Road, Oxford, OX1 3NP, UK, EU
³ 2. Physikalisches Institut, Universität Stuttgart - Pfaffenwaldring 57, D-70569 Stuttgart, Germany, EU
⁴ Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford South Parks Road, Oxford, OX1 3QZ, UK, EU

Received: 3 February 2011
Accepted: 13 April 2011

Abstract

We study the non-equilibrium pattern formation that emerges when magnetically repelling colloids, trapped by optical tweezers, are abruptly released, forming colloidal explosions. For multiple colloids in a single trap we observe a pattern of expanding concentric rings. For colloids individually trapped in a line, we observe explosions with a zigzag pattern that persists even when magnetic interactions are much weaker than those that break the linear symmetry in equilibrium. Theory and computer simulations quantitatively describe these phenomena both in and out of equilibrium. An analysis of the mode spectrum allows us to accurately quantify the non-harmonic nature of the optical traps. Colloidal explosions provide a new way to generate well-characterized non-equilibrium behaviour in colloidal systems.