Martensitic transition in a confined colloidal suspension

We describe a nonequilibrium phase transition in a geometrically confined charge-stabilized colloidal suspension. The equilibrium configuration for the spheres in this system is a two-layer square lattice, equivalent to two layers of a body-centered cubic (bcc) crystal. After electrophoretic shear melting, the suspension rapidly crystallizes to a buckled single-layer triangular lattice. This well-ordered solid phase subsequently undergoes a martensitic phase transition back to the two-layer square lattice. We use high resolution digital video microscopy to follow the emergence and evolution of order during these phase transitions.