Entropic Self-Organization of Tri-Star Colloids

Seminar series
Physical Chemistry Seminar
Thu, May 16 12:00pm
2033 Young Hall
Speaker Kenny Mayoral
University of California, Los Angeles
Dept. of Chemistry & Biochemistry

Abstract: A dense system of hard Brownian tri-star particles in two dimensions exhibits a remarkable entropic disorder-order phase transition, reflected in its osmotic equation of state. When concentrated to high particle area fractions, φA, lithographic microscale tri-star particles under thermal excitations self-organize into an alternating stripe crystal (ASX), a broken-symmetry rectangular crystal phase. ASX exhibits two types of lock-and-key features: tri-stars arrange head-to-tail to form long linear stripes, and neighboring stripes interdigitate by pointing in alternating and opposite directions, creating an array of zippers. Using a translational-rotational cage model of tri-stars, we show that, as φA is increased, ASX yields more accessible microstates per particle than a hexagonal crystal and is therefore entropically preferred. Moreover, the ASX phase better facilitates collective translational motion of tri-stars. Thus, entropy alone can cause self-organization of certain concave shapes, such as tri-stars, into extended zipper-like interdigitated structures analogous to those formed by amyloidogenic biomolecules.