Paper Number
PO91 

Session
Poster Session

Title
Rapid colloidal self-assembly through periodic variation of inter-particle potentials

Presentation Date and Time
October 8, 2014 (Wednesday) 6:05

Track / Room
Poster Session / Poster

Authors (Click on name to view author profile)

1. Risbud, Sumedh R. (Massachusetts Institute of Technology, Department of Chemical Engineering)
2. Swan, James W. (Massachusetts Institute of Technology, Department of Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Sumedh R. Risbud and James W. Swan
Department of Chemical Engineering, Massachusetts Institute of Technology, Boston, MA 02139

Speaker / Presenter 
Risbud, Sumedh R.

Text of Abstract
We study the self-assembly of Brownian particles driven by a short-range attractive interaction. Although the equilibrium state is expected to be crystalline for high strengths of attraction, formation of a kinetically arrested gel is typically observed. Crystals form for weaker strengths of attraction, but their nucleation kinetics are slow. Under only a narrow range of conditions can crystals be self-assembled effectively. We demonstrate computationally that if the attractive potential is switched on and off periodically in time, the envelope for self-assembly is broadened considerably. Our kinetic theory calculations as well as Brownian dynamics simulations show that the rate at which particles cross energy barriers is accelerated by the pulsed potential. In the context of colloidal self-assembly, barrier crossing is the rate limiting step and responsible for both gel formation and slow nucleation. Through pulsing the inter-particle potential these physical processes are accelerated, and fine control over the rate of self-assembly is possible. Examples of switchable potentials include those due to magnetic or electric fields, those due to photo-switchable ligands, and those that are thermally responsive mediators such as DNA-coatings. Our theoretical analysis of barrier crossing with a pulsed potential, suggests that there exists an optimal frequency of switching for which a self-assembled state is attained fastest. The optimal frequency is related to the time required for particles to diffuse over the range of the attractive interaction. This allows for the release of kinetic constraints that would lead to gelation instead of crystallization. Our simulations of self-assembly in a pulsed potential reveal the formation of crystalline domains via nucleation and subsequent Ostwald ripening. These results confirm the existence of optimal switching frequency for self-assembly.