Janus Colloids Assemble into Cluster Shapes

ORAL

Abstract

We explore the assembly of two types of micron-sized, spherical Janus particles: those with opposite electric charge on both hemispheres (``bipolar'') and those hydrophobic on one hemisphere and hydrophilic on the other (``amphiphilic''). Bipolar particles form clusters, not strings, as the particle diameter exceeds the electrostatic screening length. The cluster shapes are analyzed by combined epifluorescence microscopy and Monte Carlo computer simulations with excellent agreement, indicating that the particles assemble in aqueous suspension to form equilibrated aggregates. The simulations show that charge asymmetry of individual bipolar particles is preserved in the clusters. The assembly of amphiphilic particles presents analogies to the self-assembly of molecular surfactants, forming monolayers at the air-water interface and micelles in the aqueous suspension. By tuning the salt concentration, different phases of micelle can be imaged in real space. Computer simulations confirm the geometries of these micelles and reveal possible formation mechanisms.

–

Authors

  • Liang Hong

    Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, University of Illinois at Urbana-Champaign

  • Angelo Cacciuto

    Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, University of Illinois at Urbana-Champaign, Dept of Materials Science and Engineering, Univ of Illinois at Urbana-Champaign

  • Erik Luijten

    Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, University of Illinois, University of Illinois, Urbana-Champaign, University of Illinois at Urbana Champaign, University of Illinois at Urbana-Champaign

  • Steve Granick

    Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, University of Illinois at Urbana-Champaign, University of Illinois, Dept of Materials Science and Engineering, Univ of Illinois at Urbana-Champaign, Dept. of Material Science and Engineering, University of Illinois at Urbana and Champaign