Ordered arrays of pumpkin-shaped Janus particles with tailored surface morphologies via microcontact hot embossing

Abstract

In this paper, we report the controlled fabrication of ordered arrays of pumpkin-shaped (i.e., shapes having the equatorial diameter greater than the polar diameter and being flattened at the poles) Janus polystyrene (PSt) particles with tailored morphologies. It is based on simple microcontact hot embossing of monodispersed PSt microsphere monolayers using different stamps such as glass slides, colloidal sphere monolayers, and wrinkled sheets. The resultant pumpkinshaped particles have the stamp-defined surface topographies, with one side flat and the other flat or patterned with small beads/holes and striped/dotted bulges. We systematically investigate the effect of the embossing conditions on the surface morphologies, which include the annealing temperature/time, the external load, and the structured stamps. Benefiting from the hexagonal close packing of original symmetric microspheres, well-ordered Janus particle arrays are obtained using the combined bottom-up/topdown strategy. Compared with the traditional two-stage process of fabrication and self-assembly, this method is much simpler and more straightforward, which is of significant importance for the related applications.