Self-faceting of emulsion droplets as a route to solid icosahedra and other polyhedra

Orlando Marin; Maria Alesker; Shani Guttman; Gregory Gershinsky; Eitan Edri; Hagay Shpaisman; Rodrigo E Guerra; David Zitoun; Moshe Deutsch; Eli Sloutskin

doi:10.1016/j.jcis.2018.11.111

Self-faceting of emulsion droplets as a route to solid icosahedra and other polyhedra

J Colloid Interface Sci. 2019 Mar 7:538:541-545. doi: 10.1016/j.jcis.2018.11.111. Epub 2018 Dec 2.

Authors

Affiliations

¹ Department of Physics, Bar-Ilan University, Ramat-Gan 5290002, Israel; Bar-Ilan Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
² Department of Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel; Bar-Ilan Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
³ Center for Soft Matter Research, New York University, New York, NY 10003, USA.
⁴ Department of Physics, Bar-Ilan University, Ramat-Gan 5290002, Israel; Bar-Ilan Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel. Electronic address: Eli.Sloutskin@biu.ac.il.

PMID: 30551067
DOI: 10.1016/j.jcis.2018.11.111

Abstract

Hypothesis: Temperature-controlled self-faceting of liquid droplets has been recently discovered in surfactant-stabilized alkane-in-water emulsions. We hypothesize that similar self-faceting may occur in emulsion droplets of UV-polymerizable linear hydrocarbons. We further hypothesize that the faceted droplet shapes can be fixed by UV-initiated polymerization, thus providing a new route towards the production of solid polyhedra.

Experiments: Temperature-induced shape variations were studied by optical microscopy in micron-size emulsion droplets of UV-polymerizable alkyl acrylate. When polymerized, the resultant solid particles' 3D shape and internal structure were determined by combined scanning electron microscopy (SEM) and focused ion beam (FIB) slicing. The SEM and FIB nanoscale resolution provided a far greater detail imaging than that achievable for the liquid droplets, which could only be studied by optical microscopy, severely limiting their 3D shape determination.

Findings: We demonstrate the formation of solid icosahedra, polyhedral platelets, and rods of hitherto-unreported sizes, well below the 3D-printing resolution (∼20μm). The presence of icosahedral shapes and the absence of any resolvable internal structure at sub-μm length scales, are in line with the surface-freezing-driven mechanism proposed for the faceting phenomenon. Further development of the method presented here may allow large-quantity production of shaped micron- to nano- sized colloidal building blocks for 3D metamaterials and other applications.

Keywords: Colloids; Emulsions; Faceting; Interfacial freezing; Polyhedral nanoparticles; Surface freezing.