Experimental and theoretical evidence for molecular forces driving surface segregation in photonic colloidal assemblies
Open Access
- 6 September 2019
- journal article
- research article
- Published by American Association for the Advancement of Science (AAAS) in Science Advances
- Vol. 5 (9), eaax1254
- https://doi.org/10.1126/sciadv.aax1254
Abstract
Surface segregation in binary colloidal mixtures offers a simple way to control both surface and bulk properties without affecting their bulk composition. Here, we combine experiments and coarse-grained molecular dynamics (CG-MD) simulations to delineate the effects of particle chemistry and size on surface segregation in photonic colloidal assemblies from binary mixtures of melanin and silica particles of size ratio (Dlarge/Dsmall) ranging from 1.0 to ~2.2. We find that melanin and/or smaller particles segregate at the surface of micrometer-sized colloidal assemblies (supraballs) prepared by an emulsion process. Conversely, no such surface segregation occurs in films prepared by evaporative assembly. CG-MD simulations explain the experimental observations by showing that particles with the larger contact angle (melanin) are enriched at the supraball surface regardless of the relative strength of particle-interface interactions, a result with implications for the broad understanding and design of colloidal particle assemblies.Funding Information
- National Science Foundation (DMR-1720139)
- Air Force Office of Scientific Research (MURI-FA 9550-18-1-0142)
- Air Force Office of Scientific Research (MURI-FA 9550-18-1-0142)
- Air Force Office of Scientific Research (MURI-FA 9550-18-1-0142)
- Air Force Office of Scientific Research (FA9550-13-1-0222)
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