Experimental and theoretical evidence for molecular forces driving surface segregation in photonic colloidal assemblies.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31555734.
- Also identified by DOI 10.1126/sciadv.aax1254 and PMC identifier 6754227.
- Licence recorded as CC BY-NC.
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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 (<i>D</i> <sub>large</sub> <i>/D</i> <sub>small</sub>) 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.