A Marriage of Opposites

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Science  12 Dec 2008:
Vol. 322, Issue 5908, pp. 1610
DOI: 10.1126/science.322.5908.1610a

Janus particles are colloidal particles whose two hemispheres have different properties, such as optical or magnetic behavior, polarity, or the ability to attract or repel water. Berger et al. combined two polymerization reactions to create Janus particles with distinct acid/base reactivity. Multiple silica particles 800 nm in diameter were appended to a solid wax core, after which the exposed portions were functionalized with an acrylate polymer by surface-initiated atom-transfer radical polymerization. Once released from the wax, the previously masked hemispheres were linked to pre-formed chains of poly(2-vinylpyridine). The particles were then hydrolyzed to convert the acrylate esters to acids. The distinct basicities of the two polymers led to varying charge accumulation and consequent aggregation behavior in response to pH changes. The authors envision extending this approach for use in emulsion stabilization or for control of molecular transport at the interface between two immiscible liquids. — MSL

Macromolecules 10.1021/ma802089h (2008).

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