posted on 2017-09-01, 00:00authored byYufeng Jiang, Tina I. Löbling, Caili Huang, Zhiwei Sun, Axel H. E. Müller, Thomas P. Russell
The
self-assembly and interfacial jamming of spherical Janus nanoparticles
(JNPs) at the water/oil interface were investigated. Polymeric JNPs,
made by cross-linking polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (PS-PB-PMMA), with a high
interfacial activity assemble at the water/oil interface. During the
self-assembly at the interface, the interfacial energy was reduced
and a dynamic interlayer was observed that is responsive to the pH
of the aqueous phase. Unlike hard particles, the JNPs are composed
of polymer chains that can spread at the liquid–liquid interface
to maximize coverage at relatively low areal densities. In a pendant
drop geometry, the interfacial area of a water droplet in oil was
significantly decreased and the JNPs were forced to pack more closely.
Entangling of the polymer chains causes the JNPs to form a solid-like
interfacial assembly, resulting in the formation of wrinkles when
the interfacial area is decreased. The wrinkling behavior, the retention
of the wrinkles, or the slow relaxation of the liquid drop back to
its original equilibrium shape was found to depend upon the pH.