Asymmetrically Nanostructured 2D Janus Films Obtained from Pickering Emulsions Polymerized in a Langmuir–Blodgett Trough

Abstract

Low-dimensional structures, such as two-dimensional (2D) Janus films, can be useful in studying fundamental interactions or in applications at the nanoscale. In this work, we report the fabrication of 2D polymer Janus films consisting of one smooth and another nanostructured facet on which silica nanoparticles (NPs) are self-assembled in a compact monolayer shield. The 2D films are made from Pickering emulsions of monomers in water, stabilized by NPs, which are spread over the surface of the water in a Langmuir–Blodgett trough. Following the spreading of the colloidosomes, oil droplets stabilized by NPs collapse, and the interfaces reorganize such that the NP monolayer is found exclusively at the oil/water interface. Upon compression followed by UV polymerization, a 2D solid film is formed, with one smooth and another nanostructured face. The film can be removed from the surface of the water and handled with tweezers. The 2D films exhibit different surface properties on the two sides, such as differences in water wettability. On the nanostructured side, water wettability can be tuned by tuning the surface energy of the nanoparticles, namely by changing their surface functional groups. Upon removal of NPs, the surface can be patterned with an array of circular traces.

Interfacing Langmuir–Blodgett and Pickering Emulsions for the Synthesis of 2D Nanostructured Films: Applications in Copper Ion Adsorption

“…As we will see next, the SiO 2 -PEI NPs exclusively occupy the monomer/water interface. A similar phenomenon was also observed in the case of silica nanoparticles bearing different functional groups, such as glycidyl, and was observed for other particles bearing surface functional groups with a higher component of the dispersive surface energy [26]. The monomer droplet/water interfacial tension is stabilized by the presence of the nanoparticles.…”

“…The process of forming Janus 2D P(t-BA)/SiO 2 -PEI NP films from the Pickering emulsions in an L-B trough is similar to the one we have previously reported [26]. Briefly, the Pickering emulsion droplets (colloidosomes) were added onto the surface of a Langmuir-Blodgett trough with a spatula.…”

“…The Pickering emulsions are stabilized due to the interfacial adsorption of the silica nanoparticles at the oil-water interface with the formation of a self-assembled monolayer. The monolayer of nanoparticles acts like a shield preventing the coalescence of the oil droplets [18,26]. Thus, these special structures, the liquid Pickering emulsion droplets covered by a shield of self-assembled monolayer of nanoparticles, are often referred to as "colloidosomes" and will be referred to in the same way in the current work.…”

Water-Floating Hydrogel Polymer Microsphere Composites for Application in Hydrological Mining of Cu(II) Ions

“…The method utilizes oil-in-water (o/w) Pickering emulsions, emulsions that are stabilized by silica nanoparticles, and the dispersed phase is a water-immiscible vinyl-bearing monomer. As a side note, other groups utilize the same technology for producing microporous polymer monoliths [10] and asymmetrically structured Janus membranes [26]. The silica nanoparticles utilized in the current work are 500 ± 10 nm diameter silica nanoparticles modified with glycidyl functional groups on the surface (see Figure 1A), which have been previously shown to produce preferentially o/w emulsions [27].…”

“…The implications of nanostructuring in the waterwetting of the polymer microspheres are significant. We have previously demonstrated that for a hydrophobic polymer whose typical water contact angles are around 80 • , due to the nanostructuring from a self-assembled monolayer of NP-Gly on the surface of the polymer, the wettability increases significantly, lowering the water contact angles to values below 60 • characteristic for a hydrophilic surface [26]. This improvement in water wettability due to nanostructuring has significant implications for the extraction of metal ions from aqueous solutions by these polymer microspheres.…”