Abstract
Many fields of applications require dispersion of hydrophobic particles in water, which is traditionally achieved by using surfactants or amphiphilic molecules to modify particle surfaces. However, surfactants or amphiphilic molecules may disturb the native solution or particles’ surface hydrophobicity, limiting extended applications such as oil emulsion cleaning. Recently one example of 2 μm-size polystyrene microparticles covered with ZnO nanospikes has been shown to exhibit excellent dispersity in water in spite of surface hydrophobicity. Whether this anomalous dispersion phenomenon was applicable to other hydrophobic microparticle systems was still unclear and its application scope was limited. Here the anomalous dispersities of different hydrophobic spiky micro-objects were systematically explored. The results show that the anomalous dispersion phenomenon was universally observed on different hydrophobic spiky micro-objects including different hydrophobic coating, particle sizes, material compositions and core particle morphologies. In addition, the spiky micro-objects displayed anomalous dispersity in water without compromising surface hydrophobicity, and their applications for oil spills absorption and oil emulsion cleaning were demonstrated. This work offers unique insight on the nanospikes-mediated anomalous dispersion phenomenon of hydrophobic micro-object and potentially extends its applicability and application scopes.
Highlights
Dispersion in water, the surfactant coating might reduce the surface hydrophobicity and compromise the oil absorption capability
Similar to the results of optical imaging, aggregation of PS^2 μm Smooth-F was observed (Fig. 2a11), while PS^2 μm Spiky-F displayed dispersed profiles on the supporting membrane (Fig. 2a12). These results suggested that the hydrophobic microparticles functionalized with nanospikes exhibited anomalous dispersity in water, consisting with previous report
The anomalous dispersity of hydrophobic spiky microparticles was attracting as surfactant-free dispersion strategy, yet whether this phenomenon was applicable to various hydrophobic microparticle systems was still unclear
Summary
Dispersion in water, the surfactant coating might reduce the surface hydrophobicity and compromise the oil absorption capability. Polystyrene (PS) microparticles attached with ZnO nanospikes, namely “hedgehog particles”, were found to exhibit anomalous dispersity, where excellent dispersity of hydrophobic microparticles in water was achieved without using surfactants[24] This anomalous phenomenon was hypothesized to attribute to the nanospikes providing steric hindrance between particles, reducing interparticles’ hydrophobic/ hydrophilic attractions and van der Waals forces. Systematic investigation on the anomalous dispersion phenomenon of hydrophobic microparticles including the effects of hydrophobic tethers, particle sizes, material compositions and core particle morphologies would extend the anomalous dispersion approach to a wider range of applications instead of relying on conventional surfacants. The anomalous dispersities of different hydrophobic spiky micro-objects including a broad range of conditions were systematically explored (Fig. 1), and the applications of hydrophobic spiky micro-objects for oil emulsion cleaning were demonstrated as example to show the advantage of nanospikes-mediated anomalous dispersities. This work offers unique insight on the nanospikes-mediated anomalous dispersion phenomenon of hydrophobic micro-object and its applicability and application scopes of different hydrophobic particle systems without relying on traditional surfactants
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