Nanoparticle dispersion and separation in superhydrophilic nanostructures†

Abstract

Nanostructures can have novel properties that are rarely found in macroscale materials and have been employed for a wide range of applications. The wetting properties of nanostructured surfaces are particularly interesting and are controllable by engineering structure geometry and surface chemistry to create hydrophobic or hydrophilic nanostructures. In this work, we investigate the wicking and separation of nanoparticles in droplets through size dependent interactions in superhydrophilic wicking nanostructures. This effect is investigated by studying the assembly of particles larger and smaller than silicon nanostructures, which have periods of 300 nm and are fabricated using laser interference lithography. Polystyrene and fluorescent polystyrene nanoparticles with diameters ranging from 100 to 1100 nm are applied to the fabricated structure and examined using electron, optical, and fluorescence microscopy to determine particle assembly patterns and dispersion mechanisms during wicking. Mixtures of the particles are also applied to the surface and examined to identify particle separation effects from wicking. Identifying the dispersion mechanisms for particles of various sizes during fluid transport in nanostructures will provide insight into their response to particulates. This work demonstrates that nanostructured surfaces and their wetting response can have tunable filtering interactions with nanoscale elements. Applications for such surfaces include selective particle filters for microplastic, virus capture, and other particulate matter.