Porous supraparticle assembly through self-lubricating evaporating colloidal ouzo drops

Huanshu Tan,Detlef Lohse,Hans-Jürgen Butt,Sanghyuk Wooh,Xuehua Zhang

doi:10.1038/s41467-019-08385-w

Abstract

The assembly of colloidal particles from evaporating suspension drops is seen as a versatile route for the fabrication of supraparticles for various applications. However, drop contact line pining leads to uncontrolled shapes of the emerging supraparticles, hindering this technique. Here we report how the pinning problem can be overcome by self-lubrication. The colloidal particles are dispersed in ternary drops (water, ethanol, and anise-oil). As the ethanol evaporates, oil microdroplets form (‘ouzo effect’). The oil microdroplets coalesce and form an oil ring at the contact line, levitating the evaporating colloidal drop (‘self-lubrication’). Then the water evaporates, leaving behind a porous supraparticle, which easily detaches from the surface. The dispersed oil microdroplets act as templates, leading to multi-scale, fractal-like structures inside the supraparticle. Employing this method, we could produce a large number of supraparticles with tunable shapes and high porosity on hydrophobic surfaces.

Highlights

The assembly of colloidal particles from evaporating suspension drops is seen as a versatile route for the fabrication of supraparticles for various applications
We propose a reliable, robust and cost-efficient method for supraparticle fabrication by employing a ternary liquid with appropriately chosen mutual solubilities in evaporation-driven nanoparticle assembly, which enables us to produce highly porous supraparticles with tunable shapes on commonly used hydrophobic surfaces
An oil ring emerged under the colloidal drop[31]

Summary

Introduction

The assembly of colloidal particles from evaporating suspension drops is seen as a versatile route for the fabrication of supraparticles for various applications. The dispersed oil microdroplets act as templates, leading to multi-scale, fractal-like structures inside the supraparticle Employing this method, we could produce a large number of supraparticles with tunable shapes and high porosity on hydrophobic surfaces. As recently found[31], in the evaporating ouzo drops phase separation occurs due to the preferred evaporation of ethanol and the resulting lower oil solubility (ouzo effect), preferentially at the contact line, where oil droplets first form Inspired by this phenomenon, we will employ the so-called ouzo effect to prevent the pinning of the evaporating colloidal drops. We propose a reliable, robust and cost-efficient method for supraparticle fabrication by employing a ternary liquid with appropriately chosen mutual solubilities (ouzo solution) in evaporation-driven nanoparticle assembly, which enables us to produce highly porous supraparticles with tunable shapes on commonly used hydrophobic surfaces

Methods

Results

Conclusion