Abstract
In this work, we unravel the role of surface properties of colloidal particles on the formation of supraparticles (clusters of colloidal particles) in a colloidal Ouzo droplet. Self-lubricating colloidal Ouzo droplets are an efficient and simple approach to form supraparticles, overcoming the challenge of the coffee stain effect in situ. Supraparticles are an efficient route to high-performance materials in various fields, from catalysis to carriers for therapeutics. Yet, the role of the surface of colloidal particles in the formation of supraparticles using Ouzo droplets remains unknown. Therefore, we used silica particles as a model system and compared sterically stabilized versus electrostatically stabilized silica particles—positively and negatively charged. Additionally, we studied the effect of hydration. Hydrated negatively charged silica particles and sterically stabilized silica particles form supraparticles. Conversely, dehydrated negatively charged silica particles and positively charged amine-coated particles form flat film-like deposits. Notably, the assembly process is different for all the four types of particles. The surface modifications alter (a) the contact line motion of the Ouzo droplet and (b) the particle–oil and particle–substrate interactions. These alterations modify the particle accumulation at the various interfaces, which ultimately determines the shape of the final deposit. Thus, by modulating the surface properties of the colloidal particles, we can tune the shape of the final deposit, from a spheroidal supraparticle to a flat deposit. In the future, this approach can be used to tailor the supraparticles for applications such as optics and catalysis, where the shape affects the functionality.
Highlights
The assembly of colloidal particles to supraparticles is an emerging strategy to produce functional materials.[1,2] The supraparticles gain additional functionalities compared to the individual colloidal particles, as a result of the structural arrangement of the particles, combinations of different materials, and collective effects.[1]
We have shown the effect of changing the surface characteristics of colloidal particles on the formation of supraparticles in evaporating ternary self-lubricating Ouzo droplets
We compared the behavior of silica particles that are electrostatically stabilized negatively charged or positively charged by amine-coating and sterically stabilized by PEGylation
Summary
The assembly of colloidal particles to supraparticles is an emerging strategy to produce functional materials.[1,2] The supraparticles gain additional functionalities compared to the individual colloidal particles, as a result of the structural arrangement of the particles, combinations of different materials, and collective effects.[1]. We show that the surface properties of the colloidal particles affect and can even impede the formation of supraparticles in colloidal “Ouzo” droplets. The oil becomes less soluble, phase-separates, and forms a lubricating oil ring at the contact line.[15−19] This oil ring prevents pinning and leads to the formation of a supraparticle instead of the coffee ring.[11,12]
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