Nanoscale Porosity in Microellipsoids Cloaks Interparticle Capillary Attraction at Fluid Interfaces

Abstract

Anisotropic particles pinned at fluid interfaces tend toward disordered multiparticle configurations due to large, orientationally dependent, capillary forces, which is a significant barrier to exploiting these particles to create functional self-assembled materials. Therefore, current interfacial assembly methods typically focus on isotropic spheres, which have minimal capillary attraction and no dependence on orientation in the plane of the interface. In order to create longrange ordered structures with complex configurations via interfacially trapped anisotropic particles, control over the interparticle interaction energy via external fields and/or particle engineering is necessary. Here, we synthesize colloidal ellipsoids with nanoscale porosity and show that their interparticle capillary attraction at a water−air interface is reduced by an order of magnitude compared to their smooth counterparts. This is accomplished by comparing the behavior of smooth, rough, and porous ellipsoids at a water−air interface. By monitoring the dynamics of two particles approaching one another, we show that the porous particles exhibit a much shorter-range capillary interaction potential, with scaling intriguingly different than theory describing the behavior of smooth ellipsoids. Further, interferometry measurements of the fluid deformation surrounding a single particle shows that the interface around porous ellipsoids does not possess the characteristic quadrupolar symmetry of smooth ellipsoids, and quantitatively confirms the decrease in capillary interaction energy. By engineering nanostructured surface features in this fashion, the interfacial capillary interactions between particles may be controlled, informing an approach for the self-assembly of complex two-dimensional microstructures composed of anisotropic particles.

Recent Progress of Solid–Liquid Interface-Mediated Contact-Electro-Catalysis

“…Previous studies in liquid–solid CE have demonstrated that the tribogeneration performance on a flat surface is influenced by their corresponding surface roughness. ,, Therefore, CEC efficiency is also anticipated to be affected by the surface roughness of catalytic nanoparticles, e.g., raspberry-like, patchy, and/or hollow nanoparticles. More remarkably, a recent study showcased that the nanoscale porosity on particle surfaces can effectively prevent undesired particle agglomeration upon ultrasonication , (Figure e). Improving particle dispersity is helpful to expose more surface area for liquid–solid CE.…”

“…Copyright 2022 Elsevier. (e) Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

Influence of Surface Roughness on Interfacial Properties of Particle Networks

“…An earlier study on interfacially trapped hydrophobically modified spherical particles (250 nm) revealed that the predominant interaction influencing the network formation is the capillary interaction arising from the non-uniform pinning of the three-phase contact line [59]. These interactions are usually more prominent as we move away from isotropic particles towards systems containing chemically anisotropic particles (i.e., Janus or patchy particles) [40,[60][61][62][63][64], or shape anisotropic particles [65], as well as the rough silica particles used in this study.…”

The paradoxical behavior of rough colloids at fluid interfaces

“…Among various interparticle interactions between colloids at the interface which contribute to collective interfacial microstructure and properties, attractive capillary interactions are significant and originate from curved menisci around the particle 5 . An undulated three-phase contact line has been reported to arise from either particle surface roughness in otherwise smooth spheres 5 or shape anisotropy as in ellipsoids 6 , deforming the fluid interface in a quadrupolar fashion 7,8 . While theoretical predictions of roughness causing local contact line pinning undulations that scale to a quadrupolar deviation in the far field date back to 2000 5,9 , and its impact on emulsions observed shortly thereafter 10 , it was only in 2017 that gel-trapping was used to perform ex situ measurements of the deformation to confirm 11 .…”