Nanoscale porosity in microellipsoids cloaks interparticle capillary attraction at fluid interfaces

Abstract

Anisotropic particles pinned at fluid interfaces tend towards disordered multi-particle configurations due to large, orientationally-dependent, capillary forces, which is a significant barrier to exploiting these particles to create novel 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 long-range 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 a new approach for the self-assembly of complex two-dimensional microstructures composed of anisotropic particles.

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

“…17,112,113 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 114,115 (Figure 8e). Improving particle dispersity is helpful to expose more surface area for liquid−solid CE.…”

The Paradoxical Behavior of Rough Colloids at Fluid Interfaces

“…1−4 Among various interparticle interactions between colloids at the interface that contribute to collective interfacial microstructure and properties, attractive capillary interactions are significant and originate from curved menisci around the particle. 5 In particular, far-field quadrupolar interfacial deformation 6,7 results from introducing either particle surface roughness in otherwise smooth spheres 5 or shape anisotropy as in ellipsoids. 8 The former originates from nanoscale random undulations in the contact line, which decays to a quadrupolar curved menisci, while the latter is a consequence of Young's law requiring constant three-phase contact angle around an object with varying curvature.…”

Two-dimensional glass transition–like behavior of Janus particle–laden interface

“…The existence of a slip plane separating high and low shear rate zones was an indicator that the shear thinning behavior stems from yielding of the particle layer at the interface (Barman and Christopher 2014). Shape anisotropic particles have also been studied at air-water interfaces (Beltramo et al 2017;Bertsch et al 2018;Trevenen et al 2022). Beltramo et al (2017) demonstrated a significant yield stress in interfacial networks of shape anisotropic particles (polystyrene ellipsoids 2.48-μm long and 0.45-μm wide), much higher than for spherical particles at the same interfacial coverage (Beltramo et al 2017).…”