Modular Attachment of Nanoparticles on Microparticle Supports via Multifunctional Polymers

Abstract

Nanoparticles are key to a range of applications, due to the properties that emerge as a result of their small size. However, their size also presents challenges to their processing and use, especially in relation to their immobilization on solid supports without losing their favorable functionalities. Here, we present a multifunctional polymer-bridge-based approach to attach a range of presynthesized nanoparticles onto microparticle supports. We demonstrate the attachment of mixtures of different types of metal-oxide nanoparticles, as well as metal-oxide nanoparticles modified with standard wet chemistry approaches. We then show that our method can also create composite films of metal and metal-oxide nanoparticles by exploiting different chemistries simultaneously. We finally apply our approach to the synthesis of designer microswimmers with decoupled mechanisms of steering (magnetic) and propulsion (light) via asymmetric nanoparticle binding, aka Toposelective Nanoparticle Attachment. We envision that this ability to freely mix available nanoparticles to produce composite films will help bridge the fields of catalysis, nanochemistry, and active matter toward new materials and applications.

Minimal numerical ingredients describe chemical microswimmers’ 3-D motion

“…S2†), assisted by its bottom-heaviness. 59 Notably, we find that we can reproduce the structure of the microswimmer dynamics previously seen experimentally 17–19 (see ESI, Fig. S3†), without requiring the previously hypothesised self-shadowing effects.…”

“…Motivated by the ability of the reported DPD squirmer-like microswimmers to qualitatively reproduce the behaviour of different chemical microswimmers, we then investigate strategies to promote the “lift-off” of particles from the substrate, and thus observe 3-D motion. Recently, photocatalytic microswimmers synthesised using functional nanoparticles via “Toposelective Nanoparticle Attachment” were shown to display quasi 3-D behaviour, 17–19 characterised by 2-D motioninterdispersed with “rollercoaster”-like looping behaviour. This happens in spite of their high speeds with respect to their sedimentation speed, putting them in a regime closer to the third case highlighted in Fig.…”

“…After establishing the effect of shape asymmetry on microswimmer motion in the absence of external fields and confining boundaries, we then introduce gravity and a substrate to simulate the experimental conditions in ref. 17 and 18 using m asymm = 1.25. We define V swim : V sediment ∼ 1.5 to prevent the microswimmers from escaping too far into the bulk.…”

“…55,57–59 The strength of our approach lies in its modularity, which allows the simple inclusion of these asymmetries that may have otherwise presented significant complications when considering other numerical schemes. We find that the interplay between hydrodynamic interactions, gravity, bottom-heaviness, and shape is sufficient to qualitatively capture the 2- and 3-D physics of a range of catalytic (and photo-catalytic) Janus microswimmer systems, 17,18,20 i.e. while neglecting contributions from chemical 59 and light 60,61 gradients.…”

“…10 However, controlling the motion of microswimmers in 3-D is appealing from an applications perspective, and there is a growing body of work on active materials capable of motion in all dimensions. 11–22…”