3-D rotation tracking from 2-D images of spherical colloids with textured surfaces

Abstract

Tracking the three-dimensional rotation of colloidal particles is essential to elucidate many open questions, e.g. concerning the contact interactions between particles under flow, or the way in which obstacles and...

Rotational diffusion of colloidal microspheres near flat walls

“…Very recently, Niggel and coworkers proposed a new method based on standard epifluorescence microscopy and image correlation to follow the full short-time rotational displacement of raspberry microspheres. 13 It is also worth mentioning previous works which used spherical particles enveloping an asymmetric centered fluorescent core such as an ellipse 10 or a fluorescent cluster, 12 as their scope of application is very similar to ours. These elegant techniques, particularly the former, reduce the complexity of the experimental setup, very much in the spirit of this work, but still carries higher computational costs during ex situ analysis.…”

“…These methods include depolarized light scattering, 1–3 fluorescence recovery, 4 evanescent wave scattering, 5,6 polarization microscopy, 7,8 and digital tracking of particles with an anisotropic fluorescence profile or optical reflectivity. 9–13…”

Minimal numerical ingredients describe chemical microswimmers’ 3-D motion

“…By doing so, we are able to reproduce the findings presented in. 64 Specifically, we find that for passive particles, the presence of a heavy cap and a substrate reduces the rotation “out-of-plane” ( θ x , y ) compared to in plane ( θ z ) rotations (see Fig. 1c and d) due to bottom-heaviness (see Fig.…”

“…Specifically, we reproduce the ‘classic’ Pt-SiO 2 Janus chemical microswimmers to determine whether our DPD raspberry particle model captures their dynamics. We investigate the chemical microswimmers studied by Niggel et al , 64 as the 3-D rotations of the Janus particles with fluorescent surface asperities can be tracked via correlation-based image analysis. To reproduce their experimental findings, we simulate the microswimmers with CB motion and m asymm = 1.081.…”

“…By extending the DPD numerical framework described in 55 to include the effects of mass and shape asymmetries, we have demonstrated that hydrodynamic interactions, gravity, and thermal fluctuations are sufficient to capture the dynamics of a range of experimental chemically active colloidal systems. 17,18,20,64 Promisingly, the use of DPD particles to build the overall structure of the microswimmer enables us to access to a range of more complex shapes than those described here, whose formulation would otherwise be either intractable or highly challenging when using other numerical modelling frameworks, or explicitly including chemical fields. We believe that our numerical simulations could be used in the design of new chemical colloidal swimmers, e.g.…”