Characterizing sliding and rolling contacts between single particles

Proceedings of the National Academy of Sciences, Journal Year: 2025, Volume and Issue: 122(10)

Published: March 6, 2025

Contacts between particles in dense, sheared suspensions are believed to underpin much of their rheology. Roughness and adhesion known constrain the relative motion particles, thus globally affect shear response, but an experimental description how they microscopically influence transmission forces displacements within contacts is lacking. Here, we show that innovative colloidal-probe atomic force microscopy technique allows simultaneous measurement normal tangential exchanged tailored surfaces microparticles while tracking sliding rolling, unlocking direct coefficients rolling friction, as well friction. We demonstrate that, presence sufficient traction, spontaneously roll, reducing dissipation promoting longer-lasting contacts. Conversely, when prevented, friction greatly enhanced for rough adhesive surfaces, smooth coated by polymer brushes maintain well-lubricated find surface roughness induces due load-dependent asperity interlocking, leading large off-axis particle rotations. In contrast, smooth, promote along principal axis motion. Our results offer values numerical studies interpretation onset discontinuous thickening based on them, opening up ways tailor rheology via contact engineering.

Language: Английский

---

Rotational diffusion of colloidal microspheres near flat walls

Soft Matter, Journal Year: 2024, Volume and Issue: 20(9), P. 2024 - 2031

Published: Jan. 1, 2024

We quantify the rotational diffusivity of spherical microspheres with an off-center fluorescent core. Fluorescence alone can give effective diffusivity; axis-dependent diffusivities be found when bright-field illumination is added.

Language: Английский

---

Minimal numerical ingredients describe chemical microswimmers’ 3-D motion

Nanoscale, Journal Year: 2023, Volume and Issue: 16(5), P. 2444 - 2451

Published: Dec. 29, 2023

The underlying mechanisms and physics of catalytic Janus microswimmers is highly complex, requiring details the associated phoretic fields physiochemical properties catalyst, particle, boundaries, fuel used. Therefore, developing a minimal (and more general) model capable capturing overall dynamics these autonomous particles desirable. In presented work, we demonstrate that coarse-grained dissipative particle-hydrodynamics describing behaviour various chemical microswimmer systems. Specifically, show how competing balance between hydrodynamic interactions experienced by squirmer in presence substrate, gravity, mass shape asymmetries can reproduce range seen different experimental We hope our general will inspire further synthetic work where modes swimmer motion be encoded via during fabrication, helping to realise still outstanding goal complex 3-D behaviour.

Language: Английский

---

Measuring Rolling Friction at the Nanoscale

Langmuir, Journal Year: 2024, Volume and Issue: 40(13), P. 6750 - 6760

Published: March 18, 2024

Colloidal probe microscopy, a technique whereby microparticle is affixed at the end of an atomic force microscopy (AFM) cantilever, plays pivotal role in enabling measurement friction nanoscale and high relevance for applications fundamental studies alike. However, conventional experiments, particle immobilized onto thereby restricting its relative motion against countersurface to pure sliding. Nonetheless, under many conditions interest, such as during processing particle-based materials, particles are free roll slide past each other, calling development techniques capable measuring rolling alongside sliding friction. Here, we present new methodology measure lateral forces contacts based on adaptation colloidal microscopy. Using two-photon polymerization direct laser writing, microfabricate holders that can capture microparticles, but allow their rotation. Once attached AFM upon scanning, enable both between captured substrate, depending interactions, while simultaneously giving access normal signals. Crucially, by producing with optically heterogeneous surfaces, accurately detect presence rotation scanning. After introducing workflow fabrication use probes, provide details calibration, investigate effect materials used fabricate them, report data function surface roughness particles. We firmly believe our opens up avenues characterization nanoscale, aimed, instance, engineering properties characterizing functional coatings terms

Language: Английский

---

Decoupling of rotation and translation at the colloidal glass transition

The Journal of Chemical Physics, Journal Year: 2024, Volume and Issue: 161(1)

Published: July 3, 2024

In dense particle systems, the coupling of rotation and translation motion becomes intricate. Here, we report results confocal fluorescence microscopy where simultaneous recording translational rotational trajectories from a bidisperse colloidal dispersion is achieved by spiking samples with probe particles. The latter consist particles containing two fluorescently labeled cores suited for tracking particle's orientation. A comparison experimental data event driven Brownian simulations gives insights into system's structure dynamics close to glass transition sheds new light onto translation-rotation coupling. show that increasing volume fractions, slows down drastically, whereas changes very little. We find convincing agreement between simulation experiments, even though neglect far-field hydrodynamic interactions. An additional analysis following mode theory works well structural but indicates decoupling diffusion smaller species. Shear stress correlations do not decorrelate in simulated states are affected motion.

Language: Английский

---

Is it Possible to Detect a Rotating Spherical Colloidal Particle?

Advanced Photonics Research, Journal Year: 2024, Volume and Issue: unknown

Published: Dec. 6, 2024

A single micrometer‐size spherical colloid has been set in rotation by transfer of light orbital angular momentum. This particle is floating at an air–water interface. Steady‐state rotational frequencies the order one hertz have observed, depending on topological charge beam and its power, agreement with expected values. The detection performed using Doppler shift diffused light. Two time constants evidenced velocity dynamics. first related to friction fluid (air water), whereas other principally associated wall air–liquid interface container. measurement technique makes it possible identify dynamic parameters movement any object, which usually impossible detect.

Language: Английский

---