Tuning particle aspect ratio and surface roughness to modulate properties in colloidal gels.

Hypothesis: Particle shape and surface roughness may have synergistic effects on particle network formation in colloidal gels. Particles with an aspect ratio greater than one have orientation-dependent interactions with neighboring particles compared to spheres, making their interactions highly sensitive to rotational dynamics. By adding surface roughness, we add non-central surface forces and expect to further constrain particle rotation, potentially enhancing the stability and rigidity of networks formed by these particles.

Characterizing sliding and rolling contacts between single particles.

Contacts between particles in dense, sheared suspensions are believed to underpin much of their rheology. Roughness and adhesion are known to constrain the relative motion of particles, and thus globally affect the shear response, but an experimental description of how they microscopically influence the transmission of forces and relative displacements within contacts is lacking. Here, we show that an innovative colloidal-probe atomic force microscopy technique allows the simultaneous measurement of normal and tangential forces exchanged between tailored surfaces and microparticles while tracking their relative sliding and rolling, unlocking the direct measurement of coefficients of rolling friction, as well as of sliding friction.

Tuning Colloidal Gel Properties: The Influence of Central and Noncentral Forces.

Colloidal gels, ubiquitous in industrial applications, can undergo reversible solid-to-liquid transitions. Recent work demonstrates that adding surface roughness to primary particles enhances the toughness and influences the self-healing properties of colloidal gels. In the present work, we first use colloidal probe atomic force microscopy (CP-AFM) to assess the quantitative changes in adhesive and frictional forces between thermoresponsive particles as a function of their roughness.

The 2025 motile active matter roadmap.

Activity and autonomous motion are fundamental aspects of many living and engineering systems. Here, the scale of biological agents covers a wide range, from nanomotors, cytoskeleton, and cells, to insects, fish, birds, and people. Inspired by biological active systems, various types of autonomous synthetic nano- and micromachines have been designed, which provide the basis for multifunctional, highly responsive, intelligent active materials.

Low efficiency of Janus microswimmers as hydrodynamic mixers.

The generation of fluid flows by autophoretic microswimmers has been proposed as a mechanism to enhance mass transport and mixing at the micro- and nanoscale. Here, we experimentally investigate the ability of model 2D active baths of photocatalytic silica-titania Janus microspheres to enhance the diffusivity of tracer particles at different microswimmer densities below the onset of collective behavior. Inspired by the similarities between our experimental findings and previous results for biological microorganisms, we then model our Janus microswimmers using a general squirmer framework, specifically treating them as neutral squirmers.