Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from-equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium.

1H-NMR relaxometric experiments over an extended frequency range show that ferrimagnetic colloidal nanoclusters exhibit enhanced transverse relaxivity, r2.

Active matter in a drying droplet alters the growth dynamics of coffee rings and leads to a more uniform distribution. Andac et al . investigate experimentally the drying process of a droplet containing suspended colloids in presence of motile bacteria, and find that the effect is particularly relevant in the case of slowly drying droplets. The experimental results are reproduced in the numerical simulation of a minimalistic model.

The formation of self-assembled nanotubes is usually accounted for by anisotropic elastic properties of membranelike precursors. We present experimental data as evidence of the role played by electrostatics in the formation of self-assembled tubes in alkaline aqueous suspensions of lithocholic acid (LCA). Striking salt effects are characterized by comparing the rheological, dynamical, and scattering properties of systems prepared either in stoichiometric neutralization conditions (SC) of LCA or in a large excess of sodium hydroxide (EOC, experimentally optimized conditions) and finally, in two steps: stoichiometric neutralization followed by an appropriate addition of NaCl (AISC). The SC liquid system is originally made up of loose helical ribbons (previous transmission electron microscopy data), and upon aging they exhibit both intra- and interordering processes. Initially, the helical ribbons are loose and progressively wind around a cylinder (R = 330 Å) with their edges exposed to the solvent. They can be temporarily organized in a centered rectangular two-dimensional lattice (pgg, a = 224 Å, b = 687 Å). Upon further aging, the ribbons wind into more compact helical ribbons (or tubes with helical grooves): their edges are less-exposed and their ordering vanishes. Upon addition of NaCl salt (as in the AISC systems), the specific screening of the intra-aggregate electrostatic repulsions induces the closure of the ribbons into tubes (R(ext) = 260 Å, R(int) = 245 Å as in the EOC systems). Simultaneously with the closure of the ribbons into plain tubes, a drastic enhancement of their interconnectivity through van der Waals attractions develops. Eventually, gels are obtained with networks having hexagonal bundles of tubes.

We report a self-assembled metallo suprapolymer gel exhibiting remarkable self-healing features. The Ni2BTC metallo suprapolymer gels result from the complexation of Ni(2+) metal ions by a tritopic ligand (bis-terpyridine cyclam) in dimethylformamide (DMF) and an annealing step at 50 °C for 24 hours. The self-healing properties are characterized by visual inspection, rheological and impedance spectroscopy measurements: the results are compared with those of a fatty acid-based molecular organogel chosen as a reference system. The creep-recovery analysis uses the Burgers model for low strains and characterizes a recovery capability of up to 72% of the deformation in Ni2BTC gels while it is only 32% for the fatty acid organogel. At very large strains, the impedance spectroscopy confirms the slow repairing process consistently with the visual observations. Rheological measurements demonstrate the restructuring of the fractured networks. The fatigue of the self-healed gel networks undergoing long sequences of strain-relaxation steps is characterized.

Self-organisation is driven by the interactions between the individual components of a system mediated by the environment, and is one of the most important strategies used by many biological systems to develop complex and functional structures. Furthermore, biologicallyinspired self-organisation offers opportunities to develop the next generation of materials and devices for electronics, photonics and nanotechnology. In this work, we demonstrate experimentally that a system of Janus particles (silica microspheres half-coated with gold) aggregates into clusters in the presence of a Gaussian optical potential and disaggregates when the optical potential is switched off. We show that the underlying mechanism is the existence of a hydrodynamic flow induced by a temperature gradient generated by the light absorption at the metallic patches on the Janus particles. We also perform simulations, which agree well with the experiments and whose results permit us to clarify the underlying mechanism. The possibility of hydrodynamic-flux-induced reversible clustering may have applications in the fields of drug delivery, cargo transport, bioremediation and biopatterning.

The unusual spontaneous formation of submicrometer-sized vesicles from a small, nonamphiphilic bis-biuret difluorene derivative upon dissolution of the solid in an anhydrous organic solvent was investigated using multiple scattering techniques. Time-resolved light scattering (TLS) measurements confirm that the self-assembly process is driven by hydrogen-bonding interactions, leading to the formation of vesicles at a critical concentration ∼1 × 10–4 M in tetrahydrofuran as determined by absorbance and surface tension measurements. Results from cryogenic-scanning electron microscopy (cryo-SEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) experiments are consistent with the existence of vesicle-like aggregates in solution. DLS studies indicate a broad distribution of aggregates with a mean hydrodynamic radius ⟨R H ⟩ = 303 nm (polydispersity =0.49). SAXS profiles show two decay regimes (low-Q decay, very large aggregates; large-Q decay, smaller species). The analysis models the large aggregates as vesicles (hollow spheres) with a mean external radius R o = 750 nm and an internal radius R i = 720 nm while the smaller aggregates have a mean radius R = 2.2 nm. The results obtained by cryo-SEM show spherical aggregates of vesicles size in the range ca. 100 nm to 1 μm. Transmission electron microscopy (TEM) micrographs evidence the presence of aggregates whose morphology is compatible with budding and pearling processes as possible mechanisms for the formation of vesicles.

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