The transport of motile entities across modulated energy landscapes plays an important role in a range of phenomena in biology, colloidal science and solid-state physics. Here, an easily implementable strategy that allows for the collective and monitored transport of microparticles at fluid-fluid interfaces is introduced. Adsorbed magnetic microparticles are carried on time-dependent magnetic potentials, generated by a dynamic self-assembled lattice of different-sized magnetic particles. In such binary systems, the sudden reorientation of the applied field triggers the rapid exchange between attractive and repulsive configurations, enabling for the ballistic transfer of the carriers through the lattice. As the number of motile entities increases, the induced current increases, before reaching a maximum, while the loaded interface gradually displays bidirectional transport. The described methodology can be tuned through the applied field and exploited for the monitored guidance of adsorbed molecules on liquid surfaces, the segregation of colloidal mixtures, the induced motion of defects in photonic crystals or the design of new self-assembled microrobots.
Self-assembled monolayers of microparticles encoding Archimedean and non-regular tessellations promise unprecedented structure-property relationships for a wide spectrum of applications in fields ranging from optoelectronics to surface technology. Yet, despite numerous computational studies predicting the emergence of exotic structures from simple interparticle interactions, the experimental realization of non-hexagonal patterns remains challenging. Not only kinetic limitations often hinder structural relaxation, but also programming the inteparticle interactions during assembly, and hence the…
One of the most important potential applications of self-propelled nano- and microdevices is targeted drug delivery. To realize this, biocompatible particles that can be guided collectively towards a target inside a patient's body are required. Acoustically propelled nano- and microparticles constitute a promising candidate for such biocompatible, artificial motile particles. The main remaining obstacle to targeted drug delivery by self-propelled nano- and microdevices is to also achieve a reliable and biocompatible method for guiding them collectively to their target. Here, we propose such a …
We present experiments where anisometric colloidal microparticles dispersed in a nematic liquid crystal cell with homeotropic anchoring conditions are dynamically assembled by means of liquid-crystal-enabled electrophoresis (LCEEP) using an AC electric field perpendicular to the confining plates. A nematic host with negative dielectric anisotropy leads to a driving force parallel to the cell plates. We take advantage of the resulting gliding anchoring conditions and the degeneracy in the direction of particle motion to design reconfigurable trajectories using a photosensitive anchoring layer (…
Collective control of mobile microrobotic swarms is indispensable for their potential high-impact applications in targeted drug delivery, medical diagnostics, parallel micromanipulation, and environmental sensing and remediation. Lack of on-board computational and sensing capabilities in current microrobotic systems necessitates use of physical interactions among individual microrobots for local physical communication and cooperation. Here, we show that mobile microrobotic swarms with well-defined collective behavior can be designed by engineering magnetic interactions among individual units. …
Anisotropic macromolecules exposed to non-equilibrium (active) noise are very common in biological systems, and an accurate understanding of their anisotropic dynamics is therefore crucial. Here, we experimentally investigate the dynamics of isolated chains assembled from magnetic microparticles at a liquid-air interface and moving in an active bath consisting of motile E. coli bacteria. We investigate both the internal chain dynamics and the anisotropic center-of-mass dynamics through particle tracking. We find that both the internal and center-of-mass dynamics are greatly enhanced compared t…
Controlling the flow of matter down to micrometer-scale confinement is of central importance in materials and environmental sciences, with direct applications in nano-microfluidics, drug delivery and biothechnology. Currents of microparticles are usually generated with external field gradients of different nature [e.g., electric, magnetic, optical, thermal or chemical ones] which are difficult to control over spatially extended regions and samples. Here we demonstrate a general strategy to assemble and transport polarizable microparticles in fluid media through combination of confinement and m…
We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well defined structures. We use Brownian dynamics to model the assembly of N-clusters varying in size from two to twelve outer spheres, and free energy calculations to predict the expected cluster sizes and shapes as a function of temperature and inner particle diameter. We show that the arrangements of outer spheres at finite temperatures are related to spherical codes, an ideal mathematical seque…
In complex colloidal systems, interparticle interactions strongly affect the dynamics of the constituting particles. A study of the dynamical response also provides invaluable information on the character of those interactions. Here we demonstrate how tuning the electrostatic interactions by an ionic surfactant in dispersions of magnetic nanoplatelets leads to developing new dynamic modes in magnetic response spectra. The collective modes can be induced or suppressed by either varying the concentration ratio of the magnetic nanoplatelets (MP) to the surfactant or increasing the MP concentratio…
It is well-known that magnetic forces can induce a formation of densely packed strings of magnetic particles or even sheafs of several strings (spindles). Here we show that in a sufficiently strong magnetic field, more complex aggregates of particles, translating with a much faster speed than would be for a single particle or even a spindle, can be assembled at the water-air interface. Such a superfast flotilla is composed of many distant strings or spindles, playing a role of its vessels, and moves, practically, as a whole. We provide theoretical results to interpret the effect of a collectiv…
Biomolecular motor proteins that generate forces by consuming chemical energy obtained from ATP hydrolysis are pivotal for organizing broad cytoskeletal structures in living cells. The control of such cytoskeletal structures benefits programmable protein patterning; however, our current knowledge is limited owing to the underdevelopment of an engineering approach for controlling pattern formation. Here, we demonstrate the tailoring of assembled patterns of microtubules (MTs) driven by kinesin motors by designing the boundary shape in fabricated microwells. We found an MT bundle structure along…
Using numerical modeling we study emergence of structure and structure-related nonlinear conduction properties in the self-assembled nanoparticle films. Particularly, we show how different nanoparticle networks emerge within assembly processes with molecular bio-recognition binding. We then simulate the charge transport under voltage bias via single-electron tunnelings through the junctions between nanoparticles on such type of networks. We show how the regular nanoparticle array and topologically inhomogeneous nanonetworks affect the charge transport. We find long-range correlations in the ti…
From intracellular protein trafficking to large scale motion of animal groups, the physical concepts driving the self-organization of living systems are still largely unraveled. Selforganization of active entities, leading to novel phases and emergent macroscopic properties, recently shed new lights on these complex dynamical processes. Here we show that, under the application of a constant magnetic field, motile magnetotactic bacteria confined in water-in-oil droplets self-assemble into a rotary motor exerting a torque on the external oil phase. A collective motion in the form of a large-scal…
We study the phase behaviour and the collective dynamics of interacting paramagnetic colloids assembled above a honeycomb lattice of triangular shaped magnetic minima. A frustrated colloidal molecular crystal is realized when filling these potential minima with exactly two particles per pinning site. External in-plane rotating fields are used to anneal the system into different phases, including long range ordered stripes, random fully packed loops, labyrinth and disordered states. At higher amplitude of the annealing field, the dimer lattice displays a two step melting transition where the in…
Active colloidal systems with non-equilibrium self-organization is a long-standing, challenging area in biology. To understand how hydrodynamic flow may be used to actively control self-assembly of Janus particles (JPs), we use a model recently developed for the many-body hydrodynamics of amphiphilic JPs suspended in a viscous background flow (JFM, 941, 2022). We investigate how various morphologies arise from tuning the hydrophobic distribution of the JP-solvent interface. We find JPs assembled into uni-lamella, multi-lamella and striated structures. To introduce dynamics, we include a linear…
Chiral active fluids are materials composed of self-spinning rotors that continuously inject energy and angular momentum at the microscale. Out-of-equilibrium fluids with active-rotor constituents have been experimentally realized using nanoscale biomolecular motors, microscale active colloids, or macroscale driven chiral grains. Here, we show how such chiral active fluids break both parity and time-reversal symmetries in their steady states, giving rise to a dissipationless linear-response coefficient called odd viscosity in their constitutive relations. Odd viscosity couples pressure and vor…
Different phoretic driving mechanisms have been proposed for the transport of solid or liquid microscopic inclusions in integrated chemical processes. However, the ability to reversibly address both the flow path, rate, and local reactant concentration has not yet been realized. Here we show that a substrate chemically modified with photosensitive self-assembled monolayers allows to directly command the assembly and transport of large ensembles of micron-size particles and drops dispersed in a thin layer of anisotropic fluid. Our strategy separates particle driving, realized via AC electrophor…
Multiscale geometrical and topological learning in the analysis of soft matter collective dynamics
Physics and Astronomy, University of Southampton（物理学与天文学系，索姆塞特大学）；Mathematical Sciences, University of Southampton（数学科学系，索姆塞特大学）；Department of Physics, University of Colorado（物理系，科罗拉多大学）；International Institute for Sustainability with Knotted Chiral Meta Matter (WPI-SKCM2)（结节手性超材料可持续性国际研究所）；Hiroshima University（广岛大学）；Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory（可再生与可持续能源研究所，国家可再生能源实验室）；University of Colorado（科罗拉多大学）
