Three-Dimensionally Complex Phase Behavior and Collective Phenomena in Mixtures of Acoustically Powered Chiral Microspinners

Abstract

The process of dynamic self-organization of small building blocks is fundamental to the emergent function of living systems and is characteristic of their out-of-equilibrium homeostasis. The ability to control the interactions of synthetic particles in large groups could lead to the realization of analogous macroscopic robotic systems with microscopic complexity. Rotationally induced self-organization has been observed in biological systems and modeled theoretically, but studies of fast, autonomously moving synthetic rotors remain rare. Here, we report switchable, out-of-equilibrium hydrodynamic assembly and phase separation in suspensions of acoustically powered chiral microspinners. Semiquantitative modeling suggests that three-dimensionally (3D) complex spinners interact through viscous and weakly inertial (streaming) flows. The interactions between spinners were studied over a range of densities to construct a phase diagram, which included gaseous dimer pairing at low density, collective rotation and multiphase separation at intermediate densities, and ultimately jamming at high density. The 3D chirality of the spinners leads to self-organization in parallel planes, forming a three-dimensionally hierarchical system that goes beyond the 2D systems that have so far been modeled computationally. Dense mixtures of spinners and passive tracer particles also show active−passive phase separation. These observations are consistent with recent theoretical predictions of the hydrodynamic coupling between rotlets generated by autonomous spinners and provide an exciting experimental window to the study of colloidal active matter and microrobotic systems.

Surface Engineering of Metal and Semiconductor Nanocrystal Assemblies and Their Optical and Electronic Devices

“…Taking advantage of the small size of NCs compared to the wavelength of light allows the design of assemblies with homogenized permittivity and permeability and the mixing of multiple and even orthogonal functions (e.g., optical and magnetic) and could open up new directions in reconfigurable optical metamaterials. The large-area, 3D manufacturing of colloidal NC metamaterials overcomes significant challenges in the fabrication of 3D architectures and presents opportunities to bring together the fields of nanophotonics and nanomechanics, and by releasing NC-based structures from the substrate surface and suspending them in solvent, colloidal NCs may unite and deliver new functions in the exploration of smart particles, active matter, microrobotics, and optofluidics …”

“…The large-area, 3D manufacturing of colloidal NC metamaterials overcomes significant challenges in the fabrication of 3D architectures and presents opportunities to bring together the fields of nanophotonics and nanomechanics, and by releasing NCbased structures from the substrate surface and suspending them in solvent, colloidal NCs may unite and deliver new functions in the exploration of smart particles, active matter, microrobotics, and optofluidics. 58 In semiconductor NC assemblies, the NC surface is so important to tailoring carrier type, concentration, mobility, and lifetime that considerable research is still needed, especially to extend surface chemical processes to designing III−V and I− III−VI 2 NC assemblies. For NC electronics, a good challenge is to realize not only n-type but also p-type NC assemblies with large enough E g,NC to achieve high μ n ,μ p and I ON /I OFF FETs and complementary circuits.…”

Active Synthetic Microrotors: Design Strategies and Applications

“…In addition, the angular speeds of these microplates were modulated by changing their sizes, independent of the fin number. Very recently, McNeil et al fabricated microdisks with chiral arms that spontaneously spin (with controlled chirality) in ultrasound (“100”) . Interesting collective behaviors, such as 3D assembly and phase separation, were reported.…”

Ultrasound Manipulation and Extrusion of Active Nanorods

“…[5,6] Many practical realizations of synthetic active matter rely on the effective extrusion and deposition of self-propelled DOI: 10.1002/smll.202300028 particles from liquid media in the desired location. This task is nontrivial due to the active nature of these particles, which behave differently than standard passive ones: they exhibit rheotaxis (migration against the applied flow), [7][8][9][10] self-assembly, [11][12][13] and the onset of collective behavior. [9,[14][15][16] Hydrodynamic focusing is the most common technique to concentrate and extrude passive particles.…”