Unique Orientation of the Solid-Solid Interface at the Janus Particle Boundary Induced by Ionic Liquids

Directed Autonomous Motion and Chiral Separation of Self-Propelled Janus Particles in Convection Roll Arrays

Self-propelled Janus particles exhibit autonomous motion thanks to engines of their own. However, due to the randomly changing direction of such motion they are of little use for emerging nanotechnological and biomedical applications. Here, we numerically show that the motion of chiral active Janus particles can be directed, subjecting them to a linear array of convection rolls. The rectification power of self-propulsion motion here can be made to be more than 60%, which is much larger than earlier reports. We show that rectification of a chiral Janus particle's motion leads to conspicuous segregation of dextrogyre and levogyre active particles from a racemic binary mixture. Further, we demonstrate how efficiently the rectification effect can be exploited to separate dextrogyre and levogyre particles when their intrinsic torques are distributed with Gaussian statistics.

Confined Assembly of Colloidal Nanorod Superstructures by Locally Controlling Free-Volume Entropy in Nonequilibrium Fluids

Long-range-ordered structures of nanoparticles with controllable orientation have advantages in applications toward sensors, photoelectric conversion, and field-effect transistors. The assembly process of nanorods in colloidal systems undergoes a nonequilibrium process from dispersion to aggregation. A variety of assembly methods such as solvent volatilization, electromagnetic field induction, and photoinduction are restricted to suppress local perturbations during the nonequilibrium concentration of nanoparticles, which are adverse to controlling the orientation and order of assembled structures. Here, a confined assembly method is reported by locally controlling free-volume entropy in nonequilibrium fluids to fabricate microstructure arrays based on colloidal nanorods with controllable orientation and long-range order. The unique fluid dynamics of the liquid bridge is utilized to form a local region, where the free volume entropy reduction triggers assembly near the three-phase contact line (TPCL), allowing nanorods to assemble in 2D closest packing parallel to the TPCL for the maximum Gibbs free energy reduction. By manipulating the orientation of liquid flow, microstructures are assembled with programmable geometry, which sustains polarized photoluminescence and polarization-dependent photodetection. This confined assembly method opens up perspectives on assemblies of nanomaterials with controllable orientation and long-range order as a platform for multifunctional integrated devices.

Reconfigurable assembly of colloidal motors towards interactive soft materials and systems

Due to the highly flexible reconfiguration of swarms, collective behaviors have provided various natural organisms with a powerful adaptivity to the complex environment. To mimic these natural systems and construct artificial intelligent soft materials, self-propelled colloidal motors that can convert diverse forms of energy into swimming-like movement in fluids afford an ideal model system at the micro-/nanoscales. Through the coupling of local gradient fields, colloidal motors driven by chemical reactions or externally physical fields can assembly into swarms with adaptivity. Here, we summarize the progress on reconfigurable assembly of colloidal motors which is driven and modulated by chemical reactions and external fields (e.g., light, ultrasonic, electric, and magnetic fields). The adaptive reconfiguration behaviors and the corresponding mechanisms are discussed in detail. The future directions and challenges are also addressed for developing colloidal motor-based interactive soft matter materials and systems with adaptation and interactive functions comparable to that of natural systems.

Effective Structure Control of Colloidal Molecules and the Morphology Evolution Mechanism Investigation

Colloidal molecules (CMs), nonspherical clusters of a small number of particles, can be used as building blocks for self-assembly applications. Here, we propose a novel one pot method for CMs synthesis. First, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microgels were prepared by soap-free emulsion polymerization as seed particles, then monomer styrene and cross-linking agent divinylbenzene (DVB) were added, which could be polymerized by the remaining free radicals on the seed surface in situ. P(NIPAM-co-AA)-PS colloidal molecules with a series of morphologies such as popcorn-like, CO₂-like, NH₃-like, CH₄-like and so on could be obtained. The effects of satellite colloid viscosity, interfacial tension, and polymer chain mobility on the number of satellite colloid have been investigated, and the formation mechanism of CMs is proposed based on morphology evolution investigation. Compared with the existing CM synthesis techniques, our method enables fabricating CMs from vinyl monomer in a facile and efficient way, and the scientific finding regarding the CMs formation will guide the CMs fabrication toward salable and reliable direction.