Axisymmetric Compression of a Circular Particle Raft Driven by the Diffusion of Surfactant.

Particle rafts are a new kind of soft matter formed by self-organization on the interface, which possesses mechanical properties between fluid and solid, and they have been widely used in many industrial fields. In the present study, the compression experiment of a circular particle raft is first performed, where an SDS (sodium dodecyl sulfate)-coated metal ring is placed around its periphery. When the surfactant diffuses, the particle raft shrinks, and its shrinkage ratio increases with the increase in the surfactant concentration, where the experimental results are consistent with the numerical simulation. Next, the relationship between the initial surface tension difference of SDS and the radius shrinkage of the particle raft is obtained by dimensional analysis. In what follows, the diffusion model is built to quantify the diffusion process of SDS at the liquid-gas interface, and then the analytical concentration solution of the concentration of SDS at the periphery of particle raft is given. The particle raft is viewed as an elastic circular plate under the action of the radial pressure, which originates from the surface tension difference, which has been verified by the experimental result. These explorations cast a new light on how to apply loads to measure mechanical properties of soft matter, which also provide some inspirations on the design of microsensors and microfluidics.

Configuration Evolution of a Particle Raft with a Preprepared Crack Driven by the Diffusion of a Surfactant.

In the present study, the morphology evolution of a particle raft with a preprepared crack, which is caused by injecting the surfactant sodium dodecyl sulfate (SDS) into water, is demonstrated. Experimental results on the process of crack closure and configuration evolution are captured and are in excellent agreement with the numerical simulations. Then a surface diffusion model on SDS is proposed to quantify the detailed physical scenario. The surface diffusion factor is determined through the shooting method based on the experimental result of dynamic surface tension. As a result, the analytical solution for the SDS concentration distribution is given. The theoretical result on the dependence relationship between the profile shrinkage ratio and the time variable is consistent with the experimental result. At last, the relation between the initial surface tension difference of SDS and the profile shrinkage ratio is obtained in the light of experiments and dimensional analysis, and the two results are very close. These analyses provide a comprehensive understanding of the coupling between chemicals and mechanical behaviors of soft matter, and the modulation of defects in the particle raft provides some inspiration for engineering new devices at the microscale.

A worm-inspired robot based on origami structures driven by the magnetic field.

With the rapid development of origami technology, worm-inspired origami robots have attracted tremendous interest owing to their colourful locomotion behaviours, such as creeping, rolling, climbing and obstacle crossing. In the present study, we aim to engineer a worm-inspired robot based on knitting process with paper, which could realize complicated functions associated large deformation and exquisite locomotion patterns. At first we fabricate the backbone of the robot by using the paper-knitting technique. The experiment shows that the backbone of the robot can endure significant deformation during the tension, compression and bending process, and this feature ensures it can achieve the desired targets of motion. Next, the magnetic forces and torques under the actuation of permanent magnets are analysed, which are just the driving forces of the robot. We then consider three formats of motion on the robot, i.e. the inchworm motion, the Omega motion, and the hybrid motion. Typical examples for the robot fulfil desired tasks are given, including sweeping obstacles, climbing the wall and delivering cargoes. Detailed theoretical analyses and numerical simulations are performed to illustrate these experimental phenomena. The results show that the developed origami robot is equipped with such characteristics as lightweight and great flexibility, which is sufficiently robust in various environments. These promising performances shed new light on design and fabrication of bio-inspired robots with good intelligence.