In this study, we propose a highly efficient robot platform for pollutant adsorption. This robot system consists of a flapping-wing micro aircraft (FWMA) for long-distance transportation and delivery and cost-effective multifunctional Janus microrobots for pollutant purification. The flapping-wing micro air vehicle can hover for 11.3 km with a flapping frequency of approximately 15 Hz, fly forward up to 31.6 km/h, and drop microrobots to a targeted destination. The Janus microrobot, which is composed of a silica microsphere, nickel layer, and hydrophobic layer, is used to absorb the oil and process organic pollutants. These Janus microrobots can be propelled fast up to 9.6 body lengths per second, and on-demand speed regulation and remote navigation are manageable. These Janus microrobots can continuously carry oil droplets in aqueous environments under the control of a uniform rotating magnetic field. Because of the fluid dynamics induced by the Janus microrobots, a highly efficient removal of Rhodamine B is accomplished. This smart robot system may open a door for pollutant purification.

Controllable self‐propelled droplet robots show great potential to be used as carriers, sensors and actuators in biological medicine and oil exploration. Current research mainly focuses on studying oil droplet robots floating in water phase which has limited application. Different from the previous robots, a light‐driven self‐propelled water‐phase droplet micro robot, which is doped with Fe2O3 nanoparticles, moving in oil solvent is proposed. Unlike light‐driven oil droplets, the water drop robot is constantly diving towards the light source like a submarine moving in oil environment under blue laser irradiation. Numerical simulations are performed to investigate the water/oil interface behavior and the motion mechanism of micro robots. It is found that a photocatalytic Fenton reaction occurs on the irradiated Fe2O3 nanoparticles of water droplet robot, which causes uneven ion concentration to change the interfacial tension distribution of the water drop generating Marangoni flow. In addition to phototaxis behavior, further experiments confirmed that multiple water droplet micro robots show collective behavior under the control of surface light source. The proposed water droplet micro robot provides new possibilities for the development of targeted drug delivery, oil‐water separation as well as oil pollution treatment.

We all live in a yellow submarine: Different from previous robots, a light‐driven self‐propelled water‐phase droplet microrobot, which is doped with Fe2O3 nanoparticles, moving in oil solvent is proposed. Fenton reaction occurs on the irradiated Fe2O3 nanoparticles. The continuous release of ferric ions and ferrous ions causes an uneven ion concentration to change the interfacial tension distribution between the water droplet and oil, generating Marangoni flow. The robot is constantly diving towards the light source like a submarine moving in an oil environment under blue laser irradiation. More information can be found in the Communication by Longqiu Li, Dekai Zhou et al.

Static mixers have been widely used to dilute high viscosity, high-molecular-weight polymer mother liquor for polymer flooding, in which the mixing performance plays a critical role. In this work, a novel mixing configuration, named as Helixes static mixer, was proposed to reduce high viscosity degradation rate of polyacrylamide solution resulting from mechanical shear during mixing process. Computational fluid dynamics simulations along with experiments were performed to investigate the mixing process. Several criteria such as the intensity of segregation, mixing distance, pressure loss, and shear strain rate were used to evaluate the mixing and shear performance of static mixers. Compared to the SMX and Kenics static mixer, a longer mixing distance is needed for the Helixes static mixer to achieve an ideal mixture. A lower shear strain rate along with less viscosity degradation rate is obtained in flow field of Helixes static mixer. The spiral-lead and helical directions of mixing elements were optimized to improve mixing performance. Experimental results are in good agreement with the numerical simulations on the intensity of segregation. The viscosity degradation rate of HPAM solution which flows through Helixes static mixer is lower than that of SMX and Kenics static mixers.

Ultrahigh-molecular-weight partially hydrolyzed polyacrylamides (HPAMs) are commonly used in polymer flooding to enhance oil recovery. However, the viscosity of the HPAM solution is susceptible to shear action. Viscosity change affects sweep range and displacement efficiency of the displacement fluid. Here, a macromolecular adsorption model in microcapillary is proposed to reveal the shear variation mechanism at low flow rates. The rheological behaviors of HPAMs with three different molecular weights are investigated using a stainless steel capillary. The shear rate distributions near contraction and within capillary are compared by numerical calculation using the laminar flow model. Experimental and numerical results show that the polymer solution was mechanically degraded at low flow rates, which is in agreement with the results predicted by the adsorption theory model. A new calculation method for the thickness of polymer adsorption layer at lower flow rates is proposed based on the adsorption model proposed in this study. It is found that the viscosity and adsorption of HPAM were changed with flow rate, and their changes are closely related to the displacement efficiency in the micropores of reservoirs. This study provides new perspectives for the selection of polymer injection flow rates and the water shutoff in reservoirs.