High Performance Self-Separation Of Mixed Oil Droplets Based On Wedge-Channel Spine Structure

Separating microscale immiscible droplets has important research implications in environmental protection,microchemical reactions,and recovering scarce resources.The current research primarily achieves efficient separation of mixed droplets across surfaces with asymmetric structural gradients and gradients in wettability.It mainly focuses on separating mixed droplets with high surface tension differences,such as micro-oil droplets in water.However,compared with the separation of oil-water,the effective separation of mixed oil droplets is difficult due to the low contact angle hysteresis and lower surface tension difference that completely spread on the whole surface.Although extensive research has been conducted on the manipulation of single-phase oil droplets,the spontaneous continuous,and efficient separation of multiphase immiscible oil droplets with low surface tension difference is still a pressing challenge and problem to be solved.To solve this problem,a spine with hierarchical microchannels and wedge-channel(SHMW)was prepared by the femtosecond laser precision machining technology mimicking the structure of Sarracenia trichomes and chopsticks-like.To explore the efficient and continuous separation of mixed oil droplets in the air by SHMW,analyze the influence of structural parameters such as wedge-channel apex angles on the separation efficiency of mixed oil droplets.It was revealed that the cooperative effect of the surface capillary force generated by the hierarchical microchannel structure and the asymmetric Laplace pressure generated by the wedge-channel enhanced the separation ability of mixed oil droplets,and the theoretical mechanism was analyzed.Tiny mixed oil droplets can be separated into two pure oil phases in two seconds without external energy input.More importantly,this device can spontaneously and efficiently separate mixed droplets of methanol-octane with a surface tension difference as low as 0.87 m N/m and mixed oil droplets with viscosities up to one hundred of centistokes(cst),which significantly increases the range of use for SHMW separation of mixed oil droplets.In addition to its applicability to the separation of multiple mixed oil droplets,SHMW can control the start and stop of mixed oil droplet separation by adjusting the apex angle of the wedge channel.This strategy offers a green and economical approach for separating low differences in the surface energy mixed oil droplets.The novel mixed oil droplet separation-oil collection cone designed in this study provides a green and environmentally friendly strategy for the efficient and continuous separation and collection of heterogeneous immiscible organic droplets with low surface tension difference.It has important research significance and application prospects in micro-droplet manipulation,biomedicine,microchemical reactions,and drug screening.