Directional transport or transfer of micro-objects, including solid particles and liquid droplets, exhibits a high potential in various applications, including heat dissipation, water collection, microfluidics, drug transport without pollution, targeted therapy, etc. A variety of methods have been designed to achieve efficient transport functions. However, some challenges still exist, including the directional and rapid transport of solid particles, the non-destructive and non-polluting transfer of droplets, and the precise manipulation of droplets, etc.

In this work, we mainly focused on the directional transport and fixed-point transfer of droplets. Firstly, the dynamic behavior of a droplet across the boundary of different wettability regions was studied experimentally¹, which would be the mechanism for directional transport of droplets. Then, surfaces consisting of regions of different wettability were designed, on which droplets can spread or slide directionally^{2, 3}. A magnetic sensitive flat surface was further prepared based on soft polymer materials. Under the action of magnetic field, the flat surface will partially become a rough surface. A droplet can be driven to move with a moving magnetic field due to the induced boundary between the flat and rough surface areas⁴. Finally, a magnetically responsive micro-plate-arrayed surface was designed, different secondary microstructures were further introduced on two lateral sides of each microplate, based on which droplets can be firmly grasped and easily released spontaneously under a rotating magnetic field⁵. All the experimental phenomena were reasonably explained.

The above techniques are simple and easy to implement, which should provide new concepts or technologies for the related fields of droplet manipulation and directional transport or transfer.

References

1. M. Liu, L.Y. Huang, Y. Yao, Z.L. Peng, S.H. Chen. The Journal of Physical Chemistry C, 2019, 123, 23505−23510.
2. M. Liu, Y. Yao, Y.Z. Yang, Z.L. Peng, S.H. Chen. The Journal of Physical Chemistry C, 2019, 123, 12736-12743.
3. M. Liu, Y. Yao, J.J. Li, Z.L. Peng, S.H. Chen. The Journal of Physical Chemistry B, 2020, 124, 6905-6912.
4. M. Liu, C.H. Li, Z.L. Peng, S.H. Chen, B. Zhang. Langmuir, 2022, 38, 3917-3924.
5. M. Liu, C.H. Li, Z.L. Peng, Y. Yao, S.H. Chen. Chem. Engineering. J., 2022, 430, 132749.