Morphologic transformation of ferrofluid during micropump driving under field control.

The superiority of ferrofluid pumps in the fields of biomedical, life science, energy, and power research has been experimentally demonstrated. However, the mechanisms underlying the morphological transformations of ferrofluid fusion and separation during pump driving are not completely understood. To bridge the gap between the theory and practical applications of ferrofluid pumps, we employed optical methods to record the dynamic morphological transformation of rotating and fixed ferrofluids under different magnetic field polarities, magnetic field distributions, and ferrofluid mass fractions. The magnetic field polarity causes dynamic differences in the fusion-separation process of the ferrofluid but does not affect the volume segmentation of the ferrofluid, which depends on the ratio of the magnetic field intensities. When this ratio deviates from one, the morphology of ferrofluid changes, reducing the pumping efficiency. Compared to external environmental factors, the mass fraction does not change the morphology of the ferrofluid. However, high mass fractions lead to wall-clinging of the ferrofluid, and low mass fractions induce bubbles, both of which detrimentally affect the pumping performance. This study reveals the properties of ferrofluid and the effects of external environmental conditions on the morphological transformation of ferrofluid, providing references for optimizing ferrofluid pumps.