Controlled evaporation dynamics of ferrofluid drops under a magnetic field: Experimental observation and analysis

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Over the last several years, the evaporation of magnetic fluid drops has drawn attention due to its broad range of engineering applications. In this research, the effects of substrate wettability, temperature, and magnetic field on the evaporation behavior, deposition patterns, and lifetime of water-based ferrofluid drops are studied experimentally. The ferrofluid is synthesized using the co-precipitation method. Unlike classical evaporation models, the present study reveals that magnetic-field-induced drop deformation and nanoparticle redistribution fundamentally alter evaporation kinetics and drop lifetime. Through systematic experimentation, the results demonstrate that both the evaporation rate and final deposition pattern of the drop can be regulated via magnetic field influence and substrate wettability modification. On the hydrophobic substrate, applying a DC magnetic force above the drop reduces the drop's effective cross-section against the heat flux during the evaporation process, thereby increasing the lifetime (up to a 32% increase in lifetime). Experiments performed on hydrophilic surfaces reveal an interesting phenomenon: in the absence of a magnetic field, a layer of iron particles forms beneath the drop, reducing the surface's wettability and slowing the evaporation rate, whereas applying a magnetic field disrupts this behavior, significantly altering both evaporation dynamics and particle deposition patterns. This research deepens our understanding of the interplay between magnetic force, surface wettability, and thermal effects in ferrofluid evaporation, enabling variation in drop lifetimes across a wide range. These insights hold significant implications for the design and optimization of ferrofluid-based applications, where controlled evaporation and deposition characteristics are essential.