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Field driven evaporation kinetics of a sessile ferrofluid droplet on a soft substrate.
Soft Matter ( IF 2.9 ) Pub Date : 2020-06-11 , DOI: 10.1039/d0sm00345j
Sudip Shyam 1 , Pranab Kumar Mondal 1 , Balkrishna Mehta 2
Affiliation  

We experimentally investigate the evaporation kinetics of a sessile ferrofluid droplet placed on a soft substrate in the presence of a time-dependent magnetic field. We use both bright field visualization techniques and μ-PIV analysis to gain qualitative as well as quantitative insights into the internal hydrodynamics of the droplet. The results show that the droplet evaporation rate is augmented significantly in the presence of a time-dependent magnetic field, attributed primarily to the enhanced internal flow advection. We show that the motion of the magnetic nanoparticles dictates the overall life-time of the evaporating ferrofluid droplet. At lower frequencies of the magnetic field, the magnetic nanoparticles move towards the magnet and agglomerate into a chain-like cluster formation, oriented according to the magnetic field lines. On the other hand, at higher frequencies, the magnetic nanoparticles do not have sufficient time to travel the whole characteristic length (droplet diameter). Consequently, we observe the presence of a critical frequency at which the perturbation time scale balances the advective time scale of the flow inside the droplet. We show that on account for this balance between the time scales, the droplet experiences a minimum life-time. Finally, we demonstrate that the evaporation kinetics of a ferrofluid droplet in the presence of a time-dependent magnetic field can be described through three distinguishable stages viz., the decreasing contact angle and variable radius zone, the decreasing contact angle and decreasing radius zone and the late mixed zone. The inferences drawn from this study could have far-reaching implications in fields ranging from biomedical engineering to surface patterning.

中文翻译:

固着铁磁液滴在软质基底上的场驱动蒸发动力学。

我们通过实验研究了固着的铁磁流体液滴在时间依赖性磁场存在下的蒸发动力学,该液滴位于柔软的基质上。我们使用明场可视化技术和μ-PIV分析来获得对液滴内部流体动力学的定性和定量分析。结果表明,在存在随时间变化的磁场的情况下,液滴的蒸发速率显着提高,这主要归因于内部流动对流的增强。我们表明,磁性纳米粒子的运动决定了蒸发的铁磁流体液滴的整体寿命。在较低的磁场频率下,磁性纳米粒子向磁体移动并聚集成链状簇状结构,并根据磁场线定向。另一方面,在较高的频率下,磁性纳米颗粒没有足够的时间传播整个特征长度(液滴直径)。因此,我们观察到临界频率的存在,在该临界频率处,扰动时间尺度平衡了液滴内部流的对流时间尺度。我们表明,由于时间尺度之间的这种平衡,液滴经历了最小的寿命。最后,我们证明了在存在时间依赖性磁场的情况下,铁磁流体液滴的蒸发动力学可以通过三个不同的阶段来描述 我们观察到临界频率的存在,在该临界频率处,扰动时间尺度平衡了液滴内部流的对流时间尺度。我们表明,由于时间尺度之间的这种平衡,液滴经历了最小的寿命。最后,我们证明了在存在时间依赖性磁场的情况下,铁磁流体液滴的蒸发动力学可以通过三个不同的阶段来描述 我们观察到临界频率的存在,在该临界频率处,扰动时间尺度平衡了液滴内部流的对流时间尺度。我们表明,由于时间尺度之间的这种平衡,液滴经历了最小的寿命。最后,我们证明了在存在时间依赖性磁场的情况下,铁磁流体液滴的蒸发动力学可以通过三个不同的阶段来描述,减小的接触角和可变半径区域,减小的接触角和减小半径区域以及后期混合区域。这项研究得出的推论可能会对从生物医学工程到表面图案的各个领域产生深远的影响。
更新日期:2020-07-22
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