Department of Mechanical Engineering, Sharif University of Technology, Tehran1458889694, Iran.
Langmuir. 2023 Feb 14;39(6):2246-2259. doi: 10.1021/acs.langmuir.2c02811. Epub 2023 Feb 1.
Liquid marbles are droplets enwrapped by a layer of hydrophobic micro/nanoparticles. Due to the isolation of fluid from its environment, reduction in evaporation rate, low friction with the surfaces, and capability of manipulation even on hydrophilic surfaces, liquid marbles have attracted the attention of researchers in digital microfluidics. This study investigates the manipulation of ferrofluid liquid marbles (FLMs) under DC and pulse width-modulated (PWM) magnetic fields generated by an electromagnet for the first time. At first, the threshold of the magnetic field for manipulating these FLMs is studied. Afterward, the dynamic response of the FLMs to the DC magnetic field for different FLM volumes, coil currents, and initial distances of FLM from the coil is studied, and a theoretical model is proposed. By applying the PWM magnetic field, it is possible to gain more control over the manipulation of the FLMs on the surface and adjust their position more accurately. Results indicate that with a decrease in FLM volume, coil current, and duty cycle, the FLM step length decreases; hence, FLM manipulation is more precise. Under the PWM magnetic field, it is observed that FLM movement is not synchronous with the generated pulse, and even after the coil is turned off, FLMs keep their motion. In the end, with proper adjustment of the electromagnet pulse width, launching of FLMs at a distance farther than the coil is observed.
液滴被一层疏水性微/纳米颗粒包裹，形成了液态大理石。由于液滴与环境的隔离，减少了蒸发速度，降低了与表面的摩擦，并且即使在亲水表面上也能够进行操作，因此液态大理石引起了数字微流控领域研究人员的关注。本研究首次研究了在电磁铁产生的直流和脉宽调制（PWM）磁场下对铁磁液滴大理石（FLM）的操纵。首先，研究了操纵这些 FLM 的磁场阈值。然后，研究了不同 FLM 体积、线圈电流和 FLM 与线圈初始距离下 FLM 对直流磁场的动态响应，并提出了一个理论模型。通过施加 PWM 磁场，可以更精确地控制表面上的 FLM 操纵，并更准确地调整其位置。结果表明，随着 FLM 体积、线圈电流和占空比的减小，FLM 的步长减小，因此 FLM 的操纵更加精确。在 PWM 磁场下，观察到 FLM 的运动与产生的脉冲不同步，即使线圈关闭后，FLM 仍保持运动。最后，通过适当调整电磁铁脉冲宽度，可以观察到 FLM 在距离线圈更远的地方发射。
