Locomoting non-magnetic marbles through meniscus emerged on the water surface using a magnetically actuated ferrofluid marble under pulsating and steady magnetic fields

Abstract

Recent progress in digital microfluidics has revealed the distinct advantages of liquid marbles, such as minimal surface friction, reduced evaporation rates, and non-wettability compared to uncoated droplets. This study provides a comprehensive examination of an innovative technique for the precise, contamination-free manipulation of non-magnetic water liquid marbles (WLMs) carried by a ferrofluid liquid marble (FLM) under the control of direct current (DC) and pulse-width modulation (PWM) magnetic fields. The concept relies on the phenomenon in which an FLM and WLMs form a shared meniscus when placed together on a water surface, causing the WLMs to closely track the magnetically actuated FLM. The study also explores the dynamic behavior of the marbles by assessing several influencing parameters: magnetic coil current, the starting position of the marbles from the coil, the number of WLMs carried by the FLM, the volume ratio between the WLM and FLM, and the PWM magnetic field properties, including duty cycle and frequency. The results demonstrate that increasing the magnetic coil current or reducing the volume ratio decreases the travel time and enhances the velocity of the carrier FLM under both DC and PWM magnetic fields. Notably, the FLM exhibits significant capability to transport multiple WLMs, although its average and maximum velocity decrease with each additional WLM. Moreover, the travel time of the marbles varies proportionally with the PWM frequency while exhibiting an inverse relationship with the duty cycle.