Magnetic Liquid Marbles as Thermo-Responsive Materials under Alternating Magnetic Fields

Responsive materials are essential in modern scientific and industrial fields. Within this context, the potential to control these materials using external stimuli, such as magnetic fields, is of great interest. Magnetic liquid marbles—airborne droplets surrounded by particles—are emerging as suitable candidates for such purposes. For example, their ability to open and close on-demand using static magnetic fields makes them ideal for specialized tasks, such as testing fragile entrapped species [1].<br/><br/>When exposed to alternating magnetic fields, the internal temperature of liquid marbles rises, a phenomenon attributed to magnetic energy dissipation due to magnetic relaxation and hysteresis processes. Elevated temperature can be employed for functions like amplifying DNA contained within the particle shell of these marbles [2]. Building on this, we propose utilizing magnetic heating to modulate thermo-responsive liquid marbles.<br/><br/>In our experiments, we prepared liquid marbles with a ferrofluid, which included agar powder and either maghemite nanoparticles or magnetosomes (nanoparticles from magnetotactic bacteria). The droplets were coated with either polymer or bio-particles and then exposed to an alternating magnetic field with a kHz frequency. The resulting temperature increase inside the liquid marbles initiated varied reactions depending on their particle coating. With polymer particles, a combination of partial particle fusion and enhanced evaporation led to the creation of rigid magnetic shell residuals, which could be seen as precursors to a new generation of liquid marbles [3]. On the other hand, for non-thermo-responsive particle coatings, such as <i>lycopodium </i>shell, the liquid core underwent partial disintegration driven by reversal process of gelation. The diverse structures observed after the magnetic heating procedure may provide new way for developing materials suitable for applications like smart lotions or creating new types of capsules for theranostic procedures.<br/><br/>The work was supported by Polish National Science Center through the project no. 2019/35/N/ST5/00402.<br/><br/>References:<br/>[1] Zhao, Yan, et al. "Magnetic Liquid Marbles: Toward “Lab in a Droplet”." <i>Advanced Functional Materials</i> 25.3 (2015): 437-444.<br/>[2] Li, Hualin, et al. "Magnetothermal Miniature Reactors Based on Fe₃O₄ Nanocube-Coated Liquid Marbles." <i>Advanced Healthcare Materials</i> 10.6 (2021): 2001658.<br/>[3] Bielas, Rafal, et al. “Tunable Particle Shells of Thermo-Responsive Liquid Marbles under Alternating Magnetic Field.”. <i>Journal of Molecular Liquid </i>391 (2023): 123283.