Simple and Continuous Fabrication of Janus Liquid Marbles with Tunable Particle Coverage Based on Controlled Droplet...

Liquid marbles are gaining increased attention because of their added advantages such as low evaporation rates, less friction, and ease of manipulation over the pristine liquid drop. Their functionalities could be further enhanced by incorporating different types of particles (size, hydrophobicity, chemical properties, etc.), commonly called Janus liquid marbles (JLMs). However, their fabrication process remains a challenge, especially when we require continuous production. Here, we present a simple and fast approach for the fabrication of JLMs covered with nano- and microparticles in an additive-free environment based on the controlled impact of a water drop over the particle beds. The fabrication process involves collection of polyvinylidene difluoride particles (PVDF, particle type 1) by a water drop followed by its impact over an uncompressed bed of black toner particles (BTP, particle type 2). The whole process takes a time of approximately 30 ms only. The drop impact and the condition of the JLM formation were explained based on the Weber number (We) and maximum spread (β_m) analysis. A theoretical model based on the energy balance analysis is performed to calculate the maximum spreading (β_m), and the experimental and theoretical analyses are found to be in good agreement. Tunability in particle coverage is demonstrated by varying the droplet volume in the range of 5-15 μL. We further extend this strategy for the fast and continuous production of nearly identical JLMs, which could enhance the capabilities of open-surface microfluidic applications.