Universality of Scaling Laws Governing Contact and Spreading Time Spans of Bouncing Liquid Marbles and its Physical Origin

Experimental investigation on the bouncing dynamics of a liquid marble during the impact on a hydrophilic surface

Liquid marbles are droplets coated by hydrophobic particles. At low Weber numbers (We), when impacting a hydrophilic surface, the marble may bounce on the substrate repeatedly without any rupturing until the quiescence condition is achieved. The marble bouncing has gained far less attention, although its rich underlying physics is due to the interaction between liquid core, hydrophobic grain, and surrounding air. Accordingly, this research experimentally scrutinizes the marble impact and subsequent bouncing on a hydrophilic surface for the first time. Additionally, the conversion of kinetic, gravitational potential, inertial, and surface energies occurring regularly during the impact is exhaustively surveyed. Moreover, the effect of Weber and gravitational Bond numbers (Bo) on the bouncing time, maximum spreading time, maximum spreading ratio, maximum elongation ratio, and maximum restitution are investigated, which characterize the marble impact and bouncing dynamics. This study is one of the limited investigations exploring the effects of the gravitational Bond number on the results. Dimensionless correlations are proposed for the mentioned parameters based on the experimental data. Furthermore, utilizing the simplifying theoretical presumptions, correlations are suggested based on the scale analysis for the spreading time and maximum spreading ratio. The results imply that the mentioned parameters behave differently at low and moderate Weber numbers, though the distinction is more pronounced in the case of the bouncing time, maximum spreading time and maximum spreading ratio. Although increasing with the Weber number when WeWecr. In addition, the maximum elongation ratio linearly grows with the Weber number.

Biocompatible Hydrogel-Based Liquid Marbles with Magnetosomes

Liquid marbles are widely known for their potential biomedical applications, especially due to their versatility and ease of preparation. In the present work, we prepared liquid marbles with various cores composed of water, agar-based hydrogels, magnetic fluids, or non-aqueous substances. As a coating material, we used biocompatible particles of plant origin, such as turmeric grains and Lycopodium pollen. Additionally, we provided marbles with magnetic properties by incorporating either magnetosomes or iron oxide nanoparticles as a powder or by injecting another magnetic fluid. Structures obtained in this way were stable and susceptible to manipulation by an external magnetic field. The properties of the magnetic components of our marbles were verified using electron paramagnetic resonance (EPR) spectroscopy and vibrating sample magnetometry (VSM). Our approach to encapsulation of active substances such as antibiotics within a protective hydrogel core opens up new perspectives for the delivery of hydrophobic payloads to the inherently hydrophilic biological environment. Additionally, hydrogel marbles enriched with magnetic materials showed promise as biocompatible heating agents under alternating magnetic fields. A significant innovation of our research was also the fabrication of composite structures in which the gel-like core was surrounded without mixing by a magnetic fluid covered on the outside by the particle shell. Our liquid marbles, especially those with a hydrogel core and magnetic content, due to the ease of preparation and favorable properties, have great potential for biomedical use. The fact that we were able to simultaneously produce, functionalize (by filling with predefined cargo), and manipulate (by means of an external magnetic field) several marbles also seems to be important from an application point of view.