Impact of coating particles on liquid marble lifetime: reactor engineering approach to evaporation.

Liquid marbles are soft matter objects characterised by a liquid droplet enclosed within a hydrophobic particle coating, preventing wetting. This distinctive structure serves as active sites for solid-liquid-gas reactions. However, the impact the chosen coating material has on liquid marble stability, particularly regarding the number of coating layers and material wetting, remains uncertain. There is a need for a modelling approach to predict the overall lifetime considering these coating characteristics. This study reveals that for PTFE liquid marbles evaporating at ambient temperature, smaller coating particles (250 nm) extend their lifetime by forming a multilayered coating. Conversely, using larger particle sizes (200 µm) results in the formation of monolayer liquid marbles with shorter lifetimes than their equivalent naked droplets. Additionally, a higher number of particle layers and a larger contact angle generally enhance the liquid marble's lifetime. For multilayered liquid marbles comprised of smaller particles (250 nm), the particle contact angle is found to have a more significant impact than the number of layers on lifetime extension, whereas the opposite holds true for larger particle sizes (20 µm). A modelling approach using the reactor engineering method for liquid marble evaporation demonstrates excellent agreement with experimental results, yielding an R2 of 0.996. The implementation of this specific model, capable of assessing lifetime across various physical modifications, will enhance our understanding of liquid marble properties before their application in biomedical, microreactor, and green technologies.

Liquid Marbles in Liquid.

Traditional liquid marbles (LMs), liquid droplets encapsulated by hydrophobic particles at the liquid-gas interface, are restricted by their short lifetime and low heat transfer efficiency. Herein, a new paradigm for LMs immersed in various liquid mediums with massive enhanced heat transfer and spatial recognition is designed; without compromising the structural integrity, the lifetime of the liquid marbles in liquid (LMIL) is extended by ≈1000 times compared to classical LMs in air or naked droplets in organic reagents. The LMIL shows promising reverse structural re-configurability while under external stimuli and maintaining their functionality for a very long period of time (≈weeks). These superior behaviors are further exploited as a miniature reactor with prolonged lifetimes and excellent temperature control, combined with its feasible operation, new opportunities will open up in the advanced chemical and biomedical engineering fields. It is also shown that LMIL can be applied in methylene blue degradation and 3D in-vitro yeast cell cultures. These findings have important implications for real-world use of LMs, with a number of applications in cell culture technology, lab-in-a-drop, polymerization, encapsulation, formulation, and drug delivery.