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 (βm) analysis. A theoretical model based on the energy balance analysis is performed to calculate the maximum spreading (βm), 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.

Liquid marbles (LMs), droplets encapsulated with micro/nanoparticles, have attracted significant attention owing to their potential applications in various fields, ranging from microbioreactors to sensors. The volume of the LMs is a key parameter determining their mechanical stability and gas sensing ability. It is ideal to work with small volumes because of their better mechanical stability and gas sensing power compared to the larger LMs. Though many methods exist for producing LMs in the volume range above 2 μL, no reliable method exists to prepare fully coated submicroliter LMs with tunable volume. The situation becomes even more difficult when one attempts to produce tiny Janus Liquid Marbles (JLMs). This paper presents a simple, singlestep, and efficient strategy for obtaining both the pristine LMs and JLMs in the volume range 200 nL to 18 μL. The core idea relies on the impact of a liquid drop on a particle bed at a Weber number of ∼55 to produce two daughter droplets and to convert these droplets into LMs/JLMs. The whole process takes only a few tens of milliseconds (∼50 ms). We have rendered the experimental schemes so that both the JLMs and pristine LMs can be produced in a single step, with control over their volume. The mechanical stability analysis of the prepared marbles indicates that 200 nL is 5 times more stable than 10 μL of LMs. The 0.72 μL LMs prepared with a 0.5 v/v % phenolphthalein indicator solution showed 3 times faster response time to ammonia gas sensing than 10 μL of LMs. The results presented in this work open up a new route for the rapid and reliable production of both multilayered LMs and JLMs with tunable volume in a wide range (200 nL to 18 μL).

The generation and control of microscale flows are crucial for fundamental as well as applied aspects of microfluidics. Commonly employed strategies for creating microflows are based on the electric field,...

Liquid marbles (LMs) are nonsticky droplets stabilized by hydrophobic solid particles that are adsorbed at the liquid-air interface. LMs are emerging as a potential platform in digital microfluidics, sensing applications, storage unit, biological incubation, and cosmetic applications. Incorporating multifunctional particles to form Janus liquid marble (JLM) could enhance the capabilities of the pristine LM.JLMs are multifunctional next-generation LMs comprising two hemispherical domains of distinct physicochemical properties such as size, hydrophobicity, electrical conductivity, surface functionalization, stimuli-responsivity, and so on.The JLMs offer precise control on the manipulability and enhanced performance over pristine LMs. Though the properties, applications, and progress of LMs are detailed in the recent literature, a focused review encompassing the fabrication, recent developments, potential applications of JLMs, and the challenges regarding its reliable fabrication remains a gap in the literature. The review provides insights into the importance of JLMs, systematically discussing the fabrication strategies, applications, challenges, and future directions.

In this paper, poly(dimethyl siloxane) (PDMS) which is considered chemically unreactive was successfully grafted onto the surface of iron oxide particles, forming stable hydrophobic polymer-coated particles without the usage of any external stimuli like heat or UV irradiation. Here, magnetic hydrophobic particles were prepared by a facile method of coating PDMS prepolymer oil onto Fe 3 O 4 particles via dispersion in a PDMS oil/hexane solution. The X-ray diffraction studies elucidated the successful synthesis of the magnetic particles, whereas the X-ray photoelectron spectroscopic studies ensure the successful incorporation of the polymer layer onto the particles. Two potential applications of the prepared particles were demonstrated here. The oleophilic and hydrophobic nature of the particles coated with PDMS is exploited to demonstrate the oil collection from the surface as well as in immersed conditions in an aqueous medium by using the particle-coated cotton and sponge, respectively. An oil−water separation efficiency of ∼95% was achieved for cotton and sponge against various oils with an oil adsorption capacity of 5 times and 11 times its own weight, respectively. Additionally, magnetic-responsive liquid marbles (LMs) were prepared by encapsulating liquids with the fabricated particles. Stable LMs were formed for a wide range of volumes (5−200 μL) with core liquids having different surface tensions, pH, and viscosity. The stability of the LM was tested using a dropping method and a hydrostatic pressure method.