Liquid Marbles Research Articles

Solar evaporation of liquid marbles with composite nanowire arrays

Solar interfacial evaporation is a sustainable technology to produce fresh water. The synergistic realization of broadband light absorption and good thermal insulation is crucial to improving the thermal efficiency. Here, we propose a new structure over the surface of liquid marbles, which via nanowire arrays assembled with composite nanomaterials (Fe3O4/CNT nanoparticles) to enhance the evaporation efficiency. The composite materials can effectively absorb light across the entire solar spectrum. Multiple reflections of light over nanowire array further improve light absorption. The narrow spaces and local particle aggregation of the nanowire array enhance thermal insulation to improve the evaporation efficiency. A series of experiments were conducted to verify the concept. The results showed that liquid marbles with upward Fe3O4/CNT nanowire arrays (Fe3O4/CNT-ULM) enhance the light harvesting ability and thermal insulation. Fe3O4/CNT-ULM at a volume ratio 1:2 provides the highest evaporation rate of 12.25 μg/s, which is about 1.16 and 1.53 times higher than that of Fe3O4 and CNT, respectively. Numerical analysis further illustrates that the combination of composite materials and nanowire arrays enhances concentration of electromagnetic field and heat at the air/water interfaces. This promotes rapid evaporation at the thermal boundary region, which has important implications for the structure design of solar interfacial evaporator.

Stearic Acid as Polymerization Medium, Dopant and Hydrophobizer: Chemical Oxidative Polymerization of Pyrrole.

In recent years, fatty acids have garnered significant attention as a natural phase-change material and a hydrophobizer due to their biocompatibility and biodegradability. In this study, the utilization of fatty acid is proposed as a polymerization medium for the first time. As a specific reaction, chemical oxidative polymerizations of pyrrole is conducted using ferric chloride as an oxidant in a stearic acid medium. The polymerizations resulted in the production of micrometer-sized polypyrrole (PPy) grains, which are aggregates of atypical primary particles with submicrometer size. The PPy grains are doped with stearic acid, suggesting that the stearic acid functioned as a dopant and a hydrophobizing agent as well as a polymerization medium. The dried PPy grains can adsorb at the air-water interface and function as a liquid marble stabilizer with light-to-heat photothermal properties. The liquid marble can move on a planar air-water interface by Marangoni flow induced by NIR laser light irradiation.

Fully convolutional networks-based particle distribution analysis at multiphase interfaces

The intricate interplay between droplet dynamics and particle characteristics has led to the extensive use of particle-laden droplets in diverse applications, spanning industrial engineering and scientific research. Accurate particle distribution analysis at multiphase interfaces is crucial for understanding the complex behaviors of these soft matters, for example, liquid marbles (LMs). However, traditional image analysis methods for particle-laden interfaces often rely on manual processing, which is both time-consuming and susceptible to human error. In this study, we present a pixel-level image recognition technique based on fully convolutional networks (FCNs) to automatically analyze the interfacial particle distribution of LMs exhibiting clear core-shell structures. The FCNs-based method enables efficient and accurate segmentation of target particles on sessile LMs, utilizing experimental data obtained from an in-situ optical imaging device. This approach significantly expedites the analysis of particle distribution, including proportion, concentration, and cluster centers. We assess the performance of the proposed method using image data of monolayer LMs encapsulated by dispersed polystyrene microspheres, demonstrating its superiority over traditional techniques in terms of accuracy and generalization. This investigation aims to offer novel insights into determining pertinent particulate characteristics within similar solid-liquid hybrid microsystems.

Recent advancements in liquid marbles: fabrication, materials, control mechanisms, and applications

Recent advancements in liquid marbles: fabrication, materials, control mechanisms, and applications

Dynamic Electric Discharge Paths in Liquid Metal Marble Arrays.

Electric discharge occurs ubiquitously in both natural and engineered systems, where the discharge paths provide critical information. However, control and visualization of discharge patterns is a challenging task. Here arrays of liquid metal marbles, droplets of a gallium-indium eutectic alloy with a copper-doped ZnS luminescent coating, are designed for pixelated visualization of electric discharge paths at optical imaging length-scales. The ZnS particles embed themselves into the surface of liquid metal droplets and are anchored by a self-limiting gallium oxide layer. The operation is achieved by generating spark discharges at inter-marble air gaps and reduced voltage drop across highly conducting liquid metal droplets. By taking advantage of the malleability of soft liquid metal marbles, the dynamic visualization platforms allow the manipulation of discharge path selections in configurable marble arrays and the embedding of artificial defect features. The systems are further integrated for characterizing dynamic changes in granular and soft systems, and for enabling logic computing and information encoded display. This demonstration holds promises for creating new-generation electric discharge-based optoelectronics.

Implementing a multi-cycle datapath with Liquid Marbles.

Liquid Marbles are liquid droplets encapsulated by hydrophobic powder particles; due to their non-wetting nature, they allow to manipulate liquids efficiently. Literature highlighted their potential to be employed as micro-reactors, micro-containers for growing micro-organisms and cells, micro-fluidics devices, and have also been used in the framework of unconventional computing. In this work, we discuss a theoretical implementation of all required components to define a multi-cycle datapath based on Liquid Marbles. Then, we consider issues related to scalability, by discussing how the circuits can be expanded with the growth of the inputs, and also how they can be modified to overcome the issues related to the growing time and space complexity.

Solar evaporation of liquid marbles with Fe3O4/CNT hybrid nanostructures

HypothesisThrough the rational design of nanomaterial composites, broadband light harvesting and good thermal insulation can be achieved simultaneously to improve the efficiency of water evaporation. ExperimentSolar evaporation experiments were carried out on liquid marbles (LMs) coated with Fe3O4 nanoparticles, carbon nanotubes (CNTs) and hybrid nanomaterials (Fe3O4/CNTs) with different mass ratios of 2:1, 1:1 and 1:2. FindingThe results showed that the mixture of Fe3O4/CNTs enhances the light harvesting ability and solar interfacial evaporation performance. Fe3O4/CNT-LM at the mass ratio of 2:1 case provides the highest evaporation rate of 11.03 μg/s, which is about 1.22 and 1.34 times higher than that of Fe3O4 and CNT, respectively. This high performance is mainly due to the synergistic effect between Fe3O4 nanoparticles and CNTs, as the hybrid nanostructure significantly improves the both photothermal conversion and heat localization capability. Numerical simulation further supports that the composite can concentrate the electromagnetic field and heat at the phase-change interface. This leads to a rapid evaporation of the boundary region. This study provides a novel approach to a three-dimensional interface by assembling nanomaterials on the drop surface to enhance evaporation, which may have far-reaching implications for seawater desalination.

Polyhedral Vinyl Polymer Particles Synthesized Via Solvent-Free Radical Polymerization.

Liquid marbles (LMs) with a cubic shape are created by using various vinyl monomers as an inner liquid and polymer plates with mm size as a stabilizer. The relationship between the surface tension of the vinyl monomers and formability of the LMs is investigated. LMs can be fabricated using vinyl monomers with surface tensions of 42.7-40.3 mN m-1. The cubic polymer particles are successively synthesized via free-radical polymerizations by irradiation of the cubic LMs with UV light in a solvent-free manner. In addition, controlling the number of polymer plates per one LM, the shape of the plate or the coalescence of the LMs can lead to production of polymer particles with desired forms (e.g., Platonic and rectangular solids) that correspond to the shapes of the original LMs.

Enhancing cell cryopreservation with acidic polyamino acids integrated liquid marbles

Cryopreservation is highly desired for long-term maintenance of the viability of living biosamples, while effective cell cryopreservation still relies heavily on the addition of dimethyl sulfoxide (DMSO) and fetal bovine serum (FBS). However, the intrinsic toxicity of DMSO is still a bottleneck, which could not only cause the clinical side effect but also induce cell genetic variants. In the meantime, the addition of FBS may bring potentially the risk of pathogenic microorganism contamination. The liquid marbles (LMs), a novel biotechnology tool for cell cryopreservation, which not only have a small volume system that facilitated recovery, but the hydrophobic shell also resisted the harm to cells caused by adverse environments. Previous LM-based cell cryopreservation relied heavily on the addition of FBS. In this work, we introduced acidic polyaspartic acid and polyglutamic acid as cryoprotectants to construct LM systems. LMs could burst in an instant to facilitate and achieve ultrarapid recovery process, and the hydrophilic carboxyl groups of the cryoprotectants could form hydrogen bonds with water molecules and further inhibit ice growth/formation to protect cells from cryoinjuries. The L929 cells could be well cryopreserved by acidic polyamino acid-based LMs. This new biotechnology platform is expected to be widely used for cell cryopreservation, which has the potential to propel LMs for the preservation of various functional cells in the future.

Capillarity in Interfacial Liquids and Marbles: Mechanisms, Properties, and Applications.

The mechanics of capillary force in biological systems have critical roles in the formation of the intra- and inter-cellular structures, which may mediate the organization, morphogenesis, and homeostasis of biomolecular condensates. Current techniques may not allow direct and precise measurements of the capillary forces at the intra- and inter-cellular scales. By preserving liquid droplets at the liquid-liquid interface, we have discovered and studied ideal models, i.e., interfacial liquids and marbles, for understanding general capillary mechanics that existed in liquid-in-liquid systems, e.g., biomolecular condensates. The unexpectedly long coalescence time of the interfacial liquids revealed that the Stokes equation does not hold as the radius of the liquid bridge approaches zero, evidencing the existence of a third inertially limited viscous regime. Moreover, liquid transport from a liquid droplet to a liquid reservoir can be prohibited by coating the droplet surface with hydrophobic or amphiphilic particles, forming interfacial liquid marbles. Unique characteristics, including high stability, transparency, gas permeability, and self-assembly, are observed for the interfacial liquid marbles. Phase transition and separation induced by the formation of nanostructured materials can be directly observed within the interfacial liquid marbles without the need for surfactants and agitation, making them useful tools to research the interfacial mechanics.

Non-Aqueous Polyhedral Liquid Marbles Stabilized with Polymer Plates Having Surface Roughness.

Hydrophobic polymer plates with smooth and rough surfaces are used as a stabilizer for cubic liquid marbles (LMs) to study the effect of surface roughness on their formation. The smooth and rough polymer plates can stabilize LMs using liquids with surface tensions of 72.8-26.6 and 72.8-22.9 mNm-1, respectively. It is clarified that the higher the surface roughness, the lower the surface tension of the liquids are stabilized to form the LMs. These results indicated that the introduction of surface roughness improves the hydrophobicity of the polymer plates and the rough polymer plates can stabilize LMs using liquids with a wider surface tension range. Electron microscopy studies and numerical analyses confirmed that the LMs can be formed, when the Cassie-Baxter wetting state, where θY>90° (θY: the contact angle on smooth surfaces) and θR>90° (θR: the contact angle on rough surfaces), and the metastable Cassie-Baxter wetting state, where θY<90° and θR>90°, are realized. Finally, the synthesis of cubic polymer particles are succeeded by free radical polymerization of the cubic LMs containing a hydrophobic vinyl monomer (dodecyl acrylate) in a solvent-free manner.

Evaporation of a heated saline marble: Interplay of interfacial and thermal effects

A multistage evaporation of continuously heated liquid marbles, coated with polytetrafluoroethylene colloidal particles was investigated experimentally and theoretically. Liquid marbles initially contained an almost saturated aqueous NaCl solution. Numerical heat transfer calculations and analytical evaluations of initial evaporation showed that the equilibrium marble temperature and saturated salt concentration are reached relatively rapidly compared to the “long” marble evaporation time. This means that a typical long period of marble evaporation is determined by the low permeability of the salt crust formed beneath the marble colloidal shell. A theoretical estimation of the total evaporation time of marble water based on Darcy's law for the porous crust and the marble shell is suggested. A comparison with experimental data allowed obtaining an approximate value of the very low permeability of this bilayer barrier to marble evaporation. The proposed phenomenological model of the saline marble evaporation provides insight into why marble evaporation is so slow.

PH- and Photoresponsive Liquid Plasticine.

Liquid marbles (LMs) can be prepared by adsorption of hydrophobic particles at the air-liquid interface of a water droplet. LMs have been studied for their application as microreaction vessels. However, their opaqueness poses challenges for internal observation. Liquid plasticines (LPs), akin to LMs, can be prepared by the adsorption of hydrophobic particles with a diameter of 50 nm or less, at the air-liquid interface of a water droplet. Unlike LMs, LPs are transparent, allowing for internal observation, thus presenting promising applications as reactors and culture vessels on a microliter scale. In this study, the surface of silica particles, approximately 20 nm in diameter, was rendered hydrophobic to prepare hydrophobic silica particles (SD0). A small amount of poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) was then grafted onto the surface of SD0, yielding SD1. SD0 particles exhibited consistent hydrophobicity irrespective of the environmental pH atmosphere. Under acidic conditions, SD1 became hydrophilic due to the protonation of pendant tertiary amines in the grafted PDPA chains. However, SD1 alone was unsuitable for LP preparation due to its high surface wettability regardless of atmospheric pH, attributable to the presence of PDPA-grafted chains. Therefore, to prepare pH-responsive LP, SD1 and SD0 were mixed (SD1/SD0 = 3/7). Upon exposure to HCl gas, these LPs ruptured, with the leaked water from the LPs being absorbed by adjacent paper. Moreover, clear LPs, prepared using an aqueous solution containing a water-soluble photoacid generator (PAG), disintegrated upon exposure to light as PAG generated acid, leading to LP breakdown. In summary, pH-responsive LPs, capable of disintegration under acidic conditions and upon light irradiation, were successfully prepared in this study.

Multi-Interface Electromagnetic Wave Absorbing Material Based on Liquid Marble Microstructures Anchored to SEBS.

The direct application of liquid marbles in electromagnetic wave (EMW) absorption is challenging due to their poor stability, susceptibility to gravitational collapse, and shaping difficulties. To address this issue, a novel strategy is proposed to incorporate liquid marble microstructures (NaCl/nano-SiO2) encapsulated in organic phases (Octadecane) into the rubber-matrix (SEBS) using the ultrasound-assisted emulsion blending method. The resulting NaCl/SiO2/Octadecane microstructures anchored to SEBS offer a substantial solid-liquid interface consisting of NaCl solution and SiO2. When subjected to an alternating electromagnetic (EM) field, the water molecules and polysorbate within SiO2 exhibit heightened responsiveness to the EM field, and the movement of Na+ and Cl- within these microstructures leads to their accumulation at the solid-liquid interface, creating an asymmetric ion distribution. This phenomenon facilitates enhanced interfacial polarization, thereby contributing to the material's EMW absorption properties. Notably, the latex with 16wt% SEBS (E-3), exhibiting a surface morphology similar to human cell tissues, achieves complete absorption of X-band (fE=4.20GHz, RLmin=-33.87dB). Moreover, the latex demonstrates light density (0.78gcm-3) and environmental stability. This study not only highlights the predominant loss mechanism in rubber-based wave-absorbing materials but also provides valuable insights into the design of multifunctional wave-absorbing materials.

Fabrication of stable monolayer liquid marbles with reduced particle coverage and locomotion on hydrophilic surface

Liquid marbles are non-wetting, particle-covered microdroplets with a core-shell structure that are used in sample transport, material synthesis, and real-time sensing. Optimizing the distribution of shell particles remains a challenge, due to a tendency for aggregation via spontaneous assembly, which often leads to multilayered structures. Here, we outline a simple method for fabricating water-filled, monolayer liquid marbles with adjustable particle coverage rates, greatly reducing particle consumption. The soft liquid marbles are enclosed by a small quantity of modified polystyrene microspheres and display good atmospheric stability. The rolling behavior of flexible liquid marbles with wide coverage rates is then characterized. Contrary to common perception, the marbles with transparent openings exhibit high maneuverability on hydrophilic surfaces, and also excel in fusion, reaction and surface cleaning, with an elongated operational duration and a wide visualization range. The study provides new insights into the implementation of liquid marble-based miniaturized platforms.

Magnetic nanofluid‐based liquid marble for a self‐powered mechanosensation

AbstractMagnetic nanofluid possesses the characteristic of interfering with the propagation of the magnetic field, endowing it with the sensing property in motion. However, the residual adhesion of magnetic nanofluid as it flows over solid surfaces remains an open question. Liquid marbles allow for quantities of liquids to be encapsulated by hydrophobic particles, ensuring a unique nonstick property for utilization in different applications. In this study, being capsuled by hydrophobic nano‐/microscale powders, a magnetic nanofluid‐based liquid marble (MNLM) with well mechanical stability has been fabricated. A magnetic nanofluid posture detector (MNPD), which consists of an MNLM, a magnetic tube, and coils, has been assembled that can convert mechanical energy to electricity as it freely rolls on the solid surface. Gesture recognition can be achieved when combining five MNPDs with fingers. The fabricated MNPD possesses a good signal recognition capability, which can separately distinguish the bending of each finger. Moreover, a variety of language hand gestures with specific meanings (digits, letters, “OK,” and “I Love You”) can be further recognized through corresponding combinations. The potential of MNPD in the realm of gesture recognition will offer a novel avenue for flexible wearables.

Oily wastewater detector based on superhydrophobic liquid marbles

Rapid detection of oily wastewater plays a vital role in safeguarding public health, protecting the environment, and supporting effective resource management. It serves as an indispensable tool for early warning, surveillance, and response to various challenges that can affect communities and ecosystems. Here, activated carbon was ground and modified to realize superhydrophobicity, and superhydrophobic activated carbon liquid marbles were prepared with special droplet repulsion properties. The robustness and stability of the liquid marbles were investigated. We demonstrated that the prepared liquid marbles break up immediately once contact with the oils. In addition, we developed a self-made oily wastewater detector based on the high sensitivity of liquid marbles to oily wastewater. Compared with the traditional oily wastewater detection methods, our oily wastewater detector does not require a large amount of chemical reagents, thereby reducing the environmental impact effectively. We believe that this study has a wide range of applications in pollution prevention and liquid treatment.

How Wide and High can Polyhedral Liquid Marbles be Fabricated?

AbstractLiquid marbles (LMs) are liquid droplets in gaseous phase, which are generally millimeter size, coated by solid particles. In this study, how wide and high LMs can be fabricated is investigated. Polyhedral LMs are fabricated using polymer plates with millimeter to meter sizes as a stabilizer and water as an inner liquid. Rectangular LMs with widths exceeding 1 m, the largest width ever reported, can be successfully fabricated. The height of the LMs is found to be subject to restriction by the hydrostatic pressure and cubic LMs with heights of up to 5 mm, which is the maximum height limit for LMs stabilized with nano/micrometer‐sized particles, are fabricated. Reduction of the hydrostatic pressure by changing the LM shape from cube to pyramid and introduction of particle‐stabilized bubble into the LM enabled the increase of height of the LM up to 9.8 mm, the highest height ever reported. Investigation using non‐aqueous liquids as an inner liquid confirmed that the longer the capillary length, the higher the maximum possible height of LMs. Finally, the polyhedral LMs are demonstrated to function as a microreactor for silver mirror reaction and chemical oxidative polymerization, resulting in the formation of Janus polymer plates.

Liquid Marbles and Drops on Superhydrophobic Surfaces: Interfacial Aspects and Dynamics of Formation: A Review.

Liquid marbles (LMs) are droplets encapsulated with powders presenting varied roughness and wettability. These LMs have garnered a lot of attention due to their dual properties of leakage-free and quick transport on both solid and liquid surfaces. These droplets are in a Cassie-Baxter wetting state sitting on both roughness and air pockets existing between particles. They are also reminiscent of the state of a drop on a superhydrophobic (SH) surface. In this review, LMs and bare droplets on SH surfaces are comparatively investigated in terms of two aspects: interfacial and dynamical. LMs present a fascinating class of soft matter due to their superior interfacial activity and their remarkable stability. Inherently hydrophobic powders form stable LMs by simple rolling; however, particles with defined morphologies and chemistries contribute to the varied stability of LMs. The factors contributing to this interesting robustness with respect to bare droplets are then identified by tests of stability such as evaporation and compression. Next, the dynamics of the impact of a drop on a hydrophobic powder bed to form LMs is studied vis-à̀-vis that of drop impact on flat surfaces. The knowledge from drop impact phenomena on flat surfaces is used to build and complement insights to that of drop impact on powder surfaces. The maximum spread of the drop is empirically understood in terms of dimensionless numbers, and their drawbacks are highlighted. Various stages of drop impact-spreading, retraction and rebound, splashing, and final outcome-are systematically explored on both solid and hard surfaces. The implications of crater formation and energy dissipations are discussed in the case of granular beds. While the drop impact on solid surfaces is extensively reviewed, deep interpretation of the drop impact on granular surfaces needs to be improved. Additionally, the applications of each step in the sequence of drop impact phenomena on both substrates are also identified. Next, the criterion for the formation of peculiar jammed LMs was examined. Finally, the challenges and possible future perspectives are envisaged.

Coalescence of liquid marbles on oil-infused surface

While droplets typically merge instantly in an air medium, alterations to the outer medium can complicate the coalescence process. This study investigates droplet coalescence dynamics when encapsulated by a uniform liquid–solid composite shell, aiming to understand its implications for mechanical stability and merging behavior. The uniform shell around a sessile droplet is produced by using liquid marble on oil-infused surfaces (LMOI). The coalescence dynamics was studied under two different conditions: droplet with LMOI and LMOI with LMOI. In contrast to merging of bare droplets, coalescence involving at least one LMOI reveals a three-step process, including spreading, depletion, and eventual merging phases. Higher oil viscosity influences the merging process, with increased viscosity leading to delayed merging with longer spreading and depletion phases. LMOI exhibits significant resistance to merging with another LMOI, necessitating external triggers like pressure or electric fields for coalescence. These findings provide insights into designing microreactor systems based on LMOI, contributing to the comprehension of their dynamics and functionalities.