Liquid Layer Research Articles

Preparation of a double-layer liquid crystal optical shutter with fluorescent properties and its ultraviolet shielding screening properties

ABSTRACT Polymer dispersed liquid crystal (PDLC) films and polymer-stabilised cholesteric liquid crystals (PSCLC) films have been widely applied in smart optoelectronics due to electrical switching properties. In this study, fluorescent dyes were introduced into PDLC films and combined with PSCLC films to invent a new type of optical shutter, and the optimal formulations of each of liquid crystal structural layers were investigated. Then, PDLC anti-counterfeit optical device doped with fluorescent materials were fabricated by UV curing method using polymerisation-induced phase separation. The novel optical shutter could be driven layer by layer at room temperature according to different voltages to realise the switching of three states, namely, off state, PDLC layer-driven, and full-driven (open state). Samples under optimal conditions showed that the new optical shutter could achieve 96.5% UV shielding in the off state and had a long lifetime. The results demonstrate the attractive potential of the new optical shutter for optoelectronic devices and smart curtain applications.

Combustion enhancement of boron-containing fuel-rich mixture by steam reforming in a supersonic flow

In this paper, a novel experimental investigation was conducted to enhance the combustion of boron-containing fuel-rich mixture by steam reforming in a supersonic flow. The ground direct-connected experiments were designed to simulate a flight condition at Mach number 5.9 and an altitude of 25 km. The operating characteristics and performance evaluation of the scramjet combustor were analyzed and discussed. The experimental results demonstrate that steam reforming can enhance the combustion of boron-containing fuel-rich mixtures in the supersonic flow. The performance of the combustor is firstly enhanced and then weakened with the increase of the steam-fuel ratio. The optimal steam-fuel ratio is approximately 0.189, which maximizes performance. At this steam-fuel ratio, combustion efficiency reaches 0.451, which is 9.9 % and 7.4 % higher than steam-fuel ratios of 0 and 0.395, respectively. The possible mechanism of steam reforming promoting boron combustion in the supersonic mainstream is explained. Steam accelerates the removal of the liquid oxide layer surrounding the boron particle, then combines with oxygen to produce hydrogen with good ignition-combustion characteristics and a new oxide layer. The cycle continues until the boron burns out. These conclusions can promote an understanding of enhancing the combustion of boron-containing fuel-rich mixture by steam reforming in the supersonic flow.

A physics-informed deep learning liquid crystal camera with data-driven diffractive guidance

Whether in the realms of computer vision, robotics, or environmental monitoring, the ability to monitor and follow specific targets amidst intricate surroundings is essential for numerous applications. However, achieving rapid and efficient target tracking remains a challenge. Here we propose an optical implementation for rapid tracking with negligible digital post-processing, leveraging an all-optical information processing. This work combines a diffractive-based optical nerual network with a layered liquid crystal electrical addressing architecture, synergizing the parallel processing capabilities inherent in light propagation with liquid crystal dynamic adaptation mechanism. Through a one-time effort training, the trained network enable accurate prediction of the desired arrangement of liquid crystal molecules as confirmed through numerical blind testing. Then we establish an experimental camera architecture that synergistically combines an electrically-tuned functioned liquid crystal layer with materialized optical neural network. With integrating the architecture into optical imaging path of a detector plane, this optical computing camera offers a data-driven diffractive guidance, enabling the identification of target within complex backgrounds, highlighting its high-level vision task implementation and problem-solving capabilities.

CO2 sequestration by ammonia-enhanced phosphogypsum mineral carbonation: Development and optimization of reaction kinetic model

Comparing of existing kinetic models for direct mineral carbonation by solid waste, an optimized kinetic model was developed to depict the relationship between phosphogypsum carbonation ratio and reaction time. Based on the optimized model, the reaction mechanism of CO2 sequestration by ammonia-enhanced phosphogypsum mineral carbonation was analyzed. The experimental results show that, under specific conditions, including an ammonia ratio of 2.3, room temperature (25 °C), a liquid–solid ratio of 5:1, a gas flow rate of 200 mL/min, and a rotational speed of 500 rpm, phosphogypsum achieved its peak carbonation efficiency of 91 % within 30 min. The optimized model fitting curve has a high consistency with the experimental data, and the average R2 value is 0.991. The process of ammonia-enhanced phosphogypsum mineral carbonation comprises three distinct sub-processes. It is consisted of mass transfer in gas–liquid interface and solid–liquid interface, respectively, and product layer diffusion. Among them, the gas–liquid mass transfer is identified as the rate-controlling step in the mineral carbonation process. The present study provides a basis for the operation optimization and large-scale utilization of phosphogypsum mineral carbonation.

ReaxFF molecular dynamics simulations of methane clathrate combustion.

Understanding the ignition and dynamic processes for the combustion of hydrate is crucial for efficient energy utilization. Through reactive force field molecular dynamics simulations, we studied the high-temperature decomposition and combustion processes of methane hydrates in a pure oxygen environment. We found that at an ignition temperature of 2800K, hydrates decomposed from the interface to the interior, but the layer-by-layer manner was no longer strictly satisfied. At the beginning of combustion, water molecules reacted first to generate OH•, followed by methane oxidation. The combustion pathway of methane is CH4→CH3•→CH3O•→CH2O→HC•O→HCOO•→CO(CO2). During the combustion process, a liquid water layer was formed between melted methane and oxygen, which hindered the reaction's progress. When there is no heat resistance, oxygen will transform into radicals such as OH• and O•, which have faster diffusion rates, allowing oxygen to conveniently cross the mass transfer barrier of the liquid water layer and participate in the combustion process. Increasing the amount of OH• may cause a surge in the reaction. On the other hand, when significant heat resistance exists, OH• is difficult to react with low-temperature hydrate components, but it can transform into O• to trigger the oxidation of methane. The H• generated has a sufficient lifetime to contact high-temperature oxygen molecules, converting oxygen into radicals that easily cross the water layer to achieve mass transfer. Therefore, finding ways to convert oxygen into various radicals is the key to solving the incomplete combustion of hydrates. Finally, the reaction pathways and microscopic reaction mechanisms of each species are proposed.

Sucrose Recovery from Diluted Cane Molasses by Using Mass Transfer to the Third Liquid Layer at Contacting with Ethanol

Sucrose Recovery from Diluted Cane Molasses by Using Mass Transfer to the Third Liquid Layer at Contacting with Ethanol

Ultrasound jetting and atomization of sessile and impacting droplets

We present the results of our experimental and theoretical study of the jetting and atomization of a sessile and an impacting droplet subject to an ultrasonic surface vibration with a frequency of 2.5 MHz and piezoceramic transducer (PZT) surface velocity of 0.2–1.5 ms−1. Such high-frequency vibrations result in the formation of a liquid jet shooting outwardly from the surface of the droplet, which eventually breaks up into droplets. Part of the liquid remains on the surface, which eventually goes through ultrasonic atomization. We have divided this process into three categories of (i) jetting, (ii) jet breakup and liquid layer formation, and (iii) liquid layer atomization, and characterized jetting and jet breakup separately. For impacting droplets, jetting occurs immediately and at relatively low surface vibration velocities as compared to those for sessile droplets. We have developed a model to predict the PZT surface velocity for the onset of jetting, the jet diameter, jet velocity, and spreading diameter based on momentum, force, and energy balances. The liquid jet may break up into droplets due to Rayleigh–Plateau breakup (ejecting droplets on the order of jet diameter, λa) and acoustic breakup of the jet (ejecting both few hundred micrometer and few micrometer droplets).

Motion of particles in the field of nonlinear wave packets in a liquid layer under an ice cover

Motion of particles in the field of nonlinear wave packets in a liquid layer under an ice cover

Excitation of Seismoacoustic Waves from a Singular Source Acting on the Boundary of a Liquid Layer and a Poroelastic Half-Space

Excitation of Seismoacoustic Waves from a Singular Source Acting on the Boundary of a Liquid Layer and a Poroelastic Half-Space

Superspreading‐Confined Assembly of Oriented 2D MOF Membranes for Biomimetic Cation‐Regulated Ion Transport

AbstractInspired by biological channels, metal‐organic framework (MOF) membranes with sub‐nanometer sized channels offer an ideal platform to construct high‐performance artificial nanofluidic system. However, fabricating long‐range ordered MOF membranes is still a significant challenge. Herein, a superspreading‐confined assembly method is developed to prepare large‐scale oriented 2D MOF (Zn‐TCPP (TCPP = meso‐tetra(4‐carboxyphenyl) porphine)) membranes. The superspreading of reactant liquid under oil phase to form liquid layer plays a critical role in membrane formation, which provides a dynamic confined space for layered assembly of Zn‐TCPP nanosheets. Accompanied with solvent diffusion, such liquid layer is completely converted into <001>‐oriented MOF membrane with controlled thickness. The prepared membrane exhibits distinct divalent cation (Mx2+)‐regulated ion transport behavior as that demonstrated in biological channels: K+ flux can be precisely adjusted by anchoring diverse Mx2+ ions to binding sites, which is appealing in designing high‐performance nanofluidic iontronics. Moreover, similar strategies can be employed to fabricate other MOF membranes (such as Hf‐BTB (BTB = 1,3,5‐tris(4‐carboxyphenyl)benzene) and Ni‐TCPE (TCPE = tetrakis(4‐carboxyphenyl)ethylene)), indicating the broad applicability of this method in 2D membrane fabrication.

The Concept of Using 2D Self-Assembly of Magnetic Nanoparticles for Bioassays

It can be observed that magnetic iron-oxide nanoparticles are increasingly used in bioassay methods. This is due to their stability in aqueous solutions, ease of functionalization, biocompatibility and very low toxicity. Here, we show that the recent discovery of the ability of magnetic nanoparticles to self-assemble into 2D structures of ordered chains may be exploited for bioassays. This would open up the possibility of controlled immobilization of proteins, enzymes, DNA or RNA and other molecular systems on spatially ordered nanostructures. In this work, fluorescein was used as an example. Also shown is the possibility of using Raman spectroscopy to analyze material accumulated on such structures. The observed formation of regularly spaced chains of magnetic nanoparticles takes place during the drying process of a thin layer of magnetic liquid placed on an appropriately prepared low-density polyethylene (LDPE) film.

Numerical study on the characteristics of sodium heat pipes for space application at operation limits

Sodium heat pipes are important thermal conductive components in space nuclear power sources. They efficiently transfer heat within the range of 500–1000 °C by utilizing the latent heat of phase change. However, their maximum heat transfer capacity is limited by various factors. In this study, numerical simulations were conducted to investigate the operating conditions of sodium heat pipes when encountering different heat transfer limits, with a focus on analyzing the vapor–liquid distribution and axial temperature distribution in evaporator section. It is revealed that as reaching the heat transfer limits, sodium heat pipes exhibit wall temperature fluctuations in evaporator section. When encountering the viscous limit, liquid aggregation occurs within the wick, causing discontinuous flow. As reaching the sonic limit, a vapor blockage zone forms at the outlet of evaporator section, disrupting the flow circulation within heat pipe. For the entrainment limit, the liquid inside wick is carried away by vapor flow, reducing the amount of liquid involved in phase change cycle. As in the capillary limit, inadequate liquid reflux leads to thinner liquid layer, weakening the flow circulation. During the transition from the viscous limit to the sonic limit, no significant phenomena of phase distribution occur in the evaporator section. As the sonic limit and the entrainment limit act together, both vapor blockage and liquid entrainment occur, accompanied by liquid accumulation. The phenomena when the entrainment limit and the capillary limit act together differ from those occurring individually. The simulation results provide references for a deeper understanding of heat transfer limit mechanism and other operating characteristics.

Silicon gels with sustainable self-replenishment: Fluid drag reduction through viscosity dependency

Slippery liquid infused surfaces (SLISs) provide excellent dynamic lubrication properties by storing the lubricant internally to form a homogeneous liquid layer to insulate external ambient fluids. However, the kinetic instability caused by lubricant depletion gradually degrades the surface slippery performance. Herein, inspired by skin gland secretion system, silicon gels with sustainable self-replenishment were prepared using polydimethylsiloxane (PDMS) and commercially available dimethyl silicone oils. By carefully tuning the kinematic viscosity and content of infused oil, the surfaces of corresponding silicon gels demonstrated significant syneresis behavior, and the lubricating oils released from the surface were still detected after continuous wiping for more than 120 days. More importantly, when the ratio of working fluid to infused oil was 6.8, the maximum drag reduction of silicon gel in Couette flow could reach up to about 16%, while the surfaces remained long-lasting water repellency under the continuous shear action of encapsulated water. Self-replenishable silicon gels exhibiting strong kinetic stability were expected to provide valuable design insights for robust slippery interfaces.

Temperature-Dependent Structure Formation in the Wetting Layer of the Ionic Liquid [C2C1Im][OTf] on Au(111)

Temperature-Dependent Structure Formation in the Wetting Layer of the Ionic Liquid [C₂C₁Im][OTf] on Au(111)

CO2 capture in a novel rotating spiral contactor with hydraulic seal: Hydromechanics, mass transfer and modeling

The efficient capture of CO2 has always been a goal pursued by people. However, low gas handling capacity and low gas–liquid ratio restricts existing gas–liquid contactors, especially for non-rotating ones. In this study, a gas–liquid contactor with high gas handling capacity and high gas–liquid ratio, the rotating spiral contactor, was developed. Hydrodynamic properties of the contactor were experimentally or theoretically investigated. A novel interface model was developed to describe gas–liquid interface shape. CO2 capture using MEA/DMEA aqueous solution were evaluated in terms of space–time yield (τ), overall volumetric mass transfer coefficient (KGae) and CO2 capture efficiency (η). A rate-based model was developed and applied for the first time to predict CO2 capture in the rotating spiral contactor. The hydrodynamic results showed that liquid layer thickness was below 400 μm for the liquid with viscosity of 14.5 mPa.s. Under the rotational speed of 1200 rpm, the gas–liquid ratio ranged from 525 to 2700, while the gas–liquid surface area remained around 667 m2/m3. The interface model predicted interface thickness within a relative deviation of ± 20 %. The results also showed that τ, KGae and η respectively were 3428–17021 h−1, 1.0–6.4 kmol.m−3.h−1.kPa−1 and 38–98 % at the gas–liquid ratio range of 200–1000. The predicted KGae and η by rate-based model agreed well with the experimental data within a relative deviation of ± 15 %. This rotating spiral contactor is ideally suitable for the scenarios with large gas handling requirement and high gas–liquid ratio.

Influence of parametric forcing on Marangoni instability

We study a thin, laterally confined heated liquid layer subjected to mechanical parametric forcing without gravity. In the absence of parametric forcing, the liquid layer exhibits the Marangoni instability, provided the temperature difference across the layer exceeds a threshold. This threshold varies with the perturbation wavenumber, according to a curve with two minima, which correspond to long- and short-wave instability modes. The most unstable mode depends on the lateral confinement of the liquid layer. In wide containers, the long-wave mode is typically observed, and this can lead to the formation of dry spots. We focus on this mode, as the short-wave mode is found to be unaffected by parametric forcing. We use linear stability analysis and nonlinear computations based on a reduced-order model to investigate how parametric forcing can prevent the formation of dry spots. At low forcing frequencies, the liquid film can be rendered linearly stable within a finite range of forcing amplitudes, which decreases with increasing frequency and ultimately disappears at a cutoff frequency. Outside this range, the flow becomes unstable to either the Marangoni instability (for small amplitudes) or the Faraday instability (for large amplitudes). At high frequencies, beyond the cutoff frequency, linear stabilization through parametric forcing is not possible. However, a nonlinear saturation mechanism, occurring at forcing amplitudes below the Faraday instability threshold, can greatly reduce the film surface deformation and therefore prevent dry spots. Although dry spots can also be avoided at larger forcing amplitudes, this comes at the expense of generating large-amplitude Faraday waves.

Two layer film flow on an unsteady stretching cylinder

Most of the earlier research works related to the thin film flow over a stretching cylinder are primarily limited to the boundary layer flow of a single liquid. Whereas, multilayer film coating is commonly used to coat microelectronic chips, circuits, etc. This scenario motivated us to investigate the thin double-layer liquid film development over a stretching cylinder. In the present work, the above limitations of earlier models have been removed to investigate the two-layer film flow over a stretching cylinder by considering a full set of momentum equations. The governing set of equations is transformed into a system of nonlinear partial differential equations (PDEs) by applying appropriate similarity transformation. The analytical solutions are obtained by using the asymptotic analysis method for smaller values of Reynolds number (i.e. Re1<<1). Whereas numerical solutions are obtained by implicit finite difference method for smaller as well as moderate values of Re1. It is found that the film thinning rate enhanced for both the liquid layers with raising values of the cylinder’s radius (A) and density ratio (m). It is further seen that both the liquid layers thin faster with a decreasing initial thickness ratio of both liquid layers (δ). It is also observed that the variation of film height for the first layer is very small in comparison to the second layer for increasing values of viscosity ratio parameter (n). The film height for both the liquid layers decreases very fast for a smaller Reynolds number (Re1) at the initial time but a reverse trend is noticed at large time.

Thermo-capillarity of immiscible binary fluids within serpentine micro-confinements

The thermocapillary flow of multiple liquid layers over contoured substrates finds applications in many industrial phenomena via micro-electromechanical systems/nano-electromechanical systems devices. This study theoretically explores the thermocapillary transport of binary-liquid layers in a wavy microchannel with serpentine wall profiles. Sinusoidal profiles are considered for the microchannel walls' temperature and surface topology. Patterned slip conditions at the walls are also accounted for in the analysis to make the problem more realistic. We semi-analytically solve the energy and momentum equations to understand the system's thermal and hydrodynamic characteristics for the limiting conditions of Ma, Re, and Ca. The leading- and higher-order solutions of the temperature and flow field are separately shown to demonstrate the advection terms' contribution to the transport equations. The circulatory flow obtained due to periodic thermal stimuli can be used to enhance the mixing efficiency of the system. We also present how the parameters like phase difference between the thermal stimulus, relative thermal conductivity, and relative film thickness ratio of the liquid layers can be altered to control the flow characteristics to obtain the most potent thermocapillary effect.

On A Sound-Absorbing Coating in the form of a Layer of a Viscous Liquid with Bubbles

On A Sound-Absorbing Coating in the form of a Layer of a Viscous Liquid with Bubbles

A method for controlling and maintaining the thickness of a liquid layer during ultrasonic spraying

This work is described a method for indirectly controlling the height of the film of sprayed material on the oscillating surface of ultrasonic atomizer by changing the resonant frequency of the ultrasonic oscillator. The relevance of the development of this method is due to the need for the development and widespread use of the ultrasonic spraying method to solve the most pressing problems of modern industry. In this regard, there is a need to establish the dependences of the spraying performance on the height of the film of sprayed fluid on the oscillating plane of the atomizer and to create, based on the identified dependencies, a method for controlling and maintaining the necessary and sufficient height of the fluid film, the spraying of which will provide the best dispersion characteristics of the generated aerosol at a given spraying performance. As a result of the research, it was shown that in the operating range of film height of the sprayed fluid, the change in the resonant frequency can reach 100 Hz, which is sufficient to control the film height. This made it possible for the first time to develop a method for automatically controlling the ultrasonic spraying process, ensuring the maintenance of optimal modes of ultrasonic exposure (amplitude of vibrations of the spray surface) and the thickness of the sprayed fluid height.