Wetting Liquid Research Articles

Stable Air Plastron Prolongs Biofluid Repellency of Submerged Superhydrophobic Surfaces.

Superhydrophobic surfaces find applications in numerous biomedical scenarios, requiring the repellence of biofluids and biomolecules. Plastron, the trapped air between a superhydrophobic surface and a wetting liquid, plays a pivotal role in biofluid repellency. A key challenge, however, is the often short-lived plastron stability in biofluids and the lack of knowledge surrounding it. Plastron stability refers to the duration for which a surface remains in the Cassie state before transitioning to the fully wetting Wenzel state. Here, a submersion test with real-time optical monitoring is used to determine the plastron lifetime of different superhydrophobic surfaces upon immersion in various biofluids. We find that biofluids of all types exhibit shorter plastron lifetimes compared to pure water, which is attributed to their lower surface tension and biomolecular adsorption through hydrophobic-hydrophobic interactions. Proteins and glucose are identified as the major contributors to plastron dissipation in fetal bovine serum-based biofluids. Plastron minimizes the solid-liquid interface, reducing biomolecular adsorption, making its stability crucial for biofluid repellence. Thus, the effects of surface texture, feature size, Cassie solid fraction, Wenzel dimensionless roughness, and surface chemistry on plastron stability are investigated. Our key findings indicate that prolonged plastron stability and thus enhanced biofluid repellency are achieved through a combination of larger plastron volumes, increased Wenzel roughness degrees, greater Cassie solid fractions, and smaller feature sizes. We demonstrate that with optimized parameters, our surface design can maintain plastron stability and sustain a consistent solid-liquid area fraction for over 120 h in complex biofluids containing high levels of protein and glucose, underscoring a robust design for long-term use in biomedical and antifouling applications. This research is essential for advancing the design of superhydrophobic surfaces that effectively resist biofouling in diverse medical and engineering settings.

Directional Droplet Wetting on Cellulose Surfaces with Physical Modification.

Directional wetting of liquids on solid surfaces is crucial for numerous applications. However, the impact of physical modifications on near-superhydrophilic cellulose has received limited attention as it is widely considered unfeasible. In this study, we present a previously unreported and simple but effective mechanism of directional wetting induced purely by physical modifications on pristine cellulose surfaces. By using molecular dynamics simulations, we unveil that a wedge-like surface roughness drives anisotropic water spreading, contrasting with the conventional understanding of uniform wetting on strong hydrophilic cellulose surfaces. This wedge-induced directional wetting occurs without any chemical alterations, showcasing the ability of the physical topography alone to control liquid dynamics. Our findings not only provide new fundamental insights into manipulating wetting behavior on naturally hydrophilic surfaces but also highlight a transformative approach to designing cellulose-based materials with tailored fluid flow properties for diverse applications.

Electrically switched asymmetric interfaces for liquid manipulation.

External field driven fluid manipulation, in particular electric field, offers the advantages of real-time control and exceptional flexibility, rendering it highly promising for applications in microfluidic devices, liquid separation and energy catalysis. However, it is still challenging for controlled liquid transport and fine control of droplet splitting. Herein, we demonstrate a strategy to achieve direction-controlled liquid transport and fine droplet splitting on an anisotropic groove-microstructured electrode surface via an electrically switched asymmetric interface. The balance of asymmetric capillary force generated by microstructures and electro-capillary force is critical in determining directional liquid transport and fine droplet splitting. Asymmetric bubbles generated by liquid electrolysis form an asymmetric liquid-gas-solid interface and result in gradient liquid wetting behavior on the two neighboring electrode surfaces. The electric field further enhances the asymmetric wetting of a liquid droplet on the electrode surface, exhibiting electric field direction-dependent motion. Moreover, the groove-microstructured electrode surface can strengthen the liquid droplet anisotropic wetting and correspondingly refine the volume range of the splitting sub-droplet. Even unidirectional/bidirectional liquid droplet transport can be controlled in collaboration with the asymmetric groove-microstructure and electric field. Thus, this work provides a new route for liquid transport and droplet splitting, showing great potential in controllable separation, microreaction and microfluidic devices.

Boiling performance enhancement and self-recovery of nucleate boiling regime on micro- and nanostructured porous surfaces

In this paper, we report the pool boiling experimental results for significant enhancements in the boiling heat transfer coefficient (BHTC) and CHF on various microporous surfaces. The microporous surfaces were fabricated by metal (Copper) powder sintering process, and nanostructured porous surfaces were additionally fabricated through the thermal oxidation of the metal porous surfaces. Among the examined substrates, a boiling surface with a thin metal porous layer and millimeter-sized porous pillar structures exhibited optimal boiling performance; the BHTC and CHF of the microporous surface were measured to be approximately 500 % and 270 % higher than those of a smooth reference surface, respectively. We conjecture that the results come from the combined effect of active nucleation site density enhancement, capillary wicking promotion, and separation of liquid-vapor flow paths on the microporous surface with porous pillars. On the other hands, the porous pillar surface with needle-like nanostructures showed the interesting phenomena that can be regarded to the recovery of the boiling regime from transition boiling to nucleate boiling. At the CHF, the temperature increase on the surface was slower than that on the other surfaces. Additionally, at high heat fluxes below the CHF, the overheated surface self-recovered to the nucleate boiling state, indicating the rewetting of local dry spots. We consider that the capillary wicking capability strongly improved by the nanostructures on the surface was presumably responsible for inhibiting the irreversible expansion of local dry spots. From the experimental observations throughout this study, we propose the following key requirements to design an ideal boiling surface: increasing the nucleation site density, ensuring a liquid supply path by capillary wicking, separating the liquid and vapor flow paths, and improving the liquid wettability of the solid surface by forming nanostructures.

Facile Formation of Metallic Surface with Microroughness via Spray-Coating of Copper Nanoparticles for Enhanced Liquid Metal Wetting.

This paper presents a simple, fast, and cost-effective method for creating metallic microstructured surfaces by spray-coating a dispersion of copper nanoparticles (CuNPs) onto polymethyl methacrylate (PMMA) substrates, enabling the imbibition-induced wetting of liquid metal. The formation of these microstructured patterns is crucial for the spontaneous wetting of gallium-based liquid metals. Traditional techniques for producing such microstructures often involve complex and costly lithography and vacuum deposition methods. In contrast, this study demonstrates that liquid metal wetting can occur with metal microstructures formed through a straightforward spray-coating process. To immobilize the CuNPs on the polymer substrate, an organic solvent that dissolves the polymer surface was employed as the dispersion medium. The effects of various spray-coating parameters, including distance and time, on the uniformity and immobilization of CuNP films were systematically investigated. Under optimal conditions (120 s of spray time and 10 cm spray distance), CuNPs dispersed in dichloromethane (DCM) yielded uniform and stable microstructured surfaces. The spontaneous wetting of gallium-based liquid metal was observed on the fabricated CuNP film. Additionally, liquid metal selectively wet the CuNP patterns formed by stencil techniques, establishing electrical connections between electrodes. These findings underscore the potential of spray-coating for fabricating metallic surfaces to drive the formation of liquid metal patterns in flexible electronics applications.

Instantaneous Tiltmeter Triggered by Dynamic Wetting Behavior.

A novel instantaneous tiltmeter with dynamic and static monitoring functions is reported that is based on liquid metal dynamic wetting behavior in a bio-fabricated anisotropic microchannel. The proposed system achieves instantaneous tiltmeter functionality, offering a broad detection range (-90°-90°) with high precision (0.05°), a rapid reaction time (0.11 s), and enhanced durability. Moreover, a seamless integration has enabled water wave detection, language programming, and human limb monitoring. Especially, the integration of tiltmeter and a 3D motion platform results in a surface structure scanning system capable of effectively performing large area (>200 cm2) and height difference scanning functions. This innovative approach holds great potential for transformative changes in the fields of advanced manufacturing, flexible robotics, and the flexible sensing, further facilitating widespread adoption.

Evaluation of the Impact of Parylene C Deposition Method on the Functional Properties of Fabrics.

The article presents the results of research on the impact of the use of an original, innovative method of deposition of Parylene C on the functional properties of fabrics with various potential applications (e.g., thermal and chemical protective clothing, packaging, covers and others). Verification of the effects of the method used was based on interdisciplinary research taking into account the impact of coating fabrics on changes in their structure (micro-CT), surface properties (contact angle), barrier properties (water and chemical liquid wetting), electrostatic properties (charge decay), biophysical properties describing heat and mass transfer (by the Alambeta system and thermal imaging) and flammable properties. Four fabrics made of synthetic organic fibres (meta-aramid, para-aramid) and natural inorganic fibres (basalt) were selected for testing. Given the complex structure of textile substrates, the results confirmed that the two assumed thicknesses of the Parylene C coating were consistent with the actual measurements. The findings indicated that the coatings significantly reduced water and acid absorption in the fabrics compared to unmodified ones. Thermal insulation property tests revealed that coated fabrics exhibited higher thermal conductivity than unmodified fabrics. Additionally, the presence of Parylene C on aramid fabrics resulted in a modest increase in their ignition resistance.

Chaotic Transport of Solutes in Unsaturated Porous Media.

Unsaturated porous media, characterized by the combined presence of several immiscible fluid phases in the pore space, are highly relevant systems in nature, because they control the fate of contaminants and the availability of nutrients in the subsoil. However, a full understanding of the mechanisms controlling solute mixing in such systems is still missing. In particular, the role of saturation in the development of chaotic solute mixing has remained unexplored. Using three-dimensional numerical simulations of flow and transport at the pore scale, built upon X-ray tomograms of a porous medium at different degrees of liquid (wetting)-phase saturation, we show the occurrence of chaotic dynamics in both the deformation of the solute plume, as characterized by computed chaos metrics (Lyapunov exponents), and the mixing of the injected solute. Our results show an enhancement of these chaotic dynamics at lower saturation and their occurrence even under diffusion-relevant conditions over the medium's length, also being strengthened by larger flow velocities. These findings highlight the dominant role of the pore-scale spatial heterogeneity of the system, enhanced by the presence of an immiscible phase (e.g., air), on the mixing efficiency. This represents a stepping stone for the assessment of mixing and reactions in unsaturated porous media.

Effective Unidirectional Wetting of Liquids on Multi-Gradient, Bio-Inspired Surfaces Fabricated by 3D Printing and Surface Modification.

The movement of liquid droplets on the energy gradient surface has attracted extensive attention inspired by biological features in nature, such as the periodic spindle-shaped nodes in spider silks and conical-like barbs of cacti, and the structure-property-function relationship of multifunctional gradient surfaces. In this study, a series of specific patterns are fabricated with 3D printing technology, followed by modification via the atmospheric pressure plasma treatment and liquid phase chemical deposition, resulting in enhancing the ability of water droplets of 5 μL to travel 18.47 mm on a horizontal plane and 22.75 mm against gravity at up to a 20° tilting angle. Additionally, analysis techniques have been employed, including a contact angle analyzer, ESCA, and a laser confocal microscope to evaluate the sample performance. This work could further be applied to many applications related to microfluidic devices, drug delivery and water/fog collection.

Experimental and numerical investigation of droplet flow mechanisms at fracture intersections

Understanding unsaturated flow behaviors in fractured rocks is essential for various applications. A fundamental process in this regard is flow splitting at fracture intersections. However, the impact of geometrical properties of fracture intersections on flow splitting is still unclear. This work investigates the combined influence of geometry (intersection angle, fracture apertures, and inclination angle), liquid droplet length, inertia, and dynamic wetting properties on liquid splitting dynamics at fracture intersections. A theoretical model of liquid splitting is developed, considering the factors mentioned above, and numerically solved to predict the flow splitting behavior. The model is validated against carefully-controlled visualized experiments. Our results reveal two distinct splitting behaviors, separated by a critical droplet length. These behaviors shift from a monotonic to a non-monotonic trend with decreasing inclination angle. A comprehensive analysis further clarifies the impacts of the key factors on the splitting ratio, which is defined as the percentage of liquid volume entering the branch fracture. The splitting ratio decreases with increasing inclination angle, indicating a decrease in the gravitational effect on the branch fracture, which is directly proportional to the intersection angle. A non-monotonic relationship exists between the splitting ratio and the aperture ratio of the branch fracture to the main fracture. The results show that as the intersection angle decreases, the splitting ratio increases. Additionally, the influence of dynamic contact angles decreases with increasing intersection angle. These findings enhance our understanding of the impact of geometry on flow dynamics at fracture intersections. The proposed model provides a foundation for simulating and predicting unsaturated flow in complex fractured networks.

Viscous effects in sheared unsaturated wet granular materials

We report on experiments and discrete element simulations of homogeneous, simple, normal stress-controlled, shear flows of model unsaturated granular materials: assemblies of frictional spherical particles bonded by a small quantity of a wetting liquid. The rheology of such unsaturated granular materials in the dense flow regime was characterized in recent publications of our group, in terms of internal friction coefficient μ∗ and solid fraction Φ, depending on the reduced pressure P∗ comparing capillary forces to controlled normal stress, and on inertial number I. The present study extends this description to the influence of the liquid viscosity on material rheology in the low saturation regime. The quantitative agreement of simulations with experiments is confirmed for the quasistatic limit, and our numerical results, despite some quantitative differences, capture the correct trends in the regime dominated by viscous forces. Rheological properties are then determined, to a large extent, by the same viscous numberIv as used to formulate constitutive laws in saturated, dense suspensions. More precisely, a visco-inertial numberJ, combining Iv with inertial number I as J=Iv+2I2, appears apt to describe the rheological laws, as expressed by the internal friction coefficient and the solid fraction, measured in the laboratory or in the simulations, as well as the numerically investigated internal state of the flowing material. Simulations provide insight into the role of viscous forces: predominantly tensile, they contribute to the increase with shear rate of the macroscopic friction coefficient μ∗ through a direct positive contribution to shear stress, a negative contribution to normal stresses (enhancing the strength of the contact network), and microstructural changes affecting the network of contacts and liquid bridges.

Atomic wetting of oil droplets into hexagons and stripes

HypothesisPrevious studies showed that liquid droplets can be spherical caps or polygonal shapes on patterned surfaces. We hypothesize that these phenomena can be narrowed down to nanoscale and affecting liquid molecular wetting. We anticipate observing preferential wetting on the underlying substrate with atomic crystalline lattice. ExperimentsThis study explores the wetting behavior of oil nanodroplets deposited on highly ordered pyrolytic graphite (HOPG) with atomic force microscope (AFM). Oil droplets were scanned with hydrophobic and hydrophilic AFM tips in water in peak force mode AFM, carefully controlling the scanning force. Simple modeling was carried out using Surface Evolver to simulate how oil droplets wet on HOPG with molecular lattice. FindingsThe results showed two distinct wetting behaviors: the hexagonal nanodroplets and stripe nanometric films. In both cases, the droplets appear to wet preferentially along preferred orientations which reflect the atomic periodicity of the underlying substrate. This preferential wetting occurs because the atomic roughness is significant at the length scale of the nanodroplets, while the eventual outcome of the wetting (i.e. whether the droplet settles to a finite contact angle, or wets completely into a nanometric film) is dependent on the spreading parameter of the droplet-substrate system, independent of scanning direction.

Bilayer coating fabricated on aluminum alloy substrates with superamphiphobicity, corrosion resistance, self-cleaning, and delayed icing properties

To address the functional failure caused by low-surface-tension liquid wetting and adhesion in superhydrophobic materials, in this study, we constructed a bilayer coating with superamphiphobic properties using an epoxy (Ep) bonding layer and an organosilane-grafted attapulgite (OG-ATP) layer through spray-coating technique. The prepared superamphiphobic bilayer coating exhibited high contact angles (CAs) and low sliding angles (SAs) for cold water (25 °C), hot water (85 °C), glycerol, ethylene glycol, peanut oil, and even n-hexadecane (CA = 150.4 ± 0.3° and SA = 7 ± 2°) with surface tension of 27.5 mN m−1. Surface morphology and elemental analysis confirmed the coating's unique micro-nano hierarchical structure and low surface energy characteristics. Electrochemical impedance spectroscopy (EIS) results showed that the surface charge transfer resistance (Rct) and low-frequency modulus (|Z|0.01Hz) were enhanced by 6–7 orders of magnitude compared to the bare aluminum alloy substrate. The anti-corrosion performance remained stable even after 5 days of 3.5 wt% NaCl immersion. Additionally, icing experiments with water droplets at −10 °C and −15 °C revealed a significant delay in ice formation on the substrate protected by the bilayer coating. The development of this protective material, combining superamphiphobicity, self-cleaning, corrosion resistance, and anti-icing functions, will provide advanced technological reserves in areas such as marine, aviation, transportation, and manufacturing.

Configuration design toward sustainably-released polymer electrolytes for enhancing ionic transport and cycle stability of solid lithium batteries

Poly(vinylidene difluoride) (PVDF)-based solid polymer electrolytes (SPEs) hold great promise in the practical deployment of solid lithium batteries (SLBs), but suffer from low ionic conductivity, poor interfacial compatibility, and unstable anode interface, especially without liquid wetting. Herein, we utilize poly (propylene carbonate) (PPC), which degrades into propylene carbonate (PC) when being contacted with alkaline Li-metal to construct the PVDF-based composite SPEs. Blended and bi-layered PVDF/PPC configurations are designed, of which the sustain-release effect of PPC, the ionic transport, and the cycle stability are compared. The evenly swelling of PC on PVDF enables a high ionic conductivity (1.2 × 10−4 S cm−1) and a low interfacial resistance (42 Ω cm−2) of bi-layered SPEs at 30 °°C and contributes to the homogeneous distribution of high current density inside electrolytes. Besides, the produced PC can accelerate the dissociation and decomposition of Li-salts, leading to the generation of a stable and uniform solid electrolyte interface. Consequently, the Li/LiFePO4 and Li/LiNi0.6Co0.2Mn0.2O2 cells with bi-layered SPEs deliver a capacity of 163.1 and 151.4 mAh g−1 for 100 cycles at 0.2 C and 30 °C. This study provides a rational protocol for the design of PVDF SPEs and promotes the practical application of PVDF-based SLBs with desirable performances.

Unsteady wetting of soft solids

HypothesisSpreading of liquids on soft solids often occurs intermittently, i.e., the liquid's wetting front switches between sticking and slipping. Studies of this so-called stick-slip wetting on soft solids mostly are confined within quasi-static or forced spreading conditions. In these situations, because the sticking duration is set much larger than the viscoelastic relaxation time of the solid, a ridge is persistently and fully developed at the wetting front as the soft solid yields to the liquid's surface tension. The sticking duration and spreading velocity, therefore, were shown to have little impact to the contact angle change required for stick-to-slip transitions. For unsteady wetting of soft solids, a commonly encountered but largely unexplored situation, we hypothesize that the stick-to-slip transition is controlled not only by a combination of sticking duration and the spreading velocity, but also by an increasing depinning threshold caused by the growing ridge at the wetting front. ExperimentWe performed unsteady wetting experiment on soft solids by letting water droplets spread freely on soft solid surfaces of various stiffness. We capture both the stick-slip spreading behavior and growing wetting ridges using synchronous high-speed imaging and high-speed interferometry. Recorded data of liquid spreading and solid deforming at the wetting front were analyzed to shed light on the relation between stick-slip characteristics and the growing wetting ridge. FindingsWe find that intermittent wetting on a soft solid surface results from a competition between three key factors: liquid inertia, capillary force change during sticking, and growing pinning force caused by the solid's viscoelastic response. We theoretically formulate their quantitative contributions to predict how stick-to-slip transitions occur, i.e., how the contact angle change and sticking duration depend on the liquid's spreading velocity and the solid's viscoelastic characteristics. This provides a mechanistic understanding and methods to control unsteady wetting phenomena in diverse applications, from tissue engineering and fabrication of flexible electronics to biomedicine.

Superhydrophobic nanofibrous polytetrafluoroethylene and composite membranes with tunable adhesion for micro-droplet manipulation, self-cleaning and oil/water separation

Membrane technology has been proven to be highly valuable in extensive applications, such as separation and purification, surface engineering, packaging, and electronics. Controllable surface wetting behavior is pivotal in determining the practical applications of membranes in various scenarios. In this study, a superhydrophobic nanofibrous membrane with diverse adhesion was prepared by a novel in-situ fibrillation of polytetrafluoroethylene (PTFE). The fibrous structures can be facilely manipulated by the processing temperatures, and a hierarchical structure of micro-/nano-scale PTFE fibrils simultaneously achieves superhydrophobicity with high adhesion. In contrast, a superhydrophobic surface with extremely low adhesion was fabricated by in-situ introducing SiO2 microspheres into membrane. Therefore, the distinct adhesion of the membranes enables multifunctional applications that require different liquid wettability, such as the manipulation of tiny droplets, self-cleaning, and anti-icing properties. Furtherly, the nanofibrous membranes demonstrated outstanding oil/water separation performance with great efficiency over 99.5% and flux as high as 5303 L·m−2·h−1. The fabricated nanofibrous PTFE membrane, exhibiting either a “petal effect” or “lotus effect”, along with their flexible fabrication methodology, offer a promising approach to meet the demand for chemical, environment, and biomedicine area.

Flow structure near three phase contact line of low-contact-angle evaporating droplets

Flow structure near three phase contact line (TPCL) of evaporating liquids plays a significant role in liquid wetting and dewetting, liquid film evaporation, and boiling. Despite the wide focus it receives, the interacting mechanisms therein remain elusive and in specific cases, controversial. Here, we reveal the profile of internal flow and elucidate the dominating mechanisms near TPCL of evaporating droplets, using mathematical modeling, trajectory analysis, and infrared thermography. We indicate that for less volatile liquids such as butanol, the flow pattern is dominated by capillary flow. With increasing liquid volatility, e.g., alcohol, the effect of evaporation cooling, under conditions, induces interfacial temperature gradient with cold droplet apex and warm edge. The temperature gradient leads to Marangoni flow that competes with outwarding capillary flow, resulting in the reversal of interfacial flow and the formation of a stagnation point near TPCL. The spatiotemporal variations of capillary velocity and Marangoni velocity are further quantified by mathematically decomposing the tangential velocity of interfacial flow. The conclusions can serve as a theoretical base for explaining deposition patterns from colloidal suspensions and can be utilized as a benchmark in analyzing more complex liquid systems.

Electrospun PCL Filtration Membranes Enhanced with an Electrosprayed Lignin Coating to Control Wettability and Anti-Bacterial Properties.

This study reports on the two-step manufacturing process of a filtration media obtained by first electrospinning a layer of polycaprolactone (PCL) non-woven fibers onto a paper filter backing and subsequently coating it by electrospraying with a second layer made of pure acidolysis lignin. The manufacturing of pure lignin coatings by solution electrospraying represents a novel development that requires fine control of the underlying electrodynamic processing. The effect of increasing deposition time on the lignin coating was investigated for electrospray time from 2.5 min to 120 min. Microstructural and physical characterization included SEM, surface roughness analysis, porosity tests, permeability tests by a Gurley densometer, ATR-FTIR analysis, and contact angle measurements vs. both water and oil. The results indicate that, from a functional viewpoint, such a natural coating endowed the membrane with an amphiphilic behavior that enabled modulating the nature of the bare PCL non-woven substrate. Accordingly, the intrinsic hydrophobic behavior of bare PCL electrospun fibers could be reduced, with a marked decrease already for a thin coating of less than 50 nm. Instead, the wettability of PCL vs. apolar liquids was altered in a less predictable manner, i.e., producing an initial increase of the oil contact angles (OCA) for thin lignin coating, followed by a steady decrease in OCA for higher densities of deposited lignin. To highlight the effect of the lignin type on the results, two grades of oak (AL-OA) of the Quercus cerris L. species and eucalyptus (AL-EU) of the Eucalyptus camaldulensis Dehnh species were compared throughout the investigation. All grades of lignin yielded coatings with measurable antibacterial properties, which were investigated against Staphylococcus aureus and Escherichia coli, yielding superior results for AL-EU. Remarkably, the lignin coatings did not change overall porosity but smoothed the surface roughness and allowed modulating air permeability, which is relevant for filtration applications. The findings are relevant for applications of this abundant biopolymer not only for filtration but also in biotechnology, health, packaging, and circular economy applications in general, where the reuse of such natural byproducts also brings a fundamental demanufacturing advantage.

Effect of preparation method of pyrolysis liquid mixed with coal on its ignition and combustion characteristics

Relevance. The need to develop technological solutions to increase the competitiveness of pyrolysis processing of various wastes. Combustion of pyrolysis liquid in a mixture with coal is one of these solutions, which makes it possible to stabilize the properties of the obtained fuel and use in standard energy equipment. Aim. To determine the influence of the method of preparing a mixture of pyrolysis liquid and low-grade coal on its ignition and combustion characteristics, as well as on composition of the released gas-phase products, depending on the temperature of heating medium and concentration of the additive. Methods. Pyrolysis and oxidation characteristics were studied using thermogravimetric analysis, and formal kinetic constants were calculated using the Coates–Radfern method. Samples of mixed fuels were prepared by the methods of homogeneous mixing and surface wetting of pyrolysis liquid of rubber processing and low-grade coal. Ignition and combustion characteristics were determined using an experimental stand, and composition of gas-phase combustion products was determined using once-through gas analyzer. Results. The authors have determined the features of pyrolysis and oxidation of the pyrolysis liquid as well as the values of formal kinetics constants, indicating the physical nature of the factors that defining the rate of these processes. It was found that at 600 °C the ignition of the studied mixtures weakly depended on concentration of the additive, while at 700 and 800 °C the dependence was linear, and the differences between the samples prepared using different methods were insignificant. For samples obtained by the method of surface wetting, combustion of the additive occurred in the gas phase near the surface of the sample. For the samples obtained by the method of uniform mixing, it occurred predominantly in the bulk of the backfill. This led to more intense and complete coal combustion in these compositions due to more uniform releasing of heat and initiation of coal particles. The concentration curves of the NO, CO and CO2 release demonstrated, that behavior of the fuel mixture components was additive in terms of released gas-phase combustion products, as well as the absence of significant nonlinear effects over the entire studied range of temperatures and additive concentrations.

Unraveling the permeation-enhancing effect of didecyl dimethyl ammonium chloride (DDAC) on poplar wood (Populus cathayana Rehd.)

ABSTRACT Wood is a sustainable, porous material with a diverse range of applications. However, the low permeability of liquids within wood poses significant challenges for the widespread application of advanced wood-based materials such as oil–water separation, as well as traditional chemical modification processes of wood. Surfactants exhibit potential to improve permeability of liquids within wood by effectively enhancing liquid wettability on solid surfaces. In this study, the effects of didecyl dimethyl ammonium chloride (DDAC) on liquid absorption of water and copper ethanolamine (CE) by wood were explored under atmospheric temperature and pressure. With an increase in concentration of DDAC, its promotion effect on liquid absorption of wood became more pronounced. The most notable enhancement was observed in wicking test where 0.10% DDAC increased liquid absorption of wood to water by 156.7% and to CE by 65.5%. The enhancement of liquid wettability on wood surface cannot be solely attributed to reduction of liquid surface tension, the adsorption of DDAC onto wood surface also plays a crucial role in this process. This study investigated the intrinsic mechanisms by which DDAC enhanced the permeability of liquids within wood, contributing to increased productivity and reduced energy consumption.