Surface Free Energy Research Articles

Preparation and characterization of micro-cellular melamine foam supported SiO2 aerogel for building thermal insulation

This study aims to complement the advantages of SiO2 aerogel and melamine foam (MF) to produce high-performance building insulation materials. The optimal sol–gel scheme was determined by controlling system temperature, water content, amount of ethanol and amount of acid-base catalyst (orthogonal experiment). The density and porosity of MF/SiO2 aerogel were regulated by adjusting aging time, aging temperature and type of aging agent. Furthermore, the effects of different volume fractions hydrophobic modifier on the surface free energy and wettability of MF/SiO2 aerogel were also investigated. The experiment results showed that the prepared MF/SiO2 aerogel satisfies requirements for low density (0.089 g/cm3), low thermal conductivity at room temperature (0.0256 W m−1·K−1), and excellent hydrophobic performance (the contact angle was 140.1°). Meanwhile, it was found that SiO2 aerogel was stably and uniformly distributed in the pores of the MF and effectively enhanced the mechanical property (a maximum compressive strength of 0.2058 MPa), heat-shielding performance, flame retardant property, and sound absorption capacity(αmax = 0.76, αave = 0.31).Therefore, the MF/SiO2 aerogel composites exhibit exceptional application potential in comparison to conventional building insulation materials (such as EPS, Rock wool board, etc.) due to their significantly low thermal conductivity and remarkable flame retardant properties.

How Solvation Alters the Thermodynamics of Asymmetric Bond-Breaking: Quantum Simulation of NaK+ in Liquid Tetrahydrofuran.

Gas-phase potential energy surfaces (PESs) are often used to provide an intuitive understanding of molecular chemical reactivity. Most chemical reactions, however, take place in solution, and it is unclear whether gas-phase PESs accurately represent chemical processes in solvent environments. In this work we use quantum simulations to investigate the dissociation energetics of NaK+ in liquid tetrahydrofuran (THF) to understand the degree to which solvent interactions alter the gas-phase picture. Using umbrella sampling and thermodynamic integration techniques, we construct condensed-phase free energy surfaces of NaK+ on THF in both the ground and electronic excited states. We find that solvation by THF completely alters the nature of the NaK+ bond by reordering the thermodynamic dissociation products. Reaching the thermodynamic dissociation limit in THF also requires a long-range charge transfer process that has no counterpart in the gas phase. Gas-phase PESs, even with perturbations, cannot adequately describe the reactivity of simple asymmetric molecules in solution.

Surface Modification of Feldspathic Ceramic Used for Minimally Invasive Restorations: Effect of Airborne Particle Type on the Surface Properties and Biaxial Flexural Strength.

This study aimed to evaluate the effect of airborne particle abrasion with different particles on the surface free energy, roughness, and biaxial flexural strength of a feldspathic ceramic by comparing it with hydrofluoric acid etching, the standard surface treatment, and polishing. Square-shaped feldspathic ceramic specimens (12 mm × 12 mm × 1.2 mm) were divided into subgroups as airborne particles abraded with alumina (AO3a, AO3b, AO25, AO50a, AO50b, AO90, AO110a, AO110b, AO120a, and AO120b), silica (SO50a, SO50b, SO100, and SO100/200), or nutshell granule (NS100/200), hydrofluoric acid etched, and polished (n = 12). Surface free energy (n = 5), roughness (n = 5), biaxial flexural strength (n = 12), and Weibull moduli (n = 12) were investigated. Data were evaluated with 1-way ANOVA and Tukey HSD tests, and possible correlations were investigated with Pearson's correlation (α = 0.05). SO100/200 mostly had lower surface free energy (p ≤ 0.011), and polishing and etching led to higher surface free energy than AO3a, AO3b, and AO120a (p ≤ 0.031). Polished, SO100, and SO50b specimens mostly had lower roughness and AO125 had the highest roughness (p ≤ 0.029). SO100/200 mostly had lower biaxial flexural strength (p ≤ 0.041), and etched specimens had higher biaxial flexural strength than AO120a, AO120b, and SO50b (p ≤ 0.043). AO3b had the highest (33.56) and AO120b had the lowest (11.8) Weibull modulus. There was a weak positive correlation between the surface free energy and the biaxial flexural strength (r = 0.267, p = 0.011). A larger particle size mostly resulted in higher roughness, which was also affected by the particle shape. Most of the test groups had similar biaxial flexural strength to that of the hydrofluoric acid-etched group. Therefore, for tested feldspathic ceramic, airborne particle abrasion with tested parameters may be a suitable alternative without causing any further damage.

The effect of surface roughness and wettability on the adhesion and proliferation of Saos-2 cells seeded on 3D printed poly(3-hydroxybutyrate)/polylactide (PHB/PLA) surfaces

The aim of this work is to explore the effect of surface characteristics of the 3D printed scaffolds on their suitability for Saos-2 cells growth. Two promising materials for bone tissue engineering were examined, both containing poly(3-hydroxybutyrate)/poly(d,l-lactide) plasticized blend and one of them filled with bioactive tricalcium phosphate. The surface free energy (SFE) of samples was determined by contact angle measurement with four liquids. For non-filled sample the water contact angle (WCA) was 74° and its SFE was 40 mN m−1. The composite sample exhibited substantially decreased WCA, 61°. Moreover, the addition of the tricalcium phosphate caused doubling of the polar component of the SFE which increased by a total of 13%. 3D printed surfaces prepared by fused deposition modeling method showed a profound increase of WCA due to the increase in their surface roughness which was analyzed by confocal microscopy. The change in wetting properties strongly affected the behavior of Saos-2 cells on printed surfaces. The number of cells as measured by DNA quantification linearly decreased with increasing surface WCA. The highest number of cells was observed on the pressed samples and 3D printed surfaces made of simple lines and a grid with 50 μm gap between lines. The favored surfaces exhibit WCA under 80° which is important information for the future design of the scaffolds.

Effect of laser process parameters on the pores, surface roughness, and hardness of laser selective melting of dental cobalt-chrome alloys.

To address the quality problems caused by high porosity in the preparation of dental cobalt-chrome alloy prosthetics based on selective laser melting (SLM) technology, we investigated the influence mechanism of different forming process parameters on the microstructure and properties of the materials. Moreover, the range of forming process parameters that can effectively reduce defects was precisely defined. The effects of laser power, scanning speed, and scanning distance on the pore properties, surface roughness, and hardness of dental cobalt-chrome alloy were investigated by adjusting the printing parameters in the process of SLM. Through metallographic analysis, image analysis, and molten pool simulation, the pore formation mechanism was revealed, and the relationship between the porosity and energy density of SLM dental cobalt-chrome alloy was elucidated. When the linear energy density was higher than 0.18 J/mm, the porosity defect easily appeared at the bottom of the molten pool. When the laser energy density was lower than 0.13 J/mm, defects occurred in the gap of the molten pool due to insufficient melting of powder. In particular, when the linear energy density exceeded the threshold of 0.30 J/mm or was below 0.12 J/mm, the porosity increased significantly to more than 1%. In addition, we observed a negative correlation between free surface roughness and energy density and an inverse relationship between macroscopic hardness and porosity. On the basis of the conditions of raw materials and molding equipment used in this study, the key process parameters of SLM of molding parts with porosity lower than 1% were successfully determined. Specifically, these key parameters included the line energy density, which ranged from 0.13 J/mm to 0.30 J/mm, and the scan spacing should be strictly controlled below 90 μm.

Effects of acid generator anions on radiation-induced decomposition and dissolution kinetics of chemically amplified resists

Chemically amplified resists (CARs) are widely used in lithography for manufacturing semiconductor devices. To reduce the occurrence of stochastic defects in CARs, increased acid generator concentration is required. In this study, we investigated the effects of acid generator anions on the radiation-induced decomposition of acid generators using electron pulse radiolysis and γ-radiolysis methods. Their effects on the dissolution dynamics of poly(4-hydroxystyrene) (PHS) films were also investigated using contact angle measurement and quartz crystal microbalance methods. Triphenylsulfonium trifluoromethanesulfonate, triphenylsulfonium nonafluoro-1-butanesulfonate, triphenylsulfonium 4-toluenesulfonate, and triphenylsulfonium salicylate, were used as acid generators or photodecomposable quenchers. The anions showed minimal effect on the decomposition of the acid generators and photodecomposable quenchers; however, they influenced the surface free energy, dissolution kinetics of the PHS films, and water penetration into the PHS films. In particular, the effect of salicylate on the dissolution kinetics of PHS films is significant.

Dialysis nanocomposite membranes based on carbon nanoforms inhibiting blood plasma protein adsorption.

Protein adsorption on medical devices in contact with blood is a significant issue during renal replacement therapy. Main forces determining fouling are the electrostatic interactions between membrane and charged protein, but the dialysis membrane surface charges can be adjusted by modifying the polymer matrix to decrease the blood plasma protein adsorption. In this study, polysulfone membranes (PSU) were modified by incorporation of carbon nanoparticles such as: multiwall carbon nanotubes (2 wt.% MWCNT), graphene oxide (1 wt.% GO), and graphite (5 wt.% GR) during manufacturing process (nonsolvent-induced phase separation, NIPS). The PSU flat sheet membrane was the reference sample. Observed morphology of nanocomposite membranes was similar (SEM imaging); all of them had finger-like pore structure with unimodal distribution of pore size and similar skin-to-support ratio (1:3). The carbon nanoadditives also influenced the surface wettability: hydrophobicity and surface free energy of membranes increased (polar components of energy were reduced, while the dispersive components were increased). The surface charge of nanocomposite membranes increased, when the polymer matrix has been modified with CNT or GR. This significantly affects the adsorption of proteins such as chicken (CSA) and bovine serum albumin (BSA) and reduces blood clotting on the membrane.

Optimizing the separation process for improved zirconia molding through liquid crystal display 3D printing

Mask stereolithography 3D printing for zirconia ceramics has attracted increasing attention in the industrial manufacturing due to their advantages of complex shapes, precisely controlled internal structures and fine surface effects. However, high refractive index and expensive equipment cost have always affected its development. Herein, we combine liquid crystal display (LCD) light curing 3D printing with zirconia molding, which is free from environmental and price limitations. In the conventional method of operation, the cured layer is bonded to the bottom and cannot be manufactured. We put forward a strategy for optimizing separation process and investigate the mechanism of the separation process in depth for high-quality zirconia ceramics LCD 3D printing. The results show that the controlled adjustment of the surface free energy can achieve a great reduction in the separation force, which enabled the successful printing of zirconia ceramics based on LCD. The effect of physical properties of the separation membrane on the separation process was studied and the solid content and 3D printing parameters of ceramic paste were optimized. When the solid content is 72.5 wt%, high quality zirconia ceramic parts with flexural strength of 255 MPa and relative density of 98.1 % can be obtained. This work provides new ideas for the convenient customization of zirconia ceramics in many fields.

A HKUST-1 coating with copper metal active site enables stabilized zinc metal anode

Aqueous zinc-ion batteries (AZIBs) are considered to be one of the alternatives for large-scale energy storage devices due to unique advantages. However, the harmful Zn dendrites generation of Zn anodes seriously hinders the development of AZIBs. Herein, Cu3(BTC)2 (HKUST-1) as a compact functional interface layer on the surface of bare Zn foil is shown to improve the reversibility of Zn-plating/stripping process. Interestingly, HKUST-1 possesses high porosity, large number of water molecule vacancies, and Cu active center, which help to enhance the diffusion kinetics of Zn2+ and reduce the surface free energy of Zn electrode. Combining theoretical calculations with experiments, the HKUST-1 can contribute to the desolvation process of Zn[(H2O)6]2+ and balance Zn2+ concentration, which thus accelerate Zn2+ transfer kinetics, lower interfacial energy, and homogenize ion-distribution. Attributed to these superiorities, the HKUST-1@Zn symmetric cells demonstrate excellent stable plating/stripping for over 250 h under ultra-high current density (20 mA/cm2 and 20 mAh/cm2). Furthermore, a HKUST-1@Zn||MnO2 full cell exhibits an enhanced long-cycling performance with a discharge capacity of 114 mAh/g after undergoing 500 cycles. All results demonstrate the potential application of HKUST-1 coating in AZIBs.

Multi-functional ceramic glazes with nano ZnO/Cu–ZnO incorporation

The study successfully enabled the creation of ceramic surfaces with multi functionalities, including superhydrophilicity, self-cleaning, antibacterial properties, and photocatalytic activity, by applying a glaze composition rich in nano ZnO/Cu–ZnO and utilizing surface chemistry and unique texturing on porcelain tiles. The tiles, coated with unique glaze compositions, were fired in an industrial furnace and heat treated. The crystalline phases and surface morphology of glazed surfaces were systematically evaluated using XRD, SEM, FT-IR, drop shape analyzer, and surface roughness profilometer. Key-factors affecting the wettability, self-clean ability, photocatalytic activity and antibacterial efficacy were discussed. Adding nano Cu into the glaze mixture that is rich in ZnO improves the evolution of zincite crystals, increases the specific surface energy, decreases surface roughness, provide superhydrophilicity and promotes the antibacterial effectiveness and photocatalytic activity. Superhydrophilic surfaces doped with nano Cu–ZnO display antibacterial characteristics that do not require UV or visible light. The quick achievement of complete self-cleaning, up to 100 %, is due to the presence of nano Cu particles in its structure. Hydrophilicity has the ability to improve the efficiency of photocatalysis. If a surface exhibits superhydrophilic properties, it shows exceptional photocatalytic performance. A surface that is solely photohydrophilic may not maintain self-cleaning. Hydrophilicity may be more important than photocatalysis in the self-cleaning effect.

Reducing the moisture susceptibility of recycled hot‐mix asphalt mixture with composite modification technology

AbstractStyrene–butadiene–styrene block copolymer (SBS)‐modified asphalt is a key material for constructing recycled hot‐mix asphalt mixtures (RHMAs). However, these mixtures still risk insufficient moisture stability. To this end, this study investigates the feasibility of asphalt composite modification technology to enhance RHMA performance. SBS, high‐viscosity agent (HVA) and crumb‐rubber materials (CRM) were used to prepare SBS‐HVA‐ and SBS‐CRM‐modified asphalt, with SBS‐modified asphalt as the control group, and the adhesion properties of the asphalt were evaluated using surface free energy tests. RHMAs with 50% reclaimed asphalt pavement were then prepared with each type of modified asphalt. The moisture susceptibility of these mixtures was analyzed using moisture‐induced sensitivity, freeze–thaw splitting and immersion Marshall tests. It was found that HVA significantly enhanced the adhesion of SBS‐modified asphalt under dry conditions, while CRM had a minimal effect. Compared to RHMA with SBS‐modified asphalt, HVA and CRM additives are crucial for enhancing the moisture stability of RHMA in the immersion Marshall test. However, CRM does not improve the moisture stability of RHMA in the moisture‐induced sensitivity and freezing–thaw splitting tests. From the conducted study, it can be proposed that SBS and HVA composite‐modified asphalt can be utilized in RHMAs to achieve higher moisture stability. © 2024 Society of Chemical Industry.

Rational regulation and one-step electrodeposition realization of surface textures and free energy to create mechanochemically durable superhydrophobicity for the enhanced anti-icing properties

The quest for durable superhydrophobic materials with exceptional water-repellent properties remains a pressing challenge. This study introduces an innovative methodology that exploits one-step electrodeposition realization of surface textures and free energy to create robust superhydrophobic surfaces. Leveraging copper, nickel, and polytetrafluoroethylene nanoparticles, a dendritic microstructure is fabricated. An unprecedented feature of this process is the controlled partial melting of polytetrafluoroethylene during sintering, enabling the connection of discrete polymer particles and the formation of a resilient coating skeleton. This pioneering method grows low-energy materials in situ between coatings and gives the surface greater robustness. The surface prepared by this method showed excellent non-wettability, highlighted by a remarkable water contact angle of 163.1°. The surface shows outstanding anti-icing performance: water droplets resist freezing for up to 1173 s at −20 °C with negligible ice adhesion (only 34 kPa). Importantly, this technique is amenable to large metal surfaces. This study presents a novel and effective solution to face the durability challenges (The sample can withstand 400 linear wear and is resistant to acids, alkalis and ultraviolet). It underscores the innovative fusion of micro-nanostructure construction and low surface energy material modification, promising both enhanced adhesion and the preservation of surface durability.

Investigating the morphological, mechanical, barrier, and antibacterial properties of the polycaprolactone nanocomposite films reinforced with hybrid zinc oxide/polyhedral oligomeric silsesquioxane nanoparticles

ABSTRACT The importance of biopolymer-based nanocomposites in food packaging is growing significantly. Therefore, in the present study, we aim to examine the impact of zinc oxide (ZnO), polyhedral oligomeric silsesquioxanes (POSS), and, for the first time, their hybrid on polycaprolactone (PCL) nanocomposites. For this matter, different concentrations of 1, 3, and 5 wt% of each nanoparticle and the hybrid were incorporated into the PCL nanocomposites via the solution casting method. Their chemical structures and interactions, crystalline structures, and morphology were investigated by FT-IR, WAXD, and SEM. Moreover, it was observed through contact angle and surface free energy experiments that an increase in the nanoparticle concentration corresponded to an increase in the contact angle values. The incorporation of hybrid POSS and ZnO equilibrated well between Young’s modulus, tensile strength, and elongation of the samples in their single status. Accordingly, the addition of the hybrid nanoparticles up to 3 wt% significantly increased the modulus and yield strength of PCL nanocomposites without any significant sacrifice in toughness. Also, PPZ3 (containing an optimal 3%wt. of hybrid nanoparticles) demonstrated the lowest permeability against both water vapor and O2 gas, exhibiting reductions of approximately 30 and 55% when compared to pristine PCL. Finally, the antibacterial properties of the nanocomposite films were investigated for S. aureus and E. coli bacteria and revealed. In addition to the antibacterial properties of ZnO and POSS nanoparticles, increasing the concentration of hybrid nanoparticles up to 5 wt% expanded S. aureus’s inhibitory zone. The balanced mechanical, and barrier characteristics, enhanced morphologies, and antibacterial effects of the novel hybrid nanocomposites present novel opportunities in the field of food packaging.

Synthesis and properties of silicone-modified polyurethane acrylate for magnetically driven blue light photocurable superhydrophobic coatings

A low surface energy silicone-modified polyurethane acrylate (Si-PUA) has been synthesized and employed as the primary constituent for the magnetically driven photocurable coatings. By integrating magnetically driven assembly technology with blue light photocuring technology, a superhydrophobic coating featuring low surface energy and micro/nano rough structures was successfully fabricated. The influences of hydroxy-terminated polydimethylsiloxane (PDMS) content and the R-value (-NCO/-OH) on the performance of PUA and coating systems were investigated using Photo-DSC, TGA, rheology, tensile testing machine, and SEM-EDS. The molecular structure of Si-PUA was characterized using FT-IR and 1HNMR. The result revealed that the composite coating exhibited a minimum surface energy when the PDMS content was 5 wt% and the R-value was 1.6, resulting in a surface free energy of 24 mJ/m2. When the coating formulation consists of a Si-PUA:HEA ratio of 7:3, an initiator dosage of 2% (with CQ/EDB at a 1:1 ratio), and a carbonyl iron powder (CIP) content of 100 wt%, the resulting photocured film exhibits a surface contact angle of 157.6° and a rolling angle of 5°, thereby satisfying the superhydrophobicity standard.

Nanoparticle agglomeration in molten salt nanofluids: Free energy landscape and its impacts on thermal transport property degradation

The nanofluids consisting of molten salt and nanoparticles can gain enhanced thermal performance for heat transfer and energy storage processes. Agglomeration of nanoparticles is ubiquitous in this colloidal dispersion, deteriorating the dispersed states of the nanocomposite interiors, and its microscopic mechanisms are unsatisfactorily explored. In this work, molecular dynamics simulations combined with umbrella sampling technique to capture the relative dispersion state of nanoparticles in molten salts effectively were performed to reveal the free energy landscape of agglomeration and its influence on heat transport. The dominant deep minima in the free energy surface demonstrates that the agglomeration of MgO nanoparticles in the molten NaCl salt is principally induced by van der Waals attractions between MgO nanoparticles and aggravated by large surface area. The unstable dispersion of nanoparticles is the most fatal problem for enhanced thermal conductivity during agglomeration, and the relative distance of MgO nanoparticles has less impacts on the thermal conductivity of the melt. The stronger adsorption of ions around nanoparticles can improve their relative dispersion, and utilize interfacial effects to enhance the thermal conductivity. Combined with the benefit of ordered ionic layer on the surface, the MgO nanoparticles of 10 Å diameter (specific surface area of ∼ 938.80 m2/g) become the optimal choice for molten NaCl. With the mechanisms of interfacial microstructures preventing agglomerated nanoparticles and improving heat transfer of molten salts revealed, this work can enlighten the selection or feasible modification for nanoparticles in various high-temperature molten salts, since the mechanisms are universal to other nanofluids, especially for ionic liquid based nanofluids.

Crystallisation: Solving crystal nucleation problem in the chemical engineering classroom based on the research grade experiments deployed in virtual mode

Crystallization via nucleation can isolate active pharmaceutical ingredients from their crudes. While chemical engineering textbooks provide theoretical knowledge on crystallization and nucleation theories, they often fall short in providing provide practical insights on the nucleation mechanism. To bridge this gap, we introduced a virtual experiment on nucleation in second-year chemical engineering classrooms. The main goal is to educate students on crystallization procedures in research and process industries, teaching them how to analyse and manage collected data while integrating theoretical knowledge. This includes conveying the kind of information that can be obtained from a crystallisation process and instructing students on how to analyse and manage the data collected in the light of the theories learned. We devised an original chemical engineering problem on nucleation, derived directly from the raw data collected in the classroom from virtual experiments. This method differs from the conventional approach of solving standard textbook problems. The textbook problems, regrettably often lack crucial information on how nucleation rate or surface free energy are directly obtained from raw data. By the conclusion of the virtual experiment, students have acquired a comprehensive understanding encompassing both practical and theoretical aspects of crystallization, with a particular focus on nucleation. The methodologies elucidated in this study can be applied across a spectrum of chemical engineering modules, including process engineering, unit operations in chemical engineering, mass transfer, and can even be integrated into specialized courses dedicated to crystallization.

Investigation of physico-mechanical, thermal, morphological, and antibacterial effects of bio-based epoxidized soybean oil plasticizer on PLA-ZnO nanocomposites as flexible food packaging

Polylactic acid (PLA) has attracted considerable attention because of its excellent properties compared to petroleum-based materials. However, improving its toughness, crystallization, and functionalities is challenging. Using a laboratory internal batch mixer, we produced unique blended nanocomposites comprising polylactic acid (PLA) as the host matrix, epoxidized soybean oil (ESO) as the plasticizer, and zinc oxide nanoparticles (ZnO NPs) as the reinforcements. The SEM-EDS test showed that neat PLA had a smooth surface, but the PLA-ZnO nanocomposite had rough micrographs and a uniform dispersion state of the nanoparticles. It was also found that adding ESO to the blend nanocomposites created a matrix droplet structure, and the size of the oil domains decreased as the ZnO content increased. All results derived from FTIR, XRD, and DSC tests were consistent with the morphological features in which ZnO NPs acted as the blend’s compatibilizer and heterogeneous nucleating agent. Our team observed that adding ESO decreased the PLA-ZnO nanocomposites’ glass transition temperature (Tg) by an average of 2 °C and increased the crystallization rate. It was also confirmed that the presence of ESO improved the flexibility and reduced the strength of the PLA. The tensile strength was further enhanced by incorporating ZnO into the blend. Adding 5 wt% of ZnO NPs increased the tensile strength of the PLA containing 10 wt% ESO by approximately 3.5 MPa. Furthermore, the tensile modulus was predicted using theoretical models; for example, the Paul model fitted with experimental findings. The addition of ESO increased the overall surface free energy of the nanocomposites. On the other hand, increasing ZnO content resulted in high contact angles and antibacterial properties of the blended nanocomposites. The favorable characteristics of the resulting films emphasized the potential use of these nanocomposite films as a promising choice for food packaging materials.

From Silver Nanoparticle to Thin Films Produced by Pulsed Laser Deposition: Effects of Ar Gas Pressure and Substrate Surface Free Energy

From Silver Nanoparticle to Thin Films Produced by Pulsed Laser Deposition: Effects of Ar Gas Pressure and Substrate Surface Free Energy

Study of the rolling wetting behavior of droplets on surfaces with T-shaped microstructures

The regulation of droplet wetting behavior encompasses multiple professional disciplines, and the surface microstructure has become the preferred approach for controlling droplet wetting behavior. Bionic studies have revealed that springtails can effortlessly move in water because of the T-shaped microstructures on their skin, which prompted the design of various T-shaped microstructures to effectively regulate droplet wetting behavior. Although the static wetting theory for T-shaped microstructure surfaces is well understood, the dynamic wetting theory regarding droplet rolling remains unexplored. This study aims to investigate the rolling behavior of droplets on inclined surfaces with T-shaped microstructures through theoretical analysis and numerical simulation. By analyzing the comprehensive energy transformation and gas-liquid interface morphology during the tilting processes, we revealed the mechanism by which the geometric parameters of the T-shaped microstructures influence the droplet rolling behavior and constructed an energy prediction analysis model for the final droplet morphology. The results showed that reducing the cantilever height, increasing the structural spacing, and enlarging the droplet size facilitated continuous rolling of the droplets. Additionally, we discovered that the driving energy for droplet rolling on inclined surfaces with T-shaped microstructures originates from the surface free energy. The maximum surface free energy of a droplet often occurs when the droplet begins to roll.

Thermally stable high-loading single Cu sites on ZSM-5 for selective catalytic oxidation of NH3

Rigorous comparisons between single site- and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst.