Search Results (81)

The contact angle of a liquid drop on a solid surface is a simple yet powerful experimental technique for characterizing the surface properties of materials. This method uses a liquid drop as a probe to investigate the chemical and physical properties of a solid surface, but it can also be used in reverse—a well-characterized surface can be employed to study the properties of a liquid. The versatility of the technique can also be extended to submerged systems, where a gas bubble serves as the probe. The contact angle is the angle measured at the solid–liquid and liquid–gas interfaces at the triple-phase point where a solid, liquid, and gas meet. This angle reflects the balance of forces at the three interfaces, and because this balance is highly sensitive to surface properties, contact angle is one of the most surface-sensitive techniques available. The interface can be analyzed from multiple perspectives: empirically through the measured angle (hydrophobic/hydrophilic), thermodynamically using principles such as the Young–Dupré equation, from a physical point of view (the Cassie–Baxter and Wenzel models) and from a chemical standpoint by considering intermolecular forces and the specific chemical nature of the substances involved. Despite its experimental simplicity, contact angle analysis can provide deep insights, ranging from a surface’s wettability (hydrophilicity or oleophobicity) to estimation of van der Waals interaction on a surface. Thanks to its ease of use, its flexibility, and a century of established physical and chemical theory, contact angle measurement has a wide range of applications. These include determining the surface tension of materials, determining the presence of a hierarchical nanostructure at the surface (superhydrophobicity), measuring the percentage of alcohol in a hydroalcoholic solution, assessing surface stability, and many other applications. This article presents a comprehensive review of the diverse applications of contact angle measurements, aiming to provide researchers with a detailed overview of its potential uses and the valuable information that can be obtained. Full article

Despite the fact that oxygen plasma treatments are widely used to modify the surface properties of polytetrafluoroethylene (PTFE), the long-term stability of these surface modifications has not been fully investigated. Specifically, the roles of morphological restructuring and chemical modifications at the surface remain to be understood. In this work, we treat commercial PTFE samples using O₂ plasmas at different discharge pressures to investigate their surface modifications and subsequent ageing at atmospheric pressure. We provide direct evidence that ageing behavior is governed by nanoscale and microscale restructuring of the plasma-modified interface, revealing a novel link between morphology dynamics and wettability properties. To capture this surface evolution, the modified interface was characterized using water contact angle (WCA) measurements, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and mass spectrometry (MS). Initial plasma treatment enhances PTFE hydrophobicity, shifting the WCA from ${\theta }_c\simeq 105°$ to a highly hydrophobic state of ${\theta }_c\simeq 135°$. By monitoring the samples in contact with air over a 67-day period a gradual transition toward hydrophilicity was revealed, with WCAs stabilizing at ${\theta }_c\simeq 70°$ after approximately 20 days. SEM observations identified time-dependent morphological degradation of plasma-induced nanostructures, while qualitative and quantitative FTIR analysis—utilizing the Specified Area Under Band (SAUB) method—confirmed corresponding shifts in carbonyl and hydrocarbon indices. These results demonstrate that ageing kinetics are a direct function of plasma pressure. The transition is further supported by a phenomenological fractal model, which confirms a morphological shift from an initial fractal surface ($d_s\simeq 2.25$) toward a standard flat geometry ($d_s=2$). Furthermore, calculations indicate a sign reversal in solid-gas interface tension parameters, reflecting the changed chemical nature of the surface. We conclude that the loss of hydrophobicity is driven by a synergistic interplay between morphological relaxation and chemical restructuring. Full article

Hydrophobic and superhydrophobic surfaces have emerged as key solutions for fluid transport, biofouling prevention, and energy efficiency, with market forecasts projecting a compound annual growth rate (CAGR) of over 15% through 2030 due to their broad range of applications. This review critically examines the principles of natural hydrophobicity, as exemplified by lotus leaves and shark skin, and their translation into engineered surfaces via micro/nanofabrication techniques, such as laser patterning, etching, and self-assembly. Recent advances in hybrid nanomaterials have demonstrated WCAs in the range of 140–160°, along with enhanced mechanical strength and chemical stability, enabling applications in self-cleaning, anti-corrosion, and oil–water separation technologies. Superhydrophobic coatings are particularly important for reducing ice adhesion by more than 80%, while drag reduction in pipelines can reach up to 30%, contributing to energy savings. Despite these advances, challenges remain in achieving long-term stability under harsh environmental conditions, minimizing environmental impact, and developing cost-effective, scalable fabrication techniques. Future directions focus on environmentally friendly, multifunctional nanocomposites with switchable wettability, including pH- and light-responsive coatings capable of reversibly transitioning between superhydrophilic (<5°) and superhydrophobic (>150°) states, paving the way for sustainable and adaptable surface technologies. Full article

During hydraulic fracturing, the extensive use of slickwater and post-fracturing shut-in (soaking) processes take advantage of spontaneous imbibition to displace crude oil. While nano-flooding agents are known to reduce interfacial tension (IFT) and alter wettability, a critical challenge lies in distinguishing between deep but inefficient displacement and shallow but highly efficient sweep. This study investigates the pore-scale mobilization and penetration depth of a nano-flooding agent in tight conglomerate reservoirs and focuses on the recovery per unit imbibition depth as a novel metric for evaluating the displacement efficiency. The nano-agent demonstrated excellent performance, reducing oil–water IFT to 0.141 mN/m and reversing wettability from oil-wet (148.7°) to water-wet (39.5°). Experiments revealed that the diffusion rate of the nano-agent decreases with pore size, suggesting a limited transport in confined space. Under reservoir conditions (80 °C), spontaneous imbibition in tight cores was highly permeability-dependent. High-permeability cores achieved a recovery rate of up to 44.6%, whereas low-permeability cores reached only about 12%. This work highlights that penetration depth alone does not necessarily indicate high recovery. The medium-permeability core exhibited a lower final penetration depth than the low-permeability core but achieved a much higher total recovery due to superior efficiency per unit depth, suggesting that in tight reservoirs, a shallow but highly efficient displacement mechanism can outperform a deep but inefficient one. Full article

Water blockage severely restricts gas transport in deep shale reservoirs, while effective mitigation requires a precise balance of multiple operational variables. This study utilizes core-flooding experiments to optimize the treatment processes of an amphiphobic fluorinated copolymer, focusing on the coupled roles of surfactant concentration, injected volume, and shut-in duration. The results show that permeability damage decreases rapidly with surfactant concentration, optimizing at 0.5 wt.%. Conversely, excessive liquid retention beyond a critical injection threshold of 1.0 PV triggers secondary water-blocking. Extending the shut-in duration to 8 days facilitates surfactant redistribution and interfacial equilibrium, gradually reversing rock wettability to a stable amphiphobic state. Crucially, the concurrent reduction in interfacial tension markedly lowers capillary resistance, allowing trapped water to detach and flow back under significantly lower driving pressures. This optimization effectively minimizes the energetic barrier for fluid displacement and creates a gas-preferential flow environment. The proposed laboratory operational window balances surfactant dosage, injection volume, and shut-in duration under the tested conditions, providing an experimental reference for optimizing post-fracturing cleanup, controlling liquid retention, and improving early-time gas flowback in shale gas reservoirs. Full article

To address gas channeling, low sweep efficiency, and water sensitivity in CO₂ flooding of shale reservoirs, amidine-functionalized graphene quantum dots (FN-GQDs) were synthesized via amidation of citric acid-derived GQDs. FTIR and UV-Vis confirmed successful grafting. Conductometric titration showed an optimal reaction time of 24 h with a grafting ratio of 58%, in good agreement with the 60% saturation predicted by molecular dynamics simulation. Upon CO₂ introduction, protonation of amidine groups induced a nonlinear viscosity increase from 0.298 to 2.0 mPa·s at 0.02 wt% via electrostatic attraction and hydrogen bonding, forming a dynamic crosslinking network. FN-GQDs maintained low oil-water interfacial tension of 0.12–0.25 mN/m at 80–120 °C and rapidly reversed rock wettability from strongly oil-wet to water-wet, reducing the contact angle from 141.7° to 38.9° within 80 min. The positively charged surface inhibited clay swelling, achieving 92% at 0.20 wt%. Core flooding and NMR T₂ spectra revealed that alternating CO₂ and FN-GQDs injection at a 2:1 gas–water ratio achieved a final oil recovery of 52.5%, significantly higher than pure CO₂ flooding. Through synergistic effects of interfacial tension reduction, wettability alteration, viscosity enhancement, and anti-swelling, FN-GQDs improve microscopic displacement efficiency and macroscopic sweep volume, showing great potential for CO₂-enhanced oil recovery in shale reservoirs. Full article

Fouling limits the performance and lifetime of polyethersulfone (PES) ultrafiltration membranes. We investigated the effect of blending polyaniline (PAni·DBSA) into PES on membrane morphology, wettability, permeability and antifouling behavior, and we evaluated a simple electrochemical cleaning protocol for fouled membranes. A series of PES/PAni·DBSA membranes with different PAni loadings were characterized by SEM, BET, AFM, contact angle, TGA and porosity analysis. Initial water flux (J), bovine serum albumin (BSA) rejection (RR) and flux recovery ratio (FRR) were measured in a dead-end filtration cell. Electrochemical cleaning was applied to selected fouled membranes, and post-cleaning flux and rejection were measured. PAni·DBSA incorporation produced a hierarchical pore structure and altered near-surface texture. Contact angle decreased from 76° to 54°, and swelling increased for intermediate PAni loadings. Initial pure-water fluxes ranged from 5.9 to 39.3 L·m⁻²·h⁻¹. When expressed as absolute percentages, the best performing membrane in terms of reversible fouling recovered 8.12 times of its initial flux. Multivariate analysis indicates that surface hydration and height distribution explain more variance in FRR than Rq alone, consistent with a synergistic role of texture and wettability. Electrochemical treatment substantially increased both flux and rejection for tested membranes, indicating effective foulant mobilization. Full article

Conventional liquid springs enable storage of energy in the form of interfacial tension at forcibly wetted lyophobic surfaces. The pressure–volume work performed to compress the liquid into a poorly wettable porous medium is recovered during spontaneous expulsion when pressure falls below the capillary pressure characteristic of a given system. Our study explores generalizations to easily wettable materials where liquid infiltration is opposed solely by steric hindrance exerted on liquid molecules in micro-sized pores. The concept is exemplified in molecular simulations of prototypical model systems with methanol intruding narrow slits between hydrocarbon or graphene surfaces. While these materials show significant wetting propensities at macroscopic interfaces with liquid methanol, substantial compression is required to wet molecular-sized pores barely accommodating a monolayer of liquid molecules. The observed O(10³) bar intrusion pressures secure stored energy densities competitive with supercapacitors and amenable to improvement. Wall–liquid attraction and small pore diameters lead to intrusion–expulsion pathways along cooperative-adsorption isotherms. The process avoids abrupt liquid/vapor transitions and associated nucleation barriers, responsible for cycle hysteresis in experiments with water in hydrophobic capillaries. Using open ensemble (Grand Canonical) Monte Carlo sampling, we identify the range of porosities supporting reversible energy storage/recovery operation in lyophilic media; the results can assist with the design of molecular spring devices with competitive storage and power capacities in pragmatic contexts. Full article

Background: Given their intraoral service for clinically relevant periods, it is important to clarify whether additive manufacturing parameters influence the surface characteristics of 3D-printed provisional restorations and thereby affect microbial colonization. Methods: This study evaluated the effects of printing orientation and layer thickness on surface roughness, wettability, and Streptococcus mutans biofilm formation of LCD-printed provisional restorations. Disk-shaped specimens were fabricated from a methacrylate-based provisional resin at two orientations (0° and 90°) and two layer thicknesses (50 and 100 µm) (n = 7 per group). Surface roughness (Ra) was measured by contact profilometry, wettability by sessile-drop contact angle analysis, and biofilm formation by crystal violet staining after 72 h. Results: Data were analyzed by two-way ANOVA, aligned rank transform (ART) ANOVA, and correlation analysis (α = 0.05). Orientation alone did not affect Ra (p = 0.992), whereas layer thickness (p = 0.012) and the orientation × layer thickness interaction (p = 0.002, η² = 0.339) were significant. At 50 µm, 90° oriented specimens showed higher Ra than 0° (p = 0.021); this pattern reversed at 100 µm (p = 0.020). Neither parameter significantly affected contact angle or biofilm formation (p > 0.05). Conclusions: Both printing orientation and layer thickness altered the surface microtopography of the specimens; however, no significant differences were observed in short-term S. mutans biofilm formation among the tested groups. Within the limitations of the present single-species 72 h in vitro model, the findings suggest that material-related characteristics may have contributed more prominently to the observed biofilm behavior than the printing-induced surface differences evaluated in this study. Full article

As a key technology for achieving building heating electrification and decarbonization, the air-source heat pump (ASHP) has long been constrained by outdoor heat exchanger frosting in cold and humid regions. Frosting leads to increased thermal resistance, a sharp rise in air-side pressure drop, and the attenuation of heating capacity, while traditional active defrosting methods, such as reverse-cycle defrosting, suffer from high energy consumption and heating interruption. This review aims to systematically present the recent research progress of superhydrophobic surfaces (SHSs) as a highly efficient passive anti-frosting strategy. First, the complex phase-change dynamics of frosting and key influencing factors such as environment and surface characteristics are deeply analyzed. Second, it elucidates how superhydrophobic surfaces achieve delayed frosting and sloughing off defrosting by delaying nucleation, promoting droplet self-removal, and reducing ice adhesion. Furthermore, fabrication processes suitable for complex fin structures are systematically reviewed from the perspectives of subtractive manufacturing, in situ growth, and additive coatings, and their industrialization prospects are compared. Finally, the practical effects of this technology in improving heat transfer coefficients, reducing fan energy consumption, and improving defrosting efficiency are evaluated. Although superhydrophobic technology has significant energy-saving potential, it still faces challenges such as poor long-term durability, wettability failure under extreme conditions, and residual micro-droplets. Future research should focus on the development of highly durable materials, the matching design of micro–nano structures with macro flow channels, and active–passive synergistic anti-frosting strategies. Full article

Unconventional low-permeability reservoirs present significant production challenges due to the poor imbibition and displacement efficiency of conventional polymer fracturing fluids. The injection of nanoparticle (NP) compounds into polymer fracturing fluid base systems, such as linear gels or slickwater, has garnered significant research interest due to their superior performance. However, previous studies have primarily focused on evaluating the fluid’s properties, while its imbibition and oil displacement mechanisms within reservoirs remain unclear. Herein, the imbibition mechanism of nanoparticle composite polymer fracturing fluid was systematically investigated from macro and micro perspectives using low-field nuclear magnetic resonance (LF-NMR), atomic force microscopy (AFM), interfacial rheology, and other technical means. The results showed that the imbibition recovery using polymer fracturing fluid was 10.91% higher than that achieved with conventional slickwater. Small and medium pores were identified as the primary contributors to oil drainage. Nanoparticles can be adsorbed on the rock wall in the deep reservoir to realize wettability reversal from oil-wet to water-wet, reducing crude oil adhesion. Furthermore, a strong interaction between the adsorbed NPs and cleanup agents at the oil–water interface was observed, which reduces interfacial tension to 0.95 mN·m⁻¹, mitigates the Jamin effect, and enhances interfacial film deformability. NPs increase the interfacial dilatational modulus from 6.0 to 14.4 mN·m⁻¹, accelerating fluid exchange and oil stripping. This work provides a consolidated mechanistic framework linking NP-induced interfacial modifications to enhanced pore-scale drainage, offering a scientific basis for designing next-generation fracturing fluids. We conclude that NP-compound systems hold strong potential for low-permeability reservoir development, and future efforts must focus on optimizing NP parameters for specific reservoir conditions and overcoming scalability challenges for field deployment. Full article

Horizontal wells combined with multi-stage fracturing are key techniques for extracting tight oil formation. However, due to the ultra-low permeability and porosity of reservoirs, energy depletion occurs rapidly, necessitating external supplements to sustain production. During the hydraulic fracturing process, large volumes of fracturing fluid are injected into reservoirs, increasing its pressure to a certain extent. However, due to the oil-wet nature of the formation, the fracturing fluid cannot penetrate the rock, failing to enhance oil recovery during the shut-in period. Surfactant-based nanofluids have been introduced as fracturing fluid additives to reverse rock wettability, thereby boosting imbibition-driven recovery. Although the imbibition has been studied to inspire the tight oil recovery, few studies have demonstrated the imbibition in enhanced fossil hydrogen energy, which further promotes the imbibition recovery. In this paper, complex nanofluid dispersions (CND) have been proved to enhance the tight reservoir pressure. Through contact angle and imbibition experiments, it is shown that CND can transform oil-wet rock to water-wet, reduce the adhesion of oil, and improve the ultimate oil recovery through the imbibition effect. Then, core flow testing experiments were conducted to show CND can decrease the flow resistance and improve the swept area of the injected fluid. In the end, pressure transmission tests were conducted to show CND can enhance the formation energy and production after fracturing. Results demonstrate that CND enables the fracturing fluid to travel further away from the hydraulic fractures, thus decreasing the depletion of tight formation pressure and maintaining a higher oil production rate. Results help optimize the design of the hydraulic fracturing of tight offshore reservoirs. Full article

To address the challenges of strong heterogeneity and poor crude oil mobility in tight conglomerate reservoirs of the Mahu Oilfield, this study systematically evaluated the effects of different surfactants on wettability alteration, spontaneous imbibition, and relative permeability through high-temperature/high-pressure spontaneous imbibition experiments, online Nuclear Magnetic Resonance (NMR) monitoring, and relative permeability measurements. Core samples from the Jinlong and Madong areas (porosity: 5.98–17.55%; permeability: 0.005–0.148 mD) were characterized alongside X-Ray Diffraction (XRD) data (clay mineral content: 22–35.7%) to compare the performance of anionic, cationic, nonionic, and biosurfactants. The results indicated that the nonionic surfactant AEO-2 (Fatty Alcohol Polyoxyethylene Ether) (0.2% concentration) at 80 °C exhibited optimal performance, achieving the following results: 1. a reduction in wettability contact angles by 80–90° (transitioning from oil-wet to water-wet); 2. a decrease in interfacial tension to 0.64 mN/m; 3. an imbibition recovery rate of 40.14%—5 to 10 percentage points higher than conventional fracturing fluids. NMR data revealed that nanopores (<50 nm) contributed 75.36% of the total recovery, serving as the primary channels for oil mobilization. Relative permeability tests confirmed that AEO-2 reduced residual oil saturation by 6.21–6.38%, significantly improving fluid flow in highly heterogeneous reservoirs. Mechanistic analysis highlighted that the synergy between wettability reversal and interfacial tension reduction was the key driver of recovery enhancement. This study provides a theoretical foundation and practical solutions for the efficient development of tight conglomerate reservoirs. Full article

In the field of enhanced oil recovery in low-permeability reservoirs, the application of nanomaterials has attracted widespread attention. However, conventional nanomaterials exhibit issues such as large particle size and poor dispersion stability. This study selected SiO₂ nanoparticles with a particle size of 10 nm and combined them with 12 types of commonly used oilfield surfactants. After aging at 120 °C for 48 h, using dispersion stability and interfacial tension (IFT) as evaluation criteria, hexadecyltrimethylammonium bromide (CTAB) was ultimately identified as the optimal modifier. The structure and morphology of the SiO₂ particles were characterized in detail using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The system evaluated the dispersion stability of nanofluids before and after modification, as well as the interfacial properties (IFT reduced to the 10⁻¹ mN/m range) and wettability (oil-wet surfaces reversed to strongly water-wet, with contact angles decreasing to 30°) of nanofluids with different modification degrees. Considering economic factors, the modified nano-SiO₂ system with a ratio of 1:0.5 was selected. Microvisualization experiments revealed that the modified nanoscale system achieves residual oil displacement through three mechanisms: emulsification (reducing residual oil droplet size to enhance mobility), wetting reversal (lowering contact angle to weaken adhesion), and structural separation pressure (counteracting capillary forces to destabilize residual oil). Displacement experiments reveal that in rock cores with permeability ranging from 1 to 100 mD, the modified system exhibits a recovery rate trend that initially increases and then decreases. Nevertheless, it consistently enhances recovery rates, maintaining them above 12%, demonstrating strong application potential. Full article

The pH shift generated by mixing alkaline shellac (SH) and acidic chitosan (CS) solutions may drive the formation of nanocomposites with interfacial activity. However, how the solution addition sequence affects their formation and properties remains unclear. In this study, we systematically investigated the influence of addition order on the formation, physicochemical properties, and interfacial activity of SH-CS nanocomposites. The results showed that pH variation during mixing promoted nanocomposite formation, with optimal electrostatic interactions occurring at a final pH near 5.0. The most efficient assembly was achieved at an SH: CS mass ratio of 2:3. FTIR and dissociation experiments confirmed that hydrogen bonding, hydrophobic effects, and electrostatic interactions jointly governed the assembly process. Importantly, the addition sequence determined the nanocomposite structure: adding SH to CS produced core–shell structures, whereas the reverse order yielded co-assembled hybrid nanocomposites. These distinct structures directly impacted interfacial behavior. The co-assembled nanocomposites effectively balanced the inherent hydrophobicity of SH and hydrophilicity of CS, achieving moderate wettability. This balance significantly reduced interfacial tension, thereby enhancing emulsifying performance. Overall, this study underscores the critical role of addition sequence in tailoring the properties of pH-driven SH-CS nanocomposites and highlights their strong potential as high-performance Pickering emulsifiers. Full article