In this review we focus on recent developments in applications of bio‐inspired special wettable surfaces. We highlight surface materials that in recent years have shown to be the most promising in ...their respective fields for use in future applications. The selected topics are divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability and integrated multifunctional surfaces and devices. We will present how the bio‐inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.
Recent developments in applications of bio‐inspired special wettable surfaces are reviewed. The selected topics are roughly divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability, and integrated multifunctional surfaces and devices. We try to present how the bio‐inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The wetting of 3% yttria-stabilized zirconia (YSZ) by Sn–8Zr, Sn–4Zr–4Ti, and Sn–8Ti alloys was studied at 800–900 °C. Both Zr and Ti improve the wettability via the formation of reaction products ...and adsorption. In the systems containing Zr additives in the alloys, ZrO2-x precipitates preferentially, and the wettability is dominated by interface adsorption. An anomalous temperature dependence was found in the final wettability of these systems owing to the decrease in adsorption with an increase in the temperature. The spreading dynamics are controlled by the dissolution of Zr, followed by the formation of a wetting ridge. The wettability of the Sn–8Ti/YSZ system is dominated by the precipitation of reaction products (Ti2O3 and Ti11.31Sn3O10). The reaction kinetics is the limiting factor for spreading in Sn–8Ti/YSZ, and the adsorption at the interface significantly decreased the energy barrier for wetting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Membrane distillation (MD) has been identified as a promising technology to desalinate the hypersaline wastewaters from fracking and other industries. However, conventional hydrophobic MD membranes ...are highly susceptible to fouling and/or wetting by the hydrophobic and/or amphiphilic constituents in these wastewaters of complex compositions. This study systematically investigates the impact of the surface wetting properties on the membrane wetting and/or fouling behaviors in MD. Specifically, we compare the wetting and fouling resistance of three types of membranes of different wetting properties, including hydrophobic and omniphobic membranes as well as composite membranes with a hydrophobic substrate and a superhydrophilic top surface. We challenged the MD membranes with hypersaline feed solutions that contained a relatively high concentration of crude oil with and without added synthetic surfactants, Triton X-100. We found that the composite membranes with superhydrophilic top surface were robustly resistant to oil fouling in the absence of Triton X-100, but were subject to pore wetting in the presence of Triton X-100. On the other hand, the omniphobic membranes were easily fouled by oil-in-water emulsion without Triton X-100, but successfully sustained stable MD performance with Triton X-100 stabilized oil-in-water emulsion as the feed solution. In contrast, the conventional hydrophobic membranes failed readily regardless whether Triton X-100 was present, although via different mechanisms. These findings are corroborated by contact angle measures as well as oil-probe force spectroscopy. This study provides a holistic picture regarding how a hydrophobic membrane fails in MD and how we can leverage membranes with special wettability to prevent membrane failure in MD operations.
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•Hydrophobic MD membranes are subject to oil fouling and surfactant wetting.•Omniphobic MD membranes resist surfactant wetting but not oil fouling.•Composite MD membranes resist surfactant fouling but not oil wetting.•The performance of a membrane strongly depends on the feed composition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Hydrogen is currently assessed as a future clean fuel in a hydrogen economy. However, one key problem with implementing a full‐scale hydrogen economy is hydrogen storage (as hydrogen is highly ...compressible and volatile). One solution for this problem is hydrogen geo‐storage, where compressed hydrogen is injected into geological formations, and the hydrogen can be withdrawn again at any time. However, there is a serious lack of data for realistic geologic conditions, including for hydrogen‐rock wettability, which is proven to determine injectivities, withdrawal rates, storage capacities, and containment security. We thus measured this parameter at various geo‐storage conditions. For a realistic storage scenario in a deep sandstone aquifer, we found that the rock (quartz) was weakly water‐wet or intermediate‐wet. Increasing pressure, temperature, and organic surface concentration increased hydrogen wettability. This study, thus, provides fundamental data and aids in the industrial‐scale implementation of a future hydrogen economy.
Plain Language Summary
Hydrogen is currently assessed as a future clean fuel in a hydrogen economy. However, one key problem with implementing a hydrogen economy is hydrogen storage (as hydrogen is highly compressible and volatile). One solution for this problem is hydrogen geo‐storage, where compressed hydrogen is injected into geological formations; the hydrogen can be withdrawn again at any time. However, there is a serious lack of data from realistic geologic conditions, including hydrogen‐rock wettability, which is a key parameter in this process. We thus, conducted experiments and demonstrate that sandstone is weakly water‐wet to intermediate‐wet. This study, thus, provides fundamental data and aids in the industrial‐scale implementation of a future hydrogen economy.
Key Points
Sandstone reservoirs are weakly water‐wet to intermediate‐wet at expected hydrogen storage depths
Hydrogen wettability increases with pressure and thus depth
Organic molecules on the sandstone surface strongly increase hydrogen wettability
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We review the literature data published on the topic of CO2 wettability of storage and seal rocks. We first introduce the concept of wettability and explain why it is important in the context of ...carbon geo‐sequestration (CGS) projects, and review how it is measured. This is done to raise awareness of this parameter in the CGS community, which, as we show later on in this text, may have a dramatic impact on structural and residual trapping of CO2. These two trapping mechanisms would be severely and negatively affected in case of CO2‐wet storage and/or seal rock. Overall, at the current state of the art, a substantial amount of work has been completed, and we find that:
Sandstone and limestone, plus pure minerals such as quartz, calcite, feldspar, and mica are strongly water wet in a CO2‐water system.
Oil‐wet limestone, oil‐wet quartz, or coal is intermediate wet or CO2 wet in a CO2‐water system.
The contact angle alone is insufficient for predicting capillary pressures in reservoir or seal rocks.
The current contact angle data have a large uncertainty.
Solid theoretical understanding on a molecular level of rock‐CO2‐brine interactions is currently limited.
In an ideal scenario, all seal and storage rocks in CGS formations are tested for their CO2 wettability.
Achieving representative subsurface conditions (especially in terms of the rock surface) in the laboratory is of key importance but also very challenging.
Key Points:
CO2 wettability of seal and storage rock: summary of state‐of‐the‐art
CO2 wettability of rocks
Impact on residual and structural trapping capacity
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A comprehensive understanding of the combined effects of surface roughness and wettability on the dynamics of the trapping process is lacking. This can be primarily attributed to the contradictory ...experimental and numerical results regarding the impact of wettability on the capillary trapping efficiency. The discrepancy is presumably caused by the surface roughness of the inner pore‐solid interface. Herein, we present a comparative μ‐CT study of the static fluid‐fluid pattern in porous media with smooth (glass beads) and rough surfaces (natural sands). For the first time, a global optimization method was applied to map the characteristic geometrical and morphological properties of natural sands to 2‐D micromodels that exhibit different degrees of surface roughness. A realistic wetting model that describes the apparent contact angle of the rough surface as a function surface morphology and the intrinsic contact angle was also proposed. The dynamics of the trapping processes were studied via visualization micromodel experiments. Our results revealed that sand and glass beads displayed opposite trends in terms of the contact angle dependence between 5° and 115°. Sand depicted a nonmonotonous functional contact angle dependency, that is, a transition from maximal trapping to no trapping, followed by an increase to medium trapping. In contrast, glass beads showed a sharp transition from no trapping to maximal trapping. Since both porous media exhibit similar morphological properties (similar Minkowski functions: porosity, surface density, mean curvature density, Euler number density), we deduce that this difference in behavior is caused by the difference in surface roughness that allows complete wetting and hence precursor thick‐film flow for natural sands. Experimental results on micromodels verified this hypothesis.
Key Points
Wettability, surface roughness, and pore space structure have an impact on trapping efficiency
Porous media with rough surface, as natural sands and glass‐ceramic micromodels, were studied
Wettability‐controlled crossover from snap‐off to by‐pass trapping and spontaneous precursor thick‐film flow were observed
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Wettability is an important reservoir property that can affect the distribution and migration of geofluids within shale reservoirs, which significantly influences the occurrence state of methane in ...shale pore systems and the selection of fracturing fluids during shale gas exploitation. The wettability characteristics of organic matter (OM)-rich shale are much more complicated than those of conventional reservoir rocks with a relatively homogeneous composition. In addition, the low porosity and extremely low permeability, as well as the strong heterogeneity of shale, complicate the evaluation of shale wettability. As a result, traditional wettability tests (including contact angle measurements and oil/water displacement experiments) are inapplicable for shale samples. Consequently, spontaneous imbibition experiments become a practical and effective way to establish the wettability characteristics of different shales. This paper reviews shale wettability characterization using spontaneous imbibition experiments and discusses the close relationship between shale wettability and pore structure. As reported in the literature, most shale samples can imbibe both water and oil, which indicates the co-existence of water-wet and oil-wet connected pore spaces and the mixed-wet property of shales. However, different shales show a range of oil and water imbibition behaviors, indicating the wettability differences amongst them. This review reveals that the development degrees of water- and oil-wet pores within shale determine its wettability as well as its imbibition behaviors. And four simplified pore network models are proposed for more water-wet, more oil-wet, mixed-wet and intermediate-wet shale samples respectively. This work also shows the pronounced effects of thermal maturity on shale pore structure development and shale wettability characteristics. Consequently, a simplified and empirical wettability evolution model with four stages only considering the effect of thermal maturity is established in this study.
•This paper reviews shale wettability characterization using spontaneous imbibition experiments.•This paper discusses the close relationship between shale wettability and pore structure.•A simplified and empirical wettability evolution model is established in this study.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•The Al surfaces were micro–nano structured by a picosecond laser.•The structured surfaces were pristine superhydrophilic.•They can spontaneously transit to be superhydrophobic after ...exposed in air.•Our results indicated this transition was caused by the adsorption of organic compounds.•The superhydrophilicity can be recovered by low temperature annealing.
Studies regarding the wettability transition of micro- and nano-structured metal surfaces over time are frequently reported, but there seems to be no generally accepted theory that explains this phenomenon. In this paper, we aim to clarify the mechanism underlying the transition of picosecond laser microstructured aluminum surfaces from a superhydrophilic nature to a superhydrophobic one under ambient conditions. The aluminum surface studied exhibited superhydrophilicity immediately after being irradiated by a picosecond laser. However, the contact angles on the surface increased over time, eventually becoming large enough to classify the surface as superhydrophobic. The storage conditions significantly affected this process. When the samples were stored in CO2, O2 and N2 atmospheres, the wettability transition was restrained. However, the transition was accelerated in atmosphere that was rich with organic compounds. Moreover, the superhydrophobic surface could recover their original superhydrophilicity by low temperature annealing. A detailed XPS analysis indicated that this wettability transition process was mainly caused by the adsorption of organic compounds from the surrounding atmosphere onto the oxide surface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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