Receding Water Contact Angles Research Articles

Enhancing fouling resistance and separation performance of polyethersulfone membrane through surface grafting with copolymerized thermo-responsive polymer and copper oxide nanoparticles

Surface modification is a critical aspect for improving the efficiency of membranes and reducing the risk of fouling in applications such as wastewater treatment and oil/water separation. The objective of this study is to minimize membrane fouling and maximize its rejection rate through surface modification. Here, for the first time, we developed a dual-functionalized PES membrane using a two-step process, involving grafting with a thermo-responsive polymer (P(NIPAm-co-AAm)) and subsequent functionalization with copper oxide nanoparticles. The membranes were evaluated for any changes in their chemical composition, structural properties, porosity, surface charge, and wetting characteristics. The hydrophilicity of all the modified membranes increased as indicated by a noticeable reduction in the water contact angle. The modified membranes displayed a change in their receding water contact angle based on changes in water temperature, confirming the thermo-responsive nature of PNIPAm. The receding contact angle for the PES membrane grafted with P(NIPAm-co-AAm) was significantly low (∼13°) below 33 °C but increased to 28° when the temperature exceeded 40 °C, indicating the dependence of the surface wettability of the treated PES membranes on temperature. The dual-functionalized membrane outperformed the pristine PES membrane, with a 13% increase in flux and 26% rise in flux recovery ratio. Additionally, the CuO@PES-g-P(NIPAm-co-AAm) membrane showed significant improvements in contaminant rejection and antifouling ability, with > 98% rejection rate for both oil-water emulsion and bovine serum albumin (BSA). The achieved separation and antifouling properties make the dual-functionalized membrane an excellent candidate for water treatment and demonstrate the efficacy of our simple modification process.

Wetting of Superhydrophobic Polylactic Acid Micropillared Patterns.

Superhydrophobic (SH) polylactic acid (PLA) surfaces were previously produced by various methods and used especially in biomedical applications and oil/water separation processes after 2008. However, the wettability of SH-PLA patterns containing micropillars has not been investigated before. In this study, PLA patterns having regular microstructured pillars with 12 different pillar diameters and pillar-to-pillar distances were prepared by hot pressing pre-flattened PLA sheets onto preformed polydimethylsiloxane (PDMS) soft molds having micro-sized pits. PDMS templates were previously prepared by photolithography using SU-8 molds. Apparent, advancing, and receding water contact angle measurements were carried out on the PLA patterns containing micropillars, and the morphology of the patterns was examined by optical and SEM microscopy. The largest contact angle obtained without the surface modification of the pure PLA pattern was 139°. Then, PLA micropatterns were hydrophobized using three types of silanes via chemical vapor deposition method, and SH-PLA patterns were obtained having θs of up to 167°. It was found that the highest θ values could be obtained when PLA pattern samples were coated with a silane containing a fluorine atom in its chemical structure. Washing and service life stability tests were also performed on the coated pattern samples and all of the silane coatings on the PLA patterns were found to be resistant over a 6 month period.

Development of durable and superhydrophobic nanodiamond coating on aluminum surfaces for improved hygiene of food contact surfaces

Foodborne illness outbreaks caused by bacterial pathogens may take place on a large scale and result in millions of hospitalizations and thousands of deaths every year throughout the world. One key strategy for dealing with this global issue is the design of smart surfaces and coatings which inhibit and reduce bacterial attachment. This can mitigate contamination and cross-contamination during farm-to-table food processing, promoting food safety, and hygiene. Herein, we reported a durable superhydrophobic coating on aluminum surfaces fabricated by sequential deposition of ultrahard nanodiamond, self-assembly of l-3,4-dihydroxyphenylalanine (l-dopamine), and chemical modification with an organoflurosilane. This coating achieved static, advancing, and receding water contact angles of 159.0 ± 2.5°,154.0 ± 2.4°; and 153.7 ± 1.7°, respectively, representing water super-repellency with a low overall root mean square (rms) roughness of 173.5 ± 69.6 nm. In comparison to the bare, unmodified aluminum, the coated aluminum surfaces prevented the attachment of 99.5% of applied Escherichia coli O157:H7 (E.coli O157:H7) and 99.0% of Staphylococcus aureus (S. aureus) cells. In addition, due to the presence of nanodiamond building blocks, the coated surfaces demonstrated a high mechanical resistance against scratching and endured at least 10,000 shearing/rubbing cycles with a nylon surface. Overall, we anticipate that implementation of this coating could improve safety and hygiene of food-contact surfaces that require harsher mechanical operational conditions.

A Different Silica Surface: Radical Oxidation of Poly(methylsilsesquioxane) Thin Films and Particles (Tospearl)

Surfaces that exhibit the reactivity of silica toward surface modification (silanol condensation) were prepared by treating thin films and particles of poly(methylsilsesquioxane) with aqueous potassium persulfate at elevated temperature. Parallel experiments were carried out using a highly cross-linked poly(dimethylsiloxane). Advancing (θA) and receding (θR) water contact angles for all of these oxidized surfaces were θA/θR = ∼10/∼0°, and these low values remain unchanged for months. Reactions of these silica-like surfaces with a range of functional silane reagents indicate that the surface silanol concentration is sufficient to prepare covalently attached monolayers of similar surface density to those prepared using silicon wafers as substrates.

Carbon dioxide wettability of South West Hub sandstone, Western Australia: Implications for carbon geo-storage

CO2-rock wettability is a key factor which determines the fluid dynamics and CO2 geo-storage capacity. However, the full understanding of real reservoir CO2-wettability is yet to be gained. We thus systematically analysed the wettability of CO2/brine/South West Hub sandstones at various pressures (0.1 MPa, 5 MPa, 10 MPa, 15 MPa, and 20 MPa) at 334 K. A new procedure based on organic carbon isotope tracking (δ13Corg) was proposed to eliminate the effect of artificial organic matter introduced by drilling mud penetration. The results indicate that the advancing (θa) and receding (θr) water contact angles for the CO2/brine/South West Hub sandstone system increase with increase in pressure (ranging from 71° to 118° and 66° to 111°). It can thus be suggested that the system is weakly water-wet to intermediate-wet. When the samples were treated with dichloromethane, a slight decline in organic content was observed leading to slight decrease in water contact angles (i.e. TOC decreased from 0.019% to 0.003% for core C, and the corresponding θa and θr decreased from 118° and 111° to 110° and 104°, respectively, at 20 MPa and 334 K). This wettability analysis demonstrates that (a) of the contact angle is very sensitive to the amount of organic matter and therefore care should be taken to remove artificial organic matter from the sample, and that (b) this condition prevails in a real proposed CO2-storage site. This analysis thus has important implications for assessing the feasibility of long-term CO2 storage and enabling large-scale industrial carbon geological storage projects.

Aza‐Michael Addition Chemistry for Tuning the Phase Separation of PDMS/PEG Blend Coatings and Their Anti‐Fouling Potentials

AbstractFree adjustment of micro/nanophase‐separation degrees in coatings is not easily accessible, which is a big handicap in the development of phase‐separation‐related applications. Here, by utilizing the reactivity difference between two phases, a two‐step aza‐Michael addition pre‐crosslinking strategy, demonstrated by acryloxy‐terminated polydimethylsiloxane/polyethylene glycol (PEG) blend coatings, is proposed for the first time to tune microphase separation degrees, and promote compatibility of the biphasic amphiphilic polymer blends. Followed by a systematic study of the two‐step pre‐crosslinking time, surface morphologies of samples with desired phase‐separation degrees are unveiled using optical microscopy, AFM, and XPS. The wettability, and anti‐fouling properties — for example, anti‐protein and anti‐marine bacterial (Shewanella) adhesion — of these coatings are assessed. Less protein adsorption is observed on those surfaces with lower receding water contact angles. Shewanella adhesion is efficiently discouraged by the introduction of PEG segments, but the trend evolved with surface wettability and micro/nanophase structure in a complex way.

Dual-Functional, Superhydrophobic Coatings with Bacterial Anticontact and Antimicrobial Characteristics.

Bacterial pathogens are responsible for millions of cases of illnesses and deaths each year throughout the world. The development of novel surfaces and coatings that effectively inhibit and prevent bacterial attachment, proliferation, and growth is one of the crucial steps for tackling this global challenge. Herein, we report a dual-functional coating for aluminum surfaces that relies on the controlled immobilization of lysozyme enzyme (muramidase) into interstitial spaces of presintered, nanostructured thin film based on ∼200 nm silica nanoparticles and the sequential chemisorption of an organofluorosilane to the available interfacial areas. The mean diameter of the resultant lysozyme microdomains was 3.1 ± 2.5 μm with an average spacing of 8.01 ± 6.8 μm, leading to a surface coverage of 15.32%. The coating had an overall root-mean-square (rms) roughness of 539 ± 137 nm and roughness factor of 1.50 ± 0.1, and demonstrated static, advancing, and receding water contact angles of 159.0 ± 1.0°, 155.4 ± 0.6°, and 154.4 ± 0.6°, respectively. Compared to the planar aluminum, the coated surfaces produced a 6.5 ± 0.1 (>99.99997%) and 4.0 ± 0.1 (>99.99%) log-cycle reductions in bacterial surfaces colonization against Gram-negative Salmonella Typhimurium LT2 and Gram-positive Listeria innocua, respectively. We anticipate that the implementation of such a coating strategy on healthcare environments and surfaces and food-contact surfaces can significantly reduce or eliminate potential risks associated with various contamination and cross-contamination scenarios.

Impact of Air Exposure Time on the Water Contact Angles of Daily Disposable Silicone Hydrogels.

The wettability of silicone hydrogel (SiHy) contact lens (CLs) is crucial for the pre-lens tear film stability throughout the day. Therefore, sessile drop and captive bubble setups were used to study the advancing and receding water contact angles (CA) of four SiHy materials: narafilcon A (TE), senofilcon A (AOD), stenfilcon A (MD), and delefilcon A (DT). TE and AOD have 48% and 38% water content, respectively, and no surface coating. MD (54% water) implements “smart chemistry” with just 4.4% bulk silicone content, while DT has >80% water at its surface. These SiHy were subjected to continuous blink-like air exposure (10 s)/rehydration (1s) cycles for 0, 1, 2, 3, 4, 6, 8, 10, 12, 14, and 16 h. The advancing CA, which measures the rehydration propensity of the CL surface, proved to be the most sensitive parameter to discriminate between the samples. The order of performance for the entire time scale was DT > MD >> AOD ≥ TE. The extended desiccation/rehydration cycling increased the differences between the CA of DT and MD compared to AOD and TE. This suggests that the low Si surface content and the high surface hydration are major determinants of SiHy wettability.

Insight into the dependence of dirt adsorption/desorption on the surface wetting behavior of TiO2–based nanocomposite coatings

TiO2–based nanocomposite coatings were fabricated using two silicon-oxo hybrid binders and further treated with UV-irradiation to acquire coatings with a wide range of static water contact angles (SWCA) (from 5° to 118.6°) and different dynamic surface wetting behaviors. The dirt adsorption and desorption behavior of these coatings were measured after applying modified rice-straw ash and washing with a water-spray. The results were correlated with static surface wettability and dynamic surface wettability values. It was found that the coatings with an SWCA of about 75° displayed the highest dirt adsorption regardless of the type of binder used. Lower SWCA and receding water contact angles (RWCA) allowed for better dirt desorption and hence better dirt pickup resistance. The coatings with RWCA values close to 0° exhibited self-cleaning performance even when the surface was not superhydrophilic. In addition, the amount of dirt removed from the surface of the coatings by dirt desorption tests was evaluated and used as an indicator of the ability of the coating to remove dirt from polluted air. Specific SWCA and low RWCA values seem to be critical to the coating’s ability to remove dirt from the air. In addition, the dependence of the dirt removal ability on the hysteresis of water contact angle (HWCA) was different for the two silicon-oxo hybrid binders.

Superhydrophobic SERS substrates based on silver dendrite-decorated filter paper for trace detection of nitenpyram

In the present work, highly sensitive Raman detection of nitenpyram using superhydrophobic filter paper as substrates is introduced. The process is simple, and efficient. By sequentially coating silver dendrites and Octyltrimethoxysilane (OTMOS) on filter paper, we produced highly active surface-enhanced Raman scattering (SERS) substrates which show advancing and receding water contact angles of θA/θR = 159°/156°. Nitenpyram, a type of pesticides popularly used in agriculture, can be easily detected with the detection limit as low as 1 nM using the superhydrophobic filter paper as SERS substrates, which validates their use in Raman applications.

Water entry and fall of hydrophobic and superhydrophobic Teflon spheres

Hydrophobic and superhydrophobic solid Teflon spheres have been observed while settling in water under the action of gravity, starting from different initial conditions, and have been followed until the steady-state is reached. The superhydrophobic sphere features a nano/microtextured surface and advancing and receding water contact angles equal to, respectively, and . When impacting water from air, both spheres can entrap a conspicuous amount of air deriving from the sealing of a macro-sized air cavity formed upon impact (air cavity trapping) and standing at the rear part of the settling sphere. It is shown that this air amount, like a spindle, reduces the force coefficient exerted on the sphere, basically acting on the pressure drag. However, the air cavity trapping occurs above a critical impact velocity which for the superhydrophobic spheres is significantly lower than that pertaining to the hydrophobic one; thus a certain range of impact velocities exists at which the superhydrophobic sphere experiences a lower pressure drag and a higher mean velocity. As soon as the air cavity vanishes, the dynamics of the superhydrophobic sphere becomes indistinguishable from that of the hydrophobic one, in spite of the persistence of air within the surface micro-texture.

Reversible switching of wetting properties and erasable patterning of polymer surfaces using plasma oxidation and thermal treatment

Polymer surfaces reversibly switchable from superhydrophobic to superhydrophilic by exposure to oxygen plasma and subsequent thermal treatment are demonstrated. Two inherently different polymers, hydrophobic segmented polydimethylsiloxane-urea copolymer (TPSC) and hydrophilic poly(methyl methacrylate) (PMMA) are modified with fumed silica nanoparticles to prepare superhydrophobic surfaces with roughness on nanometer to micrometer scale. Smooth TPSC and PMMA surfaces are also used as control samples. Regardless of their chemical structure and surface topography, all surfaces display completely reversible wetting behavior changing from hydrophobic to hydrophilic and back for many cycles upon plasma oxidation followed by thermal annealing. Influence of plasma power, plasma exposure time, annealing temperature and annealing time on the wetting behavior of polymeric surfaces are investigated. Surface compositions, textures and topographies are characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and white light interferometry (WLI), before and after oxidation and thermal annealing. Wetting properties of the surfaces are determined by measuring their static, advancing and receding water contact angle. We conclude that the chemical structure and surface topography of the polymers play a relatively minor role in reversible wetting behavior, where the essential factors are surface oxidation and migration of polymer molecules to the surface upon thermal annealing. Reconfigurable water channels on polymer surfaces are produced by plasma treatment using a mask and thermal annealing cycles. Such patterned reconfigurable hydrophilic regions can find use in surface microfluidics and optofluidics applications.

Receding Contact Line Motion on Nanopatterned and Micropatterned Polymer Surfaces.

Surface properties such as topography and chemistry affect the motion of the three-phase contact line (solid/liquid/air), which in turn affects the contact angle of a liquid moving on a solid surface. In this work, the motion of the receding water contact line was studied on chemically and topographically patterned surfaces obtained from the dewetting of thin polymer films. The patterned surfaces consisted of hydrophilic poly(4-vinylpyridine) (P4VP) bumps, which were either microsized and sparse or nanosized and dense, on top of a hydrophobic polystyrene (PS) background layer. These patterns are designed for atmospheric water capture, for which the easy roll off of water droplets is crucial to their efficient performance. The dynamic receding water contact angle and contact line height of the patterned surfaces were measured by vertically withdrawing the surfaces from a water bath and compared to those of a flat P4VP substrate. For both the micropatterned and nanopatterned surfaces, the height of the dynamic contact lines normalized by the capillary length was characterized by the equilibrium limit that was predicted from static states. The nanopatterned surface had a faster increase in the normalized height as the capillary number increased. The dynamic receding contact angles on all surfaces studied decreased with increasing withdrawing velocity. Surprisingly, even for these patterned surfaces with high hysteresis, the dynamic receding contact angle followed the Cox-Voinov relation at capillary numbers of between 1 × 10-5 and 5 × 10-5.

Stabilizing the Wettability of Initiated Chemical Vapor Deposited (iCVD) Polydivinylbenzene Thin Films by Thermal Annealing

Maintaining stable surface properties, such as wetting, remains a challenge for many applications of functional coatings. Here, this paper reports a study on the stability of the surface properties of polydivinylbenzene (PDVB). The PDVB thin films are synthesized via initiated chemical vapor deposition (iCVD). The decrease of receding water contact angles and increase of contact angle hysteresis of iCVD PDVB over time are found to be related with surface oxidation during air exposure. Fourier transform infrared and X‐ray photoelectron spectroscopy reveal the generation carbonyl and epoxy groups and the consumption of pendant vinyl groups in the oxidation process. A modified first‐order kinetic model describes the dynamic process, and the apparent reaction rate constant for the oxidation of iCVD PDVB is 0.0238–0.0294 h−1. In order to inhibit the oxidation and stabilize the wettability of iCVD PDVB, an in situ thermal annealing process is developed. This thermal treatment is effective in improving the cross‐linking degree of iCVD PDVB, slowing down the rate of oxidation, and therefore significantly enhancing the long‐term wettability. The advancing and receding contact angles of annealed iCVD PDVB are stable even after exposure to air for two months. The reported thermal annealing approach also improves the mechanical properties of iCVD PDVB.

CO2 storage in carbonates: Wettability of calcite

Limestone reservoirs are considered as potential candidates for CO2 geo-sequestration. In order to predict structural and residual trapping capacities of CO2 and containment security in carbonates, the wettability of the CO2/brine/rock systems plays a vital role. Calcite is the main component in limestone and thus commonly used to characterize carbonate wettability using direct contact angle measurements. Previously, several studies determined wettability of calcite/CO2/brine systems, but the data clearly lacks in terms of (a) wettability characterization for a wide range of operating conditions, and (b) published data reports contradicting results with measured wettability ranging from strongly water-wet to weakly CO2-wet. Thus, to reduce the uncertainty in the reported measurements, we conducted an experimental study to measure advancing and receding water contact angles for calcite/CO2/brine systems as a function of pressure (0.1–20MPa), temperature (308–343K) and salinity (0wt% NaCl – 20wt% NaCl). The results indicate that calcite is strongly water-wet at ambient conditions and with the increase in pressure the surface gradually loses its water-wetness. At high pressure storage conditions (20MPa and 308K), calcite surface turned weakly CO2-wet implying that an upwards directed suction force will be created and consequently leakage may occur. Moreover, with the increase in temperature contact angle decreased implying that carbonates turn more water-wet at higher temperatures. Furthermore, contact angle increased with salinity. By comparing our results with published data, we point out that apart from pressure, temperature and salinity, the surface cleaning methods and surface roughness and nature of the sample itself can be possible sources of ambiguity in literature data. We conclude that high temperature and low salinity carbonate formations with lower injection pressures are more suitable for safe CO2 storage.

Wettability alteration of oil-wet limestone using surfactant-nanoparticle formulation

Wettability remains a prime factor that controls fluid displacement at pore-scale with substantial impact on multi-phase flow in the subsurface. As the rock surface becomes hydrophobic, any oleic phase present is tightly stored in the rock matrix and produced (hydrocarbon recovery) or cleaned up (soil-decontamination) by standard waterflooding methods. Although surface active agents such as surfactants have been used for several decades for changing the wetting states of such rocks, an aspect that has been barely premeditated is the simultaneous blends of surfactants and nanoparticles. This study thus, systematically reports the behaviour of surfactants augmented nanoparticles on wettability alteration. Contact angle, spontaneous imbibition, and mechanistic approaches were adopted to assess the technical feasibility of the newly formulated wetting agents, tested over wide-ranging conditions to ascertain efficient wetting propensities. The contact angle measurement is in good agreement with the morphological and topographical studies and spontaneous imbibition. The wetting trends for the formulated systems indicate advancing and receding water contact angle decreased with increase in nanoparticle concentration and temperature, and the spontaneous water imbibition test also showed faster water-imbibing tendencies for nanoparticle-surfactant exposed cores. Thus, the new formulated nanoparticle-surfactant systems were considered suitable for enhancing oil recovery and soil-decontamination, particularly in fractured hydrophobic reservoirs.

Enhancement of Surface Wettability by Incorporating Polar Initiator Fragments at Chain Ends of Low-Molecular-Weight Polymers.

Simple methods for enhancing hydrophilicity of hydrocarbon polymers are of broad scientific and technological interest. Polystyrene was synthesized via free radical polymerization with initiator fragments incorporated at chain ends. Compared with high molecular weight polystyrene or chains with nonpolar ends, the dynamic receding water contact angle is reduced by as much as ∼30° in ∼4 kg/mol polystyrene with -COOH and nitrile chain ends. This remarkable enhancement results in surface hydrophilicity that is higher than that of poly(methyl methacrylate). This effective methodology incorporating polar moieties at chain ends of nonpolar polymers can be adapted to existing formulations for enhanced surface properties.

Filamentary superhydrophobic Teflon surfaces: Moderate apparent contact angle but superior air-retaining properties

HypothesisMicro-scale textured Teflon surfaces, resulting from plasma etching modification, show extremely high water contact angle values and fairly good resistance to water penetration when hit by water drops at medium-high speed. This behavior is more pronounced when these surfaces present denser and smaller micrometric reliefs. Tailoring the top of these reliefs with a structure which further stabilizes the air may further increase resistance to wetting (water penetration) under static and dynamic conditions. ExperimentsConditions of the oxygen fed plasma were tuned in order to explore the possibility of obtaining differently topped structures on the surface of the polymer. Scanning Electron Microscopy (SEM) was used to explore topography and X-ray Photoelectron Spectroscopy (XPS) to assess chemical similarity of the modified surfaces. Beside the usual advancing and receding water contact angle (WCA) measurements, surfaces were subjected to high speed impacting drops and immersion in water. FindingsAt milder, i.e. shorter time and lower input power, plasma conditions formation of peculiar filaments is observed on the top of the sculpted reliefs. Filamentary topped surfaces result in a lower WCA than the spherical ones, appearing in this sense less superhydrophobic. However, these surfaces give rise to the formation of a more pronounced air layer when placed underwater. Further, when hit by water drops falling at medium/high speed, they show a higher resistance to water penetration and a sensitively lower surface-liquid contact time. The contact time is as low as previously observed only on heated solids. This behavior may be ascribed to the cavities formed beneath the filaments which, similarly with the salvinia leaf structures, require a surplus of pressure to be filled by water. Also, it suggests a different concept of superhydrophobicity, which cannot be expected on the basis of the conventional water contact angle characterization.

Simple processes for the preparation of superhydrophobic polymer surfaces

Abstract Two simple processes; (i) spin-coating, and (ii) doctor blade coating of silica/polymer dispersions are described for the preparation of superhydrophobic polymer surfaces. To demonstrate the versatility and broad applicability of the processes, polymeric surfaces modified included a thermoplastic resin, polystyrene (PS) and a thermoset, crosslinked epoxy resin (ER). Micro/nano hierarchical nature of the surface topographies obtained were demonstrated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and white light interferometry (WLI) studies. Roughness factor (r) and average surface roughness (Ra) values, which are critical in obtaining superhydrophobic surfaces were determined for each polymeric system. It was clearly demonstrated that increased (r) and (Ra) values resulted in superhydrophobic behavior with very high static, advancing and receding water contact angles, well above 150° and contact angle hysteresis values of less than 10°. Incorporation of small amounts (1.0% by weight) of a silicone copolymer or a perfluoroether glycol oligomer reduced the contact angle hysteresis in the epoxy resin system well below 10° and produced truly superhydrophobic surfaces.

CO2-wettability of low to high rank coal seams: Implications for carbon sequestration and enhanced methane recovery

Coal seams offer tremendous potential for carbon geo-sequestration with the dual benefit of enhanced methane recovery. In this context, it is essential to characterize the wettability of the coal–CO2–water system as it significantly impacts CO2 storage capacity and methane recovery efficiency. Technically, wettability is influenced by reservoir pressure, coal seam temperature, water salinity and coal rank. Thus a comprehensive investigation of the impact of the aforementioned parameters on CO2-wettability is crucial in terms of storage site selection and predicting the injectivity behaviour and associated fluid dynamics. To accomplish this, we measured advancing and receding water contact angles using the pendent drop tilted plate technique for coals of low, medium and high ranks as a function of pressure, temperature and salinity and systematically investigated the associated trends. We found that high rank coals are strongly CO2-wet, medium rank coals are weakly CO2-wet, and low rank coals are intermediate-wet at typical storage conditions. Further, we found that CO2-wettability of coal increased with pressure and salinity and decreased with temperature irrespective of coal rank. We conclude that at a given reservoir pressure, high rank coal seams existing at low temperature are potentially more efficient with respect to CO2-storage and enhanced methane recovery due to increased CO2-wettability and thus increased adsorption trapping.