Advancing Water Contact Angle Research Articles

Aromatic self-assembled monolayers with pentafluoro-λ6-sulfanyl (−SF5) termination: Molecular organization and charge transport properties

A series of molecules with oligophenylene backbone, thiolate anchoring group, and pentafluoro-λ6-sulfanyl (−SF5) tail group was synthesized and used as precursors to form self-assembled monolayers (SAMs) on Au(111) substrates. The resulting SAMs feature dense molecular packing, upright molecular orientation, and chemically homogeneous SAM-ambient interface, comprised entirely of the −SF5 moieties. These SAMs exhibit exceptional wetting and electrostatic properties, showing advancing water contact angles up to 103° and work function values up to 5.96 eV—probably the highest values reported for any aromatic monolayers on gold. They also feature a comparably low value of the tunnelling decay coefficient (0.38 ± 0.07 Å−1), typical of oligophenylene backbone, which is not affected by the introduction of the −SF5 group. The latter also hardly affects the current densities at a specific bias compared to analogous monolayers with other electronegative tail groups. The superior electrostatic and good charge transport properties of the designed, SF5-terminated SAMs make them potentially useful for interface engineering in organic electronics and photovoltaics.

Barrier behaviour of partially N-acetylated chitosan layers in aqueous media

Chitosan coatings of 353 ± 12 nm thickness were prepared on glass and zinc substrates by dip-coating method to study their barrier-behaviour. The coatings were chemically modified to increase their degree of acetylation (DA) from ca. 44 % up to ca. 98 % resulting a quasi-chitin coating. The effect of the acetylation reaction was studied by infrared spectroscopy, and the structural changes of the native and acetylated coatings were investigated by UV–Vis spectrophotometry and X-ray diffraction. The surface properties of the coated samples were characterized by wettability measurements – advancing water contact angle decreased from ca. 80° (native) to ca. 43° (fully acetylated) – and microscopic (SEM, AFM) studies. The barrier behaviour of the chitosan layer depending on the DA was evaluated by electrochemical impedance spectroscopy studies and with a special mesoporous silica – chitosan bilayer system by measuring the amount of dye (Rhodamine 6G) accumulated in the silica through the chitosan coating during an impregnation step. These methods showed significant decrease in the barrier-effect of the coatings with increasing DA (accumulation of approximately six times more dye and a reduction of charge transfer resistance by an order of magnitude), due to the structural and ionization changes in the coatings.

Sprayable, durable, and superhydrophobic coating of silica particle brushes based on octadecyl bonding and polymer grafting via surface-initiated ATRP for efficient oil/water separation

A facile approach to prepare sprayable, durable, and superhydrophobic coating was designed for highly efficient oil/water separation and oil absorption based on silica particle brushes via surface-initiated (SI-ATRP). Octadecyl group bonded and poly(styrene-co-acrylonitrile) (PSAN) grafted silica nanoparticles (NPs) (C18-SiO2-g-PSAN) were prepared by sequential initiator tethering and SI-ATRP processes, which were directly applied as surface superhydrophobic coating for various porous substrates. The results confirmed that octadecyl group and PSAN were successfully bonded on silica NPs. After facile spraying of C18-SiO2-g-PSAN, the coated porous substrates displayed superhydrophobicity with an advancing water contact angle (WCA) exceeding 150° due to the synergistic effects of low surface energy compositions contributed by the tethered octadecyl group and the rough structure induced by silica NPs and porous substrates. Superhydrophobic porous substrates exhibited high oil/water separation efficiency achieving 98.8% by using cotton fabric as substrate and remarkable oil absorption capacity of 39.2 g/g for isooctane using polyurethane sponge as substrate. The recyclability and strong durability against mechanical abrasion enable them to be promising candidates for industrial oil-contaminated water treatments and marine spilt oil cleanup in harsh environments.

Spontaneous Imbibition Dynamics of Liquids in Partially-Wet Nanoporous Media: Experiment and Theory

Nanoscale spontaneous imbibition is a common process in nanoporous soil and unconventional reservoirs. Due to the complexity of these natural nanoporous media, the relevant spontaneous imbibition dynamics are still unclear. Thus, this paper studies spontaneous imbibition dynamics of liquids into a nanoporous carbon scaffold (NCS, with controllable wettability and pore geometry). The effects of evaporation and surfactant on spontaneous imbibition are also examined. For low-volatility liquids, a linear relationship between spontaneous imbibition height ( $$H$$ ) and square root of time ( $$\sqrt{t}$$ ) is observed. A modified Lucas–Washburn (L–W) equation is developed to describe the corresponding dynamics and to predict the NCS effective radius and the advancing water contact angle. A dimensionless time function is presented, which includes the properties of solid and liquid and their interactions, and can be used for upscaling spontaneous imbibition data in nanoporous media from laboratory to reservoir scales. Both a larger NCS pore diameter and pore throat diameter cause faster imbibition. The addition of surfactant into an aqueous solution increases the imbibition rate, although this influence is suppressed with pore size decrease. In contrast, for high-volatility liquids, a significant deviation from the linear relationship between $$H$$ and $$\sqrt{t}$$ is found at late times. The modified L–W equation is further developed to include evaporation effect. This study thus provides fundamental understanding of spontaneous imbibition dynamics at nanoscales. The developed theoretical models are expected to be applicable to important problems such as water infiltration into soil, fracturing fluid loss in unconventional reservoirs, and electrolyte migration in electrochemical devices.

Metal-Organic Framework (MOF) Derived Recyclable, Superhydrophobic Composite of Cotton Fabrics for the Facile Removal of Oil Spills.

Marine oil spill cleanup is one of the major challenges in recent years due to its detrimental effect on our ecosystem. Hence, the development of new superhydrophobic oil absorbent materials is in high demand. The third-generation porous materials, namely metal-organic frameworks (MOFs), have drawn great attention due to their fascinating properties. In this work, a superhydrophobic MOF with UiO-66 (SH-UiO-66) topology was synthesized strategically with a new fluorinated dicarboxylate linker to absorb oil selectively from water. The fully characterized superhydrophobic MOF showed extreme water repellency with an advancing water contact angle (WCA) of 160° with a contact angle hysteresis (CAH) of 8°. The newly synthesized porous MOF (SBET = 873 m2 g-1) material with high WCA found its promising application in oil/water separation. The superhydrophobic SH-UiO-66 MOF was further used for the in-situ coating on naturally abundant cotton fiber to make a superhydrophobic MOF@cotton composite material. The MOF-coated cotton fiber composite (SH-UiO-66@CFs) showed water repellency with a WCA of 163° and a low CAH of 4°. The flexible superhydrophobic SH-UiO-66@CFs showed an oil absorption capacity more than 2500 wt % for both heavy and light oils at room temperature. The superoleophilicity of SH-UiO-66@CFs was further exploited to separate light floating oil as well as sedimentary heavy oil from water. SH-UiO-66@CFs material can also separate oil from the oil/water mixture by gravity-directed active filtration. Hence, the newly developed MOF-based composite material has high potential as an oil absorbent material for marine oil spill cleanup.

Surface hydrophilization of highly porous poly(ether imide) microparticles by covalent attachment of poly(vinyl pyrrolidone)

The realization of a permanent surface hydrophilization for highly porous microparticles designed for removing uremic toxins from the blood of renal failure patients, without altering their complex pore structure, represents a challenging task.Here we report on the hydrophilic surface functionalization of porous poly (ether imide) (PEI) microparticles, having a mean diameter of 226 ± 14 μm, a porosity of around 84 ± 2% with a mean pore diameter of 230 ± 40 nm, by covalent attachment of amino-terminated poly (vinyl pyrrolidone) (PVP–NH2) with a number average molecular weight of Mn = 5400 g mol−1. X-ray photoelectron spectroscopy confirmed a successful surface modification by a change in the surface chemistry, in particular the N/C ratio. The PEI-PVP particles exhibited an advancing water contact angle of θadv = 75° ± 5° as determined in environmental scanning electron microscopy microwetting experiments. The obtained results from mercury intrusion porosimetry and nitrogen adsorption experiments documented the preservation of the porous structure of the particles in the cause of the modification, which could be visualized by electron microscopy. The presented approach enables a covalent hydrophilization of porous particles while preserving their nanoporous morphology.

Highly Flexible Superhydrophobic Poly(Urethane Acrylate) Film for Applications Requiring High Optical Transparency

AbstractThe present work elucidates the successful attempts toward the development of a highly transparent, flexible, and superhydrophobic (HTFS) film. The HTFS film is obtained by introducing graphene oxide (GO) into micropillar‐patterned poly(urethane acrylate) (PUA), followed by siloxane functionalization via chemical vapor deposition. The fabricated SPG2 film (siloxane‐functionalized PUA incorporated with 0.1 wt% of GO) exhibits a water advancing contact angle, water receding contact angle, and sliding angle of 155.5 ± 0.3°, 143.4 ± 0.6°, and 9 ± 0.4°, respectively. The SPG2 film also exhibits an optical transmittance of ≈84% at 550 nm. Mechanical wearable tests demonstrate no significant degradation in the self‐cleaning properties and optical transparency. The fabricated HTFS film (SPG2) is used as a protective layer for a solar module. This solar module shows improved power conversion efficiency (PCE) compared to that of a bare solar module owing to the high optical transparency and light‐trapping effect of the fabricated film that reduce the light reflectance. Furthermore, the SPG2‐protected solar cell demonstrates superior PCE under different surface contamination conditions comparing to other cells. The fabricated micropatterned SPG2 film can be used for various outdoor applications that require high optical transparency, flexibility, and superior self‐cleaning performance.

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.

The Effect of Poly(ethylene glycol) (PEG) Length on the Wettability and Surface Chemistry of PEG-Fluoroalkyl-Modified Polystyrene Diblock Copolymers and Their Two-Layer Films with Elastomer Matrix.

Diblock copolymers composed of a polystyrene first block and a PEG-fluoroalkyl chain-modified polystyrene second block were synthesized by controlled atom transfer radical polymerization (ATRP), starting from the same polystyrene macroinitiator. The wettability of the polymer film surfaces was investigated by measurements of static and dynamic contact angles. An increase in advancing water contact angle was evident for all the films after immersion in water for short times (10 and 1000 s), consistent with an unusual contraphilic switch of the PEG-fluoroalkyl side chains. Such a contraphilic response also accounted for the retained wettability of the polymer films upon prolonged contact with water, without an anticipated increase in the hydrophilic character. The copolymers were then used as surface-active modifiers of elastomer poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS)-based two-layer films. The elastomeric behavior of the films was varied by using SEBS matrices with different amounts of polystyrene. Whereas the mechanical properties strictly resembled those of the nature of the SEBS matrix, the surface properties were imposed by the additive. The contraphilic switch of the PEG-fluoroalkyl side chains resulted in an exceptionally high enrichment in fluorine of the film surface after immersion in water for seven days.

Zwitter‐wettable acrylic polymeric coating on glasses for anti‐fog applications

AbstractAnti‐fog coatings have received significant attention because of their versatile applications to reduce light scattering during high humid conditions. Primarily, hydrophilic/superhydrophilic coatings are applied upon the transparent substrate to improve visibility at high humidity. The high solubility of the hydrophilic/superhydrophilic coatings in water is the main drawback for their long‐term operational durability. We will report for the first time the development of functional copolymers which produces water insoluble hydrophilic coating upon application on glass surfaces. Such surfaces are commonly known as “Zwitter‐Wettable” surfaces that have been developed from entirely polymeric substances using methacrylic and acrylic monomers. A series of random copolymers were synthesized using free radical polymerization of the common and commercially available monomers which were subsequently characterized using various analytical techniques, such as, GPC, 1H‐NMR, and FTIR. These newly designed copolymers contained both the hydrophobic parts made up of methyl and 2‐ethylhexyl groups, which provide good stability under high humid conditions and hydroxyl and carboxylic acid groups which will provide the required hydrophilicity or water absorption capacity. These polymeric coatings on the glass surfaces exhibit water advancing contact angles in the range of 57 ± 3° to 78 ± 3° with excellent anti‐fog property. The anti‐fog property of the polymeric films could be tuned easily by changing the ratio of hydrophobic and hydrophilic monomers.

Surface Modification of Polymeric Fibers to Control the Interactions with Cement-Based Matrices in Fiber-Reinforced Composites

There is evidence that the fiber-matrix interaction in fiber-reinforced cementitious composites is determined by the wettability and roughness of the fibers. Due to the high ionic strength in the hydrated cement, also the surface charge or acid/base behavior of the fibers is assumed to play a role. To create fibers with alkaline and acidic surface functionalities, water-insoluble poly (vinyl alcohol) fibers were permanently modified by adsorption of various polyelectrolytes. X-ray photoelectron spectroscopy, zeta potential, and contact angle measurements revealed acidic, alkaline or amphoteric fiber surfaces with advancing water contact angles between 34° and 58°. In a first step to study the interaction with cementitious materials, the interaction of these fibers with pore solution (the liquid phase of hydrated cement) and the adsorption of calcium ions on the fiber surface were investigated. The work will be continued by studying the fiber-matrix interaction in cementitious matrices and its influence on the composite strength.

Influence of immersion time and cationic latex nanoparticles concentration on flotation recovery

ABSTRACTThe influences of different concentrations of Polystyrene/Dodecyltrimethylammonium bromide latex nanoparticles and immersion times of mineral surfaces on flotation recovery have been investigated. Advancing water contact angle (θa) on the glass slides surfaces measured after conditioning them in different concentrations of diluted latex (0.028, 0.28, 0.56 g/L) at different immersion times (1, 10, 20, 30 min). Under these conditions, θa was changed between 29 and 105 degrees. The results showed that the concentrations of diluted latex as well as immersion time have important roles on the hydrophobic property of surfaces that covered with cationic latex nanoparticles.

Surface Modification of Polystyrene with O Atoms Produced Downstream from an Ar/O2 Microwave Plasma

Because discarded polystyrene (PS) is little affected by degrading agents, PS was treated with a remote microwave (MW) plasma discharge of an Ar/O2 mixture in the absence of radiation to increase wettability and introduce functional groups which make the waste more liable to degradation and useful for technological applications. X-ray photoelectron spectroscopy (XPS) detected decreases in the aromatic sp2 and aliphatic sp3 carbons with treatment and, initially, increases in C–O and carbonyl groups, present in the formation of ethers, epoxides, alcohols, ketones and aldehydes. At longer treatment times, ester, O–C=O; carbonate-like, O–(C=O)–O; and anhydride, O=C–O–C=O; moieties are observed with an overall oxygen saturation level of 23.6 ± 0.9 at% O. Atomic Force Microscopy (AFM) measurements detected little change in surface roughness with treatment time. Advancing water contact angle decreased by ca. 50% compared to pristine PS indicating an increase in hydrophilicity because of oxidation. Washing the treated samples in deionized water decreased the oxygen concentrations at the saturation treatment times down to 18.6 ± 1 at% O due to the washing away of a weak boundary layer.

The Synthesis and Surface Properties of Newly Eco-Resin Based Coconut Oil for Superhydrophobic Coating

The paper presents the synthesis of newly eco-resin based on coconut oil for superhydrophobic coating. Superhydrophobicity of the coating provide a self-cleaning or water-repellent characteristic that prevents peeling, thereby extend the life expectancy of the coating. The use of newly synthesized eco-resin offer a sustainable, eco-friendly and cost effective source of nature. The synthesis and formulation of different percentages of coconut oil which is 20, 40, 60 and 80 weight by weight percentage (wt/wt%) consists of three phases to form superhydrophobic coating. The first phase involved alcoholysis step, condensation step and third phase purification through alcoholysis. The adhesion test (ASTM D3359-03) results was obtained the highest classification grading of 5B for coating at 80% (wt/wt) of coconut oil with 9 layer whereas the rate of adhesion is 9.87% of the area affected. It is shows that the small flakes of coating are detached at intersections. Scratch resistance test was evaluated in terms of pencil hardness grade, which is increased from grade HB to 6H and there is minor scratch occurs for 9 layer coating. The water droplet test was demonstrated that the advancing water contact angle up to 60% of coconut oil at 169.22o with the smooth surface roughness at 0.2448 μm.

Functionalisation of Ti6Al4V and hydroxyapatite surfaces with combined peptides based on KKLPDA and EEEEEEEE peptides

Surface modifications are usually performed on titanium alloys to improve osteo-integration and surface bioactivity. Modifications such as alkaline and acid etching, or coating with bioactive materials such as hydroxyapatite, have previously been demonstrated. The aim of this work is to develop a peptide with combined titanium oxide and hydroxyapatite binders in order to achieve a biomimetic hydroxyapatite coating on titanium surfaces. The technology would also be applicable for the functionalisation of titanium and hydroxyapatite surfaces for selective protein adsorption, conjugation of antimicrobial peptides, and adsorption of specialised drugs for drug delivery. In this work, functionalisation of Ti6Al4V and hydroxyapatite surfaces was achieved using combined titanium-hydroxyapatite (Ti-Hap) peptides based on titanium peptide binder (KKLPDA) and hydroxyapatite peptide binder (EEEEEEEE). Homogeneous peptide coatings on Ti6Al4V surfaces were obtained after surface chemical treatments with a 30wt% aqueous solution of H2O2 for 24 and 48h. The treated titanium surfaces presented an average roughness of Sa=197nm (24h) and Sa=128nm (48h); an untreated mirror polished sample exhibited an Sa of 13nm. The advancing water contact angle of the titanium oxide layer after 1h of exposure to 30wt% aqueous solution of H2O2 was around 65°, decreasing gradually with time until it reached 35° after a 48h exposure, suggesting that the surface hydrophilicity increased over etching time. The presence of a lysine (L) amino acid in the sequence of the titanium binder resulted in fluorescence intensity roughly 16% higher compared with the arginine (R) amino acid analogue and therefore the lysine containing titanium peptide binder was used in this work. The Ti-Hap peptide KKLPDAEEEEEEEE (Ti-Hap1) was not adsorbed by the treated Ti6Al4V surfaces and therefore was modified. The modifications involved the inclusion of a glycine spacer between the binding terminals (Ti-Hap2) and the addition of a second titanium binder (KKLPDA) (Ti-Hap3 and Ti-Hap4). The combined Ti-Hap peptide which exhibited the strongest intensity after the titanium surface dip coating was KKLPDAKKLPDAEEEEEEEE (Ti-HAp4). On the other hand, hydroxyapatite surfaces, exhibiting an average roughness of Sa=1.42μm, showed a higher fluorescence for peptides with a higher negative net charge.

UV-Curable Contact Active Benzophenone Terminated Quaternary Ammonium Antimicrobials for Applications in Polymer Plastics and Related Devices.

A series of UV active benzophenone ([C6H5COC6H4-O-(CH2)n-N+Me2R][X-]; 4, R = C12H25, n = 3, X- = Br-; 5a-c, R = C18H37, n = 3, X- = Cl-, Br-, I-; 6a-c, R = C18H37, n = 4, X- = Cl-, Br-, I-; 7a-c, R = C18H37, n = 6, X- = Cl-, Br-, I-) terminated C12 and C18 quaternary ammonium salts (QACs) were prepared by thermal or microwave-driven Menshutkin protocols of the appropriate benzophenone alkyl halide (1a-c, 2a-c, 3a-c) with the corresponding dodecyl- or octadecyl N,N-dimethylamine. All new compounds were characterized by NMR spectroscopy, HRMS spectrometry, and, in one instance (4), by single-crystal X-ray crystallography. Representative C12 and C18 benzophenone QACs were formulated into 1% (w/v) water or water/ethanol-based aerosol spray coatings and then UV-cured onto plastic substrates (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyether ether ketone) with exposure to low to moderate doses of UV (20-30 J cm-2). Confirmation as to the presence of the coatings was detected by advancing water contact angle measurements, which revealed a more hydrophilic surface after coating. Further confirmation was gained by X-ray photoelectron spectroscopy analysis, time of flight secondary ion mass spectrometry, and bromophenol blue staining, all of which showed the presence of the attached quaternary ammonium molecule. Analysis of surfaces treated with the C18 benzophenone 5b by atomic force microscopy and surface profilometry revealed a coating thickness of ∼350 nm. The treated samples along with controls were then evaluated for their antimicrobial efficacy against Gram-positive (Arthrobacter sp., Listeria monocytogenes) and Gram-negative (Pseudomonas aeruginosa) bacteria at a solid/air interface using the large drop inoculum protocol; this technique gave no evidence for cell adhesion after a 3 h time frame. These antimicrobial materials show promise for their use as coatings on plastic biomedical devices with the aim of preventing biofilm formation and preventing the spread of hospital acquired infections.

Robust Fluorine-Free Superhydrophobic Amino-Silicone Oil/SiO2 Modification of Electrospun Polyacrylonitrile Membranes for Waterproof-Breathable Application

Superhydrophobic waterproof-breathable membranes have attracted considerable interest owing to their multifunctional applications in self-cleaning, anti-icing, anticorrosion, outdoor tents, and protective clothing. Despite the researches pertaning to the construction of superhydrophobic functional membranes by nanoparticle finishing have increased drastically, the disconnected particle component is easy to fall off from the membranes under deformation and wear conditions, which has restricted their wide use in practice. Here, robust superhydrophobic microporous membranes were prepared via a facile and environmentally friendly strategy by dip-coating amino-silicone oil (ASO) onto the electrospun polyacrylonitrile (PAN) membranes, followed by SiO2 nanoparticles (SiO2 NPs) blade coating. Compared with hydrophilic PAN membranes, the modified membranes exhibited superhydrophobic surface with an advancing water contact angle up to 156°, after introducing ASO as low surface energy substance and SiO2 NPs as filler to reduce the pore size and construct the multihierarchical rough structure. Varying the concentrations of ASO and SiO2 NPs systematically, the PAN electrospun membranes modified with 1 wt % ASO and 0.1 wt % SiO2 NPs were endowed with good water-resistance (74.3 kPa), relative low thermal conductivity (0.0028 W m-1 K-1), modest vapor permeability (11.4 kg m-2 d-1), and air permeability (20.5 mm s-1). Besides, the inorganic-organic hybrid coating of ASO/SiO2 NPs could maintain its superhydrophobicity even after 40 abrasion cycles. The resulting membranes were found to resist variations on the pH scale from 0 to 12, and retained their water repellent properties when exposed to harsh acidic and alkali conditions. This facile fabrication of durable fluorine-free superhydrophobic membranes simultaneous with good waterproof-breathable performance provides the advantages for potential applications in self-cleaning materials and versatile protective clothing.

The rose petal effect and the role of advancing water contact angles for drop confinement

We studied the role of advancing water contact angles on superhydrophobic surfaces that exhibited strong pinning effects as known in nature from rose petals. Textured surfaces were engineered in silicon by lithographical techniques. The textures were comprised of hexagonal microstructures superimposed with randomly distributed nanospikes and were coated with a hydrophobic fluorocarbon agent. A step in the advancing water contact angle bounding specific areas was obtained by engineering a corresponding topographic step in the hexagonal micro-texture. This enabled a surface texture design confining drops to areas with a lower advancing contact angle.

Exploring the Role of Adsorption and Surface State on the Hydrophobicity of Rare Earth Oxides.

Rare earth oxides (REOs) are attracting attention for use as cost-effective, high-performance dropwise condensers because of their favorable thermal properties and robust nature. However, to engineer a suitable surface for industrial applications, the mechanism governing wetting must be first fully elucidated. Recent studies exploring the water-wetting state of REOs have suggested that these oxides are intrinsically hydrophobic owing to the unique electronic structure of the lanthanide series. These claims have been countered with evidence that they are inherently hydrophilic and that adsorption of contaminants from the environment is responsible for the apparent hydrophobic nature of these surfaces. Here, using X-ray photoelectron spectroscopy and dynamic water contact angle measurements, we provide further evidence to show that REOs are intrinsically hydrophilic, with ceria demonstrating advancing water contact angles of ≈6° in a clean surface state and similar surface energies to two transition metal oxides (≳72 mJ/m2). Using two model volatile species, it is shown that an adsorption mechanism is responsible for the apparent hydrophobic property observed in REOs as well as in transition metal oxides and silica. This is correlated with the screening of the polar surface energy contribution of the underlying oxide with apparent surface energies reduced to <40 mJ/m2 for the case of nonane adsorption. Moreover, we show that the degree of surface hydroxylation plays an important role in the observed contact angle hysteresis with the receding contact angle of ceria increasing from ∼10° to 45° following thermal annealing in an inert atmosphere. Our findings suggest that high atomic number metal oxides capable of strongly adsorbing volatile species may represent a viable paradigm toward realizing robust surface coating for industrial condensers if certain challenges can be overcome.

Vacuum UV photo-oxidation of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation using a microwave (MW) plasma of Ar as the radiation source and the results were compared to treatment with O atoms produced from a remote MW plasma of a gaseous mixture of Ar-O2 in the absence of radiation. X-ray photo-electron spectroscopy (XPS) detected a lower saturation level for the atomic % of O with VUV photo-oxidation (32 at%) than with O atom treatment (34 at% O). The C 1s curve fitting results for both treatment methods show a decrease in aromatic sp2 carbons and an increase in the amount of carbon-oxygen bonding due to the formation of the carbonyl (C=O) and carbonate-like (O-(C=O)-O) moieties for VUV photo-oxidation; and C-O-C, C=O, and O-C=O moieties for O atom treatment, respectively. Advancing water contact angle measurements showed more of an increase in hydrophilicity with the O atom treated samples than VUV photo-oxidation. Atomic Force Microscopy images displayed smoother surfaces after VUV photo-oxidation while O atom treatment resulted in insignificant changes in surface roughness. Rinsing the treated surfaces with ethanol solvent partially decreased the at% O indicating the formation of a weak boundary during treatment.