Sessile Drop Contact Angle Measurements Research Articles

Wettability Behaviour of Metal Surfaces after Sequential Nanosecond and Picosecond Laser Texturing.

This study examines the wettability behaviour of 304 stainless steel (304SS) and Ti-6Al-4V (Ti64) surfaces after sequential nanosecond (ns) and picosecond (ps) laser texturing; in particular, how the multi-scale surface structures created influence the lifecycle of surface hydrophobicity. The effect of different post-process treatments is also examined. Surfaces were analysed using Scanning Electron Microscopy (SEM), a white light interferometer optical profiler, and Energy Dispersive X-ray (EDX) spectroscopy. Wettability was assessed through sessile drop contact angle (CA) measurements, conducted at regular intervals over periods of up to 12 months, while EDX scans monitored elemental chemical changes. The results show that sequential (ns + ps) laser processing produced multi-scale surface texture with laser-induced periodic surface structures (LIPSS). Compared to the ns laser case, the (ns + ps) laser processed surfaces transitioned more rapidly to a hydrophobic state and maintained this property for much longer, especially when the single post-process treatment was ultrasonic cleaning. Some interesting features in CA development over these extended timescales are revealed. For 304SS, hydrophobicity was reached in 1-2 days, with the CA then remaining in the range of 120 to 140° for up to 180 days; whereas the ns laser-processed surfaces took longer to reach hydrophobicity and only maintained the condition for up to 30 days. Similar results were found for the case of Ti64. The findings show that such multi-scale structured metal surfaces can offer relatively stable hydrophobic properties, the lifetime of which can be extended significantly through the appropriate selection of laser process parameters and post-process treatment. The addition of LIPSS appears to help extend the longevity of the hydrophobic property. In seeking to identify other factors influencing wettability, from our EDX results, we observed a significant and steady rate of increase in the carbon content at the surface over the study period.

Hydrophobic fouling-resistant electrospun nanofiber membranes from poly(vinylidene fluoride)/polyampholyte blends.

This study reports the fabrication of non-woven fibrous membranes from electrospinning blended solutions of PVDF with polyampholytes in N,N-dimethylformamide and methanol. Polyampholytes are macromolecules that have both positive and negative charged units in different side groups attached to the backbone. In this study, we used a random polyampholyte amphiphilic copolymer (r-PAC) synthesized by co-polymerizing a hydrophobic monomer in addition to the positive and negative charged monomer units, to reduce the fouling propensity of PVDF electrospun membranes while preserving its inherent hydrophobicity. Blends of PVDF/r-PAC were electrospun across the full range of compositions from 0/100 to 100/0. Scanning electron microscopic analysis showed formation of beaded fibers with average fibril diameters from 0.09-0.18 μm. The variation in the fiber diameters is caused by the change in surface charge density, dynamic viscosity of the solution, and the instability of the Taylor cone. Bead formation was observed in the mats electrospun from less viscous solutions. Wide angle X-ray scattering showed that electrospun fibers of PVDF crystallized into the electro-active β and γ crystal phases, whereas polyampholytes were amorphous. Thermogravimetry showed that the PVDF/r-PAC blends have a multi-step thermal degradation mechanism while PVDF homopolymer showed single-step thermal degradation. Sessile drop contact angle measurements confirmed that fibers possess high hydrophobicity and super-oleophilicity. Adsorptive fouling experiments with a fluorescently labeled protein confirmed that the fiber mats obtained from the PVDF/r-PAC blends resist protein adsorption, exhibiting highly enhanced fouling resistance compared to the fibers obtained from homopolymer PVDF.

Development of substrate free polymer composite for Pb2+ ion sensor

In the present study we focused on utilizing differential pulse voltammetry (DPV) for detecting Pb2+ ions by electrochemical technique. Polyvinyl butyral (PVB) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) based composite system (PVB/PEDOT:PSS/MoS2) (PPM) modified by Molebdenum disulphide (MoS2). Structural characterization of PPM composite was done by x-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, revealing phase transitions and chemical functionalities within the ternary system. E2g and A1g Raman active modes related C α -C β interactions were observed by Raman spectroscopy. Scanning electron microscopy (SEM) forseen uniform filler distribution in homogeneous polymer matrix. Atomic force microscopy (AFM) reveals decreased surface roughness. Sessile drop contact angle measurements were confirmed hydrophilic properties, feasible for sensing applications. Cyclic voltammetry was performed in a 1 M acetate buffer solution, aligned with electrochemical impedance spectroscopy (EIS) results. The sensing capacity of PPM films was examined using differential pulse voltammetry (DPV). Sensor demonstrated effective detection of Pb2+ ions, with a low detection limit (LOD) of 27.77 μM and a linear detection range of 25–60 μM. Developed sensor exhibited excellent repeatability (with relative standard deviation (RSD) 0.6%) and strong selectivity. Sensor electrode performed appriciable trace of Pb2+ ions in drinking water at high concentration.

Soil organic matter facilitates the transport of microplastic by reducing surface hydrophobicity

Groundwater contamination by microplastic (MP) causes increasing concern about the critical factors that determine MP transport mechanisms in the vadose zone. Strong water repellency of native microplastic surfaces and respective attractive hydrophobic interactions with components of the soil matrix limits its mobility. However, adsorption of dissolved organic matter (DOM) onto microplastic surfaces can potentially make them more hydrophilic, enhancing their mobility. Consequently, the main objective of this study was to systematically determine the effects of DOM on both the surface properties and the mobility of polystyrene microplastic (PSP), and to use the extended DLVO theory (XDLVO) to predict PSP transport behavior with natural DOM for the first time. Breakthrough experiments were conducted in columns filled with quartz sand, through which PSP (1 µm) were percolated at either 0 or 5 mg/L dissolved organic carbon (DOC) derived from beech (Fagus sylvatica) litter at ionic strengths ranging from 0.5 to 2.5 mM CaCl2, since the cation background also affects wettability and mobility. Using sessile drop contact angle and zeta potential measurements, XDLVO interaction energy components including Lewis acid-base energies were approximated. Breakthrough curve analysis confirmed that DOM coming from natural sources strongly enhanced the mobility of PSP in the quartz sand matrix, in particular at higher ionic strength. At 2.5 mM CaCl2, the presence of DOM increased PSP breakthrough from 1 % to 60 %. Consequently, in the absence of DOM, laser microscope images showed much more pronounced formation of microplastic clusters on quartz grain surfaces than at co-percolation of PSP with DOM. This behavior could be clearly predicted with the XLDVO approach, which suggests at 0 mg/L DOC a deep primary energy minimum between individual PSP and between PSP and quartz surfaces. In contrast, repulsive hydrophilic interactions between the surfaces were predicted at 5 mg/L DOC. We conclude that even low concentrations of DOM, as usually found in subsoil, can significantly enhance the mobility of microplastic in soils via rendering the surfaces more hydrophilic. This implies potentially serious repercussions for the spread of this contaminant in the environment.

Mechanistic investigation of using optimum saline water in carbonate reservoirs low asphaltenic crude oil with high resin content: A carbonate-coated microfluidic study

Many mature reservoirs around the world have entered the second period of their life and their production rates are going to decline. In addition, after producing from the reservoir at the primary and secondary stages more than 50 percent of hydrocarbons would remain in place. Therefore, it is essential to find a suitable method to increase oil recovery in the tertiary stage. In recent two decades, smart water or low saline water (LSW) flooding has been introduced as a dominant method, especially on wettability alteration from oil-wet to water-wet or neutral wet conditions, which is leading to more oil production. On the contrary, there are an inadequate number of researches on low asphaltenic crude oil with high resin content in water flooding. In this type of crude oil, the role of asphaltene in changing the wettability and reducing the interfacial tension (IFT) is not as great as the other surface active agents of crude oil. Hence, the role of each ion and its synergism with the surface active agents of crude oil may be different from previous studies. The fluid–fluid and rock-fluid interactions between diluted seawater and a low asphaltenic crude oil were investigated by performing different types of experiments, such as pendant drop IFT measurement tests, sessile drop contact angle (CA) measurement experiments, zeta potential analysis, and pH determination. In the next step, the impact of ten different salts on reducing the interfacial tension, and wettability alteration was determined to show the underlying mechanisms of optimum brine based on the same ionic strength (IS). Finally, some microfluidic tests were utilized in a carbonate-coated micromodel to show the confirmation of previous results in porous media visually and determine the fluid–fluid and rock-fluid interactions on the recovery factor (RF). Based on IFT and CA results, the optimum brine was seawater (SW) that could reduce the IFT from 21.13 to 16.21 mN/m and change the CA from 137° to 46° (Δϴ = 91°). Due to the lower asphaltene content in such crude oil, the presence of Na+ with SO42-, and Mg2+ with Cl- plays a significant role in IFT reduction by creating a synergistic effect between these ions with a high fraction of resin. Na2SO4 and MgSO4 reduce the IFT from 21.13 to 6.21 and 8.46 mN/m, respectively due to the existence of the high amount of Mg and SO4 in aqueous solution which has a considerable effect on fluid–fluid interaction. Also, Mg2+ and SO42- can obtain 89° wettability alteration (Δϴ) and provide a water-wet condition (ϴ = 48°) because of the synergistic of the presence of divalent anions and cations through the solution and the presence of high resin content that leads to excellent wettability change. Additionally, Na2SO4 can change the contact angle from 137° to 67° (Δϴ = 70°). Although the greatest impact of single salts on IFT reduction and wettability alteration was obtained by Na2CO3 and NaHCO3 because of saponification and pH elevation; however, the concentration of these salts in SW was negligible. Thus, the main salts for fluid–fluid and rock-fluid interactions in SW/low asphaltenic crude oil/calcite systems were Na2SO4, MgSO4, and MgCl2. Moreover, due to the presence of Na+, Mg2+, and SO42- in SW, the wettability of the pore surface was altered from oil-wet to water-wet during SW flooding in the micromodel. Furthermore, reducing the IFT and changing the wettability lead to decreasing the capillary number and delay in breakthrough (BT) time, which consequently improved the oil recovery from 25.42 % (DIW flooding) to 46.59 %. The findings of this study can help for a better understanding of the effect of low asphaltenic with high resin crude oil and ions on the fluid–fluid and rock-fluid interaction through porous media at static and dynamic conditions in order to increase the final oil recovery.

Effect of oil chemistry on the performance of low-salinity waterflooding in carbonates: An integrated experimental approach

Chemical enhanced oil recovery (cEOR) relies on the interactions between surface-active components (SACs) of the oil-in-place and injected chemicals to induce favorable physico-chemical changes. This study investigates the effect of oil chemistry on the performance of chemically-tuned waterflooding (CTWF) in carbonate rocks. Coreflood experiments were performed at 90°C using four model oils, each containing a single SAC (acetic acid, decanoic acid, stearic acid or quinoline) to evaluate the effect of oil composition on oil recovery. Complementary characterization techniques including thermal gravimetric analysis (TGA), attenuated total reflectance (ATR-FTIR) and zeta potential (ζ) were used to understand the underlying rock-oil-brine interactions that take place during CTWF, including SAC adsorption to the rock surface, strength of adsorption, partitioning into the brine phase, and electrostatic interactions, respectively. Sessile drop contact angle measurements were also performed to quantify the wetting behavior of the different SACs. Results of this study show that oil chemistry plays a significant role in triggering different oil-brine-rock interactions. Characterization of those interactions is crucial to explain the discrepancies in oil recovery observed in the CTWF literature. In this study, differences in the underlying oil-brine-rock interactions translated into significant variation in oil recovery ranging between 8.9 and 43.9 % after one pore volume injected (PVI). ATR-FTIR results showed that in-situ soap generation was detected for oils with longer chain carboxylic acids, whereas no soaps were observed for oils that have acetic acid or quinoline. Combined with sessile-drop contact angle measurements, a relationship is observed between SAC partitioning into the brine phase and water-wetting behavior. Additionally, TGA measurements suggested that long chain carboxylic acids chemisorb to the rock surface, making wettability alteration to a less oil-wetting state during CTWF more challenging, whereas intermediate chain carboxylic acids only physisorb leading to a more pronounced wettability alteration to a less oil-wetting state, ultimately yielding the highest recovery of ∼49.9 %. Finally, TAN was found to be an insufficient oil descriptor, where oils with the same TAN yielded different CTWF effects. Hence, a more robust oil analysis is crucial for more accurate prediction and modeling of CTWF behavior.

Characterizing surface porosity of porous membranes via contact angle measurements

This investigation attempts to establish and verify a novel method for quantifying surface porosity of porous polymeric membranes via contact angle measurements. Herein, we fabricate a series of porous membranes via nonsolvent induced phase separation (NIPS) comprising different concentrations of polyvinylidene fluoride (PVDF) and PVDF-poly (methyl methacrylate) block co-polymer (PVDF-PMMA) with different concentrations of water and isopropyl alcohol (IPA) in the coagulation bath. Both sessile drop and captive bubble contact angle measurements are used to determine contact angles (and porosity) for both dry and wet membranes, respectively. The former method is probably applicable for membrane distillation, aeration and de-aeration where liquid water does not saturate the membrane, whereas the latter may be more indicative of pressure-driven aqueous membrane separations where the membrane is saturated through its cross-section. Image analysis of scanning electron microscope (SEM) images quantified dry membrane surface porosity. We propose a simple analytical model to obtain wet and dry membrane surface porosity from contact angle measurements. Our results suggest that the surface porosity calculated from both wet and dry contact angle data correlates strongly with the surface porosity calculated from SEM values. However, wet contact angles of the membranes with high porosities produce significantly higher porosity values, which also establishes the importance of porous membrane swelling in determining membrane porosity for aqueous membrane separations.

Investigating the role of excipients on the physical stability of directly compressed tablets

Stability studies are an integral part of the drug development process for any drug product. In addition to monitoring chemical degradation, the physical stability of a drug product must also be evaluated to ensure that the drug release and performance is not affected by storage. In this study, directly compressed tablets of 16 different formulations were exposed to an accelerated stability program to quantify changes in tablet breaking force, porosity, contact angle and disintegration time. Tablets were exposed to five different storage conditions from 37∘C/30% relative humidity (RH) to 70∘C/75%RH with testing after 2 and 4 weeks of storage. Each formulation contained two different fillers (47% w/w each), a disintegrant (5% w/w) and magnesium stearate (1% w/w). The results show that tablets stored at high humidity show increases in porosity and decreases in tensile strength, particularly if they contain a highly hygroscopic filler such as microcrystalline cellulose (MCC). For tablets stored at high temperature, the most commonly affected property was the tablet wettability, measured by sessile drop contact angle measurements. These results are considered in combination with the performance-controlling disintegration mechanism (Maclean et al., 2021) to identify the critical properties which influence the performance after storage.

Fabricating Janus membranes via physicochemical selective chemical vapor deposition

AbstractMembranes with asymmetric wettability‐Janus membranes‐have recently received considerable attention for a variety of critical applications. Here, we report on a simple approach to introduce asymmetric wettability into hydrophilic porous domains. Our approach is based on the physicochemical‐selective deposition of polytetrafluoroethylene (PTFE) on hydrophilic polymeric substrates. To achieve selective deposition of PTFE, we inhibit the polymerization reaction within the porous domain. We prefill the substrates with glycerol, containing a known amount of free radical inhibitor, and utilize initiated chemical vapor deposition (iCVD) for the polymerization of PTFE. We show that the glycerol/inhibitor mixture hinders the deposition of PTFE within the membrane pores. As a result, the surface of the substrates remains open and porous. The fabricated Janus membranes show stable wetting‐resistant properties, evaluated through sessile drop contact angle measurements and direct contact membrane distillation (DCMD).

Wettability of Gas Diffusion Electrode Materials for CO2 Reduction

Rapidly decreasing cost of wind and solar electricity coupled with the increasingly urgent need to reduce carbon emissions motivate the decarbonization of the electric power sector and offer exciting opportunities for the electrification of the chemical industry. The development of efficient carbon dioxide (CO2) electroreduction processes, which leverage renewable electrons, would simultaneously curb anthropogenic CO2 emissions and provide sustainable pathways to a range of fuels, chemicals, and plastics. While progress has been made in CO2 electrocatalysis, most materials are evaluated in electrochemical cells that operate at relatively low current density (ca. 1 – 10 mA·cm-2). In contrast, practical electrolyzers must achieve current densities in the range of 0.5 – 1 A·cm-2, typical of existing industrial electrochemical processes (e.g., chlor-akali electrolyzers), which are needed to enable cost-effective scaling, without sacrificing efficiency1. Aqueous-phase CO2 delivery at ambient conditions is hampered by low solubility and diffusivity which, in turn, lead to mass transport limitations that set an upper limit on current density of 10 – 20 mA·cm-2. Gas-phase delivery offers an alternative configuration whereby gaseous CO2 is fed into an electrolysis cell and interfaces with a liquid electrolyte or ion-selective membrane via catalyst-coated gas diffusion electrodes (GDEs), which were originally developed to manage gas, liquid, electron, and heat transport at electrochemical interfaces within polymer electrolyte fuel cells (PEFCs). In this configuration, the high diffusive rates of gaseous CO2 and shorter diffusion lengths enable increased current densities, typically an order of magnitude or larger, over atmospheric liquid-phase cell designs. As such, most emerging gas-fed CO2 electrolyzers employ GDEs based on repurposed PEFC materials, which demonstrate high geometric-area-specific electrochemical activity for a variety of both CO- and hydrocarbon-selective metal catalysts although longevity remains a challenge2. While differential conditions are typical of laboratory scale flow cells, industrial electrolyzers will likely operate near maximum single-pass conversion to reduce the necessity for material recycling and to avoid high separation costs associated with dilute product streams. Achieving high conversion requires either high current densities and/or long residence times which, for gas-to-liquid electrolysis, lead to organic product enrichment (e.g., formic acid, ethanol) and the formation of mixed aqueous-organic electrolytes. Such mixtures are anticipated to interact with the GDEs differently than water, which is the benchmark fluid for the wettability of gas diffusion layer (GDL) materials in the context of PEFC cathodes3. Conventionally, GDL engineering has focused on hydrophobicity/-philicity in order to manage cathode flooding in PEFC operating at high power. However, the addition of organic species to the electrolyte environment for CO2 electrolysis complicates the existing GDL design space because common wet-proofing materials (i.e., PTFE) may not repel aqueous-organic mixtures. In this talk, we will discuss the fundamental interactions of CO2-reduction-associated liquids (e.g., water, formic acid, ethanol)/electrolytes (e.g., carbonates, hydroxides) with a variety of solid materials (e.g., carbon, PTFE, metals). Sessile drop contact angle measurements on flat substrates provide simple, yet clear insights into surface wettability. However, they can also provide misleading information for porous materials where roughness and entrapped gases obscure the apparent contact angle4. For porous materials, we conduct studies involving capillary pressure phenomena (e.g., imbibition, Washburn method) to obtain information about the internal wettability in a format more aligned with GDE operation. While the propensity of pure liquid components to either resist wetting (solid-liquid contact angles > 90°) or readily wick (solid-liquid contact angles < 90°) into porous media may be known, the behavior of mixed organic-aqueous electrolytes is less obvious. Adding organic CO2-reduction-product species to a solution is anticipated to reduce the surface tension and density, while increasing the electrolyte salt concentration is expected to increase the surface tension and the density. The nuanced interplay between these two trends is understood neither in the absence nor in the presence of solid surfaces. To our knowledge, a focused study of such mixed electrolyte-solid interactions in the CO2 electrolysis field has not yet been compiled and may provide useful design principles for future GDE engineering. Funding Acknowledgement We gratefully acknowledge funding support from the US Department of Energy SBIR Program Grant # DE-SC0015173. References (1) Pletcher, D. Electrochemistry Communications 2015, 61, 97–101. https://doi.org/10.1016/j.elecom.2015.10.006. (2) Chen, C.; Khosrowabadi Kotyk, J. F.; Sheehan, S. W. Chem 2018. https://doi.org/10.1016/j.chempr.2018.08.019. (3) Gostick, J. T.; Ioannidis, M. A.; Fowler, M. W.; Pritzker, M. D. Journal of Power Sources 2009, 194 (1), 433–444. https://doi.org/10.1016/j.jpowsour.2009.04.052. (4) Cassie, A. B. D.; Baxter, S. Transactions of the Faraday Society 1944, 40, 546. https://doi.org/10.1039/tf9444000546.

Probing Surface Characteristics of Rare Earth Minerals Using Contact Angle Measurements, Atomic Force Microscopy, and Inverse Gas Chromatography.

Rare earth minerals (REMs) such as bastnaesite, monazite, and xenotime are of considerable significance since they are the main commercial sources for rare earth elements (REEs) with cutting-edge applications. Fundamental understanding of surface properties of REMs is essential to identify the reactions taking place at different interfaces to develop more robust technologies for the recovery of REEs. The goal of this study is to provide a comprehensive investigation on the surface energy characteristics of bastnaesite and xenotime, as the primary sources of light and heavy rare earth elements, respectively. Crystal’s orientation of REMs was identified using surface X-ray diffraction analysis, whereas the morphology and elemental composition were characterized using scanning electron microscopy and energy dispersive spectra analyses. Wettability of REMs was studied using sessile drop contact angle measurement technique, and the surface energy and its constituents were evaluated using Fowkes, van Oss–Chaudhury–Good, Owens–Wendt–Rabel–Kaelble, Zisman, and Neumann models. Atomic force microscopy (AFM) was used to compare the local surface properties and work of adhesion of REMs by analyzing the force profile between the mineral surfaces and a n-type silicon tip. Inverse gas chromatography (IGC) was employed to study the surface energy heterogeneity of REM powders and evaluate the dispersive and Lewis acid–base interactions. Results indicated that the dispersion forces have a larger contribution to the surface energy of both REMs in comparison with the polar interactions. The surface energy values obtained using contact angle measurements were lower than those obtained using IGC, however, the IGC results seemed to be closer to reality since the contact angle results showed a strong dependence on probe liquids, roughness, and local properties of the surfaces. Contact angle measurements and AFM analysis indicated that bastnaesite had higher hydrophobic character, whereas the IGC analysis revealed that the surface energy of xenotime was lower than that of bastnaesite at higher surface coverages. Despite the shortcomings of each method, results showed that a combination of these techniques could provide a deeper understanding of surface energy and wetting behavior of minerals.

On the size-dependent behavior of drop contact angle in wettability alteration of reservoir rocks to preferentially gas wetting using nanofluid

Wettability alteration of rock surfaces toward gas wetting have been recognized as a practical approach for maximizing the production from the gas condensate reservoirs. Most of the reported work in this area applied the so called sessile drop contact angle measurement technique to examine the change in wetting state of a surface. However, the size-dependent wetting behavior of drop which could affect the exact determination of wettability and wettability changes was not well discussed in the previous studies. Therefore, in this work, the size dependency of contact angle for four different liquid-solid-gas systems; i.e., water-calcite-air, water-treated calcite-air (nanofluid treated calcite), oil-calcite-air, and oil-treated calcite-air, were investigated. To provide a better understanding of the displacement of reservoir gas and liquid following the wettability alteration process, a dynamic contact angle measurement approach was designed. The effect of drop size and surface roughness on the wetting state of calcite rock samples at the initial and altered condition of wettability was then investigated through experimental and modeling approaches. The surface roughness of calcite samples and drop contact angles were determined using Atomic Force Microscopy and Low bond axisymmetric drop shape analysis method, respectively. Analysis of results demonstrated that size dependency of contact angle imposed an error as high as 22.2° on the measurement of achieved wettability alteration in the case of water-calcite/treated calcite-air system. On the basis of calculated pseudo-line tension from the modeling schemes, it was also revealed that the surface roughness had a significant impact on wettability measurements. Both low and high pseudo-line tension values of order 10−9 and 10−6 N, respectively, could dictate some level of errors in contact angle measurements. However, high values were supposed to have a considerable degree of importance in gas condensate applications. The results of this study could provide a better understanding of the contact angle measurement experiments for petroleum engineers to evaluate the wettability alteration schemes.

The hydrophobic surface state of talc as influenced by aluminum substitution in the tetrahedral layer

Talc is both an important industrial mineral product recovered by flotation, and also in other cases, a gangue mineral of concern in the flotation of certain sulfide ores, such as the PGM ores from South Africa and from the United States. The talc face surface is naturally hydrophobic with a water sessile drop contact angle of nearly 80°, which accounts for its flotation recovery in one case, and its contamination of sulfide mineral concentrates in other instances. Due to the presence of impurities in the talc structure the surface properties change. One such effect is the presence of aluminum, which can replace silicon in the silica tetrahedral layer of the talc structure. This results in a charge imbalance on the face surface because Si+4 is replaced by Al+3. Sessile drop contact angle and bubble attachment time measurements were made, and these results were compared to the results from molecular dynamics simulations (MDS). The extent of aluminum substitution in the silica tetrahedral layer was considered, and the sessile drop contact angle was found to decrease with increased aluminum content, decreasing from about 80° for no substitution (talc) to 0° for extensive substitution (phlogopite). The water film was found to be stable at the surface of highly aluminum substituted crystals due to the interaction between water molecules and the increased polarity of the surface state. This stable water film restricts the air bubble from attaching to such face surfaces. However, in the absence of aluminum substitution, no interactions between the water molecules and the face surface were observed and the air bubble readily attached to the face surface. This study provides additional understanding of how aluminum substitution in the tetrahedral layer affects the fundamental surface properties of talc, paving the way for the design of improved reagents for talc flotation as an industrial mineral product, and for talc depression in the recovery of sulfide mineral concentrates.

Wettability control of PET surface by plasma-induced polymer film deposition and plasma/UV oxidation in ambient air

The surface modification of poly (ethylene terephthalate) (PET) film was achieved by two sequential atmospheric pressure plasma jet (APPJ) treatments: plasma-induced polymer coating with hexamethyldisiloxane (HMDSO) and plasma oxidation with nitrogen gas. For comparison with APPJ-oxidation, oxidation by excimer ultra violet (UV) light irradiation was performed. The sessile drop and Wilhelmy contact angle measurements revealed that the PET film subjected to APPJ-coating showed superior water repellency and subsequent APPJ- or UV-oxidation made the PET film super-hydrophilic. UV-oxidation was also performed on the PET film treated by APPJ-coating, covered by a metal mesh. The difference in the contact angles between the surface areas covered with and without the metal strip mask was evident based on the Wilhelmy contact angle measurement. Both hydrophobic and hydrophilic surfaces did not exhibit contact angle hysteresis and had excellent stability of wettability. Furthermore, the hydrophilic surface treated only by APPJ- or UV-oxidation exhibited contact angle hysteresis and hydrophobic recovery with prolonged storage. Field emission scanning electron microscopy (FE-SEM) and SEM observation revealed that the morphology of the PET surface became granular after APPJ-coating. From the analyses of X-ray photoelectron spectroscopy (XPS) and grazing-angle attenuated total reflectance Fourier transform infrared (GATR-FTIR) spectroscopy, the APPJ-coated film composed mainly of inorganic SiO2 with traces of carbon derived from CH3 group, which makes the coating surface more hydrophobic. The subsequent oxidation process of APPJ or UV light leads to the decomposition of the methyl group at the surface. The antifouling properties of the PET surface against soil particulates deposited from air and their removal in aqueous detergent solution, were improved by APPJ-coating and subsequent APPJ-oxidation, respectively.

Variability in Microplate Surface Properties and Its Impact on ELISA.

Microplate-based immunoassays are widely used in clinical and research settings to measure a broad range of biomarkers present in complex matrices. Assay variability within and between microplates can give rise to false-negative and false-positive results leading to incorrect conclusions. To date, the contribution of microplates to this variability remains poorly characterized and described. This study provides new insights into variability in immunoassays attributable to surface characteristics of commercial microplates. Well-to-well assay variation in γ-treated and nontreated 96-well opaque microplates suitable for chemiluminescence assays was determined by use of a validated sandwich ELISA. Microplate surface characteristics were assessed by sessile drop contact angle measurements, scanning electron microscopy, energy dispersive x-ray spectroscopy, and atomic force microscopy. All microplate types tested exhibited vendor-specific assay response profiles; and "rogue" plates with very high intraassay variation and deviant mean assay responses were found. Within-plate, location-dependent bias in assay responses and variability in well contact angle were also observed. We demonstrate substantial differences in well-surface properties with putative effects on protein-coating reproducibility and hence consistency in immunoassay responses. A surface "cleaning" effect on manufacturing residues was attributed to γ-irradiation, and treated microplates manifest increased polar functionalities, surface roughness, and assay responses. Our data suggest that tighter control of variability in surface roughness, wettability, chemistry, and level of residual contaminants during microplate preparation is warranted to improve consistency of ELISA assay read out.

Organosilane Chemical Gradients: Progress, Properties, and Promise.

Chemical gradients play an important role in nature, driving many different phenomena critical to life, including the transport of chemical species across membranes and the transport, attachment, and assembly of cells. Taking a cue from these natural processes, scientists and engineers are now working to develop synthetic chemical gradients for use in a broad range of applications, such as in high-throughput investigations of surface properties, as means to guide the motions and/or assembly of liquid droplets, vesicles, nanoparticles, and cells and as new media for stationary-phase-gradient chemical separations. Our groups have been working to develop new methods for preparing chemical gradients from organoalkoxysilane and organochlorosilane precursors and to obtain a better understanding of their properties on macroscopic to microscopic length scales. This review highlights our recent work on the development of controlled-rate infusion and infusion-withdrawal dip-coating methods for the preparation of gradients on planar glass and silicon substrates, on thin-layer chromatography plates, and in capillaries and monoliths for liquid chromatography. We also cover the new knowledge gained from the characterization of our gradients using sessile drop and Wilhelmy plate dynamic water contact angle measurements, X-ray photoelectron spectroscopy mapping, and single-molecule tracking and spectroscopy. Our studies reveal important evidence of phase separation and cooperative interactions occurring along multicomponent gradients. Emerging concepts and new directions in the preparation and characterization of organosilane-based chemical gradients are also discussed.

Effect of dimethyl sulfoxide on dentin collagen

ObjectivesInfiltration of adhesive on dentin matrix depends on interaction of surface and adhesive. Interaction depends on dentin wettability, which can be enhanced either by increasing dentin surface energy or lowering the surface energy of adhesive. The objective was to examine the effect of dimethyl sulfoxide (DMSO) on demineralized dentin wettability and dentin organic matrix expansion. MethodsAcid-etched human dentin was used for sessile drop contact angle measurement to test surface wetting on 1–5% DMSO-treated demineralized dentin surface, and linear variable differential transformer (LVDT) to measure expansion/shrinkage of dentinal matrix. DMSO-water binary liquids were examined for surface tension changes through concentrations from 0 to 100% DMSO. Kruskal–Wallis and Mann–Whitney tests were used to test the differences in dentin wettability, expansion and shrinkage, and Spearman test to test the correlation between DMSO concentration and water surface tension. The level of significance was p<0.05. ResultsPretreatment with 1–5% DMSO caused statistically significant concentration-dependent increase in wetting: the immediate contact angles decreased by 11.8% and 46.6% and 60s contact angles by 9.5% and 47.4% with 1% and 5% DMSO, respectively. DMSO-water mixtures concentration-dependently expanded demineralized dentin samples less than pure water, except with high (≥80%) DMSO concentrations which expanded demineralized dentin more than water. Drying times of LVDT samples increased significantly with the use of DMSO. SignificanceIncreased dentin wettability may explain the previously demonstrated increase in adhesive penetration with DMSO-treated dentin, and together with the expansion of collagen matrix after drying may also explain previously observed increase in dentin adhesive bonding.

Fundamental Bonding Properties of Douglas-Fir and Southern Yellow Pine Wood

Abstract Bonding properties of southern yellow pine (Pinus spp.) and Douglas-fir (Pseudotsuga menziesii) were compared in terms of density, chemical composition, surface energy, shear stress, percent wood failure, and delamination. Specimens were taken from two trees of loblolly pine (Pinus taeda) and one tree of Douglas-fir. Density measurements showed that for mature wood, southern pine exhibited a higher average density than Douglas-fir, but for juvenile wood, southern pine showed a lower average density than Douglas-fir. Chemical analysis determined that southern yellow pine contained higher percent hemicellulose, lignin, and extractives, whereas Douglas-fir had higher percent cellulose. Static sessile drop contact angle measurements revealed that southern yellow pine specimens exhibited a lower average contact angle than Douglas-fir and, accordingly, higher average surface energy. Shear strength, percent wood failure, and delamination due to accelerated weathering were measured for bonded specimens constructed with either a one-part moisture-cure polyurethane (PUR) or a two-part ambient-curing phenol-resorcinol-formaldehyde (PRF) and three different assembly time combinations. Shear strength for southern yellow pine was affected the most by assembly time, whereas Douglas-fir shear strength was affected by the type of adhesive and interaction with the growth region at the bond. Delamination results showed that southern yellow pine exhibited less delamination than Douglas-fir when using PRF. Delamination measurements from the PUR bonds were similar and extremely high for both wood types. Although statistically significant differences were found in a few wood factors, limited differences were found in shear strengths, percent wood failure, and delamination due to accelerated testing for the two wood types.

Pervaporation dehydration of ethanol-water mixture using crosslinked poly(vinyl alcohol) membranes

Crosslinked poly(vinyl alcohol) (PVA) composite membranes were synthesized by casting selective crosslinked PVA films on the polyacrylonitrile (PAN) porous substrates. The PVA films were prepared by in-situ crosslinking technique using four different crosslinking agents, such as glutaraldehyde, fumaric acid, maleic acid and malic acid. The separation performance in terms of permeation flux and separation factor of prepared membranes were evaluated for pervaporation dehydration of ethanol/water mixture of 80/20 wt% at 60 oC. The prepared membranes were also characterized by FTIR, SEM, swelling and sessile drop contact angle measurements. It was found that the chemical structure of the PVA membrane was changed via crosslinking reaction. The physicochemical properties (hydrophilicity and swelling degree) and separation performance of the prepared membranes were affected by the chemical structures of the crosslinking agents. Furthermore, there was a trade-off between permeation flux and selectivity of the resulting membranes. When the flux increased, the separation factor decreased. The results of this study contributed to enrich the data of the crosslinking reaction of PVA membranes, and expected to help researcher in suitable choosing crosslinking agent for producing pervaporation PVA membrane for dehydration of ethanol solutions.

Obtaining a full range of surface energies on single wall carbon nanotube samples through photo-initiated chemical vapor deposition

Event Abstract Back to Event Obtaining a full range of surface energies on single wall carbon nanotube samples through photo-initiated chemical vapor deposition Seyedehsan Hosseininasab1, Nathalie Faucheux2, Gervais Soucy2 and Jason R. Tavares1 1 Polytechnique Montreal, Chemical engineering, Canada 2 Université de Sherbrooke, Chemical and Biotechnological Engineering, Canada Introduction: Despite all the distinctive properties of carbon nanotubes (CNTs), their commercial use in biomedical applications is limited by their cytotoxicity [1]. Several factors can explain the CNT cytotoxicity including their dimension, surface hydrophobicity and degree of agglomeration [1],[2]. However, the effect of surface energy on the cytotoxicity of single wall carbon nanotubes (SWCNTs) has to be investigated further. For this purpose, well-characterized SWCNTs bearing similar functionalities with properties ranging from super-hydrophobic to super-hydrophilic must be prepared. In this study, photo-initiated chemical vapor deposition (PICVD) using a syngas precursor [3] was applied to SWCNTs and is presented as a viable technique to fulfill this goal. Materials and Methods: Raw-SWCNTs (R-SWCNTs) were first purified by a multi-step protocol as previously described [4]. Efficiency of purification was assessed by transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). These purified SWCNTs (P-SWCNT) were then dispersed in ethanol via sonication and immediately filtered under vacuum upon a polycarbonate membrane. The resulting “buckypaper” was placed in a vacuum oven to ensure complete ethanol evaporation. The surface of SWCNTs was then treated according to a method developed by Dorval Dion et al (2014) [3]. Briefly, P-SWCNTs were placed inside a UVC-illuminated quartz micro-reactor. After inert gas purging, the syngas precursor (CO and H2) was introduced at various ratios along with H2O2 as a radical photo-initiator (PI). To obtain the desired surface functionality, the process could be implemented under pressure (+15 kPag) or slight vacuum (-15 kPag). Hydrophilic surfaces were typically obtained under slight vacuum, while hydrophobic surfaces were achieved under pressure [3]. The surface energy of the treated P-SWCNTs was determined by applying the Owens-Wendt model [5]. Results and Discussion: TEM was used to both confirm the efficiency of the purification protocol and assess the morphology of P-SWCNTs after treatment. As shown Fig. 1A, the impurities in R-SWCNTs included amorphous and graphitic carbon, as well as catalytic metal nanoparticles, while these impurities in P-SWCNTs were decreased (Fig. 1B) (from 29% to 14% based on TGA results). Surface wetting of SWCNT samples was assessed through sessile drop contact angle measurements. The average contact angle of P-SWCNT samples was 79±2°, while it varied from 0+3° to 165±3° for treated nanotubes (T-SWCNTs) as a function of the molar ratio of H2/CO (Fig. 2). Conclusion: Using PICVD with a syngas precursor, we successfully functionalized P-SWCNTs bearing various oxygen-containing groups with properties ranging from superhydrophilic to superhydrophobic. This PICVD method will be helpful to better determine the effect of surface energy on the cytotoxicity of SWCNTs bearing similar functionalities. Fig. 1. TEM images of A) R-SWCNTs, B) P-SWCNTs. Fig. 2. Blue lozenge) Contact angle measurements of T-SWCNTs obtained by tensiometry in terms of molar ratio of H2/CO, Red Square) Surface energy measurements that have been plotted in terms of molar ratio. This project is supported by FRQNT Foundation