The stability and geometrical characteristics of solid-liquid interfacial nanobubbles in complex aqueous solution environments

Abstractauthoren Nickel thin films were deposited on Ti6Al4V and surface treated with nanosecond pulse ultraviolet laser in ambient conditions using a fluence of 3.68 J cm−2. A twofold to threefold increase in contact angle was observed for water, ethylene glycol, and diiodomethane following laser treatment, with recorded contact angles for water in excess of 130°. No additional treatment was used to hydrophobize the surface. Three different micro‐ and nanometric levels of roughness were generated on the thin film surface, which can be related to the rastering parameters of the laser and to the increase in apparent contact angle. Melt droplets were identified as a main contribution to the nanometric roughness level, indicating that melting and melt ejection play an important role in surface nanostructuring.Micro‐ and nanopatterning obtained after UV laser treatment of nickel thin films, highlighting the different scales of the generated features.

Surface control additives (SCAs), or surfactants, can obstruct the wetting of liquid films on lyophilic surfaces even though they lower surface tension. In this work, this unusual behavior was used to decrease the widths of printed organic and nanoparticle lines on different homogeneous surfaces. A decrease in line width accompanied a change in its cross section. The ability of a SCA to decrease the line width was correlated with contact angle but not the surface tension of the solution. Line refinement was consequently attributed to an increase in contact angle. Because there were no reports that surfactants increased contact angles, the mechanisms to increase contact angle were discussed in static and dynamic terms. First, Owens and Wendt’s theory revealed that contact angle changes depended on SCA-induced modification of polar and dispersive interfacial components. However, a definitive increase in contact angle could not be deduced from this theory alone. Second, the effect of solutal Marangoni forces induced by the SCAs on contact angle was discussed by considering the wetting behaviors of binary solvents. SCA concentration dependence of surface tension at higher than the initial SCA concentration correlated well with the ability of the SCA to decrease line width.

CO2 laser processing of nylon 6,6 can modify its wettability and biomimetic characteristics. This paper discusses comparatively the use of a CO2 laser for surface patterning and whole area processing, detailing the effects on the wettability and osteoblast cell response. White light interferometry found that the largest increase in surface roughness, with an Sa of 4 μm was obtained with the large area processed sample using an irradiance of 510 Wcm-2. The surface oxygen content was increased by up to 5 %at for all laser irradiated samples. A sessile drop device determined that the laser patterned samples gave rise to an increase in contact angle, whereas a decrease in contact angle was observed for the large area patterned samples in comparison to the as-received nylon 6,6. The increase in contact angle is explained by the likely existence of a mixed-state wetting regime.The bioactive nature of the samples were analysed by seeding osteoblast cells onto the nylon 6,6 samples for 4 days. It was found that most laser surface treated samples gave rise to a more biomimetic surface. Some samples gave a less enhanced biomimetic which can be attributed to an increase in surface toxicity. Also, generic wettability characteristics have been forged which can predict the biomimetic nature of laser surface treated nylon 6,6.

Ten full-time adolescent wheelchair users (ages 13–18) completed a total of three propulsion trials on carpet and tile surfaces, at a self-selected velocity, and on a concrete surface, at a controlled velocity. All trials were performed in their personal wheelchair with force and moment sensing wheels attached bilaterally. The first two trials on each surface were used as pre-intervention control trials. The third trial was performed after receiving training on proper propulsion technique. Peak resultant force, contact angle, stroke frequency, and velocity were recorded during all trials for primary analysis. Carpet and tile trials resulted in significant increases in contact angle and peak total force with decreased stroke frequency after training. During the velocity controlled trials on concrete, significant increases in contact angle occurred, as well as decreases in stroke frequency after training. Overall, the use of a training video and verbal feedback may help to improve short-term propulsion technique in adolescent wheelchair users and decrease the risk of developing upper limb pain and injury.

Effect of nonionic surfactant on wetting behavior of an evaporating drop under a reduced pressure environment

Semiconductors are the center of the fourth industrial revolution as they are key components for all electronics. To manufacture chips, semiconductor companies purchase bare wafers and perform many different processes to ensure the finest quality of each chip. Exposed wafers made of silicon (Si), which can easily oxidize, convert to silicon dioxide (SiO2). The surface of SiO2 wafers consists of many Si-OH bonds, allowing them to easily bond with water, resulting in a “wet” or hydrophilic condition. The hydrophilic condition of a wafer can be problematic as the fin can collapse during water rinsing. We sought to determine a way to modify the surface of SiO2 wafers to become hydrophobic to ensure safe wet cleaning. We hypothesized that treating the surface of the wafer with hydrophobic chemicals like chlorotrimethylsilane (CTS) could address this problem by converting the surface of the wafer into Si-OR (R group being hydrocarbons). This conversion would prevent hydrogen bonds from forming with water, which would then convert the wafer from hydrophilic to hydrophobic. After executing the experiment, the hydrophobicity was analyzed by measuring the contact angle of the wafer, where increases in contact angle portrayed a more hydrophobic surface. In our results, there was an increase in contact angle, which concluded that coating the SiO2 wafer with CTS repels water from the surface, therefore allowing for a safe cleansing process. The prevalence of semiconductors today makes it especially important for maximum efficiency in the industry; a rinsing process minimizing risks would curtail costs and time.

An in vitro technique for measuring contact angles on the corneal surface and its application to evaluate corneal wetting properties of water soluble polymers

Unlike conventional oil production methods, enhanced oil recovery (EOR) processes can recover most oil products from the reservoir. One method, known as wettability alteration, changes the hydrophilicity of the reservoir rock via decreased surface interactions with crude oils. The mitigation of these attractive forces enhances petroleum extraction and increases the accessibility of previously inaccessible rock deposits. In this work, silica nanoparticles (NPs) have been used to alter the wettability of two sandstone surfaces, Berea and Boise. Changes in wettability were assessed by measuring the contact angle and interfacial tension of different systems. The silica NPs were suspended in brine and a combined solution of brine and the Tween®20 nonionic surfactant at concentrations of 0, 0.001, and 0.01 wt% NP with both light and heavy crude oil. The stability of the different nanofluids was characterized by the size, zeta potential, and sedimentation of the particles in suspension. Unlike the NPs, the surfactant had a greater effect on the interfacial tension by influencing the liquid-liquid interactions. The introduction of the surfactant decreased the interfacial tension by 57 and 43% for light and heavy crude oil samples, respectively. Imaging and measurements of the contact angle were used to assess the surface-liquid interactions and to characterize the wettability of the different systems. The images reflect that the contact angle increased with the addition of NPs for both sandstone and oil types. The contact angle in the light crude oil sample was most affected by the addition of 0.001 wt% NP, which altered both sandstones’ wettability. Increases in contact angle approached 101.6% between 0 and 0.001 wt% NPs with light oil on the Berea sandstone. The contact angle however remained relatively unaffected by addition of higher NP concentrations, thus indicating that low NP concentrations can effectively be used for enhancing crude oil recovery. While the contact angle of the light crude oil plateaued, the heavy crude oil continued to increase with an increase in NP concentration; therefore indicating that a maximum contact angle in heavy crude oil was not yet achieved. The introduction of NPs in light and heavy crude oil samples altered both the Berea and Boise sandstone systems’ wettability, which in turn indicated the efficacy of the silica NPs and surfactants in generating a more water-wet reservoir. Consequently, silica NPs and surfactants are most promising for EOR across the range of oil types.

Numerical simulation on the effect of contact angle on the permeation of emulsions through a membrane in premix membrane emulsification

The relationship between perturbations to contact angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium contact angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high contact angle and the droplet completely contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high contact angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of contact-angle amplification or attenuation and distinguishes between the increases in contact angles due to roughening or texturing surfaces and perturbations to the resulting contact angles. The theory is applied to predicting contact-angle hysteresis on rough surfaces from the hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.

This paper investigates influence of the inner wall wettability on mass flow rate and discharge coefficient (Cd) for the flow of water through a 1 mm diameter capillary tube with circular cross-section. The wettability of the inner wall of the tube was modified by dip coating of the capillary tubes in the solution made out of Trichloro(1H,1H,2H,2H-tridecafluoro-n- octyl) silane (FOTS) and n-hexane. Further, the coated capillary tube is heated to 250 ⁰C and 350 ⁰C for a time span of 2 hours to enable effectiveness of coating. Upon coating and heating to 250 ⁰C, the contact angle was incremented from 32.72° (for uncoated capillary tube), to 114.92°. At the same time, the inner surface contact angle has reduced to 67.72⁰ while heating the coated tube to 350 ⁰C. In order to analyse the effect of length to diameter ratio of the capillary tube on fluid flow behaviour, three different orifices with the length of 10mm, 15mm, and 30mm were chosen with three different wettability conditions. The increase in contact angle resulted in higher mass flow rates and Cd for all the capillary tubes considered in this study. The uncoated orifice tubes resulted in the lowest flow performance, while the orifice with a contact angle of 114.92° led to the highest efficiency, implying that reduced contact of the wall with water liquid minimizes the energy dissipation and enhances the fluid transport. The consistency in the trends which has been observed across the different Length to Diameter ratios proposes the idea that wettability modification can be used as an effective and scalable method for enhancing fluid transport systems. And by refining of this property gives precise manipulation of fluid transports in applications like microfluidics, fuel injection and bio medical devices

The adsorption and wetting on quartz surfaces by aqueous solutions of xylyl-substituted biquaternary ammonium salt gemini surfactants with different spacer groups (C3 and C6), have been investigated. The interfacial properties of surfactant solutions such as contact angle, adhesional tension (γLV cos θ), quartz-water interfacial tension (γSL) as well as adhesion work (WA) have been estimated. The obtained results show that C3 and C6 have similar adsorption behavior on quartz surfaces. Before critical micelle concentration (cmc) is reached, the contact angles of gemini surfactants slowly increase with the increasing concentration, and the adsorption amount at the water-air interface is almost the same as those at a quartz-water interface. After reaching cmc, the gemini surfactant Cn molecules form a more compact adsorption film through bending the flexible spacer chain, instead of forming a bi-layer. As a result, a further increase in quartz-liquid interfacial tension (γSL) and a consequent increase in contact angle have been observed after cmc. Gemini C6 shows a stronger ability towards hydrophobic modification at a quartz surface than C3, demonstrating the contribution of the longer methylene spacer to the hydrophobic modification of the quartz surface.

Characterization of active chitosan films as a vehicle of potassium sorbate or nisin antimicrobial agents

A range of surfaces coated with spherical silica particles, covering the size range from nanometer to micrometer, have been produced using Langmuir-Blodgett (LB) deposition. The particles were characterized both in suspension and in the Langmuir trough to optimize the surface preparation procedure. By limiting the particle aggregation and surface layer failures during the preparation steps, well-defined monolayers with a close-packed structure have been obtained for all particle sizes. Thus, this procedure led to structured surfaces with a characteristic variation in the amplitude and spatial roughness parameters. In order to obtain robust surfaces, a sintering protocol and an AFM-based wear test to determine the stability of the deposited surface layer were employed. Hydrophobization of the LB films followed by water contact angle measurements showed, for all tested particle sizes, the same increase in contact angle compared to the contact angle of a flat hydrophobic surface. This indicates nearly hexagonal packing and gives evidence for nearly complete surface wetting of the surface features.

The evaporation process in porous media typically experiences three main periods, among which the first period, named the constant rate period (CRP), performs most efficiently in removing liquid. We aim to prolong the CRP to very low degrees of saturation (S) and increase its evaporation rate by playing with heterogeneity in wettability and pore size. First, we show that a porous medium with a smaller contact angle at the surface and increasing contact angle towards the inside generally dries out faster compared with that with uniform contact angle. Second, a constant contact angle porous medium with smaller/larger pores in the surface/inside part dries out faster than a medium with uniform pore size. The underlying mechanism is the occurrence of a capillary pressure jump at the border between the two layers accompanied by enhanced capillary pumping, increasing/maintaining the interfacial area in the surface pores. Harnessing the potential of this mechanism, we propose an optimized strategy by combining two heterogeneity effects: increasing contact angle and pore size towards the inside. This strategy is found to be robust both for multilayer and larger systems. In this case, a small drying front first penetrates fast towards the inside and then expands, followed by a horizontal drying front moving back layer by layer to the surface. Quantitatively, compared with evaporation from a homogeneously porous medium with uniform contact angle where CRP stops at $S=0.64$ , our optimized design can extend the CRP down to $S=0.12$ , and decrease five-fold the drying time needed to reach $S=0.05$ .