Wide Range Of Wettability Research Articles

Deposition of Chitosan on Plasma-Treated Polymers-A Review.

Materials for biomedical applications often need to be coated to enhance their performance, such as their biocompatibility, antibacterial, antioxidant, and anti-inflammatory properties, or to assist the regeneration process and influence cell adhesion. Among naturally available substances, chitosan meets the above criteria. Most synthetic polymer materials do not enable the immobilization of the chitosan film. Therefore, their surface should be altered to ensure the interaction between the surface functional groups and the amino or hydroxyl groups in the chitosan chain. Plasma treatment can provide an effective solution to this problem. This work aims to review plasma methods for surface modification of polymers for improved chitosan immobilization. The obtained surface finish is explained in view of the different mechanisms involved in treating polymers with reactive plasma species. The reviewed literature showed that researchers usually use two different approaches: direct immobilization of chitosan on the plasma-treated surface or indirect immobilization by additional chemistry and coupling agents, which are also reviewed. Although plasma treatment leads to remarkably improved surface wettability, this was not the case for chitosan-coated samples, where a wide range of wettability was reported ranging from almost superhydrophilic to hydrophobic, which may have a negative effect on the formation of chitosan-based hydrogels.

Physics-Driven Investigation of Wettability Effects on Two-Phase Flow in Natural Porous Media: Recent Advances, New Insights, and Future Perspectives

Leveraging high-fidelity lattice Boltzmann simulations combined with analytical modeling, we establish a comprehensive micro-scale description of immiscible two-phase fluid displacement occurring during favorable and unfavorable displacement conditions in a heterogeneous porous medium under a wide range of wettability. The emergence of corner-flow events is found to promote a compact displacement pattern, leading to a maximum recovery efficiency of the defending fluid under the strong imbibition for both favorable and unfavorable displacement scenarios. Saturation of the invading fluid manifests the crossover in the displacement patterns from fingering to stable flow, as the wetting varies from drainage to strong imbibition. Quantifying the corner flow under both displacement conditions and strong imbibition reveals that corner-flow events are preferentially hosted by small-size pores and predominantly concentrated ahead of the primary fluid–fluid interface without perturbing the stability of the pore-body displacement. In addition to the numerical simulation, we developed an analytical model that can predict the saturation profile of invading fluid under given boundary conditions. Our study elucidates the fundamental control and interaction of wettability and heterogeneity on the dynamics of immiscible fluid displacement in porous media with implications in the description of subsurface flow and processes.

Structure induced wide range wettability: Controlled surface of micro-nano/nano structured copper films for enhanced interface

The wettability of materials used in the production of devices employed in various technological domains have attracted significant attentions. Therefore, it is important to design the surfaces of these materials such that they can provide the required surface free energy and simplify the interfacial structure. Herein, various Cu films with a highly controllable surface wettability and a wide range of contact angles ranging from 6° to 152° were fabricated, and the corresponding mechanism was discussed. A wide range of wettability was realized by controlling the surface structure of the Cu film. The nanogap structure of the vertical nanowire-array film led to a high surface free energy. Similarly, the oblique nanowire-array film increased the surface free energy; however, the surface free energy was dependent on the size of the nanowires rather than on the nanogaps owing to the crystallinity of the film. Additionally, cluster-nanowire-array films were designed to realize a wettability transition from hydrophilicity to hydrophobicity with a constant surface free energy. The Cu foam possessed a superhydrophilic surface owing to its high porosity, whereas the cluster-nanoparticle structure possessed a superhydrophobic surface. In addition, we noted that the structure-induced wettability played an important role in tuning the semiconductor and metal interfacial stress and simplifying the interfacial structure. Furthermore, the outstanding electrical conductivity of the Cu films indicates its promising potential as an electrode. The structure-induced wettability proposed in this study can be applied for a wide range of materials, particularly for films used for advanced applications.

Convective meniscus splitting of polysaccharide microparticles on various surfaces

In contrast to convective self-assembly methods for colloidal crystals etc., “convective meniscus splitting method” was developed to fabricate three-dimensionally ordered polymeric structures. By controlling the geometry of evaporative interface of polymer solution, a deposited membrane with uniaxial orientation and layered structures can be prepared. Here it is demonstrated that xanthan gum polysaccharide microparticles with diameter ~ 1 µm can bridge a millimeter-scale gap to form such a membrane because the capillary force among the particles is more dominant than the gravitational force on the evaporative interface. This method is applicable for various substrates with a wide range of wettability (water contact angle, 11°–111°), such as glass, metals, and plastics. The specific deposition can be also confirmed between frosted glasses, functional-molecules-modified glasses, and gold-sputtered substrates. By using such a universal method, the membrane formed on a polydimethylsiloxane surface using this method will provide a new strategy to design a functional polysaccharide wall in microfluidic devices, such as mass-separators.

The effect of curing and zirconium content on the wettability and structure of a silicate hybrid sol-gel material

Functional hybrid sol-gel coatings have been developed for numerous applications with a wide range of wettabilities. This study proposes to investigate the relationship between the structure and the wetting properties of a zirconium modified silicate hybrid sol-gel coating. The structures of the coatings were altered by varying the content of zirconium, and the curing process, while keeping the sol-gel preparation conditions identical. The structure of the materials was characterized by FTIR, 29Si NMR and SEM. The thermal properties and the wettability are identified by DSC and contact angle measurements, respectively.By corroborating the structural and wettability analyses, it is shown that the transition metal minimizes the thermally-assisted condensation of the silicate network and enables to stabilize the wetting properties at higher hydrophilic values. This article highlights that the wettability of hybrid sol-gel coatings can be controlled by both the curing process and transition metal content.

Droplet impact and LFP on wettability and nanostructured surface

The Leidenfrost point (LFP) of a single deionized water droplet on various wettability surfaces was investigated by high-speed visualization. Manipulating both the chemical and geometric properties of a silicon wafer substrate, we prepared test samples with a wide range of wettabilities, from superhydrophilic (<10°) to superhydrophobic (>165°). Nanoscale wire or needle-shaped structures were fabricated by etching process on the silicon substrate. The effects of wettability on LFP were investigated by analyzing how the droplets rebound on the overheated surface. The results show that the more hydrophilic condition, the higher LFP. As the hydrophilic surface causes vigorous nucleate boiling and large viscous dissipation during the droplet contact, higher superheated condition of the substrate is required to trigger the rebounding dynamics and stable film boiling state. Furthermore, the superhydrophilic surface, which was assisted by nanostructures, contains many cavities and produces strong capillary wicking upon droplet contact; hence, explosive transition boiling in the droplet was observed. This study provides a detailed physical understanding of droplet dynamics on overheated nanostructures and its relation on LFP evaluation.

Influence of tube wettability on water contact angle of powders determined by capillary rise

Abstract During a recent literature review, we have noticed that researchers used tubes made of materials having a wide range of wettability, including plastics and metals, to pack powders for wettability determination using the Washburn capillary rise (WCR) method. Most studies applying WCR have focused on the effects of powder properties and their packing methods on the contact angle, while neglecting the role of packing tube. Although the ratio of packed powder surface area to tube surface area is large, we believe that tube wettability could have a significant effect on powder wettability determined using the WCR method. In this paper, we report that when water was penetrating the packed powder inside hydrophobic tubes, the water front along the tube wall was severely pinned, and in some cases, it was completely pinned at the support/packing/tube wall interface until the water had penetrated all the way up the packed powder. Using hydrophobic tubes limited the water rise to the powder region, which resulted in contact angles that were larger (up to ∼37°) than ones obtained using hydrophilic tubes, especially when the tube size was small.

Controlled Wetting on Electrodeposited Oxide Thin Films: From Hydrophilic to Superhydrophobic

We have explored how surface morphology and structure affect wetting properties of electrodeposited oxide thin films notwithstanding chemical modifications. Microstripes of self-assembled monolayers (SAMs) on gold were prepared using a microcontact printing (μCP) technique, which served as molecular templates to guide the electrochemical deposition of zirconia in aqueous solution. The wetting properties of the thus-prepared zirconia oxide thin films are shown to be tunable; i.e., a wide range of wettabilities from hydrophilic to superhydrophobic can be obtained by simply varying the SAM template and the electrodeposition conditions (potential scan rate and number of cycles). In particular, a “two-tier” micro/nanoscale roughness was achieved on the gold substrate patterned with alternating stripes of 1-octadecanethiol and 6-mercapto-1-hexanol SAMs, which leads to a superhydrophobic surface (water contact angle ∼150°). Of great significance is the demonstrated ability herein to convert an intrinsically hydrophilic into a hydrophobic surface by changing the conditions for materials fabrication, which does not involve any chemical modifications.

Relation between Contact Angle and the Cross-Sectional Area of Small, Sessile Liquid Drops

In this theoretical study, the cross-sectional areas of small, sessile drops were calculated for solid surfaces with a wide range of wettability. These areas were then used to estimate obstruction of rectangular gas flow channels by sessile liquid drops. Our findings suggest that even a small improvement in wettability (i.e., a lower contact angle) will lead to a substantial decrease in blockage. This work has implications for small channels that contain two-phase flow, such as those found in fuel cells.

Adhesion of mouse fibroblasts on hexamethyldisiloxane surfaces with wide range of wettability

Surface wettability is an important physicochemical property of biomaterials, and it would be more helpful for understanding this property if a wide range of wettability are employed. This study focused on the effect of surface wettability on fibroblast adhesion over a wide range of wettability using a single material without changing surface topography. Plasma polymerization with hexamethyldisiloxane followed by oxygen (O2)-plasma treatment was employed to modify the surfaces. The water contact angle of sample surfaces varied from 106 degrees (hydrophobicity) to almost 0 degrees (super-hydrophilicity). O2 functional groups were introduced on polymer surfaces during O2-plasma treatment. The cell attachment study confirmed that the more hydrophilic the surface, the more fibroblasts adhered in the initial stage that includes super-hydrophilic surfaces. Cells spread much more widely on the hydrophilic surfaces than on the hydrophobic surfaces. There was no significant difference in fibroblast proliferation, but cell spreading was much greater on the hydrophilic surfaces. The fibronectin adsorbed much more on a hydrophilic surface while albumin dominated on a hydrophobic surface in a competing mode. These findings suggest the importance of the surface wettability of biomaterials on initial cell attachment and spreading. The degree of wettability should be taken into account when a new biomaterial is to be employed.

Adhesion of Hydrophilic Particles to Polymer Substrates Immersed in Aqueous Media

Abstract Various factors affecting the extent of adhesion of hydrophilic particles to polymer surfaces have been evaluated. Specifically the kinetics of adhesion, and the influence of substrate surface tension, ionic strength, pH, and surface tension of the suspending liquid medium have been investigated. In addition the role of divalent cations has been assessed. The substrates examined exhibit a wide range of wettability and the hydrophilic particles used were both fresh and glutaraldehyde-fixed human erythrocytes. The extent of particle adhesion to various polymer surfaces is also a function of solution pH and ionic strength. At a constant pH of 6 virtually no erythrocyte adhesion occurs at ionic strengths less than 0.05. Adhesion increases with increasing ionic strength and reaches a limiting plateau value at an ionic strength of approximately 0.1. The actual level of the plateau value is quite different for each polymer. Particle adhesion is also pH dependent. For conditions of constant ionic strengt...

The wettability of fluoro- and chlorocarbon trialkoxysilane films adsorbed on glass and metal surfaces

Abstract Adsorbed films having a wide range of wettabilities were formed on silica, Pyrex, aluminosilicate, α-alumina, steel and gold by trialkoxysilane (and trichlorosilane) compounds. These compounds had the general formulas, RSi(OR) 3 or RSiCl 3 , where R—was a fluorocarbon or a chlorocarbon group and -OR was -OCH 3 or -OCH 2 CH 3 . The fluorocarbon films had γ e values of γ e values of >40 dynes/cm and water contact angles of 80–90 degrees. Film thickness, determined by ellipsometry, was consistently greater than a monolayer of the trialkoxysilane. Desorption experiments suggest that the films were composed of a polysiloxane network along with unhydrolyzed adsorbate, small polysiloxane molecules and solvent.