Factors affecting the wettability of polymer surfaces

The inconsistencies in contact angle data presented in the literature can be attributed to a number of factors. The awareness of these factors would allow novice researchers to make meaningful contact angle measurements and interpretations. In this survey the effects of surface roughness and heterogeneity, surface preparation and the presence of contaminants, the vapor environment, pressure and temperature, drop size, electrical charge, and heat transfer on the wettability of polymer surfaces were examined.     

Dynamic Wettability of Different Machined Wood Surfaces

Wetting dynamics on machined wood surfaces is of great interest for the adhesive bonding technology of wood. In this work, the change of apparent contact angles with time of phenolresorcinol-formaldehyde (PRF), polyvinyl-acetate (PVAc), and a series of probe liquids on sawed, planed, sanded, and razor-blade-cut wood surfaces of Southern pine was studied by the sessile drop method using a CCD camera technique. The results indicate that the fastest wetting of the probe liquids occurs on the sanded surfaces because of higher surface roughness and the resulting increase in capillary forces as compared with the sawed, planed and razor blade cut surfaces. The fastest wetting of the PRF and PVAc resins occurred on the comparably smooth planed and razor-blade-cut wood surfaces. A smoother wood surface seems to provide better wetting and penetration properties for high-viscosity liquids such as adhesives, which probably can be attributed to less entrapment of air between the resin and the wood structure.     

Dynamic Wettability of Different Machined Wood Surfaces

Wetting dynamics on machined wood surfaces is of great interest for the adhesive bonding technology of wood. In this work, the change of apparent contact angles with time of phenolresorcinol-formaldehyde (PRF), polyvinyl-acetate (PVAc), and a series of probe liquids on sawed, planed, sanded, and razor-blade-cut wood surfaces of Southern pine was studied by the sessile drop method using a CCD camera technique. The results indicate that the fastest wetting of the probe liquids occurs on the sanded surfaces because of higher surface roughness and the resulting increase in capillary forces as compared with the sawed, planed and razor blade cut surfaces. The fastest wetting of the PRF and PVAc resins occurred on the comparably smooth planed and razor-blade-cut wood surfaces. A smoother wood surface seems to provide better wetting and penetration properties for high-viscosity liquids such as adhesives, which probably can be attributed to less entrapment of air between the resin and the wood structure.     

相容剂对木塑复合材料润湿性及力学性能的影响

采用不同的相容剂改善木塑复合材料界面相容性,通过接触角测定仪测定不同液体在复合材料表面的接触角,得知其表面润湿性,进而推导出其表面自由能。结果表明:相容剂均可有效提高木塑复合材料的界面结合性而,且相容剂5108的改性效果最好。     

Intensive electric arc interaction with polymer surfaces: reorganization of surface morphology and microstructure

Intense electrical arcs were applied to thermoplastic (polyamide 66) and thermoset (fiber reinforced laminated polyester) materials and the resulting carbonization/metallization process was studied on a sub-micron scale with atomic force microscopy to understand very initial stage of reorganization of surface morphology. These changes can be critical in dramatic changes in surface resistivity preceding electric breakthrough. The surface microroughness and the localization of micro- and nanoparticles at the center (arc initiation area) and along the edges of the samples were significantly different for different arc regimes. We suggested that for thermoset, the material is pulled out of the surface in the arc formation area (the center of sample). Afterwards, the intensive re-deposition occurred along the edges enhancing non-uniform ablation around the arc initiation area. In contrary, for thermoplastic samples, the entire polymer surface was re-melted that resulted in dramatic smoothing of the initially non-uniform surface morphology.     

Advanced polymer processing technologies for micro- and nanostructured surfaces: A review

Functional surfaces with attractive properties, such as superhydrophobicity and omniphobicity often rely on the synergy between intrinsic material properties and dual scale micro- and nano-hierarchical structures for achieving desired wettability. Historically, engineered liquid repellent surfaces have attracted a great deal of interest from academia and industry due to their broad application prospects. Hence, for several years, there have been significant scientific efforts by researchers exploring state of the art manufacturing technologies that are efficient and yet cost effective to produce functional liquid repellent surfaces at an industrial scale. This technical review summarizes the various advanced and state of the art polymer processing technologies employed to fabricate the micro- and nanostructured polymer surfaces, with a special focus given to superhydrophobic and omniphobic applications. Here, we discuss the merits and limitations of each fabrication methods available for micro- and nanostructuring of polymer-based surfaces. In addition, an attempt has been made to provide insight into the relationship between geometry of micro/nanostructures (size and shape) and intrinsic wettability on liquid repellency. A special section has been devoted to feature and document all commercialization efforts, including various commercially available products that were developed in the past decade. Finally, outlook and the development trend in the polymer micro- and nanostructured surfaces are highlighted to lead future research.     

Contact Ratio: A New Precise Measurement for Wettability

According to Young's equation, the contact angle “Θ” is considered as the measurable wettability parameter. The rate of change in the contact angle has been commonly used as the relevant parameter of spreading dynamics notwithstanding the difficulties associated with contact angle measurements that are well recognized in the literature. Considering that the velocity of the contact line is the pertinent quantity, it is, therefore, reasonable to regard the change in the contact area as the flux of the process. In this study, we have introduced a new measuring parameter for wettability based on the liquid/solid contact area. The term “contact ratio” has been coined to account for this new measurable parameter. The contact ratio is defined as the ratio between the spreading contact area of liquid over solid surface and the surface area of the spherical drop before spreading. The measurements of contact areas and low‐rate dynamic contact angles for various liquid/solid systems were conducted independently using the ADSA‐P technique. The theoretical relation between the contact ratio and the contact angle is derived based on spherical cap approximation. The results show that there is a good correlation between the theoretical relation and the experimental values. Since the contact angle of a specific system is a unique parameter of the system, the contact ratio can also be presented as a unique parameter of the system. Nevertheless, contact ratio presents a more precise measure of wettability.     

Wettability of kraft pulps-effect of surface composition and oxygen plasma treatment

Wettability and ESCA studies have been carried out using unextracted and extracted kraft pulps with different amounts of lignin. The effect of oxygen plasma treatment was investigated. The wettability was studied by placing a drop of water on a sheet made from the pulp and following the decrease in drop volume and apparent contact angle with time. The first reading is taken after about 0.1 s. Extrapolation to zero time gives the initial contact angle. The initial absorption rate was also determined. Good correlation between the initial contact angle and the oxygen to carbon atomic ratio was found for the pulps without extractives. Pulps containing extractives are very hydrophobic, but an oxygen plasma treatment renders these pulps as hydrophilic as the purest pulps. It is concluded that the oxygen plasma treatment oxidizes the lignin and the extractives but reduces the pure cellulose surface. The oxidized extractives appear to act as wetting agents. The initial absorption rate is strongly dependent on the amount of extractives in the pulp. An oxygen plasma treatment improves the absorption rate, especially if the pulp contains high amounts of extractives.     

Adhesion of anionic surfactants to polymer surfaces and low-energy materials

To study the adhesion of the anionic surfactant sodium dodecyl sulfate (SDS) to various materials, a schematic molecular model of SDS was used which optimally correlates with its critical micelle concentration (c.m.c.) values under various conditions. Using the surface tension components and parameters of (a) the SDS apolar and polar moieties and (b) the polymeric surfaces of cellulose and nylon, the energy of adhesion of SDS to these polymeric surfaces as well as to a typical low-energy material (greasy dirt) in the guise of hexadecane was determined. It could be quantitatively shown (using a surface-thermodynamic approach) that SDS, in water, adheres more strongly to the low-energy (greasy dirt) compounds than to the polymeric materials. The c.m.c. of SDS was derived directly from the surface tension components and parameters of its apolar and polar moieties, and the ζ potential of its polar heads. The c.m.c. values obtained using this model correlate well with the published c.m.c. values obtained experimentally at different ionic strengths.     

塑料表面糙化处理对其润湿性能的影响

采用化学糙化法对塑料表面进行处理,测定了处理前后表面的粗糙度及接触角。研究结果表明,塑料表面经糙化处理后,其润湿性能得到显著的提高。通过实验数据的回归,得出了润湿准数的关联式。该研究结果对塑料的工程应用具有参考价值。     

Wettability reversal of reservoir rock surface through surfactant stabilized microemulsion

In the process of the tertiary recovery of oil and gas resources, it is necessary to use external fluids to displace the crude oil in the reservoir. Whether the crude oil on the surface of the rock can be effectively displaced and the wettability of the rock can be changed to avoid re-adsorption by the crude oil is directly related to the level of oil recovery. Therefore, it is critical to study the cleaning and wettability reversal of reservoir rock surface. Because microemulsions have outstanding performance in changing the wettability of rocks and solubilizing crude oil, this paper uses cetyl trimethyl ammonium bromide (CTAB) as a surfactant and n-butanol as a co-surfactant to prepare microemulsions. The performance of microemulsions with different microstructures on the cleaning and wettability changes of crude oil on the rock surface were studied. The results show that the water-in-oil (W/O) microemulsion has good cleaning efficiency, and the oil removal rate on the sandstone core surface can reach 79.65%. In terms of changing the wettability of the rock surface, W/O, bi-continuous phase (B.C.) and oil-in-water (O/W) microemulsions can change the core surface from lipophilic to hydrophilic. And the effects of the B.C. and O/W microemulsions are more obvious. The microemulsion system that was prepared based on cationic surfactants has a good application prospect in changing the wettability of the reservoir and cleaning the adsorbed crude oil.     

Wettability modification of zirconia by laser surface texturing and silanization

This paper presents the modification of wettability by nanosecond laser surface textured followed by silanization to fabricate the superhydrophobic zirconia surface. Surface modification by varying the pitch between channels leads to micro-channel and micro-grid pattern with different surface roughness. The generated morphological and metallurgical modifications of the surface are measured by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Numerous micro-pits and cracks in the laser-treated areas can be observed from SEM, which indicates crack propagation dominating the process of laser ablation of zirconia. The surface is superhydrophilic with laser-texturing instantly, whose wettability is modified over time. By analyzing the XPS, carbon content, especially C-C (H) groups, is important for the time-dependent wettability. The hydrophobicity of all laser-textured surfaces is improved after silanization. Laser texturing with smaller pitch (50 μm and 70 μm) leads to superhydrophobic surfaces after silanization, which may be due to the modification of physicochemical properties of substrate by very rapid local heating and cooling on the thick surface layer. Overall, the investigations indicate that wettability modifications can be attributed to the surface's microstructure, which depend on laser processing parameters, and chemical composition, especially in terms of −CF₃, −CF₂, and C-C (H).     

Understanding surfaces and buried interfaces of polymer materials at the molecular level using sum frequency generation vibrational spectroscopy

This paper reviews recent progress in the studies on polymer surfaces/interfaces using sum frequency generation (SFG) vibrational spectroscopy. SFG theory, technique, and some experimental details have been presented. The review is focused on the SFG studies on buried interfaces involving polymer materials, such as polymer–water interfaces and polymer–polymer interfaces. Molecular interactions between polymer surfaces and adhesion promoters as well as biological molecules such as proteins and peptides have also been elucidated using SFG. This review demonstrates that SFG is a powerful technique to characterize molecular level structural information of complicated polymer surfaces and interfaces in situ. Copyright © 2006 Society of Chemical Industry     

聚合物表面接枝对润湿性影响的研究进展

综述了近几年国内外常用的表面接枝方法 (表面光接枝、化学接枝、等离子体接枝、臭氧引发接枝) 对聚合物表面润湿性改性的研究进展。并展望了表面接枝改性聚合物润湿性的研究发展     

Wettability between Fe-Al alloy and sintered MgO

In the current study, the wettability between Fe-Al alloy and sintered MgO substrate was investigated. The stable contact angle between the sintered MgO substrate and the liquid iron was approximately 134° at 1550 °C, hardly influenced by Al concentrations of 18 ppm and 370 ppm in the liquid iron. By changing hydrogen partial pressure from 0 vol% to 1 vol%, the oxygen partial pressure decreased. Meanwhile, the contact angle between the MgO substrate and the liquid iron with 370 ppm Al increased with the decrease of oxygen partial pressure. The oxygen partial pressure and contact angle were scarcely affected by increasing hydrogen partial pressure from 1 vol% to 5 vol%. In all cases with 370 ppm Al in the liquid iron, oxide layers were detected on the surface of iron samples. The oxidation of iron could be effectively prevented by increasing the hydrogen partial pressure. The MgO substrate was reduced to Mg vapor in the reducing atmosphere at a high temperature. Then the Mg vapor was dissolved into the iron even before iron melting. Under thermodynamic equilibrium condition, an oxide layer containing two components, i.e. MgO·Al₂O₃ phase and CaO-SiO₂-MgO-Al₂O₃ phase, was generated on the surface of the iron sample. Due to the different wettability between the iron and the two phases, MgO·Al₂O₃ phase was repelled, while the CaO-SiO₂-MgO-Al₂O₃ phase adhered to the inside area.     

Ice adhesion on different microstructure superhydrophobic aluminum surfaces

The adhesion of ice to high -voltage overhead transmission lines should be small to ensure ease of ice shedding under small external forces. In this work, we studied the influence of the microstructure of superhydrophobic surfaces on the strength of ice adhesion at a working temperature of ?6?°C. Compared to a bare aluminum surface, the microstructure superhydrophobic aluminum surfaces did decrease ice adhesion strength. The superhydrophobic aluminum surfaces with a larger number of micro-holes produced the lowest strength of ice adhesion; its ice adhesion strength was ～163.8 times lower than that for the bare aluminum samples. Furthermore, such microstructure aluminum surfaces had water contact angles larger than 150° and water sliding angles of less than 8.2° even at a working temperature of ?6?°C. The low values of the ice adhesion strength of the above samples were mainly attributed to the superhydrophobic property, which was obtained by creating a structure of micro-nanoscale holes on the aluminum surface after treatment with a low- surface-energy fluoroalkylsilane (FAS).     

Time dependent wettability of mineral and metal surfaces in the presence of thiol surfactants

The decrease in wettability of mineral and metal surfaces due to the adsorption of surfactants is crucial for flotation recovery and upgrading of these materials in mineral processing. Because of limited residence time in flotation processing, the kinetics of the wettability changes of the mineral surface becomes an important issue. The time dependent wettabilities of silver and galena (PbS) surfaces in aqueous solutions of di-isobutyl dithiophosphinate, a commercial flotation reagent, were determined from in situ measurements of advancing and receding bubble contact angles. Kinetic parameters were calculated from these data. By comparing the in situ measurements with ex situ measurements of water contact angles and external reflection FTIR of the adsorbed organic films on silver, a physical interpretation of the wettability data is given in terms of the evolution of these thin organic films on the mineral surfaces.     

The Relationship between the Wettability and Aggregation of Ultrafine Minerals in Methanol-Water Mixtures

A thermodynamic expression for describing the relationship between the wettability and aggregation of fine minerals has been derived using the critical adhesion tension concept. The approach has been confirmed qualitatively by measurements of the above phenomena on magnesite and dolomite fines hydrophobized by sodium oleate in methanol-water mixtures. The role of interfacial interactions expressed through γ_SL has been documented.     

Wettability and osteoblastic cell adhesion on ultrapolished commercially pure titanium surfaces: the role of the oxidation and pollution states

The oxidation state of the surfaces of titanium-based biomaterials strongly depends on their previous history. This factor affects the titanium wettability and it probably conditions the success of the implanted biomaterials. However, the separate role of the pollution and oxidation states of metallic titanium surfaces remains still controversial. To elucidate this, it is required to standardize the initial surface state of titanium in terms of roughness and surface chemistry, and then, to monitor its wettability after the corresponding treatment. In this work, we studied finely polished surfaces of commercially pure titanium (cpTi) which were subjected to cleaning surface treatments. X-Photoelectron spectroscopy was used to characterize the surface chemistry and the oxide film thickness. The contact angle hysteresis in underwater conditions was measured with the growing/shrinking captive bubble method, which allowed for mimicking the real conditions of implantable devices. The water wettability of smooth cpTi surfaces was stabilized with weak thermal oxidation (230?°C, 30?min). The osteoblastic cell response of the stabilized and non-stabilized cpTi surfaces was analyzed. Although the oxidation and pollution states were also stabilized and normalized, no correlation was observed between the stable response in wettability of titanium and its cell adhesion.     

Temperature‐Induced Changes in the Surface Wettability of SBR + PNIPA Films

We report a novel rubber film made by a simple mixing method, which realizes a steep temperature dependence of the contact angle of water at a critical temperature of 41 °C. We mixed a common SBR with a known temperature‐responsive PNIPA to make a thermo‐responsive rubber. This rubber film distinctly showed a switch of surface wettability between hydrophilic below 41 °C and hydrophobic above 41 °C. The switching property is possibly controlled by the mixing ratio of PNIPA to SBR, preparation method, added chemicals, and so on. This mixing technique will be applied for the control of surface wetting properties by temperature on various SBR‐like rubber materials, such as wet‐brake performance of automobile tires on a rainy day.