Polar Component Of Surface Energy Research Articles

Effect of hydrophilic graphite flake on thermal conductivity and fracture toughness of basalt fibers/epoxy composites

In this work, we fabricated basalt fiber-reinforced epoxy composites using natural graphite flakes. The composites were reinforced with various concentrations of natural graphite flakes. Natural graphite flakes significantly enhanced the mechanical properties of the composites, such as the critical stress intensity factor (KIC) and critical strain energy release rate (GIC). In particular, basalt fiber-reinforced composites containing 20 wt% of natural graphite flakes exhibited highest mechanical behavior compared. The fracture toughness mechanisms were illustrated using a crack theory based on morphology analyses of fracture surfaces. In addition, the composites exhibited high thermal stability and thermal conductivity, attributed to the exceptional thermal stability and thermal conductivity inherent in the natural graphite flakes. We observed a direct linear relationship between thermal conductivity and fracture toughness through certain polar components of surface energy. The natural graphite flake particles improved mechanical and thermal properties by performing a crack pinning role in the epoxy-matrix composites.

Predicting microcapsules morphology and encapsulation efficiency by combining the spreading coefficient theory and polar surface energy component

The morphology and encapsulation efficiency of thermoregulating microcapsules based on a spreading coefficient theory and polar surface energy component were evaluated. For this purpose the microencapsulation of phase change materials (PCMs) with different copolymer shells and using different suspending agents by the suspension-like polymerization technique has been carried out. Contact angles and interfacial tensions were measured, and results were discussed with respect to the internal structure as well as encapsulation efficiency of the microcapsules. A core/shell structure was expected as the equilibrium morphology, whereas the experimental structure exhibited a matrix morphology. A core-shell structure was favored by increasing the polarity of the polymer and decreasing the solubility between the core and shell. The type and amount of suspending agent do not have a significant influence on the final characteristic of the microcapsules. Shells with various polarities were synthesized from styrene (S), divinylbenzene (DVB) and hexa(methacryloylethylenedioxy)cyclotriphosphazene (PNC-HEMA), and it was found that a core-shell structure was only obtained for microcapsules with a high polar surface energy component.

Direct Effect of Dielectric Surface Energy on Carrier Transport in Organic Field-Effect Transistors.

The understanding of the characteristics of gate dielectric that leads to optimized carrier transport remains controversial, and the conventional studies applied organic semiconductor thin films, which introduces the effect of dielectric on the growth of the deposited semiconductor thin films and hence only can explore the indirect effects. Here, we introduce pregrown organic single crystals to eliminate the indirect effect (semiconductor growth) in the conventional studies and to undertake an investigation of the direct effect of dielectric on carrier transport. It is shown that the matching of the polar and dispersive components of surface energy between semiconductor and dielectric is favorable for higher mobility. This new empirical finding may show the direct relationship between dielectric and carrier transport for the optimized mobility of organic field-effect transistors and hence show a promising potential for the development of next-generation high-performance organic electronic devices.

Calculation of the Free Surface Energy of Coals from the Donets Basin and Graphites

The methodologies of the determination of the free surface energy of solids were analyzed. It was shown that the currently available models for the calculation of free surface energy are based on the measurements of the angles of contact, and they contain an internal contradiction that consists in the fact that the surface energy is divided into two or three components: a polar component, hydrogen bonds, and a dispersion component. The free surface energy was calculated for the metamorphic series of coals from the Donets Basin (long-flame, gas, coke, and lean coals and anthracites) and graphites. Considerable differences in the values of free surface energy for different coalmine beds of anthracites were not revealed. Technical-grade and spectral graphites are insignificantly different from anthracites in terms of free surface energy, but a polar component of free surface energy has lower values of 0.0054–0.0117 J/m2.

Effect of Nonionic Surfactants on Dispersion and Polar Interactions in the Adsorption of Cellulases onto Lignin.

Residual lignin in pretreated biomass impedes enzymatic hydrolysis. Nonionic surfactants are known to enhance the enzymatic hydrolysis of lignocellulosic biomass but their mechanisms of action are incompletely understood. This study investigates the effect of a nonionic surfactant, Tween 80, on the adsorption of cellulases onto model lignin substrates. Lignin substrates were prepared by spin coating of flat substrates with three different types of lignin: organosolv lignin, kraft lignin, and milled wood lignin. The functional group distributions in the lignins were quantitatively analyzed by 31P NMR spectroscopy. The surface energies and surface roughnesses of the substrates were determined by contact angle measurements and atomic force microscopy, respectively. Tween 80 and cellulase adsorption onto the lignin substrates was analyzed with a quartz crystal microbalance with dissipation monitoring. Tween 80 adsorbed rapidly and primarily (≥85%) via dispersion interactions onto the lignin substrates and effected solubilization of lignin molecules, most notably with organosolv lignin, having the largest dispersive surface energy component and smallest molar mass. Cellulase adsorption onto the lignin substrates was mostly irreversible and had both a rapid and a gradual adsorption stage. Rapid cellulase adsorption was primarily (≥64%) mediated by dispersion interactions. The subsequent gradual mass increase is postulated to involve swelling of the lignin substrates. Adsorbed Tween 80 rendered lignin surfaces more hydrophilic by increasing their polar surface energy component and reduced both the extent of rapid cellulase adsorption as well as the rate of the subsequent gradual mass increase. The effect of Tween 80 on the rate and extent of the gradual mass increase depended strongly on the chemical properties of the lignin.

Infused-liquid-switchable porous nanofibrous membranes for multiphase liquid separation

Materials with selective wettabilities are widely used for effective liquid separation in environmental protection and the chemical industry. Current liquid separation strategies are primarily based on covalent modification to control the membranes’ surface energy, or are based on gating mechanisms to accurately tune the gating threshold of the transport substance. Herein, we demonstrate a simple and universal polarity-based protocol to regulate the wetting behavior of superamphiphilic porous nanofibrous membranes by infusing a high polar component of surface energy liquid into the membranes, forming a relatively stable liquid-infusion-interface to repel the immiscible low polar component of surface energy liquid. Even immiscible liquids with a surface energy difference as small as 2 mJ m−2, or emulsions stabilized by emulsifiers can be effectively separated. Furthermore, the infused liquid can be substituted by another immiscible liquid with a higher polar component of surface energy, affording successive separation of multiphase liquids.

Effects of atmospheric plasma treatment on adhesion and tribology of aromatic thermoplastic polymers

After cold plasma treatment of poly(ethylene terephthalate) and poly(ether‐ether ketone) surfaces by dielectric barrier discharge (DBD) under atmospheric (air) conditions, variations in surface chemistry, and morphology were investigated in relation with adhesion and tribological properties. According to XPS measurements, surface oxidation caused the formation of low molecular weight moieties of carboxylic acids. The latter resulted in more hydrophilic surfaces according to water contact angle measurements, with mainly a higher polar surface energy component. In parallel, the surface roughness of originally polished surfaces reduced due to flattening of local surface asperities after DBD. The DBD significantly improved the adhesive shear strength for different glue types in polymer/polymer and polymer/steel joints, while the best adhesion was observed for a two‐component epoxy type adhesive. Under dry sliding conditions, the coefficients of friction were lower after DBD compared to pristine samples only under mild sliding conditions (v = 0.05 m/s; p < 1 MPa.m/s), while the higher normal loads caused an increase in coefficients of friction likely due to the higher contributions of surface deformation. Most interestingly, the lower coefficients of friction after DBD were observed under oil lubrication and after cleaning the sliding track (“run‐out” condition), due to the better retention of oil at the sliding surface for plasma‐treated polymers. POLYM. ENG. SCI., 58:E93–E103, 2018. © 2017 Society of Plastics Engineers

Characterization of Water Transport in PEMFC Electrode Using the Washburn Method

Proton exchange membrane fuel cells (PEMFCs) are promising power sources for automotive use. Despite the numerous efforts made the recent years, water management still remains a major limiting factor to PEMFC performance and durability. Specifically, the performance of catalyst layers (CLs), where the electrochemical conversion takes place, is heavily affected by mass transport limitations. Understanding liquid-water transport phenomena inside catalyst layers is vital and must be achieved by a basic understanding of the wetting and morphological properties of the pore structure. This requires measuring and quantifying several properties including surface energy and internal contact angle. In this work we present a method for estimation of the internal contact angle to water (and other different liquids) and the surface free energy of CLs with different ionomer/carbon ratios. The method combines the Washburn technique [1] and the Owens-Wendt model [2]. A similar approach was already used by other researchers to determine the wetting properties of fuel cell gas diffusion layers [3,4] but, to the best of our knowledge, such method was never used for catalyst layers. The CLs (carbon-ionomer films) used in this study were fabricated by the 3M Company. They consisted of Vulcan™ XC-72 carbon dispersed in a 3M brand ionomer matrix. Being very thin, these films are not stiff enough to immerse into the liquids. Therefore, each sample was prepared by hot-pressing the carbon-ionomer film on both sides of an Ethylene Tetrafluoroethylene (ETFE) film (120 μm thick) with a surface of 10 mm x 5 mm (see Figure 1.a). The internal contact angle was measured by a dynamic sorption experiment according to the Washburn method [1] using a Krüss tensiometer K100 (Krüss GmbH, Hamburg, Germany) operated at room temperature. A set of six wetting liquids was tested: n-hexane, acetone, methanol, water, Fluorinert™ FC-3283 (3M Company) and toluene. As shown in Figure 1.a, when the sample (10 mm x 5 mm) came into contact with the surface of the desired liquid, the liquid was drawn up as a result of capillary action. The increase in sample mass due to the added liquid weight was determined with respect to time during the measurement. Using the Washburn method [1], internal contact angle can be obtained from the slope of the linear region of the square of the mass against time, Figure 1.b. These contact angles measurements were used to extract both dispersive and polar component of the solid surface energy using the Owens–Wendt model [2-4]. Materials with different ionomer/carbon ratio were used to determine the influence of the ionomer on electrode water uptake and transport. The effect of platinum loading on water transport was also investigated. Acknowledgement The authors thank Andrew Haug of 3M Company for providing materials tested in this study.

Improvement of Interaction in a Composite Structure by Using a Sol-Gel Functional Coating on Carbon Fibers.

The modification of carbon fibers for improving adhesion between fibers and an epoxy resin in composite materials has become the focus of attention. In this work the carbon fiber coating process has been devised in a way preventing the stiffening and clumping of fibers. To improve interactions between coated fibers and a resin in composites, four types of silica coatings with different organic functional groups (3-aminopropyl–coating 1, 3-mercaptopropyl–coating 2, 2-(3,4-epoxycyclohexyl) ethyl–coating 3, methyl–coating 4) were obtained. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to distinguish the changes of a carbon fibers surface after coating deposition. The thickness of the obtained coatings, including the diversity of thickness, was determined by transmission electron microscopy (TEM). The increase in surface free energy (SFE) of modified fibers, including the distinction between the polar and dispersive parts, was examined by wettability measurements using a tensometric test. The developed coating preparation process allowed to cover fibers separately with nanoscale silica layers, which changed their morphology. The introduction of organic functional groups resulted in surface free energy changes, especially an increase in specific polar surface energy components.

Oxygen doping effect on the wettability of diamond-like carbon thin films

Diamond like carbon (DLC) thin films as a great coating to protect biomedical tools and optical devices are being developed. Modifying the surface properties, such as wettability, is necessary in some application. In this research, oxygen doping effect on the DLC films wettability was investigated. Oxygen doped diamond-like carbon (DLC) thin films were deposited by the RF-PECVD method with different oxygen concentrations in feeding gas (0.0, 1.9, 3.8, 5.6, 7.4 and 9.1vol%). The film's structure was studied by Raman spectroscopy (RS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The chemical composition was determined by a combination of elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). Surface roughness and morphology of the films were analyzed by an atomic force microscopy (AFM). Wettability of the films was characterized by measuring the contact angles of the films with water. The results showed that by increasing the incorporation of oxygen into the films' structure, the contact angles of water with films were reduced. The increase in the oxygen content of the films, from zero to 11at%, caused to reduce water contact angles from 78.4° to 66.0°. By adding the oxygen into the film's structure, CO and CC bonds content increased in the films. Due to the more polarizability of CO and CC bonds in comparing with CC and CH bonds, a polar component of films' surface energy was increased by adding the oxygen to the films' structure. The surface roughness of the un-doped and doped DLC films were so low (less than 1nm) that they had no roles in the films' surface energy. Doping the DLC films with oxygen caused to increase wettability, without no significant change in the morphology and surface roughness.

Interfacial adhesion properties of carbon fiber/polycarbonate composites by using a single-filament fragmentation test

To reveal the interfacial adhesion nature between a carbon fiber (CF) and its surrounding polycarbonate (PC) matrix, the carbon fibers were electrochemically oxidized to differentiate the surface roughness and chemistry status. The fiber surfaces were characterized by SEM, XPS, AFM and dynamic contact angle measurements. Both surface-coating and hot-pressing methods were adopted to prepare specimens for evaluating the CF/PC interfacial adhesion properties by single-filament fragmentation tests. The surface-coating method gave a relatively weak interfacial shear strength (IFSS) result, which varied almost monotonously with the fiber surface roughness, suggesting that in this case the interfacial properties should be dominated by a mechanical interlocking mechanism. However, the hot-pressing process gave a 46–81% higher IFSS result than the solution-coating one, and the IFSS data increased almost linearly with polar component of the carbon fiber surface energy. It was very possible that the interfacial adhesion properties were largely controlled by the chemical reactions (e.g., ester-exchange reaction) at high temperature, which were easy to occur in the presence of oxygenated functionalities at CF surfaces.

Wettability of carbon nanotube fibers

Carbon nanotube (CNT) fibers are interesting alternatives to carbon fibers as fibrous reinforcement. However, good interfacial adhesion between the fibers and the matrix is difficult to control. Wetting of the fiber reinforcement with the matrix strongly determines the interfacial strength. Therefore, accurate characterization of the wettability of CNT fibers is one of the most important cornerstones to improve the interfacial adhesion. In this work, dynamic contact angle measurements were conducted on individual CNT fibers by using a modified tensiometric method based on the Wilhelmy method combined with a synchronized optical observation. The CNT fiber-liquid interactions were monitored in-situ, and accurate measurements of the contact angles were achieved. Contact angles on CNTs were estimated through a modified Cassie-Baxter model on the basis of the experimental contact angle values of CNT fibers. Subsequently, the non-polar and polar surface energy components of the CNTs were obtained. Then, the wetting parameters (work of adhesion, spreading coefficient and wetting tension) were predicted by using the surface energy values of both the CNTs and a series of polymers (PP, MAPP, PET, PVDF, and PVA). The results indicate that PVA is in terms of wetting the most suitable matrix for the preparation of CNT fiber polymer composites.

Wettability of Complex Fluids and Surfactant Capped Nanoparticle-Induced Quasi-Universal Wetting Behavior.

Even though there are quite large studies on wettability of aqueous surfactants and a few studies on effects of nanoparticles on wettability of colloids, to the best of authors' knowledge, there is no study reported on the combined effect of surfactant and nanoparticles in altering the wettability. The present study, for the first time, reports an extensive experimental and theoretical study on the combined effect of surfactants and nanoparticles on the wettability of complex fluids such as nanocolloids on different substrates, ranging from hydrophilic with a predominantly polar surface energy component (silicon wafer and glass) to near hydrophobic range with a predominantly dispersive component of surface energy (aluminum and copper substrates). Systematically planned experiments are carried out to segregate the contributing effects of surfactants, particles, and combined particle and surfactants in modulating the wettability. The mechanisms and the governing parameters behind the interactions of nanocolloids alone and of surfactant capped nanocolloids with different surfaces are found to be grossly different. The article, for the first time, also analyzes the interplay of the nature of surfaces, surfactant and particle concentrations on contact angle, and contact angle hysteresis (CAH) of particle and surfactant impregnated colloidal suspensions. In the case of nanoparticle suspensions, the contact angle is observed to decrease for the hydrophobic system and increase for the hydrophilic systems considered. On the contrary, the combined particle and surfactant colloidal system shows a quasi-unique wetting behavior of decreasing contact angle with particle concentration on all substrates. Also interestingly, the combined particle surfactant system at all particle concentrations shows a wetting angle much lower than that of the only-surfactant case at the same surfactant concentration. Such counterintuitive observations have been explained based on the near-surface interactivity of the particle, fluid, and surfactant molecules based on effective slip length considerations. The CAH analyses of colloidal suspensions at varying surfactant and particle concentrations reveal in-depth physical insight into contact line pinning, and a unique novel relationship is established between the contact angle and differential energy for distorting the instantaneous contact angle for a pinned sessile droplet. A detailed theoretical analysis of the governing parameters influencing the wettability has been presented invoking the principles of DLVO (Derjaguin-Landau-Verwey-Overbeek), surface energy and interaction parameters influencing at the molecular scale, and the theoretical framework is found to support the experimental observations.

Modification of aluminum alloy surface properties by wave-long laser texturing

Change of the static contact angle (SCA) of 10 μL distilled water droplet on laser textured aluminium alloy (AMG-6) substrates was studied. The texture was deposited by a laser system based on a fiber laser. An increase in the power of laser radiation is found to lead to a decrease in the SCA measured on the first day after texturing. Change of dispersion and polar surface energy components of textured substrates is determined. Under the influence of the environment, the surface properties of AMG-6 change with time. SCA increased and reached stable state on the twentieth day after texturing.

Comparative study on structure and wetting properties of diamond-like carbon films by W and Cu doping

By specifically selecting the carbide-forming metal (W) and non-carbide-forming metal (Cu) as the doped metal, we fabricated the W and Cu doped diamond-like carbon (W-DLC and Cu-DLC) films by hybrid ion beam system, respectively. And a comparative study on structure and wetting properties of W-DLC and Cu-DLC films was focused. For Cu-DLC films, the wettability transformation from hydrophilicity (76.56°) to hydrophobicity (105.6°) was observed. While in case of W-DLC films, the wettability of films maintained the hydrophilicity (73.6±3.93°) within the presented W concentration. Based on the surface energy calculation and electronic structure analysis from first-principles calculations, we firstly gained insight into the wettability behavior of W-DLC and Cu-DLC films in terms of the bond characteristics formed between doped metal and C atoms. Results showed that the anti-bonding characteristic between Cu and C atoms reduced the polar components of surface energy and dangling bonds, contributing to the improvement of hydrophobic property, while the non-bonding characteristic for WC bond resulted in the appearance of dipoles, leading to the hydrophilic character. It was in particularly concluded that the different bond characteristic between metal and C atoms played a key role in the wettability of metal doped DLC films. The obtained results offer a facile strategy to design DLC films with tailored wettability properties for the promising hydrophobic applications.

Tensiometric method to reliably assess wetting properties of single fibers with resins: Validation on cellulosic reinforcements for composites

Wetting properties and capillary parameters are of first interest for composite and especially bio-composite manufacturing, interface compatibility between reinforcement and matrix, and durability. Few studies have been dedicated in literature to continuous textile fibers and uncured liquid resins wetting properties, and particularly the methods used may be ambiguous, revealing a wide dispersion in results. In this work a reliable method is proposed to determine properly the wetting properties of fibers and some resins commonly used for composite applications. Firstly, a procedure to characterize dispersive and polar components of surface tension for an epoxy and a partially bio-based resin with a tensiometer is proposed. Then a new method was applied on single fibers of semi-synthetic cellulose (viscose), which allows deriving representative values of contact angles from a series of measurements, minimizing the measurement scatter even when using a conventional tensiometer. Resin components and contact angles between cellulose fibers and test liquids, including resins, led to characterize dispersive and polar components of fiber surface energy.

Effect of cold atmospheric pressure plasma gas composition on the surface and cyto-compatible properties of low density polyethylene (LDPE) films

In the present investigation, we have studied the influence of oxygen (O2) flow rate in the atmospheric pressure argon (Ar) plasma zone for improvement of the surface and cell compatible properties of LDPE film. Various characterization techniques such as contact angle (CA), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), etc were used to investigate the hydrophilicity, surface chemistry and morphology of LDPE films respectively. Fowke's approximation method was used to evaluate the polar and dispersion components of the total surface energy of LDPE films using contact angle values of three testing liquids. Moreover T-peel and lap shear tests were used to analyze the adhesive strength of the surface modified LDPE films. Finally cyto-compatibility of the surface modified LDPE film was analyzed by in vitro cell compatibility analysis which includes the cell viability and adhesion using NIH-3T3 fibroblast cells. The results obtained from various characterization techniques evidently revealed that cold atmospheric pressure (CAP) plasma treatment enhanced the surface properties (hydrophilicity, surface morphology and surface chemistry) of LDPE film. Owing to tailored physico-chemical changes induced by the CAP plasma treatment facilitates improvement in adhesive strength as well as adhesion and proliferation of cells on the surface of LDPE films.

Titanium nitride deposition on aluminium for adhesion promotion

This investigation highlights the adhesion characteristics of unmodified and titanium nitride deposited aluminium. Due to titanium nitride deposition on aluminium, surface energy, especially the polar component of surface energy of aluminium, increases considerably. There is a significant change in physicochemical characteristics due to titanium nitride deposition on aluminium observed under atomic force microscopy and X-ray photoelectron spectroscopy analysis. Lap shear tensile test results reveal that due to titanium nitride deposition on aluminium, the adhesive joint strength of aluminium to aluminium increases considerably and increases further if silicate nanoparticulates are dispersed into the epoxy adhesive. Dispersion of silicate nanoparticles into the silicon adhesive deteriorates the adhesive bond strength. Failure mode of adhesive bonding of unmodified aluminium is primarily interfacial and changes to cohesive due to the titanium nitride deposition on aluminium.

Correlation of nanoscale behaviour of forces and macroscale surface wettability.

In this manuscript, we demonstrate a method based on atomic force microscopy which enables local probing of surface wettability. The maximum pull-off force, obtained from force spectroscopy shows a remarkable correlation with the macroscopically observed water contact angle, measured over a wide variety of surfaces starting from hydrophilic, all the way through to hydrophobic ones. This relationship, consequently, facilitates the establishment of a universal behaviour. The adhesion forces scale with the polar component of surface energy. However, no such relation could be established with the dispersive component. Hence, we postulate that the force(s) which enable us to correlate the force spectroscopy data measured on the nanoscale to the macroscopic contact angle are primarily arising from electrostatic-dipole-dipole interactions at the solid-liquid interface. London forces play less of a role. This effect in is line with density functional theory (DFT) calculations suggesting a higher degree of hydroxylation of hydrophilic surfaces. This result shows that molecular simulations and measurements on an atomic scale can be extrapolated to macroscopic surface wetting problems.

Surface and spectroscopic properties of CdSe/ZnS/PVC nanocomposites

It is valuable to understand the way the wettability is affected by the solid and the liquid surface free energies. For this study, transparent films of CdSe/ZnS/PVC nanocomposites have been prepared and characterized by FTIR and contact angle measurements. Moreover, the presence of polar interactions at the liquid/polymer interfaces, which show a proportionality to the polar components of the liquid surface energy for pure polyvinyl chloride (PVC) and all CdSe/ZnS/PVC nanocomposites, is also studied. By using the surface polarizability hypothesis, there is possibility to obtain the dispersion component of surface‐free energies of pure PVC and also its nanocomposites from the contact angles measurement of only polar liquids. This approximately is coincident with that published data for pure PVC obtained from both polar and nonpolar liquids' contact angles. In addition to this, the absorption spectra and the photoluminescence illustrate clearly the effect of CdSe/ZnS quantum dots on their host matrix. The calculated values of the optical parameters, such as energy gap and Urbach energy, illustrate an inverse proportionality between them. POLYM. COMPOS., 38:749–758, 2017. © 2015 Society of Plastics Engineers