Changes In Surface Free Energy Research Articles

Dispersion Interactions as Criterion of Optimization of Cementless Composite Binders

The specimens of fine cementless composite binders with various contents of polymineral sand have been prepared. The relative change in surface free energy (δES) has been calculated for these silica-containing systems and the ultimate compression strengths of their composites have been determined. The functional relationships of the mineral fine compositions have shown high negative correlation between the compared parameters. The validity of the mathematical model for the evaluation of dispersion interaction in the composites based on fine mineral particles has been confirmed. The parameter δES has been recommended for the choice of the optimal composition of the mixture characterized by the maximum compression strength.

How To Measure Work of Adhesion and Surface Tension of Soft Polymeric Materials

Knowledge of the work of adhesion and surface tension directs the design of new materials for coatings, adhesives, and lubricants. We develop an approach to determine both properties from analysis of equilibrium indentations of rigid particles in contact with soft polymeric materials. In accord with coarse-grained molecular dynamics simulations, the indentation depth is described by the crossover expression combining together the adhesion and wetting models, which takes into account both the elastic energy of the contact and full surface free energy change outside and inside the contact area. The crossover expression is applied to obtain the work of adhesion and substrate surface tension for polystyrene (PS), carboxyl-modified polystyrene (PS-COOH), and poly(methyl methacrylate) (PMMA) particles in contact with poly(dimethylsiloxane) (PDMS) networks made of brush-like and linear chains. This analysis results in the work of adhesion W = 48.0 ± 2.9 mN/m for PS/PDMS, W = 268.4 ± 27.0 mN/m for PS-COOH/PDMS, a...

Correlation of Surface Free Energy and Hydrophobicity of Aluminum Alloy with and without Corrosion Resistant Organic Coatings

Crambe oil, castor oil and two different proportions of crosslinking agent (Trimethylolpropane) were made to react to form two types of hydroxylated polyesters. Hexamethylene diisocyanate was reacted with castor oil and oxygenated organic compounds to produce a prepolymer. The polyesters were combined with prepolymer in two different proportions to result four polyurethane resins which were applied on AA1200 aluminum alloy surface, giving to the aluminum alloy high corrosion resistance in 3.5% NaCl aqueous solution at 25 oC [1]. This study deals with the wetting characteristic of bare and coated aluminum surfaces by measuring the dynamic contact angle. The determination of the contact angle has helped to interpret the hydrophobic and hydrophilic character of the surface. Surface free energy components (γs, γs p, γs d), and adhesion work (WA) values were calculated by the OWRK method (Owens-Wendt-Rabel and Kaelble) according to the contact angle (Ө) data. For comparison, three liquids with different polarities (distilled water, ethylene glycol and ethanol) were used on the surface of the aluminum alloy with and without organic coating. The results of the contact angle measurements allowed to evaluate the wettability of the substrate surface (with and without coating) and to estimate the free surface energy. The greater the contact angle of the liquid in the organic coating, the more hydrophobic the surface is, and consequently less susceptible to wetting and corrosion. Compared to the substrate (AA1200 aluminum) contact angle of 102.4°, the coatings are less hydrophobic (PEC2 H3 1:2 contact angle of 73.6° and PEC2 H3 1:3 equal to 82.0°). Already the coatings have higher surface energy: substrate (22.2 mN/m), PEC2 H3 1:2 (31.3 mN/m) and PEC2 H3 1:3 (25.4 mN/m). Changes in contact angle and surface free energy are associated with the possibility of forming more hydrogen bonds with the coating. Reference [1] J.V. Nardeli, D.V. Snihirova, C.S. Fugivara, M.F. Montemor, E.R.P. Pinto, Y. Messaddecq, A.V. Benedetti, Localised corrosion assessement of crambe-oil-based polyurethane coatings applied on the ASTM 1200 aluminum alloy, Corros. Sci. 111 (2016) 422-435. Acknowledgement Process FAPESP: 2015/10554-9.

Initial lamellar thickness dependency of recrystallization behavior of poly(4‐methyl‐1‐pentene)

ABSTRACTThe isothermal crystallization and subsequent melting process in semicrystalline poly(4‐methyl‐1‐pentene) were investigated via temperature‐dependent small‐ and wide‐angle X‐ray scattering and Flash DSC techniques. In a phase diagram of inversed crystalline lamellar thickness and temperature, the crystallization and melting lines can be described by two linear dependencies of different slopes and different limiting temperatures at infinite lamellar thickness. Upon subsequent heating, recrystallization lines with different slopes were observed for samples with different lamellar thickness, indicating changes in surface free energy difference between stabilized crystallites and mesomorphic phase. The surface free energy of native crystallites with extended‐chain conformation decreased with increasing lamellar thickness due to a more ordered surface region and less chain ends which changes cooperatively with mesomorphic phase. The surface free energy of stabilized crystallites remained unchanged for all lamellar thickness. Therefore, the recrystallization lines with different slopes are consequences of changes in surface free energy of mesomorphic phase. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 219–224

Laser induced periodic surface structures on polymer nanocomposites with carbon nanoadditives

Laser induced periodic surface structures (LIPSS) are formed on poly(trimethylene terephthalate) and its composites with single-walled carbon nanotubes (SWCNT) and with both SWCNT and expanded graphite (EG) upon irradiation with a Q-Switched Nd:YAG laser (266 nm, 8 ns). The morphology of the polymer films was characterized by atomic force microscopy. A cantilever with a colloidal probe was used to obtain information about surface adhesion. Surface energies were estimated by contact angle measurements using different liquids. Chemical modification in the materials upon irradiation was assessed by Raman spectroscopy. Results show a dependence of the number of pulses required for LIPSS formation as a consequence of the presence of the carbon nanoadditive and an increase of the hydrophilic character of surfaces after irradiation. Moreover, the polar component of the surface free energy changes significantly and surface adhesion increases by the addition of the additive to the polymer matrix. Additionally, the adhesion force decreases after laser nanostructuring as a consequence of a lower contact area in the nanostructured material.

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.

Thermodynamic properties of high-rank tectonically deformed coals during isothermal adsorption

The adsorption capacity and thermodynamic properties of high-rank tectonically deformed coal (TDC) samples from the Yangquan coalfield in North China were analyzed by combining isothermal adsorption and Polanyi potential theory. The adsorption capacities of mylonitic- (10.7015–17.2065 cm3/g) and scaly (9.8237–11.5386 cm3/g) coals are higher than those of cataclastic- (8.3496–9.5238 cm3/g) and schistose (7.7990–8.0467 cm3/g) coals. The primary- and wrinkle coals have the lowest adsorption capacities. The adsorption potential (the change of surface free energy per mole during physical adsorption) decreases with the increasing adsorption space in a parabola characteristic. For different TDCs, the interval length of the adsorption potential distribution is in the same order with the adsorption capacity. The interval lengths of primary-, schistose-, and mylonitic coals are 0–0.014, 0–0.020, and 0–0.025 cm3/g, respectively. The reduction amounts of surface free energy for mylonitic- (6.040–10.082 kJ/cm2) and scaly (2.075–6.047 kJ/cm2) coals are higher than those of the cataclastic- (3.069–4.249 kJ/cm2) and wrinkle (2.222–3.434 kJ/cm2) coals. The initial and saturated adsorption surface free energies of mylonitic- and scaly coals are higher than those of the primary- and schistose coals. Based on the difference in the surface free energy reduction values, the TDCs, especially the mylonitic- and scaly coals, have a greater adsorption potential than primary- and other TDCs.

Some problems of characterization of a solid surface via the surface free energy changes

During the processes occurring at a solid surface, the changes in the surface free energy take place. The knowledge about surface free energy is very helpful for understanding the processes taking place on the surface. However, experimental determination of solid surface free energy is still not a fully solved problem. In this paper, some problems dealing with calculation of solid surface free energy from contact angle are discussed based on literature values of advancing and receding contact angles measured on four different fluoropolymers surface. The four approaches most often used for the calculation are described and especial focus on the approach in which both the advancing and receding contact angles is paid. It is concluded that using probing liquids the absolute value of solid surface free energy cannot be determined. However, the determined apparent values of the energy are very helpful to understand the conditions necessary for a given process to occur.

Atomistic simulations of wetting properties and water films on hydrophilic surfaces.

We use molecular simulations to investigate the wetting behavior of water at flat polar surfaces. Introducing a computational procedure based on thermodynamic integration methods, we determine the equilibrium water film thickness on the surface at given vapor density as well as the corresponding change of the surface free energy. The wetting film is relevant on polar surfaces near the wetting transition and significantly alters the surface contact angle. For thin films, the surface free energy change increases linearly with the thickness, as predicted by simple thermodynamic arguments. For thick films we observe deviations from linearity, which we rationalize by the formation of hydrogen bonds between water molecules in the film. Our approach provides an efficient and accurate technique to calculate the wetting properties of surface layers, which we verify by simulating water droplets on the surfaces.

Impact of atmospheric pressure nonequilibrium plasma discharge on polymer surface metrology

Due to the attraction of plasma technologies as a clean and efficient means of surface modification, significant research has gone into the physical and chemical aspects of polymer functionalization. In this study, it was shown that the use of an atmospheric plasma jet can efficiently modify the surface of polyethylene terephthalate samples and change their hydrophobic properties to more hydrophilic characteristics. The dependence on the changes with respect to time, distance, and atomic oxygen (O I) intensity were considered as factors. It was found that with closer proximity to the plasma source (without causing thermal degradation) and with increasing levels of O I, that the changes of water contact angle and surface free energy can be maximized. It was also observed that the electron energy distribution function, for a given chemistry, significantly differed with changes in distance from the jet nozzle. This shows that for this type of plasma jet system, the bulk of the chemical reactions occur in the nozzle of the jet and not in the surrounding atmosphere. Therefore, this leads to more efficient energy transfer, higher gas temperatures, and better surface activation of samples when compared to systems that produce external chemical reactions due to more diffusion in the surrounding atmosphere and loss of reactive species to other atoms and molecules that are present.

Model study of biostability of DPPC layers deposited by LB/LS on Ti–6Al–4V alloy

This paper reports surface property research on bare Ti–6Al–4V alloy covered with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), which is the main component of cell membranes. The monolayer and bilayer of the phospholipid were deposited by the Langmuir–Blodgett (LB)/Langmuir–Schaefer (LS) technique, and their biostability was investigated in water, phosphate-buffered saline (PBS), simulated body fluid (SBF) and 1% Triton X-100 aqueous solution at 37°C. Moreover, their biostability is compared with that of films prepared by spreading method. The surface free energy changes calculated by Lifshitz–van der Waals/acid–base and contact angle hysteresis measurement are consistent with the changes in surface roughness obtained by optical profilometry. The films prepared by both methods were relatively stable in water. PBS and SBF solutions caused large effects in the change in the layers’ polar component – that is, the electron donor parameter. Also, significant changes took place when Triton X-100 solution was applied, probably because of the DPPC film removal by the surfactant. Finally, it appeared that no drastic differences in the energy changes were observed between the DPPC layers dried overnight in a vacuum desiccator and those dipped into the SBF solution immediately after their deposition on Ti–6Al–4V alloy by the LB/LS method.

Application of thin-layer wicking method for surface free energy determination

The determination of solid surface free energy is still not a fully solved problem. There are several approaches to calculating the energy from the measured contact angles of probe liquids. Surface free energy changes accompany all processes occurring at a solid surface. Therefore, knowledge about these changes is very helpful for better understanding and prediction of their occurrences. In the case of a flat solid surface, contact angle measurement is a principal method for surface free energy determination, but many naturally occurring or artificial solids occur only as powders. In the case of such systems, the thin-layer wicking method, originally proposed by Giese, Constanzo and van Oss and further developed by Chibowski and Hołysz, is useful for determination of the surface free energy. The experimental methods for the determination of solid surface free energy bear some doubts, and the obtained results may be debatable. Nevertheless, even the determined relative changes in the energy shed light on the investigated process, helping in its handling. In this paper the theoretical fundamentals of the thin-layer wicking method as well as some practical guidelines are described. Moreover, literature data of the energy determination for some powdered solids and fabrics are reported.

Neutron-induced modifications on Hostaphan and Makrofol wettability and etching behaviors

Understanding the nature of polymers used as nuclear detectors is crucial to enhance their behaviors. In this work, the induced modifications in wettability and etching properties of Hostaphan and Makrofol polymers irradiated by different fluences of thermal neutrons are investigated. The wetting properties are studied by contact angle technique which showed the spread out of various liquids over the irradiated polymers surfaces (wettability enhanced). This wetting behavior is attributed to the induced changes in surface free energy (SFE), morphology, roughness, structure, hardness, and chemistry. SFE values are calculated by three different models and found to increase after neutrons irradiation associated with differences depending on the used model. These differences result from the intermolecular interactions in the liquid/polymer system. Surface morphology and roughness of both polymers showed drastic changes after irradiation. Additionally, surface structure and hardness of pristine and irradiated polymers were discussed and correlated to the surface wettability improvements. The changes in surface chemistry are examined by Fourier transform infrared spectroscopy (FTIR), which indicate an increase in surface polarity due to the formation of polar groups. The irradiated polymers etching characteristics and activation energies are discussed as well. Lastly, it is evident that thermal neutrons show efficiency in improving surface wettability and etching properties of Hostaphan and Makrofol in a controlled way.

Effect of annealing dependent surface free energy change of Cu foil during graphene growth on quality of monolayer continuous graphene

We report on the characteristics of graphene synthesized on 25 μm thin Cu foil by the chemical vapor deposition (CVD) technique with various surface free energy (SFE) conditions of the Cu foil by annealing. The SFE of Cu foil during graphene growth was changed depending on the pre-annealing time of Cu foil under H2 gas and was characterized by giving priority to its surface morphology. While the higher SFE of Cu foil during graphene growth is beneficial for the fabrication of continuous graphene film, a lower SFE is favorable for the formation of low-defect graphene (lower ID/IG ratio of Raman spectrum); however, a single layer and continuous graphene film does not form. Furthermore, the formation of monolayer graphene is also influenced by the average SFE of Cu foil during the graphene growth stage, resulting in higher I2D/IG ratio of 2.8422, confirming the existence of monolayer graphene. The graphene on high SFE Cu foil was better for optical transmittance due to the high monolayer coverage with moderate electrical properties. Furthermore, graphene with a high ID/IG ratio showed poor mechanical stability during the transfer process due to tearing and defects in the transferred graphene.

Development of a superhydrophobic polyurethane-based coating from a two-step plasma-fluoroalkyl silane treatment

A method of achieving a superhydrophobic surface based upon a highly filled polyurethane (PU) paint coating has been demonstrated through the use of a combined oxygen/argon plasma pretreatment and a fluoroalkyl silane (FAS) final treatment.The combined plasma-FAS treated PU surface has been investigated and characterised using: field emission gun secondary electron microscope (FEG-SEM); X-ray photoelectron spectroscopy (XPS); energy-dispersive X-ray spectroscopy (EDX); water contact angle analysis (WCA); atomic force microscopy (AFM), and; Fourier transform infrared spectroscopy (FTIR).It was found that the oxygen/argon plasma treatment increased both the surface roughness (Ra) and surface free energy (SFE) of the PU paint coating from approximately 60–320nm, and, from ~52 to ~80mN/m respectively. It was also found that the plasma process created a multiscale roughened texture through the process of differential ablation between the PU polymer and the barium sulphate solid content, which is present in the paint as an extender, and other additives. In addition, the process also imparted favourable polar groups into the PU surface from the ionised and radical oxygen species in the plasma.When the FAS coating was subsequently applied to the PU without prior plasma treatment, there was a significant increases in water contact angles. This parameter increased from approximately 60° on untreated PU to around 130° with FAS applied. In this case, the SFE decreased to ~7.5mN/m and showed 42.0at% fluorine present as indicated by XPS.However, subsequently applying the FAS polymer after plasma pretreatment takes advantage of the known synergistic relationship that exists between surface roughness and low surface free energy coatings. The two processes combined to create superhydrophobicity with a surface that exhibited water contact angles up to 153.1°. With this optimised process, the apparent SFE was 0.84mN/m with a more highly fluorinated surface present. In this case 47.2at% surface fluorine was observed by XPS.In addition to changes in SFE, plasma treatment was also observed to alter levels of surface gloss and colour. After exposure to 600s of plasma gloss levels are shown to reduce from values of from ~50 to ~21 (GU), with small but significant corresponding increases in the lightness and yellowness of the surface.

Influence of downstream pressure on pervaporation properties of PDMS and POMS based membranes

Abstract Properties of one POMS and two PDMS based (Pervatech, Pervap 4060) membranes in recovery of various organic components (acetone, butanol, ethanol, ethyl acetate) from aqueous binary mixtures (4 wt.% of organics) were determined during pervaporation at various permeate pressures (1–25 mbar). Performances of membranes were compared, finding that Pervap 4060 is the most effective membrane in all systems tested, whereas Pervatech is the least effective. Permeances of organics and water increased with an increase of pressure on the permeate side in the most of the tested binary aqueous mixtures. Selectivity of the tested membranes towards organics was improved by increase of permeate pressure. Comparing the effectiveness of membranes, it was found that it is related to the hydrophobicity of membranes expressed by surface free energy (SFE) parameter. SFE changes in the following order: Pervap 4060 > POMS > Pervatech. Membrane performances also follow this order during pervaporation.

Tailoring surface properties of polyethylene separator by low pressure 13.56 MHz RF oxygen plasma glow discharge

Low-pressure plasma surface modification in a radio-frequency capacitively coupled glow discharge of oxygen gas was carried out to induce polar functional groups onto polyethylene membrane separator surfaces to enhance its hydrophilicity. The surface changes in surface free energy were monitored by static contact angle measurement. A significant increase in the surface energy of polyethylene membrane separators caused by the oxygen gas plasma modifications was observed. The static water contact angle of the plasma-modified membrane separator significantly decreased with the increase in treatment duration and plasma power. An obvious increase in the surface energy of the membrane separators owing to the oxidative effect of oxygen-gas-plasma modifications was also observed. Optical emission spectroscopy was carried out to analyze the chemical species generated by oxygen gas plasma surface modification. The variations in the surface morphology and chemical structure of the separators were confirmed by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS showed significantly higher surface concentrations of oxygen functional groups in the oxygen-gas-plasma-modified polymeric separator surfaces than in the unmodified polymeric separator surface. The experimental results show the important role of chemical species in the interaction between oxygen gas plasmas and the separator surface, which can be controlled by surface modification to tailor the hydrophilicity of the separator.

Improving the hydrophilicity of metallic surfaces by nanosecond pulsed laser surface modification

The objective of this work was to investigate the surface wettability alteration of the titanium and 316L grade stainless steel by nanosecond pulsed laser processing method. For this purpose, various processing conditions were studied extensively. Different analyses, including the study of the surface morphology, free energy, oxidation, and roughness changes, were assessed in correlation with wettability. It is shown that laser processing in air up to 1 J/cm2 laser fluences enhances the surface roughness which in turn promotes the hydrophilicity. The shape and distribution of the created surface structures are also effective in this regard. On the other hand, the surface free energy as well as oxygen content also increases significantly on the laser-irradiated surfaces. According to these results, it is more logic to conclude that all of these cooperative chemical and physical changes are involved in increasing the surface wettability and causing it to be more hydrophilic.

Wettability of Binary Solid-Supported Films of Zwitterionic/Anionic Phospholipids

The effect of different amounts of anionic phosphatidylglycerol in the zwitterionic phosphatidylcholine monolayers on their properties was quantitatively described in terms of the interactions between these two compounds as well as the changes of mixed monolayers' apparent surface free energy and its components. For all Langmuir films, surface pressure–area per molecule (π–A) isotherms were used to monitor the surface thermodynamics (i.e. the excess area and excess free enthalpy of mixing). This allowed to evaluate the kind and magnitude of interactions that have an influence on the phase behaviour and structural properties of the monolayers. Then, assuming that the molecular properties of Langmuir films are preserved upon transfer to a solid support, further characterizations were accomplished with advancing and receding contact angle measurements on the Langmuir–Blodgett films deposited at 35 mN/m on mica. These enabled the possibility to track changes in the wettability of the tightly packed or phase-separated phospholipid films and their surface free energy as a function of the monolayer composition. It is believed that these results throw a light on better understanding of the organizational structure of lipid films and their interactions with the surrounding environment. Moreover, the obtained results can be also helpful to identify the optimal lipid composition in the production of more effective therapeutic surfactants.

Wettability of Graphene-Coated Surface: Free Energy Investigations Using Molecular Dynamics Simulation

A clear understanding of the wettability of graphene and graphene-coated surfaces is of critical importance for the practical applications of graphene. The present study provides microscopic and thermodynamic perspectives into the wettability of graphene-coated surfaces by molecular dynamics simulations along with free energy calculations utilizing the umbrella sampling. The water droplet adhesion process on graphene-coated surface was characterized by the change in surface area, mean force, and free energy of the droplet. The thermodynamic landscape analysis reveals that the different contributions to the free energies from different underlying substrates induce different entropic resistances from graphene, which leads to the similarity in wettability for graphene-coated silicon and hydroxylated silicon dioxide substrates.