Surface Free Energy Values Research Articles

Polymers containing phtalimidoalkyl groups in the side chains. effect of the alkyl groups in monolayers at the airwater interface

AbstractSurface activity of poly(methacrylate)s containing phthalimidoalkyl groups was studied. Surface pressure-area isotherms ( -A) at the air-water interface were determined. These polymers form stable and condensed monolayers. The monolayers are more condensed and the limiting surface area A0 values decrease when the number of the methylene groups in the lateral chains increases. Surface pressure variation at the semidilute region of the monolayers was expressed in terms of the scaling laws as power function of the surface concentration. The static elasticity εo and the exponent of the excluded volume υ were determined. The hydrophobicity degree of polymers was estimated from the determination of the total surface free energy values by wettability measurements. Molecular dynamic simulation (MDS) was performed in order to explain the experimental behavior of polymers at the air-water interface.

Modelling the surface free energy parameters of polyurethane coats—part 1. Solvent-based coats obtained from linear polyurethane elastomers

Polyurethane elastomers coating were synthesised by using typical diisocyanates, polyether and polyester polyols and HO-tertiary amines or diols as a chain extenders. Mole fractions of structural fragments (κ exp) responsible for the polar interactions within polyurethane chains were calculated by 1H NMR method. Obtained results were confronted with the analogous parameter values (κ theor) calculated on the basis of process stoichiometry, considering the stage of the production of isocyanate prepolymers and reaction of their extension for polyurethanes. Trials of linear correlation between the κ exp parameters and surface free energy (SFE) values of investigated coatings were presented. SFE values were determined by Owens–Wendt method, using contact angles measured with the goniometric method. Based on achieved results, another empirical models, allowing for prediction the influence of the kind of polyurethane raw materials on SFE values of received coatings were determined. It was found that it is possible to regulate the SFE in the range millijoules per cubic metre by the selection of appropriate substrates. It has been found that use of 2,2,3,3-tetrafluoro-1,4-butanediol as a fluorinated extender of prepolymer chains is essential to obtain coatings with increased hydrophobicity, applied among others as biomaterials—next to diphenylmethane diisocyanate and polyoxyethylene glycol.

Enhanced solder wettability of oxidized‐copper with lead‐free solder via Ar‐H2 plasmas for flip‐chip bumping: the effects of H2 flow rates

PurposeThe purpose of this paper is to investigate the effects of H2 flow rate on improving the solder wettability of oxidized‐copper with liquid lead‐free solder (96.5Sn‐3Ag‐0.5Cu) by Ar‐H2 plasmas. The aim was to improve the solder wettability of oxidized copper from 0 per cent wetting of copper oxidized in air at 260oC for 1 hour to 100 per cent wetting of oxidized‐copper modified by Ar‐H2 plasmas at certain H2 flow rates and to find correlations between the surface characteristics of copper and the solder wettability with liquid lead‐free solder.Design/methodology/approachTo reduce the copper oxides on the surfaces of oxidized‐copper for improving solder wettability with liquid lead‐free solder, this study attempted to apply Ar‐H2 plasmas to ablate the copper oxides from the surfaces of oxidized‐copper by the physical bombardment of the Ar plasmas and to reduce the surfaces of oxidized‐copper by the chemical reaction of H2 plasmas with the surfaces of oxidized‐copper.FindingsThe solder wettability of oxidized‐copper was found to be highly dependent on the surface characteristics of the copper. The values of polar surface free energy and dispersive surface free energy on the surfaces of oxidized‐copper modified by Ar‐H2 plasmas were close to those values of solid lead‐free solder, which resulted in improved solder wettability with liquid lead‐free solder. Auger spectra indicated that the Ar‐H2 plasma modification was used to remove the copper oxides from the surfaces of oxidized‐copper.Originality/valueThe surface characterization of copper surfaces is typically determined by expensive surface analysis tool such as Auger Electron Spectroscopy (AES). This paper reports the results of a study of a promising technique called the sessile drop test method, for examining the surface free energies such as total surface free energy, polar surface free energy and dispersive surface free energy on the surfaces of copper to clarify how the solder wettability of oxidized‐copper with liquid lead‐free solder was enhanced by Ar‐H2 plasmas.

Differences in Charge Density Distribution and Stability of Two Polymorphs of Benzidine Dihydrochloride

Charge density distribution analysis supplemented by energy studies of two known (previously reported) polymorphic forms of benzidine dihydrochloride — triclinic P1̅ (TP) and orthorhombic Pbcn (OP) — is presented. High resolution X-ray diffraction measurement results were additionally related to the theoretically evaluated charge density distribution on the basis of periodic ab initio computations. In the case of TP, collected neutron diffraction structural data were included in the high resolution X-ray multipole refinement procedure. Although TP and OP form generally similar layered crystal architectures, the two structures differ significantly in details, due to slightly different conformations of the benzidinium cation, different packing, and thus intermolecular interactions. This is reflected in charge density distribution, crystal morphology, and growth. For TP, the integrated charge for the chloride anions is equal to ca. −0.90e, while for OP it is −1.07e. In consequence, charges for the benzidinium cation are equal to +1.85e for TP and +2.12e for OP. Different charge distributions for both polymorphs cause significant differences in the electrostatic potential. In the case of OP, the electrostatic potential for the −NH3+ group is substantially higher than for TP. Lower values of charge density at aromatic rings of the benzidinium cation for TP can be associated with significant contribution of stacking type of interactions. TP is slightly (ca. 10–15 kJ·mol–1) more thermodynamically advantageous than OP, however, the difference constitutes just a small percentage of the total cohesive energy derived (ca. −1500 kJ·mol–1). Therefore, both polymorphic forms can be obtained simultaneously from one solution under the same conditions. On the other hand, TP is characterized by a more homogeneous distribution of ionic fragments in its crystal lattice than OP. The straightforward comparison of the crucial interlayer interaction energies and the surface free energy values between both polymorphs shows that in the case of TP crystal faces should more preferably grow, being slightly less stable than in OP. Lower surface free energy in OP, and especially low interlayer interaction energy of (100) slabs, presumably hampers further growth of the initially formed crystals, explaining the difficulties in obtaining OP crystals of the size suitable for neutron diffraction experiments. Naturally, kinetic and solvent effects should not be neglected. Nevertheless, the energy results show that despite the resemblance of the cohesive energy values of polymorphs, the character and features of their crystal architectures may cause significant differences in crystallization mechanisms and crystal quality. It appears that there is little correlation between geometrical parameters of hydrogen bonds and their energies.

Film Properties of Poly(lactic Acid) Comprising N-Methyl-2-Pyrrolidone

Poly (lactic acid) (PLA) has many potential uses, for example as packaging, textiles, biomedical fields, including suture, bone fixation material, drug delivery microsphere, and tissue engineering. However, PLA shows the poor toughness, slow degradation rate and relatively hydrophobic. The aim of this study was to investigate the ability of N-methyl-2-pyrrolidone (NMP) to improve the characteristics of PLA film. PLA films were prepared using a solvent casting method and their various properties were investigated. From tensile strength (TS), elongation at break (E) and young’s modulus (ε) determinations, the incorporated PLA films exhibited the softer behavior than plain PLA film. On the other hand, from the contact angle and surface free energy values, the PLA films incorporated with NMP could improve the wettability of solvents and also increased % water sorption (WS) and % weight loss (WL) than PLA films with NMP dose dependent. However SEM photographs revealed the more rather rough and cracked surface as the higher amount of NMP was incorporated in PLA film.

Waterborne cationomer polyurethane coatings with improved hydrophobic properties

AbstractThe AFM method was used to investigate the phase structure of the coatings, which have been obtained after application of polyurethane cationomers, synthesized in the reaction of 4,4′‐methylenebis(phenyl isocyanate) or isophorone diisocyanate with polyoxyethylene glycol (M = 600) and N‐methyl or N‐butyldiethanolamine with 2,2,3,3‐tetrafluoro‐1,4‐butanediol. Changes were discussed in the surface‐free energy (SFE) and its components, as calculated independently according to the method suggested by van Owens–Wendt, in relation to chemical structures of cationomers, as well as morphology of coating surfaces obtained from those cationomers. Fluorine incorporated into cationomers (about 2–5%) contributed to lower SFE values, down to about 30 mJ/m2. An attempt was made to use 1H‐NMR spectroscopy to provide more extensive grounds for the effect of polyurethane chemical structures (by parameters κ) on the SFE of coatings obtained from such polyurethanes, with the values of SFE (γS, γ) and determined by the Owens–Wendt method. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Wettability study of surface modified silica aerogels with different silylating agents

In wettability study, surface free energy interactions are of crucial importance for silica aerogels in which absorption of organic liquids and transportation of chemicals carried out for chemical and biotechnological applications. In present study, we have used Lifshitz–van der Waals/acid–base approach for calculation of surface free energy of aerogel sample. We have investigated that the surface free energy values of aerogels are 45.95, 51.42 and 45.69 mJ/m2 by modifying their surfaces using 7 % chlorotrimethylsilane (TMCS), dimethyldichlorosilane (DMDCS) and hexamethyldisilazane (HMDZ) silylating reagents with solvent, respectively. The alcogels were prepared by two step acid–base catalyzed process where the molar ratio of precursors tetraethoxysilane:methanol:oxalic acid:NH4OH:NH4F was kept at optimal value of 1:16.5:0.71:0.58:0.60:0.98, respectively. To modify gel surfaces, TMCS, DMDCS and HMDZ concentration have been varied from 5 to 12 % and such alcogels were dried at ambient pressure. The aerogels have been characterized by fourier transform infrared spectroscopy, scanning electron microscopy, thermo-gravimetric and differential thermal analysis and Wetting properties of silica aerogel surfaces was studied by contact angle measurements. The surface chemical composition of DMDCS modified silica aerogels was studied by using X-ray photoelectron spectroscopy. As there is not any direct method, we have used Lifshitz–van der Waals/acid–base approach which gives, polar and non-polar components of aerogels surface free energy.

Surface free energy of polyurethane coatings with improved hydrophobicity

The polarity of polyurethane coats was studied on the basis of the goniometric method for determination of wetting angle values, on the basis of calculated surface free energy (SFE) values by the van Oss–Good and Owens–Wendt methods, and on the basis of polarity measurements with the use of the 1H NMR spectra. Test polyurethanes were synthesised in the reaction of methylene diphenyl 4,4′-diisocyanate (MDI) or 3-izocyanatomethyl –3,5,5- trimethylcyclohexyl isocyanate (IPDI) and polyoxyethylene glycols or polyesters poly(ε-caprolactone) diols and poly(ethyleneadipate) diol with different molecular weights, and some diols as chain extenders, in dioxane. The type of raw material was found to significantly affect the phase structure of the obtained polyurethane elastomers and to control physical interactions within those structures, thus influencing the SFE values. Fundamental reduction in the SFE value of a coating below 28 mJ/m2 was achieved by the use of 2,2,3,3-tetrafluoro-1,4-butanediol as the urethane prepolymer chain extender.

Influence of Diameter on Surface Dispersive Free Energy of Polyethersulfone Nano-fibers

Nano-fibers have been applied in many fields because of their unique properties. Quantifying and characterizing the surface free energy and researching the influence of fiber diameters on surface free energies is important. In this paper, three kinds of polyethersulfone nano-fibers with the average diameter of 873, 567 and 254 nm were successfully fabricated by electrospinning at room temperature. The surface dispersive free energy of the three fibers and polyethersulfone (PES) macro-size particles were measured by inverse gas chromatography technique at 30, 40 and 50°C. It was found that the surface dispersive free energy decreased with decreasing fiber diameter. The rationality of the measured values of surface free energy was validated with a BSA adsorption experiment.

An Innovative Non-contact Method to Determine Surface Free Energy on Micro-areas

Surface free energy (SFE) is a property which depends on the chemical state and roughness of the surface and it is necessary to develop a reliable method to evaluate SFE value on a small area, taking into account these two different contributions. Today contact angle methods are the most used and they allow to evaluate the global mean value of SFE on areas of mm2 size. With these methods, it is not possible to evaluate the effects of roughness, surface defects, chemical contamination on SFE value. In addition, it is difficult to determine the surface free energy value on small components which have dimensions smaller than drop diameter. Nanoindentation and atomic force microscopy techniques provide alternative direct measurement methods to evaluate the SFE on small areas (on the order of μm2 or nm2) through a contact mechanism triggered by the contact of two bodies. In order to evaluate the adhesion properties, currently three models, Johnson– Kendall–Roberts, Maugis–Dugdale and Derjaguin–Muller–Toporov, use the value of pull-off force (force required to separate the indenter tip from the sample). All influences of surface morphology on SFE values are lost using these methods. In fact the adhesion value obtained refers to the energy balance between two conformal surfaces, which depends mainly on the morphology of the harder material (i.e., diamond tip). In this work we describe a new methodology for the SFE determination consisting in the modeling and quantitative evaluation of the interaction between the tip and sample surface during the approach phase in a nanoindentation test. During the test, the nanoindenter tip is attracted to the sample surface until the sample reaction forces become significant (in this case physical contact between two bodies is achieved). The SFE value is evaluated using experimental force of attraction and displacement of the nanoindenter spherical tip when it approaches the sample surface. In this method the sample surface is not altered by the tip, therefore unlike pull-off force method, it could be very useful to evaluate the actual SFE considering the effect of sample morphology (controlled roughness or pattern).

An easy way to measure surface free energy by drop shape analysis

The drop shape analysis is a conventional method to evaluate wettability and surface free energy. The analysis of drop profile is commonly used for the contact angle measurement between the liquid drop and sample surface.In many cases such as confined surfaces, it is difficult to carry out this measure, therefore it is necessary to evaluate the shape of the drop from top view point.The aim of this work was to develop a procedure in order to measure wettability and surface free energy values by means of the analysis of the drop shape from top view point. Starting from Tadmor equation, a polynomial function was obtained to correlate the drop diameter to its contact angle on a flat horizontal sample surface.In addition, analyses were carried out in order to study the shape of liquid drop varying the tilt of sample surface. In this case was shown a correlation between the tilt grade and the maximum characteristic lengths (parallel and orthogonal to pitch) of a drop shape on a tilt surface sample.Using the maximum characteristic lengths and a polynomial function previously obtained, it is possible to establish values of pitch, surface free energy and wettability of sample surface.In order to confirm the developed procedure, tests on three different materials have been performed obtaining these three performance indexes.All results obtained by means of this alternative analysis have been compared and corroborated by the classical method using the contact angles of the drop analyzed from a lateral view.

Evaluation of the possibility of using surface free energy study to design protective fabrics

Contact angle measurements, using the dynamic contact angle and Washburn methods, were taken for 100% aramid and viscose fabrics, as well as for 50:50 aramid and viscose mixed fabrics of different structure. Based on the measurements of contact angles wetted with hexane, water and formamide, the fabric surface free energy was calculated by means of three (Owens–Wendt, Wu and van Oss–Chaudhury–Good) theoretical models. The aim of the study was to analyze the usefulness of the dynamic contact angle and Washburn methods for assessing surface properties of textile materials, using selected measurement liquids, and to relate the results to the further investigation of actual wetting and penetration of model fabrics designed to protect against hazardous or irritant liquids. It was found that both methods are useful for determining the fabric surface free energy values; the Washburn method is characterized by the high practical value in assessing surface properties of textile materials, regardless of their structure, whereas the dynamic contact angle method allows for more thorough observation of how the fabric structure of the same raw material composition exerts its effect on the wettability and surface free energy value.

Surface and Cell Affinity Properties of Chitosan-Gelatin-Hydroxyapatite Composite Films

Addition of hydroxyapatite (HAp) into polymeric matrices and use them as supporting material for tissue engineering has gained attraction since hydroxyapatite (HAp) type crystals are the main inorganic components of the bone structure. In this study, composite films were prepared from chitosan (C) and gelatin (G) with addition of HAp, and the surface characterization and cell affinity properties were examined. The hydrophilicities and morphologies of the films were investigated by contact angle measurements and by scanning electron microscopy (SEM), respectively. Cell affinities were studied by using human osteosarcoma (SaOs-2) cell line. Crosslinked and HAp containing films were found to be more hydrophilic than that of the others, while surface free energy (SFE) values were almost similar for all films. Cell proliferation and spreading of SaOs-2 cells were higher for the films with high gelatin content and no HAp; whereas for HAp containing composites higher cell affinities were obtained for the samples which have high chitosan content.

Comparison of phase structures and surface free energy values for the coatings synthesised from linear polyurethanes and from waterborne polyurethane cationomers.

WAXS, DSC and AFM methods were employed to compare phase structures of the coatings obtained from waterborne polyurethane cationomers which had been synthesised in the reaction of some diisocyanates (MDI, IPDI, TDI and HDI) with polyoxyethylene glycols (M = 600 and 2,000) and butane1,4-diol or N-methyl- or N-butyldiethanolamine and 2,2,3,3-tetrafluoro-1,4-butanediol. The structures were also analysed of the coatings derived from linear polyurethanes which had been synthesised on the basis of similar raw materials. Better rigidity was found for generally amorphous cationomer coats. Changes were discussed in the surface free energy (SFE) values and in their components, as calculated independently with the use of the van Oss–Good and Owens–Wendt methods. Polyurethane coats turned out more hydrophobic as compared to cationomer ones. In both coat types, fluorine incorporated into cationomers contributed to lower SFE values: from 50 down to about 30 mJ/m2.

Effect of surface composition and roughness on the apparent surface free energy of silica aerogel materials

Surface chemical composition and morphology play an important role in determining the superhydrophobic behavior of solids. To provide insights on the influence of surface chemical composition and roughness on superhydrophobic behaviour of tetramethoxysilane based silica aerogel materials over a wide range, we have carried out a quantitative study of the effect of hydrophobic agent on contact angle and surface free energy of silica aerogels. The apparent surface free energy values were calculated using Zisman method and validated by Fowkes-Girifalco-Good theory.

Wettability and surface composition of partly and fully regenerated cellulose thin films from trimethylsilyl cellulose

The wettability and surface free energy (SFE) of partly and fully regenerated cellulose model surfaces from spin coated trimethylsilyl cellulose were determined by static contact angle (SCA) measurements. In order to gain detailed insight into the desilylation reaction of the surfaces the results from SCA measurements were compared with data from other surface analytical methods, namely thickness measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Additionally, the influence of ultra high vacuum treatment (UHV) during XPS measurements on the water wettability and surface morphology of regenerated cellulose thin films was investigated. The wetting of polar and non-polar liquids increased with prolonged regeneration time, which is reflected in the higher SFE values and polarities of the films. After UHV treatment the water SCA of partly regenerated films decreases, whereas fully regenerated cellulose shows a higher water SCA. Therefore it is assumed that volatile desilylation products tend to adsorb on partly regenerated films, which strongly influences their wettability.

Nucleation kinetics, micro-crystallization and etching studies of l-histidine trifluoroacetate crystal

The metastable zone width and induction period were determined for the aqueous solution growth of l-histidine trifluoroacetate (LHTF). The surface free energy values were calculated from the experimental data. The nucleation parameters such as volume free energy change, critical radius and critical free energy barrier have also been evaluated. Growth morphology depending on the pH values was studied using the micro-crystallization method. Bulk single crystal without any macroscopic defects has been successfully grown based on our investigation results. Furthermore, etch patterns on the {0 1 0} and {−1 0 1} facet of the crystal were also illustrated and described.

The Effect of Exposed Glass Fibers and Particles of Bioactive Glass on the Surface Wettability of Composite Implants

Measurement of the wettability of a material is a predictive index of cytocompatibility. This study was designed to evaluate the effect of exposed E-glass fibers and bioactive glass (BAG) particles on the surface wettability behavior of composite implants. Two different groups were investigated: (a) fiber reinforced composites (FRCs) with different fiber orientations and (b) polymer composites with different wt. % of BAG particles. Photopolymerized and heat postpolymerized composite substrates were made for both groups. The surface wettability, topography, and roughness were analyzed. Equilibrium contact angles were measured using the sessile drop method. Three liquids were used as a probe for surface free energy (SFE) calculations. SFE values were calculated from contact angles obtained on smooth surfaces. The surface with transverse distribution of fibers showed higher (P < 0.001) polar (γ P) and total SFE (γ TOT) components (16.9 and 51.04 mJ/m2, resp.) than the surface with in-plane distribution of fibers (13.77 and 48.27 mJ/m2, resp.). The increase in BAG particle wt. % increased the polar (γ P) value, while the dispersive (γ D) value decreased. Postpolymerization by heat treatment improved the SFE components on all the surfaces investigated (P < 0.001). Composites containing E-glass fibers and BAG particles are hydrophilic materials that show good wettability characteristics.

Investigation of fullerene depth distribution in PMMA‐C60 blends using dual beam ToF‐SIMS

AbstractNanocomposites, and in particular, Polymer–Fullerene blends, have recently drawn strong attention owing to their properties and their numerous applications in new‐generation electronic and optoelectronic devices. The fullerene concentration in the material is critical since it dictates its electrical behavior. In this context, precise knowledge of the fullerene depth distribution in the blends is needed. Here, we investigate the capability of the ToF‐SIMS technique to provide quantitative information on PMMA‐C60 blends with extremely small C60 concentrations. Smooth PMMA layers of ∼130 nm thickness ranging from 0 to 0.04 wt% C60 were deposited on Si wafers. Samples were analyzed with an ION‐TOF TOF SIMS V instrument in negative mode. Using low‐energy Cs+ sputtering (250 eV) and Bi3+ as the analysis ion allowed monitoring of C60 characteristic secondary ions, namely C60− and its isotopes at m = 720,721,722,723,724,725 u. Operating the beams in noninterlaced mode enabled successful depth profiling of samples with very little signal decay. Improvement of depth resolution was achieved by cooling the sample while profiling; AFM study of crater bottoms showed reduced roughness at low temperature, justifying the improvement. Segregation in depth of C60 against PMMA was not observed, in agreement with surface free energy values determined by a contact angle method. Point‐by‐point normalization of C60 signal (C60−, m = 720 u) to PMMA monomer signal (C5H9O2−, m = 101 u) was found to give a linear function of C60 concentration with excellent regression coefficient. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Wettability of ZnO: A comparison of reactively sputtered; thermally oxidized and vacuum annealed coatings

We have studied the wettability of sputter deposited ZnO, thermally oxidized Zn–ZnO and vacuum annealed ZnO coatings. The X-ray diffraction patterns showed the formation of hexagonal-wurtzite structure of ZnO, which was further confirmed by micro-Raman spectroscopy data. The X-ray photoelectron spectroscopy data indicated that the sputter deposited ZnO coatings were more stoichiometric than thermally oxidized Zn–ZnO and vacuum annealed ZnO coatings. The wettability measurements indicated that water contact angles of 158.5° and 155.2° with sliding angles of 2° and 4° were achieved for thermally oxidized Zn–ZnO and vacuum annealed ZnO coatings, respectively. The superhydrophobicity observed in thermally oxidized Zn–ZnO and vacuum annealed coatings is attributed to the nanorod cluster like morphology along with the presence of high fraction of micron scale air pockets. The water droplet on such surfaces is mostly in contact with air pockets rather than solid surface, leading to high contact angle. Whereas, the sputter deposited ZnO coatings exhibited a maximum water contact angle of 110.3°. This is because the sputter deposited ZnO coatings exhibited a densely packed nanograin-like microstructure without any air pockets. The work of adhesion of water was very low for thermally oxidized Zn–ZnO (5.06mJ/m2) and vacuum annealed ZnO coatings (6.71mJ/m2) when compared to reactively sputtered ZnO coatings (90.41mJ/m2). The apparent surface free energy (SFE) for these coatings was calculated using Neumann method and the SFE values for sputter deposited ZnO, thermally oxidized Zn–ZnO and vacuum annealed ZnO coatings were 32.95, 23.21 and 18.78mJ/m2, respectively.