Γs Values Research Articles

The effects of humidity and surface free energy on adhesion force between atomic force microscopy tip and a silane self-assembled monolayer film

The relationship between atomic force microscopy probe-sample adhesion force and relative humidity (RH) at five different levels of surface free energy (γs) of an organic self-assembled monolayer (SAM) has been investigated. Different γs levels were achieved by exposing a patterned SiO2/CH3-terminated octyldimethylchlorosilane SAM sample to an ultraviolet (UV)/ozone atmosphere. A model consisting of the Laplace-Kelvin theory for capillary condensation for nanosized probe and probe-sample molecular interaction was derived to describe the adhesion force as a function of RH from 25 to 90% for different SAM γs values. The equations were solved analytically by using an equivalent curvature of the probe tip shape. Experimental results show that the adhesion force increases slightly with RH for nonpolar SAM. However, for polar SAM surfaces, it increases at first, reaches a maximum, and then decreases. Both the rate of increase and the maximum of the adhesion force with humidity are γs-dependent, which is in good agreement with theoretical prediction. The large rise in the adhesion force in this RH range is due to the capillary force.

Hydrogen bonding interactions, crystallization, and surface hydrophobicity in nanostructured epoxy/block copolymer blends

AbstractHydrogen bonding interactions, phase behavior, crystallization, and surface hydrophobicity in nanostructured blend of bisphenol A‐type epoxy resin (ER), for example, diglycidyl ether of bisphenol A (DGEBA) and poly(ε‐caprolactone)‐block‐poly(dimethyl siloxane)‐block‐poly(ε‐caprolactone) (PCL–PDMS–PCL) triblock copolymer were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, transmission electron microscopy, small‐angle X‐ray scattering, and contact angle measurements. The PCL–PDMS–PCL triblock copolymer consisted of two epoxy‐miscible PCL blocks and an epoxy‐immiscible PDMS block. The cured ER/PCL–PDMS–PCL blends showed composition‐dependent nanostructures from spherical and worm‐like microdomains to lamellar morphology. FTIR study revealed the existence of hydrogen bonding interactions between the PCL blocks and the cured epoxy, which was responsible for their miscibility. The overall crystallization rate of the PCL blocks in the blend decreased remarkably with increasing ER content, whereas the melting point was slightly depressed in the blends. The surface hydrophobicity of the cured ER increased upon addition of the block copolymer, whereas the surface free energy (γs) values decreased with increasing block copolymer concentration. The hydrophilicity of the epoxy could be reduced through blending with the PCL–PDMS–PCL block copolymer that contained a hydrophobic PDMS block. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 790–800, 2010

Gypsum Scale Control by Nitrilotrimethylenephosphonic Acid

In this paper the retardant effect of nitrilotrimethylenephosphonic acid (NTMP) on calcium sulfate dihydrate nucleation kinetics is evaluated by means of an optical technique able to accurately measure the induction period. A laboratory-scale experimental apparatus is used, in which sodium sulfate and calcium chloride are mixed to obtain a supersaturated calcium sulfate dihydrate solution; all experiments are carried out for various values of NTMP concentrations (0.005−0.05 g/L) in solution, while changing the saturation index in the range of 4.04 − 4.82; the temperature was varied in the interval 15−45 °C. Experimentally measured induction times are used to evaluate the interfacial tension (γS) between crystals and mother solution and to estimate the activation energy (Eatt) for precipitation in the presence of NTMP. The measured values of γS and Eatt are compared with those found in the absence of any additive and in the presence of citric acid, showing that NTMP is a very strong retardant for gypsum nucleation.

Pyroelectric properties of RbTiOAsO4 single crystals in the 4.2–300 K temperature range

AbstractThe temperature dependence of the pyroelectric coefficient, γs, of RbTiOAsO4 single crystals grown by seeded pulling from high‐temperature self‐fluxes has been studied in the low‐temperature range. The results show that in the 4.2–250 K temperature range the γs(T) behavior is similar to those of the isomorphic crystals belonging to the KTP (KTiOPO4) family of compounds, and at temperature of 250 K the RTA pyroelectric coefficient γs = –(5.6 ± 0.3) × 10–5 C/m2 K. However, at temperatures above 275 K, the superionic conductivity increases significantly, while the electrical conductivity originating from the release of charge carriers associated with trace impurity point defects increases additionally above room temperature. These effects have been taken into account in experimental evaluation of the true γs values, especially above 275 K. The peculiarities revealed in the RTA pyroelectric coefficient temperature dependence are also discussed in terms of the structural changes associated with the temperature increase and isomorphic ion substitutions. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparative study of surface free energy and surface resistivity of polypropylene and polystyrene thin films after DC plasma treatment

30 o C, pressure 200 Pa). The effects of time (up to 110 s) and power (1 W or 5 W) of the treatment on the values of free energy (γs) of PS and PP samples and γS components — dispersive (γS D ) and polar (γS P ) ones — were determined. With prolonged time of interaction the values of γS and γS P increased, especially in the region of first 35—50 s, while γS D values kept the similar level during the whole time of exposure. The dependence of PP and PS surface resistance on the same parameters as above (time and power of interaction) has been also found. For both polymers this resistance decrease with prolonged time and growing power of exposure.

Evaluation of the Surface Properties of BPDA-BAPE Polyimide by Using a Quantitative Imaging Analysis

In order to predict the behavior of polyimides and to optimize their fabrication, it is important to understand the relationship between polyimide’s structure and their surface properties. The surface properties (water sorption and repellency, adhesion) are closely related to the surface tension of polymer solid. Critical surface tension γC and surface tension γS of a polymer solid have generally been estimated by the contact angle method. BPDA (3,3′,4,4′-biphenyltetracarboxylic dianhydride)–BAPE (1,2-di(4-aminophenoxy) ethane) polyimide was successfully synthesized. Testing liquids, e.g., dispersion, polar, hydrogen bonding liquids were used to measure the contact angle θ whose values were determined by a quantitative imaging system. Unlikely the existed contact angle measurements, our lab-made quantitative imaging system could provide accurate and reproducible values of the contact angles. The critical surface tensions γC were analyzed by a Zisman plot, a Young-Dupré-Good-Girifalco plot, and a log(1 + cos θ) vs log γL plot. The surface tension γS of BPDA-BAPE polyimide was calculated using the geometric mean equation and multiple regression analysis. The Zisman plot is essentially a downwardly convex curve with polar and hydrogen bonding liquids having γC << γL. The calculated values of γSd (a dispersion component), γSp (a polar component), γSh (a hydrogen bonding component), and γS are 29.69, 13.17, 0.25, and 43.11 mN·m–1, respectively. The γS of BPDA-BAPE polyimide is 43.11 mN·m–1 which is 1.05 and 1.14 times higher than those of Kapton® H films, respectively. The polarity of BPDA-BAPE polyimide is 0.311 whose value was located between 0.87 and 1.39 magnitudes of Kapton® H films’ polarity, respectively.

Relationships of fracture toughness and dislocation mobility in intermetallics

An analytical method has been developed and used to compute the Peierls-Nabarro (P-N) barrier energy, UP-N, for relevant slip systems in several intermetallics, including NiAl, FeAl, Nb-Ti-Al (B2), Ni3Al (L12), TiAl (L10), TiCr2, NbCr2 (C14, C15), Nb5Si3 (D8l), Mo5SiB2 (D8l), and Mo5Si3 (D8m). The P-N barrier energy and a generalized fault energy, γF, are combined and used as a measure of dislocation mobility. Furthermore, a fracture model has been developed to describe the process of thermally activated dislocations moving away from the crack tip and to predict the corresponding fracture resistance. A ductility index defined in terms of the ratio of γs/(UP-N+γF), where γs is the surface energy, is used to correlate with the fracture toughness, KC, of individual intermetallics. The correlation indicates that fracture toughness increases with increasing values of γs/(UP-N+γF), in accordance with the fracture model formulated based on thermally activated slip. The use of the fracture model for predicting the effects of slip behavior, temperature, and alloy additions on fracture resistance is demonstrated for selected intermetallics including NiAl, TiAl, Laves phase, and Nb5Si3.

Surface and printing properties of synthetic film papers

AbstractWe studied the surfaces, including both the composition effects and the processing rates, of polypropylene (PP) composite films used for synthetic paper to determine the surface free energy (γs) and the irregularities on the film surfaces. We correlated these two characteristics to the printing quality by assessing the facility with which the offset ink was removed from the surface of the paper and also the ink absorption. Five films with different compositions were uniaxially oriented with a flat‐die extruder at two different stretching rates. The results of scanning electron microscopy (SEM) of the films showed good dispersion and distribution of the filler particles used in the compositions of the films and also of the polystyrene (PS) dispersed throughout the PP matrix. The SEM analysis also revealed slightly high surface irregularities on the film surfaces through a high concentration of CaCO3, which thus increased the coefficients of static and kinetic friction and the γs values. These film properties created better printing quality and also more strongly fixed offset ink onto the film. However, the films with high relative quantities of PS in their composition showed a high polar component in their total γs when compared to films with less PS or no PS in their compositions. However, because of the apolar characteristic of the offset printing ink, the ink absorption worsened. The films underwent stretching at two different rates, which did not significantly affect the γs values or the friction coefficients; however, they did slightly change the printing quality and ink adhesion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2346–2355, 2003

Large‐eddy simulation of a bluff‐body flow on unstructured grids

AbstractLarge‐eddy simulations of the flow around a square cylinder on coarse unstructured grids are investigated. The numerical solver is based on a mixed finite‐volume/finite‐element formulation. A modified Roe scheme is employed for convective terms, together with the MUSCL method to increase the order of accuracy. An upwinding parameter, γs, directly controls the numerical diffusion, which is formed of fourth‐order space derivatives. The eddy‐viscosity Smagorinsky model and its dynamic version are used for the subgrid scale (SGS) terms in the LES equations. The effects of upwinding, and, in particular, the interaction between SGS and numerical dissipation, are studied by varying the value of γs. The sensitivity to grid inhomogeneity and to SGS modelling are also investigated. Results are compared to those obtained in other LES in the literature and to experimental data. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Peculiarities in the Hydration of Cellulose in Air and Water Suspensions as Studied by 1H NMR Spectroscopy

Bound water layers in hydrated powders and aqueous suspensions of microcrystalline cellulose were investigated by 1H NMR methods. The characteristics of such layers were calculated and the magnitude of the interfacial energy (γs ) at the cellulose/water interface in an aqueous environment determined. It was found that the concentration of strongly bound water and the value of γs were strongly dependent on the concentration of cellulose in suspension. This is probably due to the strong interaction between cellulose particles. At very high suspension concentrations, the concentration of water inside the cellulose filament decreased by more than three-times while the value of γs decreased from 31 J/g to 9 J/g as a result of surface forces.

Measuring induction period for calcium sulfate dihydrate precipitation

AbstractHomogeneous nucleation of CaSO4·2H2O (gypsum) based on an optical diagnostic technique was studied within a supersaturation range of 1–4 at 25–90°C. The experiments were carried out using an experimental apparatus consisting of a batch crystallizer with the related measurement devices. Signals of scattered and transmitted light coming from a He–Ne laser source were analyzed to measure the induction period (tind), that is, the time delay necessary for homogeneous nucleation to take place. As expected from theory, it was found that tind decreases when either temperature or supersaturation increase; from the dependence of tind on supersaturation, it was possible to distinguish between the mechanisms of homogeneous and heterogeneous nucleation. From the experimental data relative to homogeneous nucleation, the interfacial tension (γs) between CaSO4·2H2O and the surrounding aqueous solution and the activation energy (Eatt) for CaSO4·2H2O crystallization were evaluated. In particular, the dependence of tind on temperature made it possible to evaluate Eatt at 30 kJ/mol and the dependence of tind on supersaturation offered the value of γs to be about 37 mJ/m2, which does not vary with temperature in the interval explored.

Surface characterization of polyimide films

Various kinds of poly(amide acid)s were prepared by the reaction of four kinds of acid dianhydride and three kinds of diamine in N,N-dimethylacetamide (DMAc). Polyimide films were prepared by casting the poly(amide acid) solution on soda glass substrates, followed by thermal imidization at various temperatures. Contact angles of polyimide films for the sides in contact both with air and with glass substrate (air side and glass side, respectively) were measured to evaluate the dispersive component (γDS) and the nondispersive component (γPS) of surface free energy (γS) of polyimide films. It was shown that, for the air side, γPS value decreased greatly and γDS values increased slightly with the development of imidization. Values of γPS for the glass side were much higher than those for the air side. Poly(amide acid) solution was also cast on quartz glass and silicone rubber, and was thermally imidized. The γPS for the quartz glass side was almost the same as that for the soda glass side. But the γPS for the silicone rubber side was as low as the γPS for the air side. Attenuated total reflection infrared spectroscopy of polyimide films showed that the degree of imidization for the glass side surface was not as high as that for the air side surface, and that the amount of polar groups for the glass side surface was higher than that for the air side surface. Among the various kinds of polyimides, there is a slight but clear difference in the values of γS and its components, which can be rationalized from the difference in the chemical structure. It was also found that thermal degradation and oxidation can be easily detected from the change of surface free energy and its components for the polyimide films after being treated at high temperatures in both air and vacuo.

Wave transformation across the inner surf zone

Sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches (a steep concave‐up beach, a gently sloped approximately planar beach, and a beach with an approximately flat terrace adjacent to a steep foreshore) were depth limited (i.e., approximately independent of the offshore wave height), consistent with previous observations. The wave evolution is well predicted by a numerical model based on the one‐dimensional nonlinear shallow water equations with bore dissipation. The model is initialized with the time series of sea surface elevation and cross‐shore current observed at the most offshore sensors (located about 50 to 120 m from the mean shoreline in mean water depths 0.80 to 2.10 m). The model accurately predicts the cross‐shore variation of energy at both infragravity (nominally 0.004 &lt; f &lt; 0.05 Hz) and sea swell (here 0.05 &lt; f ≤ 0.18 Hz) frequencies. In models of surf zone hydrodynamics, wave energy dissipation is frequently parameterized in terms of γs, the ratio of the sea swell significant wave height to the local mean water depth. The observed and predicted values of γs increase with increasing beach slope β and decreasing normalized (by a characteristic wavenumber k) water depth kh and are well correlated with β/kh, a measure of the fractional change in water depth over a wavelength. Errors in the predicted individual values of γs, are typically less than 20%. It has been suggested that infragravity motions affect waves in the sea swell band and hence γs, but this speculation is difficult to test with field observations. Numerical simulations suggest that for the range of conditions considered here, γs is insensitive to infragravity energy levels.

96/03583 Surface free energy and floatability of low-rank coal

Measurements were made of zeta potential of low-rank coals, the surface of which was previously covered with apolar liquid to different degrees. The zeta potentials were then used for determination of the film pressure of this liquid, making it possible to calculate the apolar Lifshitz-van der Waals (γsLW) component of the coal surface free energy. Electron donor (γs−) and electron acceptor (γs+) polar components were determined by measurement of water and glycerol contact angles on coal plates. The values of γs− and γs+ were then compared with the non-dispersion component, γsn, of the surface free energy. The values of the surface free energy components confirmed that the hydrophobic properties of a coal surface increase with increasing degree of coalification. This was also confirmed by tests on the natural floatability of these coals in a Hallimond single-bubble tube.

Analysis of Surface Segregation in Blends of Acrylate Copolymer with Fluoro-Copolymer

The surface segregation of poly(2-ethylhexyl acrylate-co-acrylic acid-co-vinyl acetate) P(2EHA-AA-VAc)/poly(vinylidene fluoride-co-hexafluoro acetone) P(VDF-HFA) blends was investigated by FT IR in surface analysis, the miscibility of blends examined by both the Prigogine-Flory-Patterson’s theory and the thermo-photometry and surface tension γs. From 1 to ∼2μm of the surface in P(2EHA-AA-VAc)/P(VDF-HFA) (50/50) blend, the variation in P(VDF-HFA) concentration with increasing distance from the surface was observed by use of ATR-FT IR with incidence angle dependence. It was suggested that the surface segregation of P(VDF-HFA) took place in the blends. The P(2EHA-AA-VAc)/P(VDF-HFA) blends were revealed to be heterogeneous systems by the results of state parameters and thermo-photometry. The γs of P(2EHA-AA-VAc) and P(VDF-HFA) were evaluated according to Prigogine’s corresponding state theory, as extended for surfaces by Patterson and co-workers. The values of γs of P(2EHA-AA-VAc) and P(VDF-HFA) were 28.3 and 20.4 (dyn cm−1), respectively. Therefore, it was expected that surface segregation in P(2EHA-AA-VAc)/P(VDF-HFA) blends may occur, when the blend is immiscible and difference in γs between components is large.

Critical surface tension of poly(vinylidene fluoride-co-hexafluoroacetone) by the contact angle method

Abstract The contact angles θ of dispersion (D), polar (P) and hydrogen bonding (H) liquids on poly(vinylidene fluoride-co-hexafluoroacetone) (P(VDF-HFA); HFA content 6.5, 8.3 and 10.4 mol%) were measured. The critical surface tensions γc of P(VDF-HFA) were evaluated by the Zisman plot (cos θ versusγL), Young-Dupre-Good-Girifalco plot (1 + cos θ versus 1 γ 0.5 L ) and the log(1 + cos θ) versus log (γL) plot. The following results were obtained: the γc values of P(VDF-HFA) evaluated for the P liquids were larger than those for the D and H liquids; the γc values estimated by the Zisman plot were smaller than those obtained by the other plots; the surface tension γs values of P(VDF-HFA) revealed a minimum at the HFA content of 8.3 mol%. It was expected that P(VDF-HFA) with HFA = 8.3 mol% induced surface segregation most easily.

Surface Free Energy Components of Clay-Synthetic Humic Acid Complexes from Contact-Angle Measurements

AbstractThe surface free energy components of clay-organic complexes were determined to assess to what extent an organic adsorbate modified the surface properties of the mineral, insofar as the stability of soil aggregates is concerned. Adsorption isotherms for two synthetic, humic acid-like polymers were determined on a Ca-montmorillonite. From contact-angle measurements performed on dry surfaces, the surface free energy properties of the clay-organic complexes were determined using the two-liquid-phases method (water and hydrocarbons). This method allows both the dispersive and nondispersive components of the solid surface free energy, γDS and γPS, to be determined. The results show that a very small amount of polymer (1% by weight) adsorbed on the external surfaces of the montmorillonite decreased markedly the surface free energy components of the clay: γDS decreased from 75 to 28 mJ/m2 for polycondensate catechol (PC) and from 75 to 30 mJ/m2 for polycondensate catechol triglycine (PCT), whereas γPS ranged from 35 to 16 mJ/m2 (PC) and from 35 to 17 mJ/m2 (PCT). Although their chemical compositions were different, both polymers similarly modified γDS and γPS. Increasing the amount of polymer adsorbed (from 1% to 3.5% by weight) affected mostly γPS, which became as low as 5 mJ/m2; meanwhile, γDS decreased from 30 to 23 mJ/m2. Possibly, the molecular orientation of the adsorbate changed in the process of dehydration. Following adsorption of synthetic humic acid-like polymers, dry Ca-montmorillonite complexes displayed γS values &lt; 50 mJ/m2, which were consistent with the solid-water contact angles measured in air.

Adsorption of Sodium Alkyl sulfates on Nylon Particles

The adsorption of sodium alkyl sulfates (sodium decyl, sodium dodecyl, sodium tetradecyl and sodium hexadecyl sulfates) on nylon particles from their aqueous solutions was investigated by the electrokinetic method. The equilibrium adsorption isotherms of the surfactants were obtained from the electrokinetic potentials of particles dispersed in aqueous solutions of sodium alkylsulfates at different temperatures. The equilibrium constant of adsorption, K, and the saturated adsorption amount, Γs, were determined from Langmuir plots. The values of K and Γs by the electrokinetic method were compared with those obtained by the electric conductivity method under the same experimental conditions, The values of K and thermodynamic parameters determined by the electrokinetic and electric conductivity methods agreed with each other. The values of Γs obtained by the former method, however, were from 1/40 to 1/50 those calculated by the latter. Comparison of Γs by the both methods provided information on the slipping plane and the dissociation degree of the adsorbed surfactants.

The effect of topically applied fluorides on the surface free energy of human dentin.

The surface free energy γs of human dentin treated with sodium fluoride, acidulated phosphate fluoride, and aminfluoride solutions has been determined by means of contact angle measurements. Application of an aminfluoride solution slightly increased the total surface free energy from 75 to 80 erg. cm−2. The γs values of dentin after a neutral sodium fluoride application decreased to 62 erg. cm−2. APF solutions hardly influenced the surface free energy γs. This study showed that fluoride applications change the surface free energy of human dentin.Extrapolation of the results of this study and the in vitro results on cell spreading indicated that aminfluoride applications might be favorable for the reattachment of periodontal tissues.

Temperature dependence of the nonlinear susceptibility in spin glasses

In most metallic spin glasses the nonlinear susceptibility χ2 =d3M/dH3‖H→0 exhibits a singular behavior at the freezing temperature Tf. Within the framework of the molecular field theory, χ2 is proportional to (T−Tf)−1. However, several experimental results show that χ2 is proportional to (T−Tf)−γs(T) over a wide range of temperature, with temperature dependent values of γs greater than 1. A similar discrepancy is observed for the paramagnetic susceptibility χ0=dM/dH‖H→O of amorphous ferromagnets. We have shown earlier that this anomaly in amorphous ferromagnets results from the noncritical interplay between the magnetic correlations and the spatial fluctuations of the exchange interaction, and it was described by a spatially correlated molecular field theory. We now apply this theory to spin glasses and show that the staggered susceptibility exhibits an anomalous (T−Tf)−γψ(T), (γψ≳1) behaviour in a wide range of temperature, and argue that the nonlinear susceptibility χ2 shows a similar behaviour. We suggest, therefore, that the anomalous behaviour of χ2 does not represent a critical phenomenon, thus the value of γs(T) can be dependent both on the system and temperature.