Low-rate dynamic contact angles on polystyrene and the determination of solid surface tensions

Low-rate dynamic contact angles of 13 liquids on a polystyrene polymer are measured by an automated axisymmetric drop shape analysis – profile (ADSA-P). It is found that 7 liquids yielded non-constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the other 6 liquids, it is found that the liquid-vapor surface tension times cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γ_lvcosθ depends only on γ_lv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non-inert (polar and non-polar) surfaces (7–13, 24–26). The solid-vapor surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions (33) is found to be 29.8 mJ/m², with a 95% confidence limit of ±0.5 mJ/m² from the experimental contact angles of 6 liquids.     

Contact angle measurements and interpretation: wetting behavior and solid surface tensions for poly(alkyl methacrylate) polymers

Low-rate dynamic contact angles of a large number of liquids were measured on a poly(ethyl methacrylate) (PEMA) polymer using an automated axisymmetric drop shape analysis profile (ADSA-P). The results suggested that not all experimental contact angles can be used for the interpretation in terms of solid surface tensions: eight liquids yielded non-constant contact angles and/or dissolved the polymer on contact. From the experimental contact angles of the remaining four liquids, we found that the liquid-vapor surface tension times the cosine of the contact angle changes smoothly with the liquid-vapor surface tension, i.e. γlv cos ζ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is again in harmony with those from other methacrylate polymer surfaces of different compositions and side-chains. The solid-vapor surface tension of PEMA calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 33.6 ± 0.5 mJ/m2 from the experimental contact angles of the four liquids. The experimental results also suggested that surface tension component approaches do not reflect physical reality. In particular, experimental contact angles of polar and nonpolar liquids on polar methacrylate polymers were employed to determine solid surface tension and solid surface tension components. Contrary to the results obtained from the equation-of-state approach, we obtained inconsistent values from the Lifshitz-van der Waals/acid-base (van Oss and Good) approach using the same sets of experimental contact angles.     

DETERMINATION OF SOLID SURFACE TENSION FROM CONTACT ANGLES: THE ROLE OF SHAPE AND SIZE OF LIQUID MOLECULES

Accurate surface tension of Teflon® AF 1600 was determined using contact angles of liquids with bulky molecules. For one group of liquids, the contact angle data fall quite perfectly on a smooth curve corresponding to γ_sv = 13.61 mJ/m², with a mean deviation of only ±0.24 degrees from this curve. Results suggest that these liquids do not interact with the solid in a specific fashion. However, contact angles of a second group of liquids with fairly bulky molecules containing oxygen atoms, nitrogen atoms, or both deviate somewhat from this curve, up to approximately 3 degrees. Specific interactions between solid and liquid molecules and reorientation of liquid molecules in the close vicinity of the solid surface are the most likely causes of the deviations. It is speculated that such processes induce a change in the solid–liquid interfacial tension, causing the contact angle deviations mentioned above. Criteria are established for determination of accurate solid surface tensions.     

Surface tension parameters of ice obtained from contact angle data and from positive and negative particle adhesion to advancing freezing fronts

From contact angle data obtained on flat ice surfaces with a number of liquids, combined with data on particle and macromolecule adhesion or non-adhesion to advancing freezing fronts, the apolar (Lifshitz-van der Waals or LW) and polar (Lewis acid-base or AB) surface tension (γ) components and parameters have been determined. At 0°C these are γ^LW _iee = 26.9 and γ^AB _ice = 39.6 mJ/m². The latter consists of an electron-acceptor (γ^⊕) and an electron-donor (γ^?) parameter: γ^⊕ = 14 and γ^? = 28 mJ/m².     

Influence of different alkyl side chains on solid surface tension of polymethacrylates

Low‐rate dynamic contact angles on poly(t‐butyl methacrylate) (PtBMA) were measured by an automated axisymmetric drop shape analysis profile (ADSA‐P). The solid surface tension of PtBMA is calculated to be 18.1 mJ/m², with a 95% confidence limit of ±0.6 mJ/m². This value was compared to previous results with different homopolymeric polymethacrylates [poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(n‐butyl methacrylate) (PnBMA)] and with copolymeric polymethacrylates {poly(methyl methacrylate/ethyl methacrylate, 30/70) [P(MMA/EMA, 30/70)] and poly(methyl methacrylate/n‐butyl methacrylate) [P(MMA/nBMA)]}. It was found that increasing length and size of the alkyl side chain decrease the solid surface tension, as expected. Comparison with pure alkyl surfaces suggests that the surface tension of PtBMA is dominated by the very hydrophobic t‐butyl group. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2493–2504, 2000     

Critical Surface Tension of Wetting and Flotation Separation of Hydrophobic Solids

Abstract

Wetting characteristics of a number of minerals including layer-type hydrophobic minerals as well as common sulfides were investigated. For the majority of the minerals, the critical surface tension of wetting, γ_c determined using Zisman's technique was in the range of 40 to 45 mN/m. Surface pressures of water, II_e, on molybdenite and coal samples were determined from adsorption isotherms. The dispersion component of the surface-free energy, γ_s ^d, for molybdenite was estimated to be 113 ± 3 mJ/m² as compared to the γ_s ^d value for graphite, 109 mJ/m². The wettability data of aqueous methanol solutions, presented in the form of adhesion tension diagrams, yielded significantly lower γ_c values. Flotation behavior of common sulfides, which was similar to that of inherently hydrophobic polymers and minerals, was attributed to elemental sulfur formation. The relevance of critical surface tension of wetting to selective flotation and separation of hydrophobic solids is discussed.     

Effect of woody biomass surface free energy on the mechanical properties and interface of wood/polypropylene composites

The aim of this study is to investigate the effect of surface free energy of wood flour (WF) and silanized WF on the mechanical properties and interface of wood/polypropylene (PP) composites. The contact angles of three probe liquids against unmodified and modified spruce WF were tested by capillary rise method based on the Washburn equation. Then the surface free energy and its corresponding dispersion and polar components were calculated according to the method developed by Owens–Wendt–Kaelble. The tensile strength and flexural strength of the wood/PP composite samples made with unmodified and modified WF were tested and the flexural fracture surfaces were analyzed by scanning electron microscopy (SEM). The results showed that the surface free energy of WF increased from 26.0 to 36.1?mJ/m², which was higher than that of PP (29.4?mJ/m²), and its corresponding polar component decreased from 13.1 to 4.4?mJ/m², and the dispersion component increased from 12.9 to 31.7?mJ/m² after the modification with 4 wt.% vinyltriethoxy silane, which makes it possible for spreading of PP on the surface of WF, the tensile strength and flexural strength of wood/PP composites made with modified WF were obviously improved. In addition, the improved compatibility between WF and PP was well confirmed by SEM.     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d _s and γ^d _l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d _s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^?2 K^?1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d _s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d _s and d(γ^d _s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

A Study on the Impact of the Adhesion of Penicillium expansum on the Physicochemical Surface Properties of Cedar Wood

The sessile drop technique was used to investigate the evolution of the physicochemical properties of cedar wood as a function of contact time with the Penicillium expansum spores. The most important finding showed that the impact of different contact periods (2, 4, 6, 8, 10, and 24 hr) on the wood surface were very indicative. In fact, after 2 hr of contact, the results have shown a significant impact of the bioadhesion of spores to the substrate on both the hydrophobic character (θ_W = 108.5°; ΔGiwi = ?28.25 mJ/m²), the electron donor (γ^? = 13.63 mJ/m²), and the electron acceptor (γ⁺ = 4.35 mJ/m²) parameters that were significantly reduced compared to the initial wood (θ_W = 118.5°; ΔGiwi = ?6.29 mJ/m²; γ^? = 32.1 mJ/m²; and γ⁺ = 9.1 mJ/m²). In addition, this decrease of parameters continued over time to stabilize after 10 hr of contact. Indeed, after 24 hr, the acid/base properties were almost zero and the contact angle with water decreased to 30°. Moreover, it was found that the coefficient of correlation (r²) was strong between the contact angle with water, the surface energy, and the electron acceptor character with the contact time parameter with values (r² = 0.65), (r² = 0.79), and (r² = 0.68), respectively.     

Dairy biofilm: an investigation of the impact on the surface chemistry of two materials: silicone and stainless steel

Biofilms are the most common mode of bacterial growth in nature and the formation will occur on organic or inorganic solid surfaces in contact with a liquid. The aims of this study were, by combining numeration and sessile drop technique, (i) to characterize the structural dynamics of dairy biofilm growth and the physico chemical properties on silicone and stainless steel and (ii) to evaluate the impact of bio-adhesion on chemistry of surfaces at different times of contact (2, 7, 9 and 24?h). Significantly, greater biofilm volumes were observed after 48?h on two materials. Gram-positive bacteria and fungal population exhibited a significantly higher biofilm organization than gram-negative (43–64%). Elsewhere, after 48?h, results showed a slight difference on gram-negative adhered cells on stainless steel than silicone (2.6?×?10⁷?cfu/cm² and 4.7?×?10⁵?cfu/cm², respectively). Moreover, the physico chemical properties of the surfaces showed that the silicone and stainless steel have a hydrophobic character (Giwi?=??68.28?mJ/m² and ?57.6?mJ/m², respectively). Also, both the surfaces present a weak electron donor character (γ ^??=?2.2?mJ/m² and 4.1?mJ/m², respectively). The real-time investigation of the impact of dairy biofilm on the physico chemical properties of the materials has shown a decrease of hydrophobicity degree of the silicone surface that becomes hydrophilic (ΔGiwi?=?11.47?mJ/m²) after 7?h and the increase of electron donor character (γ ^??=?75.8?mJ/m²). Elsewhere, bio-adhesion on stainless steel was accompanied with a decrease of hydrophobicity degree of the surface, which becomes hydrophilic after 7?h of contact (ΔGiwi?=?6.62?mJ/m²) and the increase of the electron donor character (γ ^??=?44.8?mJ/m²). While, after 24?h of contact, results showed a decrease of the hydrophilicity degree and surface energy components of silicone and stainless steel that become hydrophobic (ΔGiwi?=??21.2?mJ/m² and ΔGiwi?=??56.51?mJ/m², respectively) and weak electron donor (γ ^??=?14.0 and 2.3?mJ/m², respectively).     

Low-rate Dynamic Contact Angles on Poly(methyl methacrylate/n-butyl methacrylate) and the Determination of Solid Surface Tensions

Low-rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/n-butyl methacrylate) P(MMA/nBMA) copolymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 6 liquids yield non-constant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining 6 liquids, it is found that the liquid- vapour surface tension times the cosine of the contact angle changes smoothly with the liquid-vapour surface tension, i.e., γ_iv cos θ depends only on γ_iv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and noninert (polar and non-polar) surfaces [34-42, 51 -53]. The solid-vapour surface tension calculated from the equation-of-state approach for solid -liquid interfacial tensions [14] is found to be 34.4 mJ/m², with a 95% confidence limit of \pm 0.8mJ/m², from the experimental contact angles of the 6 liquids.     

Comparison of the Lifshitz–van der Waals/acid–base and contact angle hysteresis approaches for determination of solid surface free energy

Total surface free energy, γ_S ^TOT, for several solids (glass, PMMA, duralumin, steel and cadmium) was calculated from the surface free energy components: apolar Lifshitz–van der Waals, γ_S ^LW, and acid–base electron–donor, γ_S ^-, and electron–acceptor, γ_S ⁺. Using van Oss and coworkers' approach (Lifshitz–van der Waals/acid–base (LWAB) approach), the components were determined from advancing contact angles of the following probe liquids: water, glycerol, formamide, diiodomethane, ethylene glycol, 1-bromonaphthalene and dimethyl sulfoxide. Moreover, receding contact angles were also measured for the probe liquids, and then applying the contact angle hysteresis (CAH) approach very recently proposed by Chibowski, the total surface free energy for these solids was calculated. Although the thus determined total surface free energy for a particular solid was expected to depend on the combination of three probe liquids used (LWAB approach), as well as on the kind of the liquid used (CAH approach), surprisingly the average values of the surface free energy from the two approaches agreed very well. The results obtained indicate that both approaches can deliver some useful information about the surface free energy of a solid.     

Interfacial tension from the height and diameter of sessile drops and captive bubbles with an arbitrary contact angle

A method has been developed to calculate the interfacial tension of sessile drops and captive bubbles of arbitrary contact angle by measuring the drop diameter and vertical distance to the apex at arbitrary horizontal planes within the drop. The procedure works in theory for any contact angle with an accuracy on the order of 0.1%. However, practical limitations reduce the range of angles to roughly 50°–180° but do not restrict the range of interfacial tensions (at least 0.01 mJ/m² to 72.0 mJ/m²). The optimal strategy is to use the method at several points on a single drop and to calculate the mean and standard deviation of the resulting interfacial tensions.     

Quantification of Bacillus subtilis and Bacillus sp. Adhesion on Fez Medina Cedar Wood

The adhesion of Bacillus subtilis and Bacillus sp. isolated from Fez cedar wood decay has been investigated. Furthermore, the physicochemical proprieties including hydrophobicity and electron donor/electron acceptor (Lewis acid–base) of both bacteria and substrata were evaluated using contact angle measurements. The results show that Bacillus subtilis has a hydrophobic character (ΔG _iwi = –20 mJ/m²). In contrast, Bacillus sp. exhibits a hydrophilic (ΔG _iwi = –20 mJ/m²), electron donating (γ^–) and weakly electron accepting (γ⁺) character. With respect to the substrata surface, we found that the cedar wood used in this work, was hydrophobic in character, having relatively more electron-donor that electron-acceptor properties (γ^– = 6 ± 4 mJ/m²; γ⁺ = 0 ± 3 mJ/m²). The phenomena of adhesion were observed by environmental scanning electron microscopy (ESEM) and cell adhesion was quantified using a Matlab program. The analysis of images obtained by ESEM show that the both cells was able to adhere to the wood substrata and the quantitative adhesion results showed that the surface coverage by Bacillus sp. (90%) was higher than that by the Bacillus subtilis strain (40%).     

Surface energy of liquid copper and single-crystal sapphire and the wetting behavior of copper on sapphire

The wetting behavior of liquid copper on sapphire is affected by the crystallographic orientation of the sapphire surface, the oxygen partial pressure, and the temperature. The influences of each of these conditions have been studied by the sessile drop technique over the oxygen partial pressure range 10^-2-10^-20 atm at temperatures of 1100 and 1250°C. The effect of oxygen partial pressure on the liquid copper surface energy follows the Gibbs-Langmuir law. The contact angle varies with the crystallographic orientation of the sapphire surface. This variation is more significant at higher oxygen partial pressures, but is eliminated at higher temperatures. The liquid copper surface energy was determined to be γ_lv = 1.757-3.3 x 10^-4T(°C) J/m². The solid surface energy of sapphire was estimated as γ_sv = 1.961-4.7x 10^-4T(°C) J/m², which applies only to the temperature range 927-2077°C.     

Studies on the surface free energy and surface structure of PTFE film treated with low temperature plasma

The surface free energy and surface structure of poly(tetrafluoroethylene) (PTFE) film treated with low temperature plasma in O₂, Ar, He, H₂, NH₃, and CH₄ gases are studied. The contact angles of the samples were measured, and the critical surface tension γ_c (Zisman) and γ_c (max) were determined on the basis of the Zisman's plots. Furthermore, the values of nonpolar dispersion force γ^a_s, dipole force γ^b_s, and hydrogen bonding force γ^c_s to the surface tensions for the plasma-treated samples were evaluated by the extended Fowkes equation. Mainly because of the contribution of polar force, the surface free energy and surface wettability of PTFE film which was treated with H₂, He, NH₃, Ar, and CH₄ for a short time increased greatly. Electron spectroscopy for chemical analysis (ESCA) shows that the reason was the decrease of fluorine and the increase of oxygen or nitrogen polar functional group on the surface of PTFE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1733–1739, 1997     

Physicochemical characterization of actinomycetes isolated from decayed cedar wood: contact angle measurement

Physicochemical characterization of microorganism is very important in a wide range of scientific and technological fields. In this study, we reported the isolation and the molecular identification of actinomycetes recovered from cedar wood decay. The isolates named H5 and H8 were identified by 16S rDNA sequencing and were shown to belong to the genus Nocardia and Streptomyces, respectively. Furthermore, physicochemical proprieties including hydrophobicity, electron donor/acceptor, and the Lifshitz–van der Waals (γ^LW) of these strains were evaluated using contact angle measurements. The results showed that Nocardia sp. (H5) had a hydrophobic (ΔGiwi?=??78.56?mJ/m²) and a weak electron donor/acceptor character. In contrast, results from contact angle measurements showed that the surface free energy of Streptomyces strains (H2, H3, and H8) were ΔGiwi?=?20.71?mJ/m², ΔGiwi?=?30.63?mJ/m², and ΔGiwi?=?15.35?mJ/m², respectively, classifying these microorganisms as hydrophilic bacterium. Moreover, the three strains were predominantly electron donating (γ^–?) and exhibit a weak electron-accepting (γ⁺) character.     

Bacillus cereus adhesion: an investigation of the physicochemical characteristics of surface and effect of bio adhesion on the properties of silicone

The initial microorganism adhesion on substrate is an important step for biofilm formation. The surface properties of the silicone and Bacillus cereus were characterized by the sessile drop technique. Moreover, the physicochemical properties (hydrophobicity; electron donor/electron acceptor) of surface adhesion and the impact of bio adhesion on the silicone were determined at different time of contact (3, 7, and 24?h). The results showed that the strain was hydrophilic (Giwi?=?3.37?mJ/m²), whereas the silicone has hydrophobic character (Giwi?=??68.28?mJ/m²). Silicone surface presents a weak electron-donor character (γ ^??=?2.2?mJ/m²) conversely to B. cereus that presents an important electron donor-parameter (γ ^??=?31.6?mJ/m²). The adhesion of B. cereus to silicone was investigated using environmental scanning electron microscope and image analysis was assessed with the Matlab^® program. After 3?h of contact, the data analysis, confirmed the bio adhesion with an amount of 9.610⁵?cfu/cm² adhered cells. After 24?h, the percentage of silicone covered reached 93%. Furthermore, despite the difference in hydrophohbicity, the interaction between B. cereus and substrata was favoured by the thermodynamic model of adhesion (ΔG _adhesion ?<?0). The real time investigation of the effect of B. cereus adhesion on the physicochemical properties of silicone has revealed that the substrata becomes hydrophilic (θ°?=?47.3, ΔGiwi?=?23.7?mJ/m²), after 7?h of contact. This bio adhesion had also favoured the increase of electron donor/acceptor character of silicone (γ ^??=?53.1?mJ/m² and γ ⁺?=?5.3?mJ/m²).     

Surface tensions and contact angles due to lignin sulphonates in the system: Liquid sulphur,aqueous zinc sulphate and zinc sulphide

Surface tension and contact angle measurements were made in the liquid sulphur-aqueous zinc sulphate-zinc sulphide system at superatmospheric pressures, and showed that, in the absence of surfactants, the liquid sulphur-aqueous solution interfacial tension was 54.0 ± 1.0 mN/m, falling to 27.0-30.0 mN/m when 0.3 g/L or more of lignin sulphonate was added to the solution. At the same time, the contact angle between liquid sulphur and the same solution increased from 80 ± 5° to 148 ± 5°. As a result, the work of adhesion between liquid sulphur and zinc sulphide falls from 63.7 mJ/m² to about 5.3 mJ/m². The results indicate that adsorption of lignin sulphonate occurs on both the mineral-aqueous and the sulphur-aqueous interfaces.     

Contact angles of binary liquids and their interpretation

Contact angles of binary liquid mixtures on Teflon FEP were measured. It was found that the equation of state for interfacial tensions, γ_SL = f (γ_LV, γ_sv), cannot be used to determine solid surface tensions from these contact angles of binary liquid mixtures. These findings are explained in terms of the thermodynamic phase rule.