Bronisław Jańczuk

Wettability of polytetrafluoroethylene by aqueous solutions of two anionic surfactant mixtures

Advancing contact angle (theta) measurements were carried out on mixtures of aqueous solutions of sodium dodecyl sulfate (SDDS) and sodium hexadecyl sulfonate (SHDSs) on polytetrafluoroethylene (PTFE). The obtained results indicate that there were only small contact angle changes over the range of surfactant concentrations in the solution, corresponding to the unsaturated surfactant layer at the aqueous solution-air interface. However, when saturation of the surfactant layer was achieved a considerable decrease in the contact angle (increase in costheta) as a function of concentration was observed. The dependence of costheta on the monomer mole fraction of SHDSs in the mixture of the surfactants (alpha) for aqueous solutions of mixtures at concentrations corresponding to the critical micelle concentration (CMC) had a maximum at alpha=0.2. From the results of these measurements and application of the Gibbs and Young equations the ratio of the excess concentration of surfactants at the solid-aqueous solution interface to the excess of their concentration at the aqueous solution-air interface was calculated. On the basis of the measurements and calculations it was found that there was a straight linear relationship between the adhesion tension and surface tension of aqueous solutions of surfactant mixtures at a given alpha, and that the slope of the obtained straight lines was equal to -1, which suggests that the surface excess of the surfactant concentrations at the PTFE-solution interface is the same as that at the solution-air interface for a given bulk concentration of the surfactant mixtures. The dependence of the surface concentration excess at the PTFE-solution interface on the monomer mole fraction of SHDSs in the mixture of the surfactants for the concentration region of the mixture of aqueous solutions, corresponding to a saturated monolayer, had a maximum at alpha=0.4, probably resulting from increased degree of binding between adsorbed surface-active ions and counterions. It was also found that the critical surface tension of PTFE wetting by aqueous solutions of two anionic surfactant mixtures was equal to 23.35 mN/m, which was higher than the critical surface tension of wetting determined from straight linear dependence between costheta and surface tension of alkanes (19.94 mN/m). This suggests that polar interaction at PTFE-aqueous solutions of surfactant mixtures can probably take place.

On the determination of the surface free energy of quartz

Abstract Studies of water vapor adsorption on quartz by the method analogous to the dynamic gas chromatography step profile method are described. The adsorption was determined by changes in the capacitance of the capacitor (detector) between the coverings of which the quartz powder was placed. Prom the adsorption isotherm the film pressure π of the water film on quartz were determined, obtaining π max = 380 erg cm 2 . An interpretation of the π changes in relation to the film thickness and the kind of wetting process has been proposed. It is concluded that the characteristic film pressure values result from the work of spreading, immersional and adhesional wetting and correspond to thicknesses of about 2, 3 and 4 statistical water monolayers, respectively. The maximum π value, however, probably corresponds to the work of quartz- water adhesion + water cohesion work. On the basis of the thus determined values of πs, π1, and πmax, the value of the polar component γqp of the quartz surface free energy was determined, using the value γ q p = 76 erg cm 2 . The calculated average of the γqp value equals 115 erg cm 2 2 .

Determination of surface free energy components of marble

From the measured values of wetting contact angles of water droplets on marble in n-alkanes the value of the dispersion component of marble surface free energy γMd was calculated. The average γMd value was 64 ergs/cm2. Measurements of water vapor adsorption on marble at 20 and 30°C were also made. From the isotherms obtained water film pressure was determined, and then, using the calculated γMd value the polar component of marble surface free energy γMp = 106.6 ergs/cm2 was determined. These values were verified by determined isoteric and “isopressure” heats.

Components of surface free energy of some clay minerals

The wetting contact angle was measured for water drops settled on the surface of pressed discs of kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite immersed in hexane, octane, dodecane, cis-decalin, and air. Minimum and maximum values of the contact angle were obtained for the given systems of solid-water drop-hydrocarbon, depending on the manner of disc preparation. Using both minimum (θmin) and maximum (θmax) values of the contact angle, values of the dispersion component (γsd) of surface free energy of these solids were calculated from the equation which was derived on the basis of an equilibrium state of the system solid-water drop-hycrocarbon for two different hydrocarbons. The values of γsd for kaolinite, alumina, bentonite, marble, montmorillonite, and quartzite obtained from θmin are 83.5, 98.1, 98.9, 80.2, 95.9, and 89.7 mJ/m2, and from θmax are 73.1, 85.0, 84.4, 75.8, 85.5, and 75.5 mJ/m2. These values for marble and quartzite are similar to those in the literature (marble = 67.7 mJ/m2; quartzite = 71.3 and 76.0 mJ/m2). The values of the dispersion components of surface free energy for marble and quartzite covered with a water film (γsfd) were found to be: 41.8, 36.9; 49.2, 42.5; 49.6, 42.2; 40.2, 38.1; 48.1, 42.8; and 44.9, 38.0 mJ/m2, respectively. Values of γsfd for kaolinite, bentonite, and montmorillonite agreed well with those obtained from hydrocarbon adsorption isotherms determined by differential thermal analysis (35.5, 36.5, and 37.4 mJ/m2).Using values of γsfd and contact angles measured in the system solid-water drop-air, the nondispersion component of the surface free energy of solids with adsorbed water film (γsfn) was calculated from the modified Young equation. The values of γsfn for kaolinite and quartzite are as follows: 55.8, 69.0; 85.6, 94.0; 52.1, 75.0; 64.7, 68.9; 54.9,71.3; and 59.2,74.4 mJ/m2. The values of the nondispersion components determined for kaolinite, bentonite, and montmorillonite agreed well with those obtained by differential thermal analysis (67.6, 78.3, and 65.5 mJ/m2, respectively). Further, based on the assumption that the adsorbed water film decreased the surface free energy of these solids by the value of the work of spreading wetting, the nondispersion component (γsn) of the surface free energy of the solids was calculated to be: 86.9,129.6; 169.5, 187.7; 67.1, 144.8; 117.5, 129.3; 83.0, 135.7 and 100.2, 143.4 mJ/m2. These calculated values of the nondispersion component of marble and quartzite surface free energy agree with those obtained from adsorption isotherms determined by chromatographic and differential thermal analysis (marble = 103.8, 106.4; quartzite = 112, 115, 153.6 mJ/m2).

Interpretation of the contact angle in quartz/organic liquid film-water system

Abstract Contact angles of water drops on a quartz optical glass plate were measured by the sessile-drop method. Before the measurements the heated plate (ca. 100°C) was dipped for a moment in an organic liquid (methanol, propanol, nitrobenzene, ethylene glycol, cyclohexanone, formamide, diacetone alcohol). The measured contact angles ranged from 14 to 30 degrees. Various models of interfaces in quartz/organic liquid-water drop-air system are discussed. The best agreement for measured and calculated contact angles is achieved when a mixed organic liquid-water film around the water drop and a spreading film of the organic liquid under the water drop is taken into account.

The surface tension components of aqueous alcohol solutions

Abstract Measurements of the contact angle were carried out in paraffin-drop of the aqueous alcohol solution-air systems for methanol, ethanol and propanol solutions in the whole range of their concentrations with special consideration of the low concentration range. On the basis of the results obtained the dispersion components of the surface tension of the solutions studied were determined. The dispersion components of the solution surface tension calculated from the contact angle were found to differ distinctly from those calculated from the interfacial tension of the alcohol solution-n-dodecane as well as from those calculated from Eqn (15). Using literature data concerning the properties of alcohols (methanol, ethanol and propanol) and n-dodecane molecules, the interaction parameters Φ were calculated, as well as the dispersion components of the surface tension of the alcohols mentioned above. These values of the dispersion component are in perfect agreement with those calculated from the alcohol-n-dodecane interfacial tension. It has been found that using the geometric-mean rule harmonic-mean rule and the parameter Φ of interfacial interactions it is possible to calculate the dispersion components of the alcohol surface tension, because the results obtained are, in principle, in good agreement. Knowing the interaction parameter Φ one may calculate the dispersion components of the surface tension of the solutions of two polar liquids from the equation derived by us earlier.

Detachment force of air bubble from the solid surface (sulfur or graphite) in water

Abstract Measurements of the force of air bubble detachment from sulfur and graphite surfaces in water were made. Simultaneously, the grain-air bubble system was photographed at the moment of detachment to measure the instantaneous contact angle. The results obtained are discussed as the relationship between detachment force and contact angle for various contact plane radii and air bubble volumes. The measured detachment force values were compared with those calculated from the contact angles. The relationship between the detachment force and the interfacial free energies of the phases in contact was derived for the systems tested.

The total surface free energy and the contact angle in the case of low energetic solids

Abstract Using the literature data of the refractive index, the structural unit molar volume of polymers and their dipole moment, as well as the literature data of the polarizability, ionization potential, and dipole moment of many liquids, values of the Φ parameter for paraffin—liquid and polymer—liquid interfaces were calculated. Next, introducing these values of Φ and the earlier measured values of the contact angle for many liquids to the Young equation, values of the surface free energy (γ S ) of paraffin, polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene terephthalate (PET), and polymethacrylate (PMMA), were determined. It was found that the average values of γ S for these solids were in agreement with those calculated on the basis of geometric, harmonic, or harmonic—geometric mean approaches. The values of the surface free energy of paraffin, PTFE, PE, PET, and PMMA were also calculated from the Young equation modified by Neumann et al. and, using the earlier measured values of the contact angle for many liquids, they were compared with the values obtained by other methods. Next, employing the mean value of the surface free energy, values of the contact angles for many liquids were calculated and compared with those measured earlier for the same liquids. It was found that for paraffin, PTFE, and PE there were big differences among the values of their surface free energies calculated from the contact angles for some liquids; however, the average values were in agreement with those obtained by other methods. The average values of the surface free energies of PET and PMMA were also in the range of the results obtained by other authors. It was also found that the average deviations of the contact angles calculated from the Young equation modified by Neumann et al. from the measured ones were slightly larger than those of the contact angles calculated from equations employing the geometric and harmonic means of the surface free energy components; the method of Neumann et al. may also be used to predict the wettability in some systems.

The changes of the surface free energy of the adsorptive gelatin films

Abstract Measurements of the contact angles for water (W), formamide (F), ethylene glycol (E) and diiodomethane (D) on polymethyl methacrylate (PMMA) covered by adsorptive gelatin films were made. Adsorption was performed from solutions in the concentration range 0–100 g/l. It was found that the biggest changes of the contact angles were up to a monolayer coverage of PMMA surface. For all liquids (besides water) the contact angle was practically constant at gelatin concentration over 2 g/l. Based on these contact angle data, it was suggested that the adsorptive gelatin film structure depended on the concentration of the aqueous gelatin solution from which the adsorption was performed. On the basis of the contact angles obtained the Lifshitz–van der Waals components and the values of the electron–acceptor and electron–donor parameters of the acid–base components of the films were calculated for three triplets of liquids (W–F–D, W–E–D and F–E–D). It was found that the water contact angle strongly influenced the Lifshitz–van der Waals component and acid–base parameters of the gelatin film surface free energy. Systems involving water gave different results than those without water. It was concluded that the gelatin film had a monopole electron–donor character and that this character was caused by the existence of carbonyl or ionised carboxyl groups on gelatin film surface.

Components of the surface free energy of low rank coals in the presence of n-alkanes

Abstract Measurements of contact angles for water, glycerol, formamide and diiodomethane on the surfaces of four low rank coals (31.1, 31.2, 32.1 and 32.2) covered with n-alkanes (n-hexane, n-undecane and n-hexadecane) were made. Using the approaches of van Oss et al., the geometric mean of the interfacial free energy, and Youngs equation, the components of the surface free energy of coals and coal precovered with n-alkane films were calculated. Also the total surface free energy was determined from the so-called equation of state. Using the values of the components of surface free energy or total free energy of the coal, the spreading of the n-alkanes at the coal/water interface and the free energy of interaction between coal particles in the water phase were determined. On the basis of these results we have stated that, on the coal surface in air, a very stable, n-alkane film, resulting from a wetting process by spreading is formed, which first of all reduces the apolar component of the surface free energy of the coal and can partially block the polar component. However, it was found that n-alkanes cannot completely spread over a coal surface immersed in water, and the contact angle depends on the type of n-alkane. It was also found that the presence of an n-alkane film on a coal surface decreased the attractive interactions between the coal particles in the water phase, owing to Lifshitz-van der Waals forces and increased interactions resulting from acid-base forces in comparison to ‘pure’ coal.