Tomasz Białopiotrowicz

The components of surface tension of liquids and their usefulness in determinations of surface free energy of solids

Measurements of the interfacial tension of glycerol-dodecane, formamide-dodecane, ethylene glycol-dodecane, and aqueous ethylene glycol solution-dodecane and the surface tension of ethylene glycol-water solutions were carried out. On this basis the surface tension components of these liquids were calculated and they were compared with values from the literature. It was found that they are close to J. Panzers (J. Colloid Interface Sci.44, 142, 1973) results obtained by using solubility parameters. In order to verify whether the determined components of the surface tension of polar liquids are valid, measurements of equilibrium contact angles for these liquids were made on the surface of paraffin, polytetrafluoroethylene, polyethylene, polyethylene terephthalate, and polymethyl methacrylate. The measured values of contact angles were compared with those calculated, using the well-known components of the surface free energy. Good agreement was achieved among measured and calculated contact angle values and those obtained by other researchers. It was found that the calculated components of the surface tension of polar liquids worked well in the studied systems, and the geometric mean used for dispersion and nondispersion interfacial interactions gives good results despite existing intermolecular forces due to hydrogen bonding.

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.

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.

Surface free energy of celestite and its flotation activity

Abstract Contact angles of water, diiodomethane and dodecylammonium chloride (DDACl) solution drops were measured on the celestite surface precovered with DDACl aqueous solutions of various concentrations. Based on these measurements, the dispersion and non-dispersion components of the surface free energy were determined as a function of the surfactant concentration. Both the flotation activity of celestite and the adsorption of DDACl on this mineral were found to correlate with the components of the surface free energy of celestite, depending on the surfactant concentration. It has been shown quantitatively that a rapid increase in the flotation activity results from the sharp decrease in the non-dispersion component of the celestite surface free energy. This is accompanied by a monolayer coverage (assuming uniform distribution of the molecules) with DDACl. It is shown that the values of the dispersion and non-dispersion components of the celestite surface free energy fulfil the thermodynamic condition for effective flotation, i.e. the work of water adhesion to the surface is smaller than the work of water cohesion.

The influence of an apolar collector on the contact angle, detachment force and work of adhesion to the coal surface in agglomeration flotation of a low rank coal

Abstract Tests on agglomeration/flotation of coal rank 32.1 for different size fractions (−0.15, −0.25, −0.385 and −0.5 mm) were made using kerosene as the collector. The overall flotation results were correlated with the contact angle, the detachment force and the work of adhesion of water to the coal surface in the system coal/n-undecane film-air bubble — water. It was found that the mass of concentrate and the amount of coal in the concentrate increased as the dosage of kerosene increased. This increase depended on the size fraction of the flotation feed. These flotation indices were improved by increasing the contact angle and the detachment force of an air bubble from the coal surface, by increasing the thickness of the apolar liquid film on the coal surface. This increase of the film thickness also caused a decrease in the work of adhesion to the coal/film surface. The efficiency of coal beneficiation in agglomeration/flotation processes was strongly influenced by contact angle, detachment force and work of adhesion of water to the coal surface.

Influence of exchangeable cations on the surface free energy of kaolinite as determined from contact angles

The influence of adsorbed H+, Na+, K+, Ca2+, Mg2+, Ba2+, and Al3+ ions on the wettability of a kaolinite surface was determined from contact angles, which were measured in kaolinite-water drop-air (saturated water vapor) and kaolinite-diiodomethane drop-air systems. From the results and using a modified Young equation, the dispersion and nondispersion components of the free energy of the kaolinite hydrated surface were determined. The dispersion component of all the tested samples was between 32.8 and 38.9 mJ/m2, but the nondispersion component changed almost linearly from 53 to 95.9 mJ/m2 with the change of the entropy of hydration of the adsorbed ions, except for K+ and Ba2+. The latter ions were exceptions, probably due to their large ionic radii.

Spreading of a water drop on a marble surface

Measurements of the wetting contact angle for a marble surface were carried out for two systems: dry marble plate-water drop-saturated water vapour and marble wetted by water-water drop-dry air (in the presence of molecular sieves). The marble plate was placed in a measuring chamber and contact angles were measured after different lengths of time; it was found that their values grew to a maximum which was reached after about 30 min. It was found that when the dry marble plate was placed in saturated water vapour for 24 h the contact angle decreased in comparison with its maximal value. To explain the results obtained, theoretical calculations were made. The theoretical calculations and measurements showed that it was possible to obtain a contact angle greater than zero on a marble surface, depending on the structure and thickness of the water film.