B. Jańczuk

Surface free-energy components of liquids and low energy solids and contact angles

Abstract Employing the values of organic liquid surface tension and interfacial surface tension of water-organic liquid, values of dispersion and nondispersion components of these liquids were calculated and compared with those obtained in another way. For these organic liquids and water, the values of the contact angle on paraffin wax, polytetrafluoroethylene, polyethylene, polyethylene terephthalate, and polymethyl methacrylate were measured. The values of dispersion and nondispersion components of surface free energy of these polymers and paraffin wax were calculated using the measured values of the contact angle for diiodomethane and water and the calculated values of the components of their surface tension. These calculated data were in agreement with the literature data. Taking our values of free energy components of liquids and solids, the values of the contact angle for these solids were calculated and compared with those measured, obtaining good agreement. On the basis of the measurements and calculations it was found that dispersion and nondispersion components of surface free energy of liquids and solids “work well” in the systems studied.

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.

A study on the components of surface free energy of quartz from contact angle measurements

Measurements of the contact angle for water, glycerol, formamide, diiodomethane and 1,1,2,2-tetrabromoethane on a quartz surface were made. Using the results obtained, the “geometric mean” approach and long-range and acid-base interaction approach, the dispersion, non-dispersion, Lifshitz-van der Waals and acid-base components of the surface free energy of quartz were determined and compared with those determined in different ways. On the basis of the measurements and calculations it was found that the surface free energy of quartz depends largely on the amounts of silanol groups and physically adsorbed water molecules on its surface. It was also found that the two tested approaches to surface free energy of solids and liquids gave similar results, and it is suggested that the surface free energy of quartz results mainly from dispersion and hydrogen-bond intermolecular interactions.

Surface free energy of cholesterol and bile salts from contact angles

Abstract Measurements of contact angles for water, ethylene glycol, diiodomethane, and bromoform on cholesterol, and water, diiodomethane, and bromoform on bile salts pellets were conducted. Using the values of the contact angles, total surface free energy of cholesterol and bile salts and components of the energy resulting from different kinds of intermolecular interactions were calculated. For this purpose, various approaches to the solid—liquid interfacial free energy have been considered, though some older ones were criticized. Thus, it was found that the surface free energy of cholesterol originates mainly from the Lifshitz—van der Waals interactions, while that of bile salts is due to apolar Lifshitz—van der Waals, and to a great extent to the polar (Lewis acid—base) electron-donor and electron-acceptor interactions. It was found that all the tested approaches to the solid—liquid interfacial energies may be useful; however, the one describing the surface free energy of a solid and a liquid in terms of apolar Lifshitz—van der Waals and polar acid—base interactions gives more information about properties of the cholesterol and bile salts surfaces. Using values of the Lifshitz—van der Waals, electron-donor, and electron-acceptor components of the surface free energy of cholesterol, bile salts, and water, the free energy of interaction between two particles of cholesterol in water, and of cholesterol—bile salt and of bile salt—bile salt immersed in water was calculated. From these calculations it appears that bile salts adsorbed on cholesterol surfaces cause the free energy of interaction between the cholesterol particles immersed in water to be positive. As a result, the cholesterol dispersions should be stable (unflocculated). However, no electrostatic interactions due to the surface electric charge were taken into account.

The influence of n-alcohols on the wettability of hydrophobic solids

Abstract Measurements were made of contact angles of air bubbles on the hydrophobic solid surface of sulphur, graphite and Teflon in aqueous solutions of methanol, ethanol and propanol. Special attention was given to the measurements at low alcohol concentrations. The greatest changes in contact angle values as a function of alcohol concentration were observed at small alcohol concentrations, where changes in the solution surface tension were small. On this basis it is concluded that polar interactions between alcohol molecules in solution and those already adsorbed are important in defining the wetting properties of the hydrophobic solid under these conditions. The calculations based on the equation of Good, Girifalco, Fowkes and Young and Tamai et al. seem to verify the above conclusion.

Surface free energy components and adsorption properties of some porous glasses

Abstract The dispersion and nondispersion components of the surface free energy were determined on the basis of literature adsorption isotherms for water and n-octane on the surface of the controlled porosity glass and thermally treated glasses with chemically bonded Carbowax 20M. Next, using the values of the mentioned components, the work of adhesion of water, n-octane, methanol, carbon tetrachloride and benzene to surface of the glasses and the ratio of the work of adhesion to the work of cohesion were calculated. Applying these calculations a correlation between the thermal treatment time of glasses (before the Carbowax 20 M bonding) and the dispersion and nondispersion components of their surface free energy was found. Additionaly the correlation between the amounts of the liquid adsorbed on the glass surface at constant equilibrium pressure and the ratio of the work of adhesion of the liquid to the glass surface to the work of liquid cohesion were estimated.

Determination of surface-free energy components of synthetic chalcocite from contact angle measurements

Abstract Measurements of the contact angle for water, glycerol, ethylene glycol, diiodomethane, bromoform and 1,1,2,2-tetrabromoethane on chalcocite, copper oxide, copper hydroxide, copper sulfate and sulphur were made. Using the ‘geometric mean’ and van Oss et al. approaches, the dispersion and nondispersion — or Lifshitz-van der Waals, electron-acceptor and electron-donor components of the surface-free energy — of the studied solids were determined and compared with those calculated from zeta potential measurements. On the basis of the results obtained it was found that the surface-free energy of the solids studied in this work originated from apolar and polar intermolecular interactions. As concentration of the hydroxyl group on chalcocite surface is increased, so the polar interactions are increased.

Components of surface free energy of galena

Measurements of the contact angle for water, diiodomethane, bromoform and 1,1,2,2-tetrabromoethane on non-oxidized and oxidized surfaces of galena were made. Using the results obtained, the “geometric mean” approach, and the long-range and short-range interactions approaches, the dispersion and non-dispersion, and Lifshitz-van der Waals and acid-base components of the surface free energy of galena were determined and compared with those calculated from adsorption isotherms ofn-octane andn-propanol. On the basis of the measurements and calculations it was found that the surface free energy of galena depends on its degree of oxidation and arise mainly from Londons and acid-base intermolecular interactions. It was also found that values of the dispersion and non-dispersion components of galena surface free energy determined from the contact angle assuming that a film is present around the water and diiodomethane drops, are close to those obtained from adsorption isotherms ofn-octane andn-propanol.

The surface free energy components of homoion1c bentonite from contact angle measurements

Abstract Wetting contact angles were measured for glycerol and diiodome-thane drops on pellets made of bentonite samples exchanged with Li+, Na+, K+, Mg2+, Ca2+, Sr2+ and Ba2+ cations. Based on the contact angle values, the dispersion and nondispersion components of the homoionic bentonite surface free energy were calculated using a modified Young equation. The exchangable cations did not cause a great difference in the dispersion components of the surface free energy and the values were similar to those for natural bentonite. However,the nondispersion components differed markedly among themselves and also from the value for natural bentonite. A linear relationship was also found between the nondispersion components of the surface free energy and the entropy of hydration of the exchanged cations, except K+ and Ba2+.

Properties of n-Alkane Films in the System: Teflon/n-Alkane-Water

Although Teflon possesses a very low surface free energy, n-alkane thick liquid films may exist in Teflon/ n-alkane-water system. We examined properties of the films by measurements of contact angle, adhesion force of air bubbles and zeta potential for Teflon/n-alkane in water. Series of hydrocarbons ranging from n-hexane to n-hexa-decane were tested. The results obtained show that equilibrium values of the measured parameters change nonlineary with chain length of the alkanes. The changesof the parameters correlate between themselves and with melting temperature of the alkanes. For Teflon/n-hexane in water system, the film pressure values were calculated from the experimental relationship between specific film volume and zeta potential. In the extreme case, about 4 statistical monolayers of n-hexane were present on the Teflon surface. If air bubbles are attached and then removed from Teflon surface wetted completely with n-hexane, they take away some amounts of n-hexane. This results in an increase in the adhesion force and decrease in contact angle, both of which reach equilibrium values. About 13 air bubbles are needed to attain the equilibrium, and 13–14 air bubbles remove the film almost completely. Comparison of the results from zeta potential and contact angle measurements leads to the conclusion that the most stable film exists at 1.5 to 2.5 statistical monolayers.