Anna Zdziennicka

RELATIONSHIP BETWEEN WETTING OF TEFLON BY CETYLTRIMETHYLAMMONIUM BROMIDE SOLUTION AND ADSORPTION

Abstract Contact angles for cetyltrimethylammonium bromide (CTAB) solution (θ) and for series of n -alkanes from n -hexane to n -hexadecane on a Teflon surface were measured. In addition, contact angle measurements for water and diiodomethane on Teflon surface covered with CTAB layer were carried out. The results obtained are used for the determination of the amount of CTAB adsorbed at the Teflon/water interface, the surface free energy of Teflon, the interfacial free energy of Teflon/CTAB solution, the standard free energy of adsorption and the standard free energy of micellization. From an adhesion tension plot of γ L cos θ vs γ L and application of the Gibbs and Young equations it appears that the amount adsorbed to the Teflon/water interface at a high equilibrium concentration of CTAB is close to that adsorbed at the water/air interface, whereas in the range of low concentrations there are considerable differences between adsorption at Teflon/water and water/air interfaces. This is confirmed by data obtained from the plot of Teflon/solution interface free energy against CTAB solution concentration. It is found that the standard free energy of adsorption at the Teflon/water interface can be determined approximately from the interfacial tail of surfactant-water, tail-tail and tail-Teflon tension data. A good agreement between the standard free energy of micellization and free energy of interactions of CTAB ions through water is found. The free energy of interactions between CTAB ions through water is determined on the basis of the surface free energy of CTAB and the ψ potential.

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.

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.

Thermodynamic properties of rhamnolipid micellization and adsorption

MEASUREMENTS of the surface tension, density, viscosity and conductivity of aqueous solutions of rhamnolipid at natural and controlled pH were made at 293 K. On the basis of the obtained results the critical micelle concentration of rhamnolipid and its Gibbs surface excess concentration at the water-air interface were determined. The maximal surface excess concentration was considered in the light of the size of rhamnolipid molecule. Next the Gibbs standard free energy of rhamnolipid adsorption at this interface was determined on the basis of the different approaches to this energy. The standard free energy of adsorption was also deduced on the basis of the surface tension of n-hexane and water-n-hexane interface tension. Standard free energy obtained in this way was close to those determined by using the Langmuir, Szyszkowski, Aronson and Rosen, Gu and Zhu as well as modified Gamboa and Olea equations. The standard free energy of rhamnolipid adsorption at the water-air interface was compared to its standard free energy of micellization which was determined from the Philips equation taking into account the degree of rhamnolipid dissociation in the micelles.

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.

Behavior of cationic surfactants and short-chain alcohols in mixed surface layers at water–air and polymer–water interfaces with regard to polymer wettability: II. Wettability of polymers

The wettability of polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) by aqueous solutions of cetyltrimethylammonium bromide (CTAB) mixtures with short-chain alcohols such as methanol, ethanol, and propanol, as well as for 1-hexadecylpyridinium bromide (CPyB) with the same alcohols, was studied on the basis of advancing contact-angle measurements by the sessile drop method over a wide range of alcohol and cationic surfactant concentrations where they can be present in solution in monomeric or aggregated form. It should be noted that the contact angles for aqueous solution mixtures of cationic surfactants with propanol on PTFE surfaces were measured earlier and presented in our previous paper. From the obtained contact-angle values the relationships between cos theta and surface tension of the solutions (gamma(LV)) and that between adhesion tension and gamma(LV) were considered. The relationship between the cos theta and the reciprocal of gamma(LV) was also discussed. From these relationships the critical surface tension of PTFE and PMMA wetting and the correlation between the adsorption of cationic surfactant and alcohol mixtures at water-air and polymer-water interfaces were deduced. On the basis of the contact angles and components and parameters of the surface tension of surfactants, alcohols, and polymers also the Gibbs and Guggenheim-Adam isotherm of adsorption and the effective concentration of alcohols and surfactants at polymer-water interfaces were calculated. Next, the work of adhesion of solution to polymer surface with regard to the surface monolayer composition was discussed. The analysis of the contact angles with regard to adsorption of surfactants and alcohols at polymer-water and water-air interfaces allowed us to conclude that the PTFE wetting depends only on the contribution of the acid-base interactions to the surface tension of aqueous solutions of cationic surfactant and alcohol mixtures, and the adhesion work of solution to its surface only slightly depends on the concentration and composition of solution, in contrast to PMMA. The critical surface tension of PTFE wetting is close to its surface tension determined for liquids in which the surface tension is two times or more higher than that of PTFE, but for PMMA it is considerably lower than its surface tension and even the Lifshitz-van der Waals component of this tension.

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.

Wettability of quartz in presence of nonionic surfactants and short chain alcohols mixtures

Measurements of advancing contact angles for aqueous solution of Triton X-100 (TX-100) with methanol, ethanol and propanol mixtures and Triton X-165 (TX-165) with the same alcohols on quartz surface were carried out. From the obtained results it appeared that the wettability of quartz depends on Tritons and alcohol concentrations and that there is a linear dependence between the adhesional and surface tension of aqueous solution of Tritons and alcohols mixtures. This dependence can be described by linear equations which constants depend somewhat on the Tritons and alchohols concentration. The slope of all linear dependencies between the adhesional and surface tension is positive. The critical surface tension of quartz wetting determined from these dependencies by extrapolating the adhesional tension to a value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of Triton or alcohols was constant. The average value at constant Tritons concentration was equal to 27.1 mN/m and was lower than that evaluated at constant alcohol concentration (29.5 mN/m). The critical surface tension of quartz wetting at constant alcohol concentration was nearly the same as the apolar component of the surface tension of quartz covered with water monolayer film. The positive slope of the adhesional-surface tension curves and the work of water adhesion, Tritons and alcohols to quartz surface indicates that the interaction between water molecules and quartz surface might be stronger than that between quartz and surface active agents molecules. So, the concentration excess of surfactants at quartz-water interface is probably negative, and the possibility of the surface active agents to adsorb at quartz/water film-water interface is higher than that at the quartz-water. However, at alcohol concentration above that of its aggregation the molecules of the surface active agents probably destroy the strongly ordered film of water.

Adsorption and volumetric properties of Triton X-100 and propanol mixtures

The adsorption behavior at the water-air interface and volumetric properties of aqueous solutions of Triton X-100 and propanol mixtures at constant Triton X-100 concentrations equal to 1x10(-7), 1x10(-6), 1x10(-5), 1x10(-4), 6x10(-4), and 1x10(-3) M, respectively, in the propanol concentration range from 0 to 6.69 M were investigated by surface tension, viscosity, and density measurements of solutions. The obtained values of the surface tension as a function of propanol concentration were compared with those calculated from the Fainerman and Miller equation. On this basis it was stated that the Fainerman and Miller equation is useful for prediction of surface tension only in the concentration range of Triton X-100 corresponding to its unsaturated monolayer in the absence of propanol. Using the measured values of the surface tension in the Gibbs equation, the surface excess concentration of Triton X-100 and propanol was calculated, and it was stated that in the case of propanol the most reliable values of its excess concentration were obtained if its activity were taken into account instead of concentration in the bulk phase. The values of the surface excess concentration were applied in different approaches for determination of the standard free energy of adsorption. The calculated values of the standard free energy of adsorption were compared with those for individual components of the studied mixtures deduced on the basis of the tail-water and tail-air interfacial tension. Beside the surface properties of the Triton X-100 and propanol mixtures their volumetric properties were established and it was found that the micellization process of Triton X-100 occurred only at a low propanol concentration at which it is present in the monomeric form. The possibility of propanol aggregates formation was deduced from the viscosity and density changes in relation to propanol concentration. From the density data it was also deduced that the apparent molar volume for aqueous solutions of the Triton X-100 and propanol mixtures can be predicted from the data of their individual components.

Adhesion work and wettability of polytetrafluorethylene and poly(methyl methacrylate) by aqueous solutions of cetyltrimethylammonium bromide and Triton X-100 mixture with ethanol.

The contact angle measurements of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (TX-100) and cetyltrimethylammonium bromide (CTAB) mixture with ethanol on polytetrafluoroethylene (PTFE) and poly (methyl methacrylate) (PMMA) were carried out in the range of the total concentration of TX-100 and CTAB mixture from 1×10(-6) to 1×10(-3) M and in the whole range of ethanol concentration. In the surfactant mixture, the mole fraction of TX-100 was equal to 0.2; 0.4; 0.6 and 0.8, respectively. From the obtained results, the critical surface tension of PTFE and PMMA wetting and the adhesion work of the solutions to the polymer surface were established. The PMMA surface tension was calculated from the Neumanns equation. It appeared that for the ethanol concentration higher than that corresponding to the association of its molecules, the surface tension of PMMA calculated from the Neumanns equation is close to the critical surface tension of PMMA wetting. It also appeared that it is possible to predict the work of adhesion of the studied solutions to the PMMA surface by using the PMMA surface tension data determined on the basis of the van Oss et al. approach to the interfacial tension and those from the Neumanns equation.