Wettability Of Polytetrafluoroethylene Research Articles

Wetting Behaviour of Water, Ethanol, Rhamnolipid, and Triton X-165 Mixture in the Polymer-Solution Drop-Air System.

Despite the fact that the wetting properties of multicomponent mixtures including the surface active compounds play a very important role in many practical applications, they are not sufficiently known. Thus, the wettability of polytetrafluoroethylene (PTFE) and poly (methyl methacrylate) (PMMA) by the water + ethanol (ET) solution of rhamnolipid (RL) with Triton X-165 (TX165) mixture was studied. The investigations involved measuring the advancing contact angles of this solution on PTFE and PMMA by varying the concentration of TX165 while maintaining a constant concentration of ET and RL. Additionally, a thermodynamic analysis was conducted to obtain the compositions and concentrations of the ET, RL, and TX165 mixtures at the different interfaces. The composition and concentration of the interface mixed layer were considered using two different approaches to the wetting process. From these considerations, it follows that, depending on the ET concentration, it is possible to form the TX165 + RL layer at the solid-water + ET mixed solvent, as well as the water + ET-air interfaces, but not at the solid-water and water-air ones. This conclusion is in accordance with the Gibbs standard free energy of adsorption of particular components of the studied mixture at the solution-air and solid-solution interfaces.

Experimental investigation of friction stir spot welding of polymer-aluminum alloy weldments

The friction stir spot welding (FSSW) process is one of the main solid-state joining methods used widely for welding different materials and dissimilar metals. In this article, the welding of Polytetrafluoroethylene (PTFE) and aluminum alloy sheets by the FSSW process will be investigated experimentally. The joining of polymer (PTFE) and metal (AA1050 aluminum alloy) was done successfully. The effect of process parameters including tool rotational speed, penetration depth, initial holding time, dwell time, and tool shoulder diameter on the joint strength and elongation of the weldments will be studied using response surface methodology (RSM). The joint strength was increased by creating a threaded hole in the aluminum sheet. A mechanical lock was created between the softened PTFE and the edge of the threaded hole. The shear-tensile tests have been carried out for 32 designed experiments. The results show that the joint strength increased by increasing the initial holding time due to the better wettability of PTFE and aluminum sheet. The joint strength increased by increasing the tool rotational speed and tool diameter (better pouring of the hole and formation of the mechanical lock). Two different fracture modes have been observed in the samples: (1) fracture in the peripheral area of the joint (partial interfacial fracture mode) and (2) fracture in the mechanically locked area (pull-out mode with tearing).

Novel additive of PTFE@SiO2 core-shell nanoparticles with superior water lubricating properties

In order to solve the problems of poor dispersibility and wettability, as well as unsatisfactory wear resistance and load capacity of polytetrafluoroethylene (PTFE) as water lubricating additive, a new type of PTFE@silica (PTFE@SiO2) core-shell nanoparticles was prepared by encapsulating SiO2 layer on the surface of PTFE via chemical bonding. Electron microscope analysis showed that the synthesized particles had well-defined core-shell morphology. Special double/multi-core structure and a reduced thickness of the intermediate shell were found, and the formation mechanisms were also explored in detail. The water contact angle measurement proved that the wettability of PTFE could be greatly enhanced by coating SiO2 layer. The friction tests were performed to investigate the water lubrication properties of PTFE@SiO2 additive, the results indicated that the core-shell PTFE@SiO2 nanoparticles possessed the superior tribological properties, and the maximum friction coefficient and wear volume were respectively decreased by 75% and 99% when compared with pure water and water with PTFE/SiO2. Based on the analysis of worn surface, it was believed that the existence of core-shell structure and the formation of robust transfer film were the key to its excellent performance, and a possible lubrication mechanism was also proposed.

Wettability of polytetrafluoroethylene and polymethyl methacrylate by aqueous solutions of TX-100 and TX-165 mixture with propanol

The measurements of the contact angle of the aqueous solutions of TX-100 and TX-165 mixture with propanol on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) were carried out. On the basis of the obtained results, the dependence between the cosine of contact angle and surface tension as well as between the adhesion and surface tension of the solutions in the light of the work of adhesion of the solutions to the PTFE and PMMA surface was discussed. The dependence between the adhesion and surface tension for PMMA was correlated to the surface concentration of propanol as well as TX-100 and TX-165 mixture concentration determined from the Frumkin equation at the PMMA-air, PMMA-solution and solution–air interfaces. For this purpose, the surface tension of PMMA covered by a surface active agent film was determined using the Neumann et al. equation and next the PMMA–solution interface tension was evaluated from the Young equation. The values of the surface tension of PMMA covered by propanol and surfactants mixture layer were applied to describe the changes of the adhesion work of solutions to PMMA surface as a function of propanol and surfactants mixture concentration. The adhesion work of the aqueous solutions of TX-100 and TX-165 mixture with propanol to the PTFE and PMMA surfaces was discussed in the light of the adhesion work of particular components of the solutions. On the basis of the results obtained from the contact angle measurements, the standard Gibbs free energy of adsorption of particular components of solution was also considered.

Wetting properties of the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and polyoxyethylene (23) lauryl ether (Brij 35) binary mixtures in the poly(tetrafluoroethylene)-solution-air system

AbstractWettability of poly(tetrafluoroethylene) (PTFE) by aqueous solutions of binary mixtures composed of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) with polyoxyethylene (23) lauryl ether (Brij 35) was considered on the basis of the measured values of contact angle and surface tension. It was shown that the value of the critical surface tension of PTFE surface wetting at the studied system (23.5 mN/m), does not depend on the concentration and composition of the binary mixtures of studied surfactants in water, and it was higer than the surface tension of PTFE (20.2 mN/m). The best wettability of polytetrafluoroethylene (PTFE) by studied aqueous solutions of binary surfactants mixtures occurs at the mixtures concentration corresponding to the critical micelle concentration of their solutions.

Wettability of polymers by aqueous solution of binary surfactants mixture with regard to adhesion in polymer–solution system I—Correlation between the adsorption of surfactants mixture and contact angle

Wettability of polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA) and nylon 6 by aqueous solutions of binary mixtures composed of cetyltrimethylammonium bromide (CTAB) with p-(1,1,3,3-tetramethylbutyl)-phenoxypolyoxyethylene glycols, Triton X-100 (TX-100) and Triton X-114 (TX-114) with regard to the tendency of their adsorption at the water–air and polymer–water interfaces was considered on the basis of the measured values of the contact angle, the dependence between the adhesion and surface tension as well as the Gibbs surface excess concentration. It was shown that the wettability of PTFE, PMMA and nylon 6 depends on the concentration and composition of the binary mixtures of surfactants in water and the best wettability occurs at the concentration of the mixtures corresponding to the critical micelle concentration of their solutions. However, at the lower concentrations the synergetic effect in the wettability of polymers by the CTAB+TX-100 and CTAB+TX-114 mixtures takes place. This effect was confirmed by the standard Gibbs free energy of adsorption of binary mixtures of surfactants at the polymer–water interface calculated on the basis of the Gu and Zhu equation. The standard Gibbs free energy of adsorption being a measure of the efficiency of a given mixture to adsorb at the polymer–water interface changes in a different way from the maximal Gibbs surface excess concentration of these mixtures calculated from the Gibbs isotherm equation which suggests that the changes of the efficiency of the adsorption process are not proportional to its effectiveness.

Surface modification of PTFE using an atmospheric pressure plasma jet in argon and argon + CO 2

Polytetrafluoroethylene (PTFE) has many successful engineering applications due to its great chemical stability. However, for some industrial applications, the poor adhesion of PTFE to other materials is a disadvantage. To extend the PTFE application range, several methods have been developed to modify its surface properties. Among these different techniques, plasma surface modification is the most promising one and therefore, an atmospheric pressure plasma jet (APPJ) will be used in this work to modify PTFE samples. Two different discharge gasses have been used: pure argon and an argon/CO 2 mixture and both plasma jets have been examined with optical emission spectroscopy to identify the plasma species present in the discharge. From these results, it was found that the discharge in argon contains argon atoms, nitrogen molecules and metastables, atomic oxygen and OH radicals, while the argon/CO 2 discharge contains also radicals containing CO groups. In a second part of the work, the chemical and physical changes induced by both discharges on PTFE surfaces have been investigated using contact angle measurements, SEM, AFM and XPS. From these results, it was found that exposure times below 20 s lead to a small contact angle decrease due to the introduction of a small amount of oxygen. In contrast, at higher treatment times, the contact angle starts to increase again due to advanced chain scissions leading to a high amount of oligomeric segments on the PTFE surface. As a result of these surface degradation processes, the wettability of PTFE could not be greatly enhanced, however, in the near future, it will be investigated whether these degradation reactions can be eliminated.

The wettability of polytetrafluoroethylene and polymethylmethacrylate with regard to interface behaviour of Triton X-165 and short chain alcohol mixtures:: II. Adsorption at water–air and polymer–water interfaces

On the basis of the contact angle data presented in the previous paper, the surface concentration of alcohols and TX-165 at PTFE–water and PMMA–water interfaces was determined. For this determination the polymer–solution interface tension was calculated from the Young equation by using the literature data of the polymers surface tension. Taking into account the Gibbs and Guggenheim-Adam adsorption isotherms of Triton X-165 and alcohols their molar fractions and activity coefficients were determined. Next, the free enthalpy of Triton X-165 and alcohols mixing in the adsorption monolayer at polymer–solution interface was calculated. From the theoretical analysis of the adsorption of the Triton X-165 and alcohols it results that the total adsorption of the mixture and its individual components at PTFE–solution and solution–air interface is nearly the same, but the total adsorption at PMMA–solution interface is considerably lower than that at solution–air one, and the composition of the mixtures at both interfaces is different. It can be also stated that the activity coefficients of Triton X-165 and alcohols in the surface region at solution–air and polymer–solution interface are different.

The wettability of polytetrafluoroethylene and polymethylmethacrylate with regard to interface behaviour of Triton X-165 and short chain alcohol mixtures: I. Critical surface tension of wetting and adhesion work

Wetting of polymers (PTFE, PMMA) by aqueous solutions of Triton X-165 mixtures with methanol, ethanol and propanol was studied in a wide range of alcohol and Triton X-165 concentration. The Triton X-165 concentration range corresponded to its unsaturated and saturated monolayer in the absence of alcohol. The wetting properties of Triton X-165 and alcohol mixtures were determined on the basis of advancing contact angles measurements by the sessile drop method. From the obtained contact angle values the relationships between cos θ, the adhesion tension and surface tension of the solutions, cos θ and the reciprocal of the surface tension were determined. On the basis of these relationships the correlation between the critical surface tension of PTFE and PMMA wetting and the surface tension of these polymers and work of adhesion of aqueous solution of TX-165 and alcohols mixtures to PTFE and PMMA surface was discussed. The critical surface tension of PTFE wetting was found to be close to its surface tension determined from the contact angles for polar liquids, but the critical surface tension of PMMA wetting considerably lower than its surface tension and even the Lifshitz–van der Waals components of this surface tension.

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 θ and surface tension of the solutions ( γ LV ) and that between adhesion tension and γ LV were considered. The relationship between the cos θ and the reciprocal of γ 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.

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and short chain alcohol mixtures

Measurements of advancing contact angles ( θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and methanol and ethanol mixtures at constant TX-100 concentration equal to 1 × 10 −7, 1 × 10 −6, 1 × 10 −5, 1 × 10 −4, 6 × 10 −4 and 1 × 10 −3 M, respectively, on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA). Using measured contact angle values the relationships between cos θ, adhesion tension and surface tension of the solutions were determined, and on their basis the critical surface tension of PTFE and PMMA wetting was calculated. The obtained average value of the critical surface tension of PTFE wetting is lying in the range of the PTFE surface tension values which can be found in the literature, while for PMMA it is even lower than the Lifshitz–van der Waals component of its surface tension. From the relationship between the adhesion and surface tension and Lucassen–Reynders equation it results that in the case of PTFE the adsorption at the PTFE–solution and solution–air interfaces is the same, which was confirmed by a linear relationship between the cos θ and 1/ γ LV and intercept on cos θ axis equal to −1. However, for PMMA the adsorption of the surface active agents at solution–air interface is higher than at PMMA–solution. Using the values of the contact angle the values of the adhesion work of solution to the PTFE and PMMA surface were also determined, which are constant for PTFE, but for PMMA decrease with alcohol concentration increase. Next, using the contact angle values in the Young equation, the PTFE(PMMA)–solution interface tension was also calculated. The obtained values of PTFE–solution interface tension were compared with those evaluated from the Szyszkowski, Connors and Fainerman and Miller equations, and good agreement between these values was observed for all series of TX-100 and alcohol mixtures at a low alcohol concentration.

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and propanol mixtures

Measurements of advancing contact angles (θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and propanol mixtures at constant TX-100 concentration equal to 1×10−7, 1×10−6, 1×10−5, 1×10−4, 6×10−4 and 1×10−3M, respectively, on polytetrafluoroethylene (PTFE) and polymethyhmethacrylate (PMMA). Using obtained results the changes of cosθ and adhesional tension against surface tension of all series of aqueous solutions of TX-100 and propanol mixtures (γLV) for PTFE and PMMA surfaces were shown. On the basis of these changes it was deduced that adsorption of TX-100 and propanol mixtures at PTFE-solution and solution-air interfaces is the same but the adsorption of TX-100 and propanol mixtures at solution-air interface is considerably higher than at PMMA-solution one. In the case of PTFE this conclusion was confirmed by relationship between cosθ and the reciprocal of the surface tension of solution. Extrapolation of the relationships between cosθ and/or adhesional tension and the surface tension of solutions to the points corresponding to the cosθ=1 and adhsional tension equal to the surface tension of solution, the critical surface tension of PTFE and PMMA wetting was determined. The average values of critical surface tension of wetting determined from these relationships for PTFE are lying in the range of its surface tension values determined from contact angles of different kinds of liquids, which can be find in the literature, but for PMMA are considerably lower than the surface tension. The double value of the critical surface tension of PTFE wetting is equal to adhesion work of the solution to its surface and for PMMA there is not any correlation between these magnitudes.Using the measured values of the contact angles and Young equation the PTFE(PMMA)-aqueous solution interfacial tension was determined. The interfacial tension values of PTFE-aqueous solution were also calculated from the Fainerman and Miller equation in which the correcting parameter of nonideality of the surface monolayer was introduced and compared to those obtained from Young equation. From this comparison it results that the changes of PTFE-solution interface tension as a function of propanol concentration can be described by the Fainerman and Miller equation.

The wettability of polytetrafluoroethylene by aqueous solution of cetylpyridinium bromide and propanol mixtures

Measurements of advancing contact angles ( θ) were carried out for aqueous solutions of cetylpyridinium bromide (CPBr) and propanol mixtures at constant CPBr concentration equal to 1 × 10 −5, 1 × 10 −4, 6 × 10 −4, 1 × 10 −3 M, respectively, on polytetrafluoroethylene (PTFE). The obtained results indicate that the wettability of PTFE by aqueous solutions of these mixtures depends on their composition and concentration. In contrast to Zisman, there is no linear dependence between the cos θ and surface tension of aqueous solutions of CPBr and propanol mixtures ( γ LV), but a linear relationship exists between the adhesion tension and the surface tension of aqueous solutions of CPBr and propanol mixtures which have a slope equal to −1, and between cos θ and the reciprocal of the surface tension of solution. The slope equal to −1 and the intercept on the cos θ axis close to −1 suggest that adsorption of CPBr and propanol mixtures and the orientation of their molecules at aqueous solution–air and PTFE–aqueous solution interfaces are the same. This also suggests that the work of solution adhesion to the PTFE surface does not depend on the concentration of propanol and CPBr. Extrapolation of the straight line to the point corresponding to the surface tension of solution, which completely spreads over the PTFE surface, gives the value of the critical surface tension of PTFE wetting equal to 24.84 mN/m. This value is higher than PTFE surface tension (20.24 mN/m) and the values of the critical surface tension of PTFE wetting determined by other investigators from the contact angle of nonpolar liquids (e.g. n-alkanes). The differences between the value of the critical surface tension obtained here and those which can be found in the literature were discussed on the basis of the simple thermodynamic rules. Using the measured values of the contact angles and Young equation the PTFE–aqueous solution interfacial tension was determined. The values of PTFE–aqueous solution interfacial tension were also calculated from Miller and co-workers equation in which the correction coefficient of nonideality of the surface monolayer was introduced. From comparison of the obtained values it appears that good agreement exists between the values of PTFE–solution interfacial tension calculated on the basis of Young and Miller and co-workers equations in the whole range of propanol concentration.

The adsorption of cetyltrimethylammonium bromide and propanol mixtures with regard to wettability of polytetrafluoroethylene: II. Adsorption at polytetrafluoroethylene–aqueous solution interface and wettability

Measurements of contact angles ( θ) of aqueous solutions of cetyltrimethylammonium bromide (CTAB) and propanol mixtures at constant CTAB concentration equal to 1 × 10 −5 , 1 × 10 −4 , 6 × 10 −4 and 1 × 10 −3 M on polytetrafluoroethylene (PTFE) were carried out. The obtained results indicate that the wettability of PTFE by aqueous solutions of these mixtures depends on their composition and concentration. They also indicate that, contrary to Zisman, there is no linear relationship between cos θ and the surface tension ( γ LV ), but a linear relationship exists between the adhesional ( γ LV cos θ ) and surface tension of aqueous solutions of CTAB and propanol mixtures. Curve γ LV cos θ vs γ LV has a slope equal −1 suggesting that adsorption of CTAB and propanol mixtures and the orientation of their molecules at aqueous solution–air and PTFE–aqueous solution interfaces is the same. Extrapolating this curve to the value of γ LV cos θ corresponding to θ = 0 , the value of the critical tension of PTFE wetting equal 23.4 mN/m was determined. This value was higher than that obtained from contact angles of n-alkanes on PTFE surface (20.24 mN/m). The difference between the critical surface tension values of wetting probably resulted from the fact that at cos θ = 1 the PTFE–aqueous solution of CTAB and propanol mixture interface tension was not equal to zero. This tension was determined on the basis of the measured contact angles and Young equation. It appeared that the values of PTFE–aqueous solution of the CTAB and propanol mixtures interface tension can be satisfactorily determined by modified Szyszkowski equation only for solutions in which probably CTAB and propanol molecules are present in monomeric form. However, it appeared that using the equation of Miller et al., in which the possibility of aggregation of propanol molecules in the interface layer is taken into account, it is possible to describe the PTFE–solution interfacial tension for all systems studied in the same way as by the Young equation. On the basis of linear dependence between the adhesional and surface tension it was established that the work of adhesion of aqueous solution of CTAB and propanol mixtures does not depend on its composition and concentration, and the average value of this work was equal to 46.85 mJ/m 2, which was similar to that obtained for adhesion of aqueous solutions of two cationic surfactants mixtures to PTFE surface.

The wettability of polytetrafluoroethylene by aqueous solution of cetyltrimethylammonium bromide and Triton X-100 mixtures

Measurements of the advancing contact angle (θ) were carried out for aqueous solution of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycol), Triton X-100 (TX100) mixtures on polytetrafluoroethylene (PTFE). The obtained results indicate that the wettability of PTFE depends on the concentration and composition of the surfactants mixture. There is a minimum of the dependence between contact angle and composition of the mixtures for PTFE for each concentration at a monomer mole fraction of CTAB, α, equal 0.2, which points to the synergism in the wettability of PTFE. In contrast to Zisman, there is no linear dependence between cosθ and the surface tension of aqueous solution of CTAB and TX100 mixtures for all studied systems, but a linear dependence exists between the adhesional tension and surface tension for PTFE in the whole concentration range, the slope of which is −1, that suggests that the surface excess of the surfactant concentration at the PTFE–solution interface is the same as that at the solution–air interface for a given bulk concentration. It was also found that the work of adhesion of aqueous solution of surfactants to PTFE surface did not depend on the type of surfactant and its concentration. It means that the interactions across PTFE–solution interface were constant for the systems studied, and they were largely Lifshitz–van de Waals type. On the basis of the surface tension of PTFE and the Young equation and thermodynamic analysis of the adhesion work of aqueous solution of surfactant to the polymer surface it was found that in the case of PTFE the changes of the contact angle as a function of the mixture of nonionic and cationic surfactants concentration resulted only from changes of the polar component of solution surface tension.

The wettability of polytetrafluoroethylene and polymethyl methacrylate by aqueous solution of two cationic surfactants mixture

Advancing contact angle ( θ) measurements were carried out for aqueous solutions of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) mixtures on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA). The obtained results indicate that the wettability of PTFE and PMMA by aqueous solutions of CTAB and CPyB mixtures depends on the composition and concentration of the mixture; however, synergism in the wettability does not exist. In the range of low concentrations of aqueous solution mixtures there is a linear dependence between the contact angle and composition of the mixtures, but at a concentration close to CMC a deviation from linear dependence is observed. In contrast to Zisman, there is no linear dependence between cos θ and the surface tension of aqueous solution of CTAB and CPyB mixtures, but a linear dependence exists between the adhesional and surface tension, and these lines have a slope −1 and −0.34 for PTFE and PMMA, respectively, which suggests that adsorption of CTAB and CPyB mixtures at water–air and PTFE–water is the same, and the orientation of the CTAB and CPyB molecules at both interfaces in the saturated monolayer should also be the same. Adsorption of these mixtures at water–air interface is considerably higher than at PMMA–water interface, and CTAB and CPyB molecules should be parallelly oriented to PMMA surface in the saturated monolayer. Extrapolation of the straight lines to the points corresponding to the surface tension of aqueous solution, which completely spreads over the PTFE and PMMA surface, gives a critical surface tension of wetting equal to 23.44 and 33.13 mN/m, respectively. The value of 23.44 mN/m is higher than that of the surface tension of PTFE, but the value of 33.13 is lower than that of Lifshitz–van der Waals components of PMMA surface tension. On the basis of the critical surface tension, the surface tension of PTFE and PMMA, the Young equation, and thermodynamic analysis of the adhesion work of aqueous solution of surfactant to polymer surface, it was found that for PTFE and PMMA the changes of the contact angle of aqueous solution of two cationic surfactants mixtures on their surfaces as a function of the solution concentration resulted only from the decrease of the polar component of the solution surface tension.

The wettability of polytetrafluoroethylene by aqueous solutions of sodium dodecyl sulfate and propanol mixtures

Advancing contact-angle ( θ ) measurements were carried out with aqueous solutions of propanol and four series of aqueous solutions of dodecyl sulfate (SDDS) and propanol mixtures at constant dodecyl sulfate concentrations equal to 1 × 10 −5 , 6 × 10 −4 , 1 × 10 −3 , and 1 × 10 −2 M , respectively. The obtained results indicate that in the range of propanol concentrations studied there were considerable contact-angle changes, with exception of the solution series at a constant concentration value of SDDS higher than its critical micelle concentration. From the results of contact-angle measurements and application of the Gibbs and Young equations the ratio of the excess concentration of surfactant and propanol at the solid–aqueous solution interface to the excess of their concentration at the aqueous solution–air interface was calculated. From the calculations it appears that there is a straight linear dependence between the adhesion tension and surface tension of aqueous solutions of SDDS and propanol mixtures, and the slope of the line is equal to −1, which suggests that the surface excess of the SDDS and propanol mixture at the polytetrafluoroethylene–solution interface is the same as the at the solution–air interface. The extrapolation of the straight line to the point corresponding to the surface tension of the aqueous solution, which completely spreads over the polytetrafluoroethylene surface, gives a critical surface tension of wetting equal to 23.7 mN/m. On the basis of the critical surface tension and the Young and modified Szyszkowski equations it was found that in a polytetrafluoroethylene–aqueous solution of the SDDS and propanol mixture, the interface tension can be predicted by the modified Szyszkowski equation.

Wettability of polytetrafluoroethylene by aqueous solutions of two anionic surfactant mixtures

Advancing contact angle ( θ) 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 cos θ) as a function of concentration was observed. The dependence of cos θ on the monomer mole fraction of SHDSs in the mixture of the surfactants ( α) for aqueous solutions of mixtures at concentrations corresponding to the critical micelle concentration (CMC) had a maximum at α=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 α, 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 α=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 cos θ 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.

Surface modification of polytetrafluoroethylene by nitrogen ion implantation

Polytetrafluoroethylene (PTFE) was implanted in vacuum by N ions. The influence of experimental parameters was studied by varying ion energy from 2 to 20 keV with the same fluence of 1.4×10 17 ions/ cm 2 . The ion energy strongly affected the surface composition, microstructure, and wettability of PTFE. Five chemical bonds, CF 3, CF 2, CF, C–O, and elemental carbon bonds, were observed on the surface of all the as-implanted samples. The content of the various chemical bonds changed with increasing ion energy. The content of elemental carbon bond reached a maximum value of 45.81% on the surface of the sample implanted with ion energy of 5 keV. Displacement of the binding energies of the C 1s peak components was observed on the surfaces of samples implanted with ion energies equal to or greater than 5 keV. Numerous microfibers drawn up in the same orientation were observed on the ion-irradiated surfaces. The droplet contact angle of the as-implanted samples increased gradually with increasing ion energy, and reached a maximum value of 117.4° on the surface of the sample implanted with ion energy of 20 keV.

Effect of aging on the morphology and wettability of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was implanted in vacuum by argon ions. The influence of experimental parameters was studied by varying ion energy from 2 to 20 keV with the same dose of 1.4×10 17 ions/cm 2. The ion energy strongly affected the surface composition, microstructure, and wettability of PTFE. All as-implanted PTFE samples were aged in air for 1 year. After aging, the surface-restructuring behavior was observed on the surface of samples implanted with ion energy of 2 and 5 keV. The water contact angle of aged samples implanted with ion energy of 5 and 10 keV decreased up to 22° and 11°, respectively.