Polytetrafluoroethylene Water Research Articles

Nonwoven PTFE Membranes Fabricated by Electrospinning Method: Preparation and Characterization

Polytetrafluoroethylene (PTFE) is one of the promising materials for the purposes of tissue engineering and chemical technology because of its excellent physico-chemical properties and mechanical characteristics. However, conventional methods of PTFE porous membranes production have several disadvantages which limit the number of potential application areas by reason of a insufficient surface-to-volume ratio and poor porosity at small thickness. In the paper the results of using PTFE water suspension with a solution of water-soluble polymer for preparation of porous membranes by electrospinning are reported. The physico-chemical characteristics of membranes were investigated depending on the content of PTFE dispersion in spinning solution. There were found high hydrophobicity and lyophilicity of PTFE electrospun membranes. Main reasons of poor mechanical properties of porous membranes at high content of PTFE suspension in spinning solution are discovered. The ways of mechanical properties improvement and areas of possible applications are proposed.

Surface tension, adsorption, and wetting behaviors of natural surfactants on a PTFE surface

The adsorption kinetics and wetting behaviors of three plant‐based natural surfactants (Reetha, Shikakai, and Acacia) on the polytetrafluoroethylene (PTFE) surface are reported in this study. Adsorption studies of these surfactants on PTFE surface show the equilibrium adsorption time is approximately 15 min, and Langmuir‐type isotherm fits well for all three surfactants. The contact angle measurements show that the value achieved by Reetha and Acacia solutions are close (∼109°), but that is low in the case of Shikakai (98.13°). Although, comparing the adsorption densities of the surfactants at PTFE–water and air–water interfaces, it has been found that adsorption densities at the PTFE–water interface are low for all three surfactants than that of air–water interface. The alcohol–Shikakai mixed solutions show nonideal behavior of surface tension reduction through a strong interaction between alcohol and Shikakai molecules, which in turn, show lower surface tension and contact angle values than that of ideal. © 2014 American Institute of Chemical Engineers AIChE J, 61: 655–663, 2015

Correlation between wetting, adhesion and adsorption in the polymer–aqueous solutions of ternary surfactant mixtures–air systems

The correlation between the wettability of polymers and adsorption of ternary mixtures including CTAB, TX-100 and TX-114 at the polymer–aqueous solution interface as well as the adhesion of aqueous solution of these mixtures to apolar polytetrafluoroethylene (PTFE), monopolar polymethyl methacrylate (PMMA) and nylon 6 was considered on the basis of the contact angle measurements and the literature data of the solutions surface tension. From these considerations it appeared that the efficiency and effectiveness of the adsorption at the PTFE–water interface are comparable to those at the water–air one, but for the PMMA–water and nylon 6–water interfaces they are lower than those for the water–air one for a given series of solutions. The efficiency and effectiveness are reflected in the composition of the mixed monolayer at the polymer–solution interface which even for the PTFE–solution interface is somewhat different from the water–air interface. The properties of the mixed monolayer at these interfaces influence the critical surface tension of polymer wetting which for PTFE is somewhat higher but for PMMA and nylon 6 considerably lower than their surface tension. From these considerations it also appeared that the work of adhesion of aqueous solutions of ternary mixtures of surfactants to the PTFE surface does not depend on the composition and concentration of solution contrary to PMMA and nylon 6. The adhesion work of these solutions to the PMMA and nylon 6 surface can be determined on the basis of van Oss et al. and Neumann et al. equations.

Adsorption Behaviors of Cationic Surfactants and Wettability in Polytetrafluoroethylene–Solution–Air Systems

Measurements of the advancing contact angle (θ) and adsorption properties were carried out for aqueous solutions of four cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C(16)PC), Guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C(16)GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride(C(16)(EO)(3)PC), and Guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C(16)G(EO)(3)PC), on the polytetrafluoroethylene (PTFE) surface using the sessile drop analysis. The obtained results indicate that the contact angle decreases to a minimum with the increasing concentration for all cationic surfactants. Surfactants with branched chain show lower θ values. Moreover, an increase of adhensional tension on the PTFE-water interface has been observed for the four cationic surfactants, and the branched ones have larger increases of adhensional tension. It is very interesting that the sharp decrease of θ appears mainly after critical micelle concentration (cmc) for C(16)GPC, C(16)(EO)(3)PC, and C(16)G(EO)(3)PC, which is quite different from traditional cationic surfactants reported in the literature. Especially for C(16)G(EO)(3)PC, there are two saturated adsorption stages on PTFE surface after cmc (which means the saturated adsorption film at air-solution interface has been formed). In the first saturated stage, the C(16)G(EO)(3)PC molecules are oriented parallel to the PTFE surface with saturated monolayer formed through hydrophobic interaction and hydrogen bond. In the second saturated stage, the hemimicelle has been formed on the PTFE surface, which can be supported by the QCM-D and SPR measurements.

Wettability of a PTFE surface by cationic–non-ionic surfactant mixtures in the presence of electrolytes

The increase in wettability of a low surface energy solid surface has become an important task for different applications, and this can be improved by the help of surfactant solutions. On the other hand, reduction of surfactant consumption without compromising the wettability may be of great importance from an environmental and economic viewpoint. So in this work, we studied the effect of two different electrolytes as additives in the presence of cationic (cetyltrimethylammonium bromide, CTAB) and nonionic (Igepal CO-630) surfactant mixtures on the wetting of a low energy PTFE (polytetrafluoroethylene) surface. Different physicochemical properties such as critical micelle concentration (CMC), surface excess (Γmax), minimum area per molecule (Amin), and interaction parameters (β) have been estimated for the mixed surfactant and mixed surfactant with electrolyte solutions. The cationic–nonionic mixed surfactant system showed a synergetic behavior and a maximum synergism was observed for the mixed surfactant in the presence of electrolytes. The addition of electrolytes in the mixed surfactant solution increases the wettability by achieving minimum contact angle (74.6°) at the PTFE–water interface and reduces the consumption of surfactants up to 85% compared to the pure CTAB.

The role of adsorption of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide surfactants in wetting of polytetrafluoroethylene and poly(methyl methacrylate) surfaces

The role of adsorption of dodecylethyldimethylammonium bromide (C12(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB) at water–air and polytetrafluoroethylene (PTFE)–water and poly(methyl methacrylate) (PMMA)–water interface, in wetting of PTFE and PMMA surface, was established from the measured values of the contact angle (θ) of aqueous C12(EDMAB) and BDDAB solutions in PTFE (PMMA)-solution drop–air system, and from the measured values of the surface tension of aqueous C12(EDMAB) and BDDAB solutions. Adsorption of C12(EDMAB) and BDDAB at water–air interface was determined earlier from the Gibbs equation. Adsorption at solid–water interface was deduced from the Lucassen-Reynders equation based on the relationship between adhesion tension (γLVcosθ) and surface tension (γLV). The slope of the γLVcosθ–γLV curve was found to be constant and equal to −1, and about −0.3 for PTFE and PMMA surface, respectively (in the case of both surfactant studied: C12(EDMAB) and BDDAB, and in the whole range of surfactants concentration in solution). It means that the amount of the surfactant adsorbed at the PTFE–water interface, ΓSL, was essentially equal to its amount adsorbed at water–air interface, ΓLV. However, ΓSL at the PMMA–water interface was about three times smaller as compared to that at water–air interface. By extrapolating the linear dependence between γLVcosθ–γLV and dependence between cosθ–γLV and cosθ=1 we determined the value of the critical surface tension of PTFE and PMMA surface wetting, γc. The obtained values of γc for PTFE surface were equal 23.4 and 23.8mN/m, 23.1 and 23.2mN/m for C12(EDMAB) and BDDAB, respectively and they were higher than the surface tension of PTFE (20.24mN/m). On the other hand, the obtained values of γc for PMMA surface were equal 31.4 and 30.9mN/m, 31.7 and 31.3mN/m for C12(EDMAB) and BDDAB, respectively and they were smaller than the surface tension of PMMA (39.21mN/m). Using the values of PTFE and PMMA surface tension and the measured values of the surface tension of aqueous C12(EDMAB) and BDDAB solutions in the Young equation, the PTFE (PMMA)-solution interfacial tension, γSL, was also determined. Next, the work of adhesion (WA) was deduced, and it occurred that the dependence between the WA and the surface tension (γLV) for both studied solids was linear. However, the values of the WA for PMMA change as a function of logC (C—surfactant concentration) changed from 91.7 to 68.5mJ/m2 and from 91.8 to 65.1mJ/m2 for C12(EDMAB) and BDDAB, respectively. On the other hand, the work of adhesion of both studied surfactants solutions to the PTFE surface was practically constant (an average value was equal 45.8 and 45.4mJ/m2, respectively). These values were close to the value of the work of water adhesion to PTFE surface (45.5mJ/m2).

Application of hyperdispersant to the cathode diffusion layer for direct methanol fuel cell

In this study, Nafion ionomer, as a kind of hyperdispersant, was added to polytetrafluoroethylene (PTFE) water dispersion system to suppress the size of PTFE particles in the ink of microporous layer (MPL). The agglomeration behavior of PTFE in ethanol and MPL were investigated by laser diffraction, dynamic light scattering (DLS) and metallurgical microscopes. The electronic resistance, pore size distribution, gas permeability and surface hydrophobic/hydrophilic properties were also characterized for prepared gas diffusion layers (GDLs). It was shown that PTFE water dispersion system suffered flocculating when dispersed in ethanol and this agglomeration behavior was reduced by employing Nafion ionomer. With the increase in the Nafion ionomer adopted in the MPL, not only the decreased hydrophobic property was shown in the MPL, but the decreased PTFE particle size was also achieved, which results in improved crosslink of carbon and pores themselves as well as the volume loss of pores in micron scale. The increased gas permeability and electronic conductivity of the GDL made the one employing the PTFE dispersion system with 1% Nafion content own its advantages as the cathode diffusion layer for a direct methanol fuel cell (DMFC) under near-ambient conditions.

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate and wettability in polytetrafluoroethylene–solution–air system

The role of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) adsorption at water–air and polytetrafluoroethylene–water (PTFE) interfaces in wetting of low energy PTFE was established from measurements of the contact angle of aqueous AOT solutions in PTFE–solution drop–air systems and the aqueous AOT solution surface tension measurements. For calculations of the adsorption at these interfaces the relationship between adhesion tension ( γ LV cos θ) and surface tension ( γ LV), and the Gibbs and Young equations were taken into account. On the basis of the measurements and calculations the slope of the γ LV cos θ– γ LV curve was found to be constant and equal −1 over the whole range of surfactant concentration in solution. It means that the amount of surfactant adsorbed at the PTFE–water interface, Γ SL, is essentially equal to its amount adsorbed at water–air interface, Γ LV. By extrapolating the linear dependence between γ LV cos θ and γ LV to cos θ = 1 the determined value of critical surface tension of PTFE surface wetting, γ C, was obtained (23.6 mN/m), and it was higher than the surface tension of PTFE (20.24 mN/m). Using the value of PTFE surface tension and the measured surface tension of aqueous AOT solution in Young equation, the PTFE–solution interface tension, γ SL, was also determined. The shape of the γ SL–log C curve occurred to be similar to the isotherm of AOT adsorption at water–air interface, and a linear dependence existed between the PTFE–solution interfacial tension and polar component of aqueous AOT solution. The dependence was found to be established by the fact that the work of adhesion of AOT solution to the PTFE surface was practically constant amounting 46.31 mJ/m 2 which was close to the work of water adhesion to PTFE surface.

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.

Adsorption of mixtures of sodium dodecyl sulphate and propanol at water–air and polytetrafluoroethylene–water interfaces

A straight linear relationship was found between the adhesion tension and surface tension of aqueous solution of surfactant and alcohol mixtures at a given constant concentration value of SDDS, and the slope of the obtained straight lines was equal to −1, which suggests that the surface excess of the surfactant and alcohol mixture concentrations at polytetrafluoroethylene (PTFE)–water interface is the same as at water–air interface for a given bulk concentration of these mixtures. It was also found that the changes of the surface tension of the aqueous solution of SDDS and propanol mixtures and PTFE-solution interface tension as a function of SDDS and propanol concentration result especially from decreased contribution of the polar intermolecular interactions in the surface and interface tensions and can be described by modified Szyszkowski equation. The analysis of the excess of SDDS and propanol concentration at PTFE–water interface based on results of the surface tension and contact angle measurements suggests that this excess is not a linear function of the mixture composition and that polar interactions can probably take place at the interface of PTFE-aqueous solution of the surfactant and propanol mixture.

Methods for measuring the skin-cleansing effect of surfactants in comparison with skin roughness and compatibility

The role of adsorption of dodecylethyldimethylammonium bromide (C12(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB) at water–air and polytetrafluoroethylene (PTFE)–water and poly(methyl methacrylate) (PMMA)–water interface, in wetting of PTFE and PMMA surface, was established from the measured values of the contact angle (θ) of aqueous C12(EDMAB) and BDDAB solutions in PTFE (PMMA)-solution drop–air system, and from the measured values of the surface tension of aqueous C12(EDMAB) and BDDAB solutions. Adsorption of C12(EDMAB) and BDDAB at water–air interface was determined earlier from the Gibbs equation. Adsorption at solid–water interface was deduced from the Lucassen-Reynders equation based on the relationship between adhesion tension (γLV cos θ) and surface tension (γLV). The slope of the γLV cos θ–γLV curve was found to be constant and equal to −1, and about −0.3 for PTFE and PMMA surface, respectively (in the case of both surfactant studied: C12(EDMAB) and BDDAB, and in the whole range of surfactants concentration in solution). It means that the amount of the surfactant adsorbed at the PTFE–water interface, ΓSL, was essentially equal to its amount adsorbed at water–air interface, ΓLV. However, ΓSL at the PMMA–water interface was about three times smaller as compared to that at water–air interface. By extrapolating the linear dependence between γLV cos θ–γLV and dependence between cos θ–γLV and cos θ = 1 we determined the value of the critical surface tension of PTFE and PMMA surface wetting, γc. The obtained values of γc for PTFE surface were equal 23.4 and 23.8 mN/m, 23.1 and 23.2 mN/m for C12(EDMAB) and BDDAB, respectively and they were higher than the surface tension of PTFE (20.24 mN/m). On the other hand, the obtained values of γc for PMMA surface were equal 31.4 and 30.9 mN/m, 31.7 and 31.3 mN/m for C12(EDMAB) and BDDAB, respectively and they were smaller than the surface tension of PMMA (39.21 mN/m). Using the values of PTFE and PMMA surface tension and the measured values of the surface tension of aqueous C12(EDMAB) and BDDAB solutions in the Young equation, the PTFE (PMMA)-solution interfacial tension, γSL, was also determined. Next, the work of adhesion (WA) was deduced, and it occurred that the dependence between the WA and the surface tension (γLV) for both studied solids was linear. However, the values of the WA for PMMA change as a function of log C (C—surfactant concentration) changed from 91.7 to 68.5 mJ/m2 and from 91.8 to 65.1 mJ/m2 for C12(EDMAB) and BDDAB, respectively. On the other hand, the work of adhesion of both studied surfactants solutions to the PTFE surface was practically constant (an average value was equal 45.8 and 45.4 mJ/m2, respectively). These values were close to the value of the work of water adhesion to PTFE surface (45.5 mJ/m2).

An assessment of interactions at the polytetrafluoroethylene–water interface from dynamic contact angle studies

At very low interfacial velocities, the free energy per unit area of the P.T.F.E.–water interface includes both dispersive and polar components, while at higher velocities only the dispersive forces need be considered.