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 cosθcosθ 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.

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