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6361723 
Journal Article 
Water transport and condensation in fluoropolymer films 
Hansen, CM 
2001 
1 
Progress in Organic Coatings
ISSN: 0300-9440 
Elsevier 
42 
3 
167-178 
WOS:000172325500006 
This report explores phenomena related to the undesired condensation of water in or under fluoropolymer films. Condensation of water in or under polymer films will occur when the local vapor pressure is higher than that corresponding to the local dew point vapor pressure. This can happen for any type of polymer film, including fluoropolymer films, even though solubility of water in the film may be extremely low. A “cold” substrate, for example, can readily lead to water condensation under a fluoropolymer film, and therefore to a reduction of adhesion or to complete delamination. These problems will not be so severe and may, indeed, disappear for acid-resistant fluoropolymer films exposed to hot and/or concentrated acids, such as sulfuric acid. The vapor pressure (activity) of the water in the acid is so reduced that condensation in or under the film will not occur at the usual temperatures encountered in practice. Diffusion coefficients, permeation coefficients, and solubilities for water in selected fluoropolymers (PVDF, ETFE, ECTFE, PFA, MFA, FEP, and PTFE) have been measured at 90°C. The diffusion coefficients are greater than 3×10-7cm2/s at this temperature. This means that a change in the environment will result in a new equilibrium condition for absorption, desorption, and/or permeation in practical fluoropolymer coatings within a maximum of a day or so for all of the materials tested. Practical free film thicknesses near 2mm were used. Approximate diffusion coefficients have also been measured by a new technique at 20°C for comparison. When the environment changes, a new condition for equilibrium is established at room temperature after times varying from several days to 2 months in these experiments which used the same practical film thicknesses. The technique involves following release of dissolved tritiated water (HTO) from a film while it is immersed in a scintillation liquid (gel) in a glass counting vial. The counting rate increases to an equilibrium level in proportion to the extent of diffusion of HTO out of the sample. 
Fluoropolymers; Blistering; Permeation; Diffusion coefficients; Tritium