Lj. Matienzo et al., SURFACE MODIFICATION OF FLUOROPOLYMERS WITH VACUUM-ULTRAVIOLET IRRADIATION, Journal of vacuum science & technology. A. Vacuum, surfaces, and films, 12(5), 1994, pp. 2662-2671
Citations number
44
Categorie Soggetti
Physics, Applied","Materials Science, Coatings & Films
Amorphous fluoropolymers (AF) have recently been developed to provide
several favorable characteristics not present in the more crystalline
materials. However, these polymers have not been fully characterized a
nd reports of surface modification are not extensive. This work presen
ts results of surface analysis and modification with vacuum ultraviole
t (VUV) irradiation of Teflon-AF-2400 using contact angle measurements
, x-ray photoelectron spectroscopy (XPS), and laser-assisted Fourier t
ransform mass spectroscopy (FTMS). Results are compared to those for o
ther, more crystalline, fluoropolymers, namely, poly(tetrafluoroethyle
ne) (PTFE) and the copolymer of tetrafluoroethylene and perfluoroalkox
yvinyl ether (PFA). These three fluoropolymers differ in structure and
amount of oxygen that they contain. Samples were irradiated for sixty
minutes downstream from a helium microwave plasma, in some instances
through a LiF crystal filter. In the latter case, modification is due
solely to photons with wavelengths greater than 104 nm. For films trea
ted without filters, reduction in the advancing contact angle was grea
test for AF-2400 and least for PTFE. XPS indicated radiation-induced d
efluorination for all polymers treated with or without filters. Concur
rently, oxygen incorporation occurs upon exposure to air during sample
transfer from the plasma reactor to the XPS instrument. Wetting for t
reated films improved as the ratio of atomic concentrations for oxygen
and fluorine, [O]/[F], increased at the surface. As expected, greater
modification was achieved with no filter, possibly due to the effect
of higher energy photons and/or helium metastable atoms. Small amounts
of nitrogen were also incorporated following treatment, upon exposure
to nitrogen gas. Laser-assisted FTMS experiments on VUV-treated PTFE
and PFA samples resulted in a series of high molecular weight fragment
s (in increments of 50 amu). This was not observed for untreated films
analyzed under similar conditions. It is proposed that VUV irradiatio
n tends to crosslink PTFE and PFA films through defluorination of the
-CF2- repeating units, while the AF-2400 is prone to ring cleavage and
does not exhibit this tendency toward crosslinking.