Argon plasma-pretreated polytetrafluoroethylene (PTFE)
films were subjected to further
surface modification by near-UV light-induced graft copolymerization
with acrylic acid (AAc), sodium
salt of styrenesulfonic acid (NaSS), and
N,N-dimethylacrylamide (DMAA). The surface
compositions and
microstructures of the modified films were characterized by
angle-resolved X-ray photoelectron
spectroscopy (XPS). A stratified surface microstructure with a
significantly higher substrate-to-graft
chain ratio in the top surface layer than in the subsurface layer was
always obtained for PTFE surface
with a substantial amount of the hydrophilic graft. The stratified
surface microstructure was consistent
with the observed hysteresis in advancing and receding water contact
angles. The graft yield increased
with Ar plasma pretreatment time and monomer concentration.
Covalent immobilization of trypsin on
the AAc polymer-grafted PTFE films was facilitated by water-soluble
carbodiimide (WSC). The effective
enzyme activities increased initially with increasing surface
concentration of the grafted AAc polymer
but became saturated at a moderate AAc polymer concentration. The
immobilized enzyme could still
retain close to 30% of its original activity. Solution-coating of
the polymeric acid-modified PTFE films
with the emeraldine (EM) base of polyaniline readily resulted in an
interfacial charge transfer interaction
and a semiconductive PTFE surface.
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