A. Mas et al., MODIFICATION OF POLY[(3-HYDROXYBUTYRIC ACID)-CO-(3-HYDROXYVALERIC ACID)] FILM SURFACES IN AN OXYGEN LOW-PRESSURE PLASMA, Macromolecular chemistry and physics, 197(7), 1996, pp. 2331-2341
Poly[(3-hydroxybutyric acid)-co-(3-hydroxyvaleric acid)] (91:9 mass-%)
(P(HB-co-9% HV)) film surfaces were modified by an oxygen plasma trea
tment (75 W, 50 Pa, 5 min). The number of oxygen atoms increases about
12-13% and the polar component of the surface energy increases from 6
.3 to 21 mN . m(-1). However, the wettability is stable only after 60
days. Untreated and treated him surfaces are studied by means of X-ray
photoelectron spectroscopy with two different depth analyses. With st
orage time, the oxygen contents of the modified film is constant at a
take-off angle of 20 degrees but decreases to the initial value at a t
ake-off angle of 70 degrees. The superficial layer of the polymer film
between the top of the film to a depth of 10 nm is divided into three
superimposing zones. The interpretation is supported by motions of mo
dified macromolecular chains and buried polar groups, chain cleavage a
nd the formation of low-molecular-weight molecules which leads to a de
crease of the glass transition temperature (plasticizer effect) and mi
gration of short chains from the lowest modified zone toward the surfa
ce.