EFFECT OF PH, FLUORINATION, AND NUMBER OF LAYERS ON THE INHIBITION OFELECTROCHEMICAL REACTIONS BY GRAFTED, HYPERBRANCHED POLY(ACRYLIC ACID) FILMS

We report the electrode-passivation properties of both fluorinated and unmodified hyperbranched poly(acrylic acid) (PAA) films as a function of pH and the number of PAA layers. Both cyclic voltammetry and ac-im pedance spectroscopy show that the extent of blocking increases with t he number of layers, regardless of the solution pH. However, passivati on resulting from unfluorinated PAA films decreases with increasing pH , while passivation due to fluorinated films increases with increasing pH. Three-layer fluorinated films can increase the charge transfer re sistance of the electrode by up to a factor of 6 x 10(4). Although Ran dles' equivalent circuit can be used to model the electrochemistry of electrodes covered with unfluorinated PAA, fluorinated PAA-coated elec trodes often require additional circuit elements due to the high resis tance of these hydrophobic films.