la036137v_si_002.pdf (38.62 kB)
Infrared Study of the Kinetics and Mechanism of Adsorption of Acrylic Polymers on Alumina Surfaces
journal contribution
posted on 2004-05-25, 00:00 authored by R. Tannenbaum, S. King, J. Lecy, M. Tirrell, L. PottsIn this paper, we studied the kinetics of the adsorption of poly(methyl methacrylate), PMMA, onto native
aluminum oxide surfaces by X-ray photoelectron spectroscopy and reflection−absorption infrared
spectroscopy, with the intent of tracking the various changes observed in the infrared spectrum of the
adsorbed polymer layer as a function of adsorption time. Specifically, we utilized the relative changes in
the absorption bands of the carbonyl, carboxylic acid, and carboxylate groups to determine the sequence
of events that culminate in the formation of bonds between carboxylate groups on hydrolyzed PMMA and
specific sites on the aluminum oxide surface. We have shown that the adsorption process involves the
hydrolysis of a fraction of the methoxy groups of the PMMA to generate COOH groups. Unlike previous
assumptions, the formation of COOH groups on the PMMA chains does not constitute a sufficient condition
for the actual chemisorption of the polymer chains onto the metal oxide surface. To promote bonding, the
acid groups must undergo dissociation to form the carboxylate groups, followed subsequently by actual
bond formation, that is, active anchoring, on the surface. This process is mediated by the aluminum oxide
sites on the surface in the presence of water. Hence, the adsorption process occurs via a two-step mechanism,
in which the first step, that is, the hydrolysis step, is a necessary but insufficient condition and the second
step, that is, the anchoring step, is largely dependent on the type of interfacial chemistry possible for a
particular polymer−metal oxide surface, the polymer conformation, the molecular weight, and the flexibility
of the adsorbing molecules.