Robust, Functionalizable, Nanometer-Thick Poly(acrylic acid) Films Spontaneously Assembled on Oxidized Aluminum Substrates: Structures and Chemical Properties

Abstract

Immersion of oxidized aluminum substrates in ethanol solutions of poly(acrylic acid) (PAA), followed by extensive solvent immersion, results in tenaciously chemisorbed, nanometer scale, controllable thickness films for a wide range of solution concentrations and molecular weights. Atomic force microscope images reveal isolated polymer globules from adsorption in low-concentration solutions with crossover to conformal, highly uniform, nanometer-thickness films at higher concentrations, an indication that the chemisorbing chains start to overlap and trap underlying segments to form planar chemisorbed films only two or three chains in thickness. Quantitative IR reflection spectroscopy in combination with chemical derivitization on a standard set of 1.0(±0.2) nm thick films reveals a film structure with 5.5(±1) chemisorbed -CO(-)(2) groups/nm(2) and 6.3 unattached -CO(2)H groups/nm(2), with up to ∼3.6/nm(2) available for chemical derivitization, a comparable number to typical self-assembled monolayer coverages of ∼4-5 molecules/nm(2). Thermal treatment of the ∼1 nm chemisorbed films, at even extreme temperatures of ∼150 °C, results in almost no anhydride formation via adjacent -CO(2)H condensation, in strong contrast to bulk PAA, a clear indication that the films have a frozen glass structure with effectively no segment and side group mobility. Overall, these results demonstrate that these limiting thickness nanometer films provide a model surface for understanding the behavior of strongly bound polymer chains at substrates and show potential as a path to creating highly stable, chemically functionalized inorganic substrates with highly variable surface properties.

In Situ Characterization of the Initial Effect of Water on Molecular Interactions at the Interface of Organic/Inorganic Hybrid Systems

“…The manufacturer of the polymer used in this work states that only benzene could occur as an impurity with a concentration smaller than 0.1%. Due to this knowledge about the polymer impurity and since it is known that surface carbon contamination is typically removed during the PAA deposition process 29 31 39 40 , we attribute this extra intensity to aliphatic adventitious carbon on top of the polymer film. It was estimated by Koo et al .…”

“…It was estimated by Koo et al . that the coverage of ambient-borne contaminants ranged between 5–10% of the uncoated substrate and it was observed that this contamination was rapidly displaced by polymer molecules at the aluminum oxide surface by immersion in the PAA solution 40 . Since this is a small contribution to the surface species and is not primarily located at the polymer/oxide interface, we assume that the effects of adventitious carbon on the interface chemistry are negligible.…”

An in situ spectro-electrochemical monitoring of aqueous effects on polymer/metal oxide interfaces

“…This estimation corresponds well with previous work. [8,42] When looking at the fitted values of the constant phase element (CPE) of the oxide layer (Q 2 ), a value around 100 ± 2.2 µF/cm 2 is obtained. If an assumption of the dielectric constant ( ) for aluminum oxide is taken to be 9.1, then a thickness estimation of 2, 9 ± 0.1 nm is retrieved.…”

In Situ Methanol Adsorption on Aluminum Oxide Monitored by a Combined ORP-EIS and ATR-FTIR Kretschmann Setup

“…[3][4][5][6][7] These diluted polymer solutions mainly consist of organic solvents and for acrylic polymers, this is commonly an alcohol. 8 Fowkes et al and Abel et al previously have shown that the nature of the solvent has an influence on the amount of polymer deposited on the substrate surface and that the solvent's acid-base properties govern the adsorption process in general. 9,10 But despite the large abundance of the solvent molecules in contact with the oxide surface, the influence of the solvent itself on the oxide chemistry is often neglected.…”