Depth-profiling X-ray photoelectron spectroscopy (XPS) analysis of interlayer diffusion in polyelectrolyte multilayers

Abstract

Functional organic thin films often demand precise control over the nanometer-level structure. Interlayer diffusion of materials may destroy this precise structure; therefore, a better understanding of when interlayer diffusion occurs and how to control it is needed. Xray photoelectron spectroscopy paired with C 60 + cluster ion sputtering enables high-resolution analysis of the atomic composition and chemical state of organic thin films with depth. Using this technique, we explore issues common to the polyelectrolyte multilayer field, such as the competition between hydrogen bonding and electrostatic interactions in multilayers, blocking interlayer diffusion of polymers, the exchange of film components with a surrounding solution, and the extent and kinetics of interlayer diffusion. The diffusion coefficient of chitosan (M = ∼100 kDa) in swollen hydrogenbonded poly(ethylene oxide)/poly(acrylic acid) multilayer films was examined and determined to be 1.4*10 −12 cm 2 /s. Using the highresolution data, we show that upon chitosan diffusion into the hydrogen-bonded region, poly(ethylene oxide) is displaced from the film. Under the conditions tested, a single layer of poly(allylamine hydrochloride) completely stops chitosan diffusion. We expect our results to enhance the understanding of how to control polyelectrolyte multilayer structure, what chemical compositional changes occur with diffusion, and under what conditions polymers in the film exchange with the solution.XPS depth profiling | layer-by-layer films | interdiffusion

Retention of poly(N-isopropylacrylamide) on 3-aminopropyltriethoxysilane

“…The decoupled peaks showed roughly 66.7%, 16.7%, and 16.7% of areas under the C-C/C-H, C-N, and N-C¼O peaks [ Table II], which were in accord with the four C-C bonds, one C-N bond, and one N-C¼O bond in the monomer unit of pNIPAAm and those reported by others. 1,25,26 Since XPS typically probes the top 10 nm of the film, 40,41 it is possible to detect a small amount of Si and O from the APTES beneath the 5-6 nm retained pNIPAAm. However, this small amount of detected APTES, whose molecule contains two C-C bonds and one C-N bond, appeared to have little contribution to the break-down of C-C, C-N, and N-C¼O in the C1s peak of these samples.…”

Covalent conjugation of mechanically stiff graphene oxide flakes to three-dimensional collagen scaffolds for osteogenic differentiation of human mesenchymal stem cells

“…2d). XPS is a sensitive surface analysis technique that measures the kinetic energy and number of electrons that escape from the top 10 nm of the material [15].…”

Design and Fabrication of Zwitter-Wettable Nanostructured Films

“…Previously, our group has demonstrated that this technique can measure atomic concentration information as well as analyze interlayer diffusion and material exchange in nanostructured polymer thin films with a resolution around 15 nm. 18 Cluster-ion C 60 etching is much less damaging to polymers than single-ion etching methods commonly used for inorganic materials. 19 As shown in Figure 2a, the depth profiling process uses iterative C 60 + etching and XPS acquisition to probe the atomic concentration profile with depth.…”