New Method to Probe the Surface Properties of Polymer Thin Films by Two-Dimensional (2D) Inverse Gas Chromatography (iGC)

Published

June 25, 2024

Author(s)

Whirang Cho, Lucas Flagg, Christopher Stafford, Jeremiah Woodcock, Daniel Burnett, Anett Kondor, Douglas Fox, John Hoffmann

Abstract

Polymer-based functional surface coatings are extensively used in advanced technologies, including optics, energy, and environmental applications. Surface thermodynamic properties profoundly impact the molecular interactions that control interfacial behaviors, such as adhesion and wettability, which in turn dictate coating processes and performance. Conventionally, contact angle measurement is used to assess the surface energy of polymer films and coatings, where the wettability of a surface is assessed using probe fluids (liquid drops) which can then be used to calculate the dispersive and polar components of the surface energy. However, contact angle measurement oftentimes fails to yield accurate surface energies due to confounding features such as roughness or chemical heterogeneity of the solid surface, as well the potential for the liquid drop to swell or even dissolve the material being measured. Alternatively, inverse gas chromatography (iGC) is a versatile technique to measure surface thermodynamics and Lewis acid-base properties, while also providing environmental control such as temperature and humidity. Despite these benefits, previous studies have focused primarily on powders or fibres while direct measurement of supported thin films or coatings is still a nascent area of research. This creates a challenge to utilize iGC as a comprehensive platform for measuring the physicochemical properties of solid surfaces. Here we demonstrate, using model materials, how to effectively use iGC to characterize the surface energy of supported polymer thin films by using a 2-dimensional (2D) film holder and modifying operational controls, such as the concentration range of the injected gas probe molecules. This enables the precise control of surface coverage required for analyzing samples having minimal surface area such as thin films. Poly(methyl methacrylate) (PMMA) was employed as a benchmark to determine suitable iGC parameters and to validate our approach on polymer thin films. We then applied our approach to films of poly(acrylic acid) (PAA), a water-soluble polymer that is difficult to measure via conventional water contact angle measurements. PAA also contains ionizable carboxylate groups where the degree of ionization, and thus surface thermodynamic properties, are sensitive to pH. Finally, we explored the effect of small-scale surface roughness by measuring poly(ethylene oxide) (PEO) thin films that are semi-crystalline, where the crystalline phase induces topography to the surface of the film. The seminal work presented here expands the capability of iGC to include supported thin films (2D iGC) that could either be smooth or display texture/roughness (patterned films), as well as coatings with heterogeneous chemical/structural composition.

Citation

Langmuir

Volume

40

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acs.langmuir.4c01400

Local Download

Keywords

sorption science, chromatography, polymer, thin films

Citation

Cho, W. , Flagg, L. , Stafford, C. , Woodcock, J. , Burnett, D. , Kondor, A. , Fox, D. and Hoffmann, J. (2024), New Method to Probe the Surface Properties of Polymer Thin Films by Two-Dimensional (2D) Inverse Gas Chromatography (iGC), Langmuir, [online], https://doi.org/10.1021/acs.langmuir.4c01400, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=957556 (Accessed December 3, 2024)