Optical Properties and van der Waals–London Dispersion Interactions of Polystyrene Determined by Vacuum Ultraviolet Spectroscopy and Spectroscopic Ellipsometry

Roger H. French; Karen I. Winey; Min K. Yang; Weiming Qiu

doi:10.1071/CH06222

RESEARCH ARTICLE

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Optical Properties and van der Waals–London Dispersion Interactions of Polystyrene Determined by Vacuum Ultraviolet Spectroscopy and Spectroscopic Ellipsometry

Roger H. French ^A ^B ^C , Karen I. Winey ^B , Min K. Yang ^A and Weiming Qiu ^A

+ Author Affiliations

- Author Affiliations

^A DuPont Central Research, E356-384 Experimental Station, Wilmington, DE 19880, USA.

^B Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.

^C Corresponding author. Email: roger.h.french@usa.dupont.com

Australian Journal of Chemistry 60(4) 251-263 https://doi.org/10.1071/CH06222
Submitted: 28 June 2006 Accepted: 11 February 2007 Published: 26 April 2007

Abstract

The interband optical properties of polystyrene in the vacuum ultraviolet (VUV) region have been investigated using combined spectroscopic ellipsometry and VUV spectroscopy. Over the range 1.5–32 eV, the optical properties exhibit electronic transitions we assign to three groupings, E₁, E₂, and E₃, corresponding to a hierarchy of interband transitions of aromatic (π → π*), non-bonding (n → π*, n → σ*), and saturated (σ → σ*) orbitals. In polystyrene there are strong features in the interband transitions arising from the side-chain π bonding of the aromatic ring consisting of a shoulder at 5.8 eV (E₁′) and a peak at 6.3 eV (E₁), and from the σ bonding of the C–C backbone at 12 eV (E₃′) and 17.1 eV (E₃). These E₃ transitions have characteristic critical point line shapes associated with one-dimensionally delocalized electron states in the polymer backbone. A small shoulder at 9.9 eV (E₂) is associated with excitations possibly from residual monomer or impurities. Knowledge of the valence electronic excitations of a material provides the necessary optical properties to calculate the van der Waals–London dispersion interactions using Lifshitz quantum electrodynamics theory and full spectral optical properties. Hamaker constants and the van der Waals–London dispersion component of the surface free energy for polystyrene were determined. These Lifshitz results were compared to the total surface free energy of polystyrene, polarity, and dispersive component of the surface free energy as determined from contact angle measurements with two liquids, and with literature values. The Lifshitz approach, using full spectral Hamaker constants, is a more direct determination of the van der Waals–London dispersion component of the surface free energy of polystyrene than other methods.

Acknowledgments

We are grateful to Dr L. K. Denoyer for software development, M. F. Lemon for VUV spectroscopy assistance, and B. B. French for editing the manuscript.

References

Optical Properties and van der Waals–London Dispersion Interactions of Polystyrene Determined by Vacuum Ultraviolet Spectroscopy and Spectroscopic Ellipsometry

Abstract

Acknowledgments

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