Interfacial effects on moisture absorption in thin polymer films

Bryan D. Vogt, Christopher L. Soles, Ronald L. Jones, Chia Ying Wang, Eric K. Lin, Wen Li Wu, Sushil K. Satija, Dario L. Goldfarb, Marie Angelopoulos

Research output: Contribution to journalArticle

66 Scopus citations

Abstract

Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced. The enhanced swelling in the thin films is due to the attractive nature of the hydrophilic substrate, leading to an accumulation of water at the silicon/polymer interface and subsequently a gradient in concentration from the enhancement at the interface to the bulk concentration. As films become thinner, this interfacial excess dominates the swelling response of the film. This accumulation was confirmed experimentally using neutron reflectivity. The water rich layer extends 25 ± 10 Å into the film with a maximum water concentration of ∼30 vol %. The excess layer was found to be polymer independent despite the order of magnitude difference in the water solubility in the bulk of the film. To test if the source of the thickness dependent behavior was the enhanced swelling at the interface, a simple, zero adjustable parameter model consisting of a fixed water rich layer at the interface and bulk swelling through the remainder of the film was developed and found to reasonably correspond to the measured thickness dependent swelling.

Original languageEnglish (US)
Pages (from-to)5285-5290
Number of pages6
JournalLangmuir
Volume20
Issue number13
DOIs
StatePublished - Jun 22 2004
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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  • Cite this

    Vogt, B. D., Soles, C. L., Jones, R. L., Wang, C. Y., Lin, E. K., Wu, W. L., Satija, S. K., Goldfarb, D. L., & Angelopoulos, M. (2004). Interfacial effects on moisture absorption in thin polymer films. Langmuir, 20(13), 5285-5290. https://doi.org/10.1021/la035830f