Effect of film thickness on the validity of the sauerbrey equation for hydrated polyelectrolyte films

Bryan D. Vogt, Eric K. Lin, Wen Ii Wu, Christopher C. White

Research output: Contribution to journalArticlepeer-review

181 Scopus citations

Abstract

The frequency and energy dissipation change of a quartz crystal microbalance during moisture absorption was measured for films with thickness ranging from 3 to 205 nm. Evidence of the viscoelastic nature of the films was observed for films thicker than 90 nm through the frequency and energy dissipation changes. For sufficiently thin films (t < 40 nm), the frequency change could be effectively modeled as a simple increase in mass, as predicted by the Sauerbrey equation. The viscosity of the swollen films was independent, of initial polymer film thickness (93-205 nm). The equilibrium swelling ratio was independent of film thickness for all films examined (3-205 nm). The transition between the observation of a rigid film and a film showing viscoelastic character was found to be at β1D = 0.26 ± 0.10, where β1 = 2π/λs, λ s is the shear wavelength, and D is the film thickness. This transition agrees with the predictions of White and Schrag (J. Chem. Phys. 1999, 111, 11192).

Original languageEnglish (US)
Pages (from-to)12685-12690
Number of pages6
JournalJournal of Physical Chemistry B
Volume108
Issue number34
DOIs
StatePublished - Aug 26 2004

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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