n-Octadecyltriethoxysilane monolayer coated surfaces in humid atmospheres: Influence of capillary condensation on surface deformation and adhesion

Sungsoo Kim, Hugo K. Christenson, Joan E. Curry

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We have investigated the effect of humidity on surface deformation and adhesion of mica surfaces coated with n-octadecyltriethoxysilane self-assembled monolayers using a surface forces apparatus. The Maugis model of contact elasticity based on linear elastic fracture mechanics is used to analyze the results. The Laplace pressure is assumed to act in the "Dugdale" zone outside the contact area to account for capillary condensation. We measure the radius of the contact area as a function of applied load and use the model to obtain the surface energy and elastic constant of these surfaces for humidities ranging from 0 to 99%. The limiting values in dry and near-saturated conditions are as expected from well-known theories. A significant result is that we also obtain the surface energy for intermediate humidities. Increasing humidity modifies the deformed shape of the surfaces in contact due to capillary condensation. The sharp bifurcation at the edge of the contact zone for low humidities (JKR-type contact) is replaced by rounded edges (DMT-type contact) with increasing humidity. This is predicted by the Maugis model and is experimentally observed using optical interference fringes of equal chromatic order. We are able to separate the capillary condensation and solid-solid contributions to the adhesive force because the Maugis model allows a direct calculation of the area on which the Laplace pressure acts. At humidities approaching saturation the forces due to capillary condensation dominate monolayer-monolayer adhesion. At lower humidities both capillary condensation and direct monolayer-monolayer interaction contribute to the overall adhesion.

Original languageEnglish (US)
Pages (from-to)3774-3781
Number of pages8
JournalJournal of Physical Chemistry B
Issue number16
StatePublished - Apr 24 2003

ASJC Scopus subject areas

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


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