SURFACE FREE-ENERGIES OF ALKYLSILOXANE MONOLAYERS SUPPORTED ON ELASTOMERIC POLYDIMETHYLSILOXANES

Self-assembled monolayers (SAMs) of alkylsiloxanes on elastomeric poly dimethylsiloxane (PDMS) are excellent model systems with which to stud y interactions between surfaces. The surface free energies of several monolayer-coated PDMS surfaces were determined by measuring the deform ations produced from the contact between semispherical lenses and flat sheets of the elastomer under controlled loads. The contact deformati ons were analyzed using the theory of Johnson, Kendall, and Roberts (J KR) to estimate the surface free energies of the monolayer films, whic h were compared with the values obtained from contact angles. It is sh own that the surface free energies of not only the apolar, but also th e polar non-associative surfaces can be adequately described by consid ering only the dispersion forces. Polarity as obtained from the contac t angles of water has no general significance in estimating the interf acial interactions across the polar nonassociative surfaces.