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Molecular Tailoring of Thin Film Adhesion

Nancy Sottos (Dept. of Materials Science and Eng., Univ. of Illinois at Urbana-Champaign), Martha Grady (), Philippe Geubelle ()

Mechanics of Thin Films and Multilayered Structures

Tue 9:00 - 10:30

Salomon 203

Self-assembled monolayers (SAMs) provide an enabling platform for molecular tailoring of the chemical and physical properties of an interface in an on-demand fashion. In this work, we systematically vary SAM end-group functionality and quantify the corresponding effect on interfacial adhesion between a transfer printed gold (Au) film and a fused silica substrate. SAMs with four different end groups are investigated: Dodecyltriethoxysilane, 11-mercapto-undecyltrimethoxysilane, 11-amino-undecyltriethoxysilane, and 11-bromo-undecyltrimethoxysilane. These monolayers have the same length of methylene chains allowing direct comparison of end groups. The adhesive strength of the SAM-mediated interfaces is measured by a non-contact laser-induced spallation method at strain rates in excess of 106 s-1. A high strain rate test method is selected to facilitate comparison with molecular dynamics simulations of the molecular failure process. Interfacial stresses are inferred from interferometric displacement measurements and finite element analysis. By making multiple measurements at increasing stress amplitudes (controlled by the laser fluence), the adhesion strengths of Au films transfer-printed on different SAM modified substrates are compared. Preliminary experiments have shown that varying the end-group functionality drastically alters the adhesion strength of Au films, leading to improved adhesion over transfer printed films on unmodified quartz.