Molecular Tailoring of Interfacial Failure

Abstract

Self-assembled monolayers (SAMs) provide an enabling platform for molecular tailoring of the chemical and physical properties of an interface. In this work, we systematically vary SAM end-group functionality and quantify the corresponding effect on interfacial failure between a transfer printed gold (Au) film and a fused silica substrate. SAMs with four different end groups are investigated: 11-amino-undecyltriethoxysilane (ATES), dodecyltriethoxysilane (DTES), 11-bromo-undecyltrimethoxysilane (BrUTMS), and 11-mercapto-undecyltrimethoxysilane (MUTMS). In addition to these four end groups, mixed monolayers of increasing molar ratio of MUTMS to DTES in solution are investigated. The failure of each SAM-mediated interface is initiated by a noncontact laser-induced spallation method at strain rates in excess of 10(6) s(-1). By making multiple measurements at increasing stress amplitudes (controlled by the laser fluence), we measure interface strengths of 19 ± 1.7, 20 ± 1.3, 52 ± 5.4, and 80 ± 6.5 MPa for interfaces functionalized with ATES, DTES, BrUTMS, and MUTMS, respectively. The interface strength is effectively tuned between the low strength of DTES and the high strength of MUTMS by controlling the concentration of MUTMS in solution. X-ray photoelectron spectroscopy of the failed interfaces reveals the influence of end group functionality on molecular dissociation, which significantly alters the failure process.

Biofilm rupture by laser-induced stress waves increases with loading amplitude, independent of location

“…A significant number of laser spallation studies incorporate images of film failure by stress wave loading [24][25][26][27][28][29]. The sequence of images indicates an increase in spall size with each increment in laser fluence, however, this trend has not been previously quantified.…”

“…The sequence of images indicates an increase in spall size with each increment in laser fluence, however, this trend has not been previously quantified. To demonstrate applicability of our approach to analyze spallation images for synthetic films, we apply our procedure to failure of several films provided to us from two prior spallation studies: gold films transfer printed onto functionalized silicon substrates (55 loaded regions) [25], sol-gel films fabricated with a Pt/Ti superlayer to impart higher tensile stresses to cause spallation (4 loaded regions) [27]. The image analysis protocol outlined above is performed with the donated images from previous studies and the trend of spall size increase is presented alongside results from this biofilm study.…”

“…Scatter plots of percent spallation areas vs the normalized fluence applied to each film. The red triangles depict the statistics for the gold film (data from [25]), the yellow squares indicate the sol-gel film (data from [27]), and the blue circles indicate the failure for the biofilms tested. All of the films show a monotonically increasing relationship as fluence increases.…”

“…The spallation region varies based on the laser loading fluence (energy per unit area), and the coating composition or growth conditions. For example, several authors [25][26][27][28][29] report a larger spall size at higher fluences when compared with the same coating loaded at lower fluences, though no systematic study has been presented. It has also been qualitatively shown that a loaded film with low adhesion strength would result in a larger spall size than that of a high adhesion strength film loaded at the same fluence.…”

“…Laser spallation has been implemented to measure adhesion of various coatings including metallic [25,[30][31][32][33] and polymeric [27,29,34] films, by obtaining the stress that causes film failure. The use of laser spallation on biological films such as cells and bacteria is a relatively newer field [35][36][37], thus these methods must be carefully examined to determine the validity of the measurements.…”