Mihail Bora | 20-FS-006
This study evaluated the feasibility of using an infrared imaging system to detect adhesion defects at polymer interfaces. The imaging system was composed of an infrared camera that images an absorption band of water at 2,750 to 2,950 nanometers, as well various illumination sources (e.g., light emitting diodes, black body, thermal emission filament). The goal of the project was to demonstrate that water accumulates preferentially at weakly bonded interfaces, and that the increase in moisture content can be detected by the imaging system to provide non-destructive diagnostics for areas prone to delamination.
We were successful in demonstrating this capability for adhesion of polyimide on glass using common microfabrication techniques. Areas of qualitatively good and bad adhesion were fabricated on the same substrate by patterning a polyimide adhesion promoter and verifying the formation of self-assembled monolayers with contact angle measurements, followed by spinning of polyimide precursor and curing at high temperature to facilitate polymerization. For adhesion testing, we showed that although no defects were observable either through visual inspection or infrared imaging when the samples were dry, immersion in water at room temperature for 15 minutes resulted in visualization of adhesion promoter patterns via infrared imaging, indicating differential water content at hydrophobic versus hydrophilic interfaces.
The work carried out during this project is paving the way to use this imaging system developed at Lawrence Livermore National Laboratory as a screening tool to evaluate the reliability of various materials and devices with relevance to national security and other Livermore missions. It provides the significant benefit of non-destructive qualitative testing adhesion without having to fabricate a sample with special structure and geometry.
Publications, Presentations, and Patents
Bora. M., et al. "Non-destructive, in-situ evaluation of water presence using thermal contrast and cooled detector," U. S. Patent Application 2019/0376847.