Probing Surface Modifications of a Chrome Oxide (CrOx) Substrate for Low-Surface Energy Applications Using Sum Frequency Generation Vibrational Spectroscopy

This study explores the use of self-assembled monolayers (SAMs) to improve release properties on chrome oxide surfaces by reducing surface energy. Four molecules (octadecanethiol (ODT), octylphosphonic acid (OPA), octadecylphosphonic acid (ODPA), and octadecyltrichlorosilane (OTS)) were investigated for self-assembly. SAM formation on the chrome oxide substrate was investigated at short (5 min) and long (1 h) time durations at a 5 mM molecular concentration. Sum frequency generation (SFG) vibrational spectroscopy and static contact angle goniometry were used as the two primary analytical techniques in this study. Different substrate pretreatments, such as air plasma treatment, air corona treatment, and chemical washing procedures (including caustic washing), were performed on the chrome oxide substrate before SAM deposition to understand the effects of changes in substrate surface chemistry on the formed SAM quality. It was discovered that plasma treatment, corona treatment, and caustic washing had an overall negative effect on the quality of the SAMs formed by all four model molecules, while other pre-SAM formation treatment methods such as washing by methanol, acetone, and isopropyl alcohol did not significantly affect the overall sample quality. A high-quality OTS SAM on the chrome oxide substrate was successfully prepared with a 5 min deposition duration using a 5 mM concentration, without any additional treatments. Annealing resulted in significantly improved SAMs for the ODPA and OPA molecules. ODT could not produce high-quality SAMs on the chrome oxide substrate regardless of the treatment type performed. In summary, we found that high-quality SAM coatings on chrome oxide surfaces could be achieved for ODPA and OPA with annealing and for OTS with no additional treatments.