Synthesis, characterization, and formation of self-assembled monolayers of a phosphonic acid bearing a vinylene-bridged fluoroalkyl chain

An unprecedented phosphonic acid with a vinylene-bridged fluoroalkyl chain (–C 6 F 12 –CH=CH–C 6 F 13 ) was synthesized and characterized. This compound comprises the perfluorohexyl (C 6 F 13 ) group, which allows the exclusion of the use and formation of bioaccumulative perfluorooctanoic-acid-related compounds (i.e., compounds containing the (C 7 F 15 )C moiety). Self-assembled monolayers (SAMs) of the novel phosphonic acid were formed on indium-tin oxide and stainless steel substrates by solution deposition. The surface properties, formation kinetics, and thermal stabilities of the SAMs were investigated by X-ray photoelectron spectroscopy, contact angle measurements, and atomic force microscopy. Compared to the SAMs of known fluorinated phosphonic acids containing C n F 2n+1 groups (n = 4, 6, 8), the SAM of this novel phosphonic acid bearing the –C 6 F 12 –CH=CH–C 6 F 13 group showed a high uniformity, a lower surface energy, and a lower contact angle hysteresis. In addition, the novel phosphonic acid allowed the rapid modification of metal oxide surfaces and imparted a superior thermal stability compared to conventional fluorinated phosphonic acids. Therefore, this phosphonic acid bearing a vinylene-bridged fluoroalkyl chain is a promising candidate for improving both surface modification and environmental properties in comparison with conventional analogs having long perfluoroalkyl chains.