Monitoring the real time growth of a self-assembled monolayer on a polymer electrolyte surface

The growth of a self-assembled monolayer (SAM) at the surface of a polymer electrolyte has been shown to inhibit the formation of the passivating layer that forms when the polymer is in contact with lithium metal. In this work, ac impedance spectroscopy was used to monitor the formation of SAM layers on polyethylene oxide (PEO) polymer electrolyte thin films as a function of time. To monitor SAM growth, thin PEO films were cast onto interdigitated electrodes. The electrodes were subsequently immersed in a saturated SAM solution and the film impedance was measured. SAM molecules with the general formula: H(CH2)32(CH2CH2O)yH (y = 2, 10, 40) were used. Growth occurred due to interactions with the ethylene oxide portion of the SAM molecules with the PEO surface. To visualize SAM growth impedance data at a single frequency sensitive to changes at the solution interface was plotted verses time. At the point of immersion, a sharp increase in impedance was observed. With time, the rate at which the impedance increased slowed and ultimately leveled off presumably indicating the point at which a nearly complete monolayer had formed. SAM growth was verified using attenuated total reflectance infrared spectroscopy (ATR-IR).