(619h) Thermal Transitions in Layer-By-Layer Assemblies Observed Using Electrochemical Impedance Spectroscopy

Layer-by-layer (LbL) assemblies have been of great interest due to their versatile functionality and ease of fabrication. The sensitivity of an LbL film to assembly conditions as well as external stimuli can be attributed to the weak nature of non-covalent interactions (electrostatic, hydrogen bonding, van der Waals) existing between the two adsorbing species. As it will be shown here, temperature is a particularly intriguing parameter in that some LbL films respond dramatically and others do not in aqueous media. The reasoning behind this phenomenon is not well understood, and is explored herein. We will present the structure and transport properties of LbL films of poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate) (PSS) as a function of temperature using electrochemical impedance spectroscopy and a redox-active probe. The effects of thickness, salt concentration, and the identity of outermost layer on the thermal transition temperature are investigated. It will be shown that equivalent circuit modeling can be applied to assess a film’s transition temperature, and results are in good agreement with calorimetry and quartz crystal microbalance with dissipation.