(577f) Thermal Transitions In Dry and Hydrated Layer-by-Layer Assemblies

Polyelectrolyte multilayer thin films have received significant attention for assembling various nanostructured coatings, but their thermochemical properties are often challenging to measure. Here, we present results regarding the thermochemical properties of a “model” layer-by-layer (LbL) assembly.  The LbL process involves alternate deposition of positively and negatively charged polymers resulting in an interpenetrating network of polyelectrolytes layers with fine structural control. Films may grow linearly or exponentially, and each type of growth is expected to give varied internal structure. Poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/PSS) LbL assemblies created from solutions of varying ionic strength are examined in their dry and hydrated states using both modulated differential scanning calorimetry and quartz crystal microbalance with dissipation monitoring. We show that both techniques can accurately measure glass transitions in PAH/PSS LbL assemblies. These techniques are then applied to evaluate how Tg-value changes with assembly condition, film thickness, and hydration. Results are compared to analogous polyelectrolyte complexes. Understanding the thermal behavior of both LbL films and complexes is important for designing thermally responsive materials, which will be a future endeavor.

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