(722g) Glass Transitions in Layer-by-Layer Assemblies Measured Using Quartz Crystal Microbalance with Dissipation

Glass transitions in thin films are commonly measured using techniques such as ellipsometry, fluorescence, dielectric spectroscopy, and others. Presented here is a new way to measure glass transitions in thin films: quart crystal microbalance with dissipation (QCM-D). A thin film is deposited onto a QCM-D crystal, and QCM-D measures the film’s change in frequency and dissipation as a function of temperature. The change in dissipation is related to the films viscoelasticity, which provides a direct link to the measurement of thermal transitions. We apply the technique to layer-by-layer (LbL) assemblies to demonstrate how exponential and linear growth are related to the films’ mobility and glass transition temperature. Specifically, strong polyelectrolyte multilayers containing poly(diallyldimethylammonium chloride) and sulfonated poly(styrene) are examined as a function of the ionic strength of the assembly solution. It was found that LbL films assembled in the presence of salt possess a measure glass transition around 48 to 56 degrees Celsius. The nature of the glass transition for LbL films is related to the dissociation of ion pairs and the subsequent relaxation of polyelectrolyte chains. The techniques presented here could be universally applied to other thin polymer films beyond just LbL assemblies.