(317v) Thermodynamics and Dynamics of Water Vapor Sorption in Thin Polymer Films

Quartz crystal microbalance/heat conduction calorimetry (1) is a new measurement technology that permits high sensitivity measurements in real time of three properties of a nanoscale coating or film undergoing chemical reaction: the mass change (to ±10 nanograms), the heat generated (to ±1 microwatt), and the change in viscoelastic stiffness (loss compliance) of the film. Polymer films of thickness 0.1 to 10 μM were prepared on the surface of a 5 MHz QCM and subjected to step-changes in relative humidity in the sample chamber of a Masscal G1 at temperature between 30 and 80 C. From the data collected it is possible to determine the water vapor sorption isotherm, the water vapor sorption enthalpy, the dependence of loss compliance on water content of the film, and the diffusion coefficient of water in the film. The water sorption enthalpies determined calorimetrically are in agreement with those derived indirectly from the van't Hoff equation relating water vapor solubility and temperature. Examples will be given of these properties in pharmaceutical film coat materials, in multilayer polymer films, and in films of importance in digital imaging technology.

1. Smith, A. L.; Shirazi, H. M., Principles of Quartz Crystal Microbalance/Heat Conduction Calorimetry: Measurement of the Sorption Enthalpy of Hydrogen in Palladium, Thermochimica Acta 2005, 432, 202-211.