Quartz Microbalance Microcalorimetry: A new method for studying polymer-solvent thermodynamics

Abstract

We have developed a sensitive method of determining enthalpy changes for gas-surface interactions: quartz microbalance microcalorimetry. We mount in an isoperibol environment both sample and reference combinations of a quartz crystal microbalance (QCM) in intimate thermal contact with a heat flow sensor. We coat the sample QCM with a thin (∼1 µm) polymer film. By exposing the film to ethanol vapor, we measure simultaneously the change in mass per unit area (to ±0.25 ng cm−2) and the resulting heat flows (to ±50 nW) when the polymer adsorbs or desorbs ethanol. The molar enthalpies of sorption of ethanol vapor in Tecoflex, an aliphatic polyurethane elastomer, are ΔadsorptionH= −53±8 kJ mol−1 and ΔdesorptionH=52±3 kJ mol−1.