A MODEL SYSTEM FOR DIFFERENTIATING BETWEEN WATER ACTIVITY AND GLASS TRANSITION EFFECTS ON SOLID STATE CHEMICAL REACTIONS

Recent debates have emerged on whether water activity (a_w) or the state of the system as dictated by the glass transition temperature (T_g) controls the rates of chemical reactions in reduced-moisture solid systems. Previously, model systems in which the effects of water activity and glass transition on chemical reactions could be evaluated independently did not exist. The use of polyvinyl-pyrrolidone (PVP) of different molecular weights allows the water activity and moisture content of the systems to be kept virtually constant while the glass transition temperature varies. At a given water activity and temperature, the equilibrium moisture content for any molecular weight of PVP differed by only 1–2%, while the T_g values differed by 20–30C. Using PVP of different molecular weights as a model system will allow the effects of water activity and glass transition on chemical reactions to be studied independently and at a constant temperature.