Glass Transition Temperature Depression

Glass transition temperature depression is the phenomenon which describes the reduction of the glass transition temperature by external factors, usually by the presence of solvent molecules or of other additives in the polymer matrix. Such additives have the capacity to enhance the mobility of the polymer chains, thus enabling long range motions at lower temperature than in the neat polymer. Although this often goes hand in hand with the phenomenon of plasticization, a reduction of the elastic modulus at room temperature, the two concepts should not be confused. Plasticization strictly refers to the mechanical properties of the polymer and the molecules, which reduce the elastic modulus of a polymer by an increase of the chain mobility generally also reduce their glass transition temperature. The opposite is not necessarily the case and it may happen that an additive, which lowers the Tg, at low concentration increases the elastic or Young's modulus at room temperature. This is then...