(747h) Establishing Structure/Property Interrelations Using Fast Scanning Calorimetry

Commercialization of differential scanning calorimetry (DSC) fifty years ago led to widespread use of calorimetric methods for thermal characterization. Modern DSC instruments can measure physical transitions, the kinetics of reactions, and other transformations quickly and easily. A material’s glass transition temperature provides insights to its mechanical, chemical and thermodynamic properties. Measuring the glass transition temperature of many functional polymer systems, is, however, often difficult due to varying molecular weights, dispersity, and low degree of crystallinity. Hence, traditional DSC methods are usually not sensitive enough to detect the heat response that reflect the material’s glass transition. Fast scanning calorimetry (FSC) can measure at rates greater than 10,000 K/s, allowing for the measurement of isothermal crystallization and study of the formation of glasses. Some semi-crystalline polymers have reported glass transition temperatures that span 50 degrees Celsius or more. Knowledge of the ‘true’ glass transition, other important phase transitions and, e.g., their solidification kinetics can be obtained by measuring relaxation enthalpies with FSC. This method of quenching from the melt and isothermally aging the material provides a glass transition temperature that is not rate dependent and can provide information on the existence of mobile and rigid amorphous phases, all of which are important in material processing as well as in establishing relevant structure/property interrelations. We discuss how the FSC technique can be used for the identification of thermodynamic transitions of donor polymers (PCDTBT) and acceptor molecules (fullerene derivatives) commonly used in the organic solar cell area. Moreover, we provide examples how the change in glass transition temperature of PCDTBT can be tracked before and after UV-light curing. Other illustrations involve inorganic/organic hybrid materials of different crosslink densities and how this affects the glass transition of the final structures. Accordingly thermal analysis can be exploited to obtain important structural information of this new class of materials and, in turn, processing guidelines can be established towards materials of specific optical or electrical characteristics.