Some insights into the structural relaxation of spin- cast, glassy polymer thin films

The widespread use of thin films in a range of applications and industries, from coatings, inks and lithography to nano-imprinting, optoelectronics, and memory devices , has made the understanding of thin films, particularly the changes induced by structural relaxation and solvent evaporation, very important. There is a need to know if a film will change in dimensions after its deposition and how fast these changes will occur. Physical ageing of thin polymer systems is, more generally, an important phenomenon in polymer physics: when a polymer is cooled quickly below its glass transition temperature (Tg) at which point freezing of the matrix takes place , it is in a non-equilibrium state. When it is aged at temperatures below Tg, a structural relaxation towards the equilibrium volume can take place 2 . (The equilibrium volume represents the volume obtained through infinitely slow cooling.) Recent works have shown that the structure, wetting, and mobility of polymers in thin films can differ greatly from those of the bulk 3 4 . For example, a well-documented property of thin polymer films that exhibits thickness dependence is its Tg 6 .