RDS study of relaxation in mechanically aligned polymer thin films

In this thesis, Reflectance Difference Spectroscopy (RDS) was used as a primary tool for the measurement of the aligned Polystyrene (PS) thin films. Through the rubbing process, anisotropy could be introduced to the PS films, which were spin coated on the cleaned Si substrates with native oxide. The molecular weights of the PS samples used were from 13.7 Kg/mol to 550 Kg/mol, with thickness from 6.2 nm to 50 nm. Atomic Force Microscope (AFM) was used to examine the rubbed surface topography and to show that the induced anisotropy was due to the orientation of the PS side groups. In the Loading Dependence experiment, the density of the rubbed PS molecules was found to increase when the number of rubbing was increased. Also, higher increases the depth of the rubbed layer, which was shown by the increasing value of the induced anisotropy. The Time Dependence experiment results show both the total amount of anisotropy reduction and the reduction rate of the induced anisotropy was higher at higher temperatures. Also, the relaxation of the films is proved to be due to the local mode motion, which can be described by two single-exponential decays plus a constant. By Temperature Dependence experiment, Tg was found at 100 ℃ and 105 [degress celsius] for 13.7 and 550 Kg/mol PS samples respectively. Further results show the slowest relaxation rate occurs at 30 nm films for the 13.7 Kg/mol PS samples