| Glassy materials, such as rubber, paint, and glue, even jelly, are used everywhere around people’s daily life. The study of glassy materials and the glass transition phenomenon have been widely investigated since long time ago. In a paper published in Nature in 1995, Anderson said, the study of glassy and glass transition might be the most interesting, deepest, but still unsolved problem in the solid theory. In 2005, Science put forward 100 important scientific questions in the 21 st century, including the study of the glass state and glass transition. Unfortunately, there is not even one unified theory to explain the phenomenon. With the rapid development of the materials technology, people have focused on the nanoscale confinement effects on the glass transition of glass forming materials. For ultrathin film systems under one-dimensional(1D) confinement, people inferred that there exists a free surface near the surface of the film, which composed by the free polymer chains and has lower density than the bulk film, and it is the free surface that cause the unexpectedly decrease of Tg. Limited to the experiment conditions, people did not directly observe the existence of free surface layer. For glass transition of the two-dimensional(2D) systems such as nanowires, nanotubes, people still get no good explanations. In this thesis, we focus on the glass transition of polymers confined in 1D and 2D geometry.(1) Ultrathin films were prepared by spin coating polystyrene(PS) solution. The PS samples were specialized to be linear or cyclic ones in molecular architecture. Polymer nanowires under 2D nano confinement were prepared by shaping poly(methyl methyl acrylate)(PMMA) into porous anodized aluminum oxide(AAO).(2) Using the Differential Scanning Calorimeter(DSC), we successfully measured the glass transition temperature of nano-liter PMMA confined in AAO. The glass transition temperature of PMMA is substantially decreased with decreasing the diameter of AAO pores, indicating the true size effect of glass transition.(3) Using the ellipsometer to monitor the thickness changes during glass transition, we investigated the glass transition of cyclic PS ultrathin films and compared to their linear counterparts. We found that the glass transition temperature of linear PS is substantially decreased with decreasing film thickness, in consistent with previous reports. The glass transition temperature of cyclic PS thin films is, however, not changed with varying the films thickness. Therefore, we believe that the surface mobile layers that cause the abnormal glass transition temperature in polymer ultrathin films arise from the end groups in linear polymers. |
