Semicrystalline Polymers under Confinement as Thin Films

Tufts University, Medford MA

Investigators

Abstract

Crystallizable polymers in the thin film geometry will be studied using electrical and optical methods. Constraints on molecular mobility that arise from the thin film geometry will be investigated and compared to behavior observed in the bulk polymers. Materials chosen for the study are model systems having well-characterized molecular weights and tacticity, comprising isotactic polystyrene (i-PS), and miscible blends of isotactic with atactic polystyrene (a-PS). Effects of film thickness on the glass transition and cold-crystallization kinetics film thickness and root mean square end-to-end distance of the polymer chain will be determined for homopolymer i-PS and blends. In nanometer-scale thin films, optical methods measuring alignment layer relaxation, and surface studies using elevated temperature atomic force microscopy, will be used to corroborate the dielectric experiments. Ex-situ characterization of the films will include thickness measurement by profilometry, and surface structure analysis by scanning electron microscopy. Degree of crystallinity of thin films will be assessed using Fourier Transform infrared spectroscopy. In bulk-scale films, simultaneous wide and small angle X-ray scattering will be performed to assess structural parameters and to determine crystallization kinetics from the time development of scattered intensity. Differential scanning calorimetry and its temperature-modulated variant will be used to determine the glass transition temperature and degree of crystallinity of thicker films. %%% Thin polymer films are being used more frequently in technological applications, and it is therefore of great practical interest to understand the structure and properties of crystallizable polymer nanometer-scale films. This work will provide fundamental information about the molecular motions and crystallization processes in thin polymer films, which impact directly the material properties and performance characteristics of thin films.