Structure and surface energy of blend films of Polystyrene and Polybutadiene

Abstract

This thesis presents data on the structure and morphology of spin-coated films of different blends of polystyrene (PS) and polybutadiene (PB). It is shown that there is a complex interrelationship between surface tension, molar mass, and film roughness that makes predicting and understanding the final morphology difficult. Both depth profiling (time-of-flight elastic recoil detection and Rutherford backscattering, as well as some cross-sectional transmission electron microscopy) and surface imaging (atomic force, optical, X-ray photoelectron, and electron microscopy) have been used alongside contact angle measurements to elucidate the three-dimensional nature and properties of these films. Spin coating is a widely employed technique for producing uniform thin films, prized for its simplicity, speed, and cost-effectiveness. It allows for precise control over film thickness by adjusting parameters such as spin speed and solution viscosity. This method is compatible with a range of materials, enhancing its versatility for both research and industrial applications. Furthermore, spin coating yields smooth and homogeneous films, making it ideal for optical, electronic, and surface-related studies. The polystyrene/polybutadiene (PS/PB) blend offers significant advantages for thin film fabrication, owing to its tunable phase separation behaviour that enables controlled microstructure development. The immiscibility of the two polymers facilitates the creation of well-defined morphologies, which can be tailored for specific applications. Moreover, the mechanical flexibility of PB effectively complements the rigidity of PS, resulting in films with well-balanced mechanical properties. This blend also demonstrates favourable film-forming characteristics during solution-based processes, such as spin coating, thereby enhancing reproducibility and uniformity. The study found that surface segregation cannot be predicted solely based on surface energy. Both polystyrene (PS) and polybutylene (BP) tend to migrate to the air or substrate interface, depending on their molar mass. Notably, polystyrene with a lower molar mass shows a preference for the surface.