Understanding the demixing behavior and structure-property correlation in graphene oxide containing LCST blends

Abstract

A number of researchers have studied about the effects of different nanoparticles on the phase separation of LCST polymer blend systems. Many nanoparticles such as carbon nanotubes and silica have been incorporated in miscible blend systems. Although the above-mentioned nanoparticles were used to study on how they affect the phase separation of different polymer blends, they tend to pose a plethora pool of limitations. Despite the fact that they possess high aspect ratio, carbon nanotubes have no functional groups on their surface. This makes it very difficult to graft different polymer chains on their surface. The creation of functional groups on their surfaces requires the use of harsh acidic treatments which usually affect the overall structure of the nanoparticles and also the process is quite cumbersome. According to the Ginzburg theory, the size and geometry of nanoparticles plays a big role in either decreasing or increasing the phase separation temperature of the miscible polymer blend systems. This greatly affects the use of silica nanoparticles because they usually come in different sizes. Henceforth in this thesis we have used graphene oxide nanosheets as our filler, taking advantage of its multiple functional groups which makes it easy for functionalization. The thesis initially focuses on the different methods used to fabricate polymer blends and how polymer blend preparation affects their thermal concentration fluctuations. A comparative study of the two methods (solution and melt mixing) was conducted in the thesis. The method of polymer blend preparation is of paramount importance because it affects the overall final properties of the blend system. After focusing on the method of polymer blend preparation, the other main thrust of this thesis was to fully understand the effects of two-dimensional graphene oxide nanosheets and their derivates (polymer grafted graphene oxide) on the demixing temperature, polymer chain dynamics and morphology evolution of PMMA/SAN. We successfully managed to graft polymer chains of different molecular weight on graphene oxide nanosheets taking advantage of the presence of multiple functional groups on their surfaces and studied on how the GO derivatives affects the miscibility and cooperative relaxation in PMMA/SAN. We went a step further by choosing a classical route of grafting polystyrene acrylonitrile polymer chains on the surface of graphene oxide making use of a solvent free reaction mechanism. This route is industrially favorable because it does not make use of large quantities of solvents which can harmful both to human life and the environment. Polymers in general are highly susceptible to UV degradation, this degradation usually leads to the breakage of polymer chains resulting in a reduction in the molecular weight hence significantly affecting their mechanical properties. Keeping this in mind the thesis also focuses on developing polymer blend composite systems which have the ability to absorb UV radiation in their different state of morphologies (miscible or immiscible). This will ensure that the polymer blend composites can perfectly absorb UV radiation irrespective of the temperature conditions in different applications.