Controlling the Kinetics of Spinodal Decomposition in LCST PS/PVME Blends in Presence of Spherical Nanoparticles

Abstract

The influence of hydrophilic spherical nanoparticles on the kinetics of spinodal decomposition (SD) in PS/PVME (polystyrene/polyvinyl methyl ether) blend was studied. For the PS/PVME 30/70 blend at 110oC a highly interconnected structure was developed in the early stages of phase separation as a characteristic of spinodal decomposition. Due to the presence of highly curved interface between the phases in a co-continuous morphology, a considerable free energy was stored at the interface. Thus, interconnected structure was not in thermodynamic equilibrium and broke up into droplet-matrix morphology. At later stages, droplets grew dramatically and a broad size distribution of droplets was observed. Phase contrast optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphological evolution of PS/PVME blends during the phase separation. In order to investigate the kinetics of phase separation in the presence of nanoparticles, OM observations and rheological analysis were employed. Nanosilica particles were strongly driven by the thermodynamic forces into the bulk of PVME-rich phase to reduce the free energy of the system during the phase separation, as verified by TEM micrographs and thermodynamic equation. Nanoparticles considerably slowed down phase separation kinetics of SD at a low volume fraction of 0.5% which was intensified as the volume fraction was increased to 1%. Surprisingly, at 2% nanoparticle loading phase separation was arrested and a stable co-continuous structure induced by SD was formed. TEM images indicated that double percolated structure was induced in the presence of 2% A200 nanoparticles: a network of nanoparticles was induced in the network of PVME-rich phase.

Keywords

• spinodal decomposition
• kinetics
• rheology
• spherical nanoparticles
• pinning