Phase separation morphology of immiscible polystyrene/poly(methyl methacrylate) single-chain nanoparticle blend films

Regulating the phase morphology structure is crucial for the fabrication of multifunctional and high performance polymer blend films. In this work, we investigate the phase separation morphology evolution of immiscible polystyrene/poly(methyl methacrylate) single-chain nanoparticle (PS/PMMA SCNP) blend films prepared by spin coating. The results show that the composition of the morphological transition from sea-island structure to co-continuous structure is between 40/60 and 35/65 in PS/PMMA linear precursor blend films, while it is between 35/65 and 30/70 in PS/PMMA SCNP blend films. The phase-separated domains of the SCNP blend films are much smaller than those of linear precursor blend films. Moreover, the domain height of PMMA SCNP-containing blends is lower than that of PS/PMMA linear precursor blends, indicating the decreased solubility of PMMA SCNPs in chloroform. X-ray photoelectron spectroscopy results reveal that the mass fraction of the PMMA component on the surface of PMMA linear precursor blend films is higher than that of PMMA SCNP blend films with the same composition, leading to different phase separation morphologies of these two blend films. The rheological results prove that the viscosity of the PS/PMMA SCNP blend solution is higher than that of the PS/PMMA linear precursor blend solution; thus, the diffusion and local relaxation of PMMA SCNPs are slower during spin-coating. Consequently, the phase separation is suppressed and the domain size decreases in PS/PMMA SCNP blend films. The phase separation process induced by the replacement of linear polymer chains by SCNPs could have significant implications for industrial applications requiring soft nanocomposite materials with excellent nanoparticle dispersion.