Morphology control of PS-b-PB-b-PMMA/PMMA blends by silica nanoparticles

The effect of the silica nanoparticles on the morphology of a blend consisting of poly(methyl methacrylate) (PMMA) and the poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate) (SBM) triblock copolymer was studied. Upon blending PMMA with SBM, macrophase separation between the block copolymer and homopolymer occurred, in which the higher molar mass chains of homopolymer separate into homopolymer-rich domains due to the 'dry-brush' regime, whereas the lower molar mass chains of homopolymer tend to be selectively solubilized in the block copolymer-rich domains due to the 'wet-brush' regime. Upon adding the hydrophilic silica nanoparticles to the PMMA/SBM blend, a significant suppression effect on the extent of macrophase separation between the homopolymer and block copolymer can be observed. It was shown that the silica particles are preferentially localized in the PMMA phase due to the strong hydrogen bonding interaction between the hydroxyl groups on the surface of silica nanoparticles with the carbonyl groups of the PMMA. The suppression effect of the silica particles may be related to the selective adsorption of the high molar mass PMMA on the surface of the silica particles, which may force the system into the 'wet-brush' regime, but this was only observed for the systems with a low silica content. For the systems with a high silica content, both the homopolymer PMMA and the PMMA block of the SBM block copolymer interact with the silica surface, which becomes the connecting part between both polymers, thereby suppressing the extent of macrophase separation.