Polyhedral oligomeric silsesquioxane (POSS) localization in ordered block copolymers
Ayandele, Ebunoluwa A.
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Polymer nanocomposites are an alternative to overcoming the problem of lower mechanical properties encountered in polymers relative to ceramics and metals. By reinforcing polymers with nanofillers, a hybrid material with superior properties to the individual polymer or nanofiller can be obtained. More recently, nanoparticles have attracted much attention due to their nanometer size and the ease at which these materials can be incorporated into polymeric materials. First, we present here a literature review of polyhedral oligomeric silsesquioxane (POSS)-based polymer nanocomposites highlighting the homogenous or heterogeneous morphology of the resulting composites, indicative of complete miscibility or macrophase separation respectively between the polymer and POSS molecules. We also cite various scenarios of enhanced properties in the resulting polymer-POSS hybrids. Then, we investigate structures formed by dispersing polyhedral oligomeric silsesquioxane (POSS) nanoparticles in Pluronic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (BCPs). Due to the amphiphilic nature of these block copolymers, they typically self-assemble to form various morphological structures in the presence of selective solvents as a result of the different affinity each block has for a certain solvent. We dispersed PEO-functionalized POSS (PEO-POSS) and isobutyl-functionalized-POSS (iBu-POSS) in Pluronic P105 and investigated the surface interactions, self-assembly and phase behaviors in various solvents (polar and non-polar). Structural characterization of the nanocomposites was achieved using polarized light and small angle X-ray scattering techniques. Finally, we draw conclusions based on our findings. Our results revealed that for the BCP-PEO-POSS systems, cylindrical structures formed by aqueous Pluronic P105 remained stable up to 15 wt% of PEO-POSS, beyond which morphological transition to a lamellar structure occurred. For the BCP-iBu-POSS systems, our results revealed that POSS particles cannot be dispersed in aqueous Pluronic, hence the introduction of an organic solvent. We observed a transition from the normal cylindrical hexagonal phase to a reverse hexagonal phase with increasing p-xylene concentration, which was different from what we observed in the PEO-POSS systems.