Alignment and Morphological Effects of Nanoplates in Lamellar Diblock Copolymer Thin Films
The ability to disperse inorganic nanoparticles (NPs) of various shapes, sizes, and compositions in polymeric matrices enables researchers to continuously engineer new material combinations with different resulting properties. Polymer nanocomposites (PNCs) can be further customized for specific applications by intentionally organizing and orienting NPs within these hybrid materials. Despite significant advances in the field of PNCs, full control over the orientation of embedded anisotropic NPs, specifically nanoplates, is not well-established without employing multistep processes. Capturing either in-plane (parallel) or out-of-plane (vertical) orientation of nanoplates in thin polymer films through a scalable method would create new opportunities for developing coating technologies that benefit from orientation-dependent properties. Within this dissertation, we accomplish, for what we believe to be the first time, both in-plane and out-of-plane alignment of nanoplates in thin film PNCs through self-assembly. Monodisperse gadolinium trifluoride rhombic nanoplates doped with ytterbium and erbium GdF3:Yb/Er (20/2 mol%) are synthesized while self-assembling lamellar-forming poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymers (BCPs) are formed. With microdomains oriented either parallel or perpendicular to the substrate, the lamellae serve as guides to direct the two modes of nanoplate alignment. To form PNCs, the nanoplate surfaces are functionalized with phosphoric acid functionalized polyethylene glycol (PEG-PO3H2) brush to create favorable interactions between the NPs and PMMA. In the parallel BCP nanocomposite system, three characteristic behaviors are observed as a function of nanoplate volume fraction (ϕ). At low ϕ, the nanoplates sequester to the PMMA domain and ordered lamellae successfully direct in-plane NP alignment. Here, the nanoplates further assemble into strings separated by small equilibrium interparticle distances. At intermediate ϕ, the PNCs phase separate into regions of ordered lamellae and regions of disordered BCP with unaligned nanoplates. While at the highest ϕ, the nanoplates jam in a kinetically trapped state and are isotropically dispersed throughout entirely disordered lamellae. Recognizing that chemical specificity and low ϕ are requisite conditions for not disrupting the equilibrium BCP morphology, vertical nanoplate alignment in PS-b-PMMA was also successfully established through self-assembly. Overall, the studies herein seek to understand the alignment and morphological effects of nanoplates in lamellar BCP thin films by identifying and understanding the thermodynamic contributions of the system.
Materials science|Polymer chemistry|Nanotechnology
Krook, Nadia M, "Alignment and Morphological Effects of Nanoplates in Lamellar Diblock Copolymer Thin Films" (2019). Dissertations available from ProQuest. AAI22589933.