UNDERSTANDING ASSEMBLY AND POROSITY IN BLOCK COPOLYMER NANOPARTICLES

Block copolymers (BCP) are known to self-assemble into highly ordered nanoscale structures. When BCP self-assembly is confined in macro and nano spheres, a variety of morphologies including onion, core and shell, bud and pupa-like can be achieved, making them attractive materials for optical, catalytic and biological (e.g. drug delivery) applications. The BCP nanoparticles` (NP) morphologies can be controlled by tailoring BCP chemical composition, solvents, confining sphere size, surface tension and process parameters. However, while many of the BCP NP applications can benefit from porous NP, typical BCP NP are non-porous.

In this research, we study the fabrication of BCP-based porous NP using two methods: (1) high-shear micro emulsion of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) or poly(styrene-block-2-vinyl-pyridine) (PS-b-P2VP) in the presence of polyvinyl alcohol (PVA), and (2) Sequential Infiltration Synthesis (SIS), a method based on atomic layer deposition chemistry that enables growth of metal oxides within polymers. The high-shear micro emulsion of PS-b-PMMA (or PS-b-P2VP) results in assembly of porous BCP nanoparticles as evident from scanning and transmission electron microscopy (SEM and TEM, respectively) (Figure 1). EM characterization revealed that PVA plays a critical role in controlling the porosity of these particles. SIS, on the other hand, enables selective growth of metal oxides in the PMMA/P2VP domains, creating hybrid organic-inorganic nanoparticles. The polymer in the hybrid particles can then be etched using oxygen plasma to create BCP-templated metal oxide NP.

Figure 1 - PS-b-P2VP porous micro particles, emulsified in a 0.1%w.t. PVA aqueous solution