Interplay of Template Constraints and Microphase Separation in Polymeric Nano-Objects Replicated from Novel Modulated and Interconnected Nanoporous Anodic Alumina

Abstract

We report on a versatile strategy to fabricate shape-controlled polymeric nano-objects with an internal compartmentalized structure by replication from pore-diameter-modulated and interconnected nanoporous anodized aluminum oxide (AAO). The AAO with modulated pore diameters is synthesized in a refined temperature-modulated hard anodization (TMHA) approach, by alternating the flow rate of an air stream cooling the electrolyte. Through pore-widening of the templates with modulated pore diameters, a stable interconnected 3D network with transversal ellipsoidal holes is fabricated as a second template structure. From these unprecedented template structures exhibiting modulated pores and an intricate 3D network structure, shape-controlled polymeric nano-objects are replicated using the melt wetting method with polystyrene homopolymer (PS) and cylinder-forming block copolymer polystyrene-block-polydimethylsiloxane (PS298-b-PDMS195). The replicated nanostructures are separated into individual anisotropically shaped nanocapsules by passing the replicas through a polycarbonate membrane followed by gentle sonication. Inside the nano-objects, the microphase separation of PS298-b-PDMS195 affords parallel aligned nanophases, in which domain sizes and morphologies are different compared to the unconfined bulk according to transmission electron microscopy analyses. These advanced AAO platforms and the nanoscale polymer replicas offer new routes for compartmentalized nano objects with potential future relevance for applications ranging from drug nanocarriers to biosensors.