Controlled orientation of polystyrene-b-poly(L-lactide) nanostructured thin films by air plasma treatment via thermal annealing

This work aims to develop a new approach for controlling the orientation of nanostructured block copolymer (BCP) thin films via thermal annealing. A thin layer of polystyrene-block-poly(L-lactide) (PS-b-PLLA) thin film is prepared by spin coating followed by air plasma treatment, giving a layer with randomly crosslinked PS and PLLA. This layer will serve as a neutral substrate for the second layer of PS-b-PLLA thin film to develop perpendicular PLLA cylinder in PS matrix from the bottom of the thin film by thermal annealing. Subsequently, the second air plasma treatment is carried on the second layer of PS-b-PLLA thin film to give a topcoat neutral layer for the development of perpendicular PLLA cylinders from the top of the thin film after thermal annealing, giving film-spanning perpendicular PLLA cylinders through self-alignment process. With the degeneration of the PLLA in the PS-b-PLLA monolith, it is possible to create PS film with prolonged cylindrical nanochannels that is appealing for applications such as NanoMEMS manufacturing, membrane fabrication and templated synthesis.