Using Sol–Gel Replications to Assess the Porosity of Block-Copolymer Derived Thin Films

Abstract

In this paper, we report the use of a sol–gel replication method to prepare high fidelity SiO2 replicas of porous thin films obtained from microphase separated block-copolymer systems as an easy, robust, and rapid way to investigate their inner morphology. The cylinder-forming poly(styrene)-b-poly(lactide) (PS-b-PLA) block copolymer, containing a sacrificial block (PLA), was used to produce porous thin films with thicknesses above one periodical distance and bearing various internal organizations and orientations of the cylinders. The porosity was first infiltrated by silica precursors using a chemical solution deposition process, before being exposed to a brief thermal treatment to provoke inorganic condensation and elimination of the PS template. SEM observations of the obtained replica gave three-dimensional view of the internal topology of the porosity, which were then compared to structural characterizations obtained directly by AFM, SEM, or GISAXS on the parent block-copolymer films. It is shown that the replication provides an ideal tool to characterize the topology of porous networks in supported polymer thin films. This method can be generalized to any type of porous polymer media, offering a unique mode of visualization of the internal topology with valuable details at the substrate interface.