Effects of nanoparticles on phase morphology in thin films of phase-separated diblock copolymers

Abstract

This study investigates the morphology changes in thin diblock copolymer (DiBCP) films occurring in the interaction with modified nanoparticles (NPs). Magnetite (Fe3O4) and silica (SiOx) were prepared and used. Poly(pentyl methacrylate-b-methyl methacrylate) (PPMA-b-PMMA) (70/30 mol mol−1, hcp cylinders of the PMMA phase) DiBCP were employed to prepare thin films having thicknesses to realize standing cylinders in pure DiBCP films. The investigations aimed at two topics: (1) morphology after controlled incorporation of organo-modified NP (gold, silver, Fe3O4, SiOx) and (2) additional solvent vapour annealing (SVA) with tetrahydrofuran (and chloroform for comparison). The laterally ordered morphology in thin films was examined by GISAXS and atomic force microscopy. Keeping the same type of morphology in nanocomposites, the dimensions of the periodic nanostructure altered depending on type and amount of incorporated NP. It was found that SiOx clusters enlarge the lateral distance of the PMMA cylinders, whereas metallic NPs reduce this parameter. Applying SVA improves the phase separation slightly, whereas lateral distances were kept constant or were reduced a little. Switching of domain orientation upon SVA could not be detected in the presence of NPs located at the polymer/substrate interface.

Thin-film morphologies of block copolymers with nanoparticles

“…In some BCP systems, for film thicknesses f well below d bulk (the “repeat distance”, which is controlled by the molar mass), standing morphologies were observed in appropriate molar ratios, while film thicknesses around and larger d bulk resulted in structures arranged parallel to the surface (Fasolka and Mayes, 2001; Krausch and Magerle, 2002). In order to alter and/or improve the morphology – also in presence of different NPs (e.g., silica, gold, silver, magnetite) – often solvent vapour annealing (SVA) was applied (Jehnichen et al , 2010; Horechyy et al , 2014).…”