Structural insights into nanofibers formed by templated polymerization-induced self-assembly through combined SANS and AFM characterizations

Abstract

This study combines Small-Angle Neutron Scattering (SANS) and Atomic Force Microscopy (AFM) to elucidate the formation and structural characteristics of poly(N,N-dimethyl acrylamide)-block-poly(2-methoxyethyl acrylate) (PDMAc-b-PMEA) block copolymer nanofibers prepared in water by the recently developed “Templated Polymerization-Induced Self-Assembly (PISA)” approach. The key feature of this technology is the use of a water-soluble macromolecular RAFT agent functionalized by a bisurea sticker (PDMAc-U₂). During the generation of the PMEA block, through reversible addition-fragmentation chain transfer (RAFT) radical dispersion polymerization, the bisurea sticker is believed to promote the 1D assembly of the block copolymers via directional H-bonding into colloidal nanofibers. In this work, Small Angle Neutron Scattering (SANS) experiments show that anisotropic objects already form at the very early stages of polymerization, then, in the course of polymerization, their diameter increases concomitantly with the increase of the PMEA chain length. Furthermore, the SANS data reveal that the nanofibers are organized in a PMEA-core/ PDMAc-shell, which was previously hypothesized but not demonstrated. Atom Force Microscopy (AFM) supported these findings through local differences in mechanical properties and detailed visualization of the nanofibers’ internal structure. The combination of SANS and AFM results allowed us to corroborate the formation and internal structure of anisotropic particle obtained by the templated PISA approach. We believe that these nanostructured materials dispersed in aqueous solutions have potential for biomedical applications, while nanopatterning applications can be envisioned after deposition on surfaces.