Fabrication of noncrosslinked poly(N-dodecyl acrylamide) monolayer-thick sheets by exfoliation using poor solvents

Abstract

Two-dimensional polymeric materials (2DPMs) have attracted increasing attention from researchers owing to their unique structural and functional properties. Most reported 2DPMs are composed of covalently crosslinked polymer networks to ensure structural integrity. Herein, we demonstrate the exfoliation of large-area noncrosslinked 2DPMs from stacked lamellar films composed of poly(N-dodecyl acrylamide) (pDDA). Generally, pDDA forms a well-oriented lamellar structure via nanophase segregation of the hydrophilic main chain and hydrophobic alkyl side chains. In this work, monolayers were exfoliated from the stacked lamellae using poor solvents. Systematic solvent-dependent exfoliation studies revealed that hexane, ethyl acetate, and 2-propanol effectively exfoliated micrometer-scale monolayer sheets, whereas the polar methanol solvent induced polymer dissolution into random coils. Atomic force microscopy and transmission electron microscopy analyses confirmed the formation of nanosheets with sizes of a few micrometers and lateral dimensions approximately equal to the monolayer thickness. Furthermore, spin-transferred 2DPMs exhibited unique dendritic or spider web-like network morphologies, which were influenced by the solvent choice and centrifugal forces. Thus, this study provides a simple and scalable approach for preparing large-area noncrosslinked 2DPMs and offers insights into controlling their morphology through solvent selection. Two-dimensional polymeric materials (2DPMs) with unique structural and functional properties are typically crosslinked for stability. Here, large-area noncrosslinked 2DPMs were exfoliated from lamellar films of poly(N-dodecyl acrylamide) (pDDA), which forms nanophase-separated lamellae via segregation of hydrophilic and hydrophobic segments. Poor-solvent exfoliation using hexane, ethyl acetate, or 2-propanol produced micrometer-scale monolayer nanosheets, whereas methanol dissolved the polymer. AFM and TEM confirmed nanosheet morphology, and spin-transferred films displayed dendritic or spiderweb-like networks dependent on solvent and centrifugal forces, offering a simple, scalable route to morphology-controlled noncrosslinked 2DPMs.