Polydopamine-Mediated Grafting of Cationic Polymer Brushes for Adsorption of Fluorinated Compounds

Understanding the adsorption behavior of charged molecular species at functionalized polymer interfaces is critical for advancing surface science and material design. Building upon recent advances in polydopamine (PDA)-mediated polymer grafting, we investigated electrostatic adsorption at cationic polymer brush surfaces. Using a grafting-to approach, we covalently attached poly(2-trimethylammonioethyl methacrylate chloride) (PTMAEMA) to PDA-coated stonewool fibers and characterized the resulting charged interface via x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). We employed perfluorooctanoic acid (PFOA) as a model anionic adsorbate to investigate binding at a quaternary amine-functionalized surface. Batch equilibrium sorption studies revealed concentration-dependent adsorption kinetics, achieving three times higher binding affinity for PTMAEMA-functionalized fibers at concentrations ranging from 0.5 to 5.0 g L^{- 1}, with equilibrium reached within 10 min. XPS analysis confirmed the successful surface functionalization with distinct nitrogen environments at 395.5 eV (PDA) and 398.5 eV (quaternary nitrogen), while thermogravimetric data indicated an organic loading of close to 28%. Our findings demonstrate that PDA-mediated polymer grafting provides a versatile platform for creating well-defined charged interfaces with tunable adsorption characteristics, and provides a methodology to explore fundamental adsorption phenomena at polymer-liquid interfaces.