A Total Internal Reflection Microscopy (TIRM)-Based\nApproach for Direct Characterization of Polymer Brush Conformational\nChange in Aqueous Solution

This study presents\na novel approach utilizing total internal reflection\nmicroscopy (TIRM) to effectively characterize the swelling and collapse\nof polymer brushes in aqueous solutions. Zwitterionic poly(carboxybetaine\nmethacrylate) (PCBMA) and nonionic poly[oligo(ethylene glycol) methyl\nether methacrylate] (POEGMA) brushes are chosen as model systems.\nBy investigation of an intriguing theory–experiment discrepancy\nobserved during the measurement of near-wall hindered diffusion, valuable\ninsights into the compressibility of polymer brushes are obtained,\nrevealing their conformational information in aqueous solution. The\nresults demonstrate that zwitterionic PCBMA brushes exhibit minimal\nantipolyelectrolyte effects in 0.1–10 mM NaCl solution but\nundergo significant swelling with increasing pH. On the other hand,\nnonionic POEGMA brushes exhibit similar responses to ionic strength\nas weak polyelectrolyte brushes. These unexpected findings enhance\nour understanding of polymer brushes beyond classical theories. The\nTIRM-based approach proves to be effective for characterizing polymer\nbrushes and other soft nanomaterials.