Sum frequency generation study on the structure of water in the vicinity of an amphoteric polymer brush

A polyampholyte brush was prepared on the surface of a quartz prism by surface-initiated reversible addition-fragmentation chain-transfer polymerization of methacrylic acid (MA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) at a monomer ratio of 1:1. The sum frequency generation method indicated that water molecules at the amphoteric polymer brush–water interfaces were not greatly oriented in comparison with those at the surfaces of bare quartz prisms, and negatively charged PolyMA and positively charged PolyDMAEMA brushes. The small perturbation effect of an amphoteric polymer brush on the structure of vicinal water was in accordance with the tendency of aqueous solution and thin films of amphoteric polymers observed by using Raman and infrared spectroscopies, respectively.

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► Amphoteric polymer brush composed of anionic and cationic monomer residues (1:1).
► Sum frequency generation analysis of water in the vicinity of the brush.
► Weak orientation of water molecules in the vicinity of the amphoteric polymer brush.
► Great orientation of water molecules in the vicinity of uniformly charged brush.
► Importance of small perturbation of interfacial water to afford biocompatibility.