Chain dimension of polyampholytes in solution and immobilized brush states

The dimensions and intermolecular interactions of surface-grafted and unbound, free polyampholytes, poly[3-(N-2methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate] (PMAPS) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estimated in an aqueous NaCl solution over a wide range of salt concentrations (Cs). The free PMAPS and PMPC fractionated by a recycling preparative size-exclusion chromatography system were characterized in aqueous NaCl solutions for Cs over a range from 0 to 5.0 M by static light scattering and dynamic light scattering (DLS) measurements. The hydrodynamic radius (RH) and the concentration coefficient of the diffusion coefficient (kD) for PMPC were independent of Cs, whereas those for PMAPS were strongly dependent on Cs. Monodisperse silica nanoparticles immobilized with PMAPS (SiNP-PMAPS) and PMPC (SiNP-PMPC) by surface-initiated atom transfer radical polymerization were characterized in aqueous NaCl solutions for Cs over a range from 0 to 5.0 M by DLS and synchrotron radiation small-angle X-ray scattering (SAXS) measurements. The SAXS profiles from SiNP-PMAPS and SiNP-PMPC solutions were well described by the core-shell model, taking into account interacting self-avoiding chains and assuming a Schulz-distributed core with two fitting parameters. Polymer Journal (2012) 44, 121–130; doi:10.1038/pj.2011.116; published online 16 November 2011