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-2-methacryloyloxyethyl-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 (C-s). The free PMAPS and PMPC fractionated by a recycling preparative size-exclusion chromatography system were characterized in aqueous NaCl solutions for C-s over a range from 0 to 5.0 M by static light scattering and dynamic light scattering (DLS) measurements. The hydrodynamic radius (R-H) and the concentration coefficient of the diffusion coefficient (k(D)) for PMPC were independent of C-s, whereas those for PMAPS were strongly dependent on C-s. 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 C-s 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