Effectsof Sodium Dodecyl Sulfate on Structures of Poly(N-isopropylacrylamide) at the Particle Surface.

Theeffect of sodium dodecyl sulfate (SDS) on the poly(N-isopropylacrylamide) (PNIPAM) tethered to nanoparticles was experimentallyinvestigated using dynamic light scattering below the lower criticalsolution temperature. A mean-field analytical model was used to calculatethe parameters of interfacial PNIPAM–SDS complexes. Particularly,the magnitude of SDS adsorption energy obtained decreases with decreasingexcluded volume parameter, implying that the partially collapsed PNIPAMbrush virtually favors the adsorption of SDS onto the PNIPAM chains.A self-consistent field theory (SCFT) model was used to get a detailedquantitative description of monomer density distribution. By loweringthe solvent quality, a number of phenomena related to the noncontinuityof monomer density are revealed. These phenomena are either referredto as the vertical phase separation or as its precursor, which canbe delayed and eventually eliminated as the SDS coverage is increased.The distribution of free chain ends was calculated using the SCFTmodel. Increasing the SDS coverage gives rise to a broader and moreasymmetric distribution of free chain ends, accompanied by a considerableexpansion of the dead zone (below which the free chain ends do notexist), but lowering the solvent quality has opposite influences.The relative thickness of the dead zone can be scaled to a mastercurve, regardless of SDS coverage. [ABSTRACT FROM AUTHOR]