Understanding the Role of ω-End Groups and Molecular Weight in the Interaction of PNIPAM with Gold Surfaces

Modification of nanoparticle surfaces by adsorption or grafting of polymers allows fine control of hybrid materials properties for diverse applications. To obtain such a control, it is of paramount importance to understand the impact of the polymer structure on the nature and strength of its interaction with the nanoparticle. We investigated here a simple model of hybrid materials made of poly(N-isopropylacrylamide) of different molar masses and end groups interacting with gold surfaces. A series of poly(N-isopropylacrylamide) with number-average molar masses ranging from 3700 to 10000 g·mol–1 were synthesized by reversible addition–fragmentation chain transfer/macromolecular design by interchange of xanthates (RAFT/MADIX). The terminal xanthate group was then reduced into either a thiol or a hydrogen group. Quartz crystal microbalance adsorption/desorption experiments demonstrated that the polymer termini have a strong impact on the mechanism of polymer adsorption on flat gold surfaces. These differences in polymer structure have, in return, a strong influence on the colloidal stability and growth mechanism of nanoparticles when directly synthesized in polymer solution. For those properties, the effect of xanthate group compared very favorably to the conventional thiol moiety. Interestingly, the properties of nanohybrids were poorly affected by the molar mass of the polymer.