Dual Polarization Interferometric Analysis on the Interaction between Fullerene Grafted Polymer and Nonionic Surfactants

Abstract

The interaction between polyelectrolyte grafted fullerenes and surfactants was elucidated using a dual polarization interferometer (DPI). The deposition of poly(2-(dimethylamino)ethyl methacrylate) (PDMA(50)-b-C(60)) at pH 6 on the surface of silicon oxynitride induced by electrostatic interaction between charged PDMA segments and negatively charged surface revealed an adsorption thickness similar to the diameter of a fullerene molecule. A second deposition of poly(acrylic acid)-block-C(60) (PAA(83)-b-C(60)) on adsorbed PDMA(50)-b-C(60) at pH 6 was facilitated by electrostatic interaction between negatively and positively charged PAA and PDMA segments, respectively. A monolayer of PAA(83)-b-C(60) adsorbed on PDMA(50)-b-C(60) layer yielded a thickness twice the diameter of C(60) molecules. As a comparison, a two end-capped C(60)-PAA(83)-C(60) was examined, where the packing thickness and mass were smaller than the monocapped system due to steric hindrance effect of fullerene molecules. The adsorption of two nonionic surfactants (i.e., polyoxyethylene 9 lauryl ether (Brij 76) and octyl phenol ethoxylate (Triton X-100 or TX100)) on the adsorbed PDMA-C(60) layer was examined. Both Brij 76 and TX100 interacted with the PDMA-C(60) layer. For TX100, the interaction was promoted by pi-pi interaction between the C(60) headgroup and phenyl ring of the surfactant. Beyond the critical micellar concentration of TX100, the adsorption was greatly reduced. The concentration effect of first layer PDMA-C(60) was evaluated, where the PDMA-C(60) molecules adsorbed on the chip at higher density, resulting in a larger layer thickness. The densely packed fullerene headgroup hindered the penetration of TX100 aromatic ring into the first layer.