Investigating polymer infiltration kinetics in nanoporous metal scaffolds using UV-vis spectroscopy

This work demonstrates that the optical response of nanoporous gold (NPG) is directly related to the infiltration extent (IE) of the polymer. Infiltration of poly(2-vinylpyridine) (P2VP) into NPG with a pore radius (<i>R</i>_p) of 34 nm was investigated at 140 °C. The UV-vis spectra of the NPG display plasmon absorption peaks due to the Au ligaments that depend on the height of the P2VP infiltration front in the NPG film. During infiltration, the absorption peak position shifts to longer wavelengths, while the peak height, width, and area increase monotonically with time. For P2VP with molecular weights (<i>M</i>_w) from 85 kDa to 940 kDa, the time to reach 80% of the IE (<i>τ</i>_80%) scales as <i>M</i>1.35w, in good agreement with <i>in situ</i> spectroscopic ellipsometer results. AFM and XPS support the strong attraction of P2VP for the Au surface and pores as demonstrated by wetting of P2VP over surface ligaments and a shift of the 4f orbital from the N on P2VP to higher binding energy, respectively. Using nanorods configured as a "T" to model ligament geometry, discrete dipole approximation (DDA) simulations capture the optical properties of the P2VP/NPG nanocomposite during infiltration and confirm experimental results. The evolution of the P2VP/NPG optical properties is attributed mainly to an increase in the effective refractive index within the pores. This study presents UV-vis spectroscopy as an alternative method for studying polymer infiltration into nanoporous metal scaffold films.