Substrate Influence on Moisture Absorption Into Thin Poly(vinyl pyrrolidone) Films
B D. Vogt, Christopher L. Soles, Hae-Jeong Lee, Eric K. Lin, Wen-Li Wu
The influence of substrate surface energy on the swelling of poly(vinyl pyrrolidone) (PVP) films was examined using x-ray reflectivity (XR) and quartz crystal microbalance (QCM) measurements. Two different silicon surface treatments were used for the PVP supporting substrate: a hydrophilic oxide (SiOx) and a hydrophobic hexamethyldisilazane (HMDS) treated surface. While the moisture absorption kinetics were unaffected by the surface treatment, the diffusivity decreased as the films became thinner than 60 nm. The reduced kinetics were attributed to a concomitant decrease in segmental mobility of the PVP as the films are increasingly confined, and a coupling of this segmental mobility to the moisture absorption kinetics. The equilibrium moisture absorption was relatively insensitive to the surface treatment in the thickest films ( 150 nm). However, strong reductions in the equilibrium uptake with decreasing PVP film thickness were observed on the HMDS surfaces, while the SiOx surface exhibited thickness independent equilibrium absorption. The decreased absorption with increasing film thinness in the former is attributed to depletion of water near the polymer/HMDS interface, arising from hydrophobic interactions between the surface and water.
interfaces, quartz crystal microbalance, reflectivity, thin films
, Soles, C.
, Lee, H.
, Lin, E.
and Wu, W.
Substrate Influence on Moisture Absorption Into Thin Poly(vinyl pyrrolidone) Films, Macromolecules
(Accessed November 28, 2023)