Role of hydrophilic support on the physical aging and stress development in thin polynorbornene films

Thin film properties can be impacted by their local environment, especially when in contact with other polymers. Here physical aging of poly(butylnorbornene-ran-hydroxyhexafluoroisopropyl norbornene), BuNB-r-HFANB, thin films coated on ultra-thin (2nm) layers of poly(acrylic acid), PAA, or poly(styrene sulfonate), PSS, is examined along with residual stress evolution in BuNB-r-HFANB during aging. Decreasing BuNB-r-HFANB film thickness tends to decrease the physical aging rate(β), but this quantitatively is altered by PSS or PAA. Even for thick films (>500nm), aging rate at 100^○C is accelerated on PAA compared to silicon, while thickness dependence of BuNB-r-HFANB aging is enhanced (compared to silicon) when in contact with PSS with apparent aging rate decreasing by a factor of 2 as film thickness decreases from 1000 nm to 250 nm. Removal of BuNB-r-HFANB from substrate enables mechanical properties (elastic modulus and residual stress, σ_R) to be resolved via wrinkling. Elastic modulus is effectively invariant of substrate (polymer layer), while there is a small effect of physical aging on the modulus. The stress in the films is compressive and evolves non-monotonically during aging. β can be mostly collapsed when scaled as hσ_R^-1/3.