Poster: How Do Ultrathin Polymers in the Softening Regime Fail?

Molecular mobility can influence the low and high strain response of ultrathin polymer films. For glassy polymer films, the average molecular mobility contributes to the decrease in maximum stress and elastic modulus. While for polymer films in the softening regime, near or above the glass transition temperature, the confinement induced changes in mobility are associated with the opposite mechanical response, an increase in elastic modulus. Here, we directly measure the stress-strain response of freestanding poly(n-butyl methacrylate) (PBMA, MW = 180 kDa, Tg = 15ºC) as a function of temperature (T= 4 – 30 °C) and film thickness (30 – 300 nm). Below the glass transition temperature, the maximum stress and elastic modulus decrease with decreasing thickness, and as the temperature increases, we observe a transition in behavior where maximum stress and elastic modulus increase with decreasing thickness. These results provide new fundamental insight into how polymer behavior is altered due to changes in molecular mobility upon confinement.