TY - JOUR
T1 - "rubbery Stiffening" and Rupture Behavior of Freely Standing Nanometric Thin PIB Films
AU - Yoon, Heedong
AU - McKenna, Gregory B.
N1 - Funding Information:
The authors gratefully acknowledge the National Science Foundation Grant DMR-1610495 and the John R. Bradford Endowment at Texas Tech, each for partial support of this work. The Office of Naval Research through the DURIP program Grant No. N00014-12-1-0876 is also thanked for instrumental support.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/12/26
Y1 - 2017/12/26
N2 - Prior bubble inflation studies have shown strong evidence of rubbery-like stiffening behaviors for several organic and inorganic thin films. The possible origin is still unclear, but recently Ngai et al. [ J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3), 214-224 ] and Li and McKenna [ Macromolecules 2015, 48 (17), 6329-6336 ] proposed that the separation of molecular motions and dynamic fragility are closely related to the observed rubber-like stiffening behavior. In the present work, we report observations from bubble inflation measurements on nanometric thin polyisobutylene (PIB) films that test the correlations suggested by the Ngai coupling model (stiffening is related to the shape parameter describing the α-relaxation) and Li and McKenna (the rubbery stiffening correlates with the dynamic fragility). Mechanical properties and surface tension of nanometric thin PIB films were investigated through strain-stress measurements for film thicknesses ranging from 13 to 126 nm. The tests were performed at room temperature far above the glass transition temperature of PIB. In addition to stiffness and surface tension, rupture strengths were also measured. We find that the stiffness increases with decreasing film thickness and that the surface tension remains constant, independent of the film thickness. The rupture stress is found to increase with decreasing film thickness, whereas the rupture strain decreases with decreasing film thickness. Similar to the prior bubble inflation measurements in polymeric thin films, the thickness dependence of the stiffening followed a power law behavior with film thickness. The observed stiffening behavior agrees with the suggestion from Ngai et al. that the rubbery stiffening should correlate with the separation of the α- and Rouse-mode relaxations. However, unlike prior results for ultrathin polymer films, the stiffening behavior of PIB did not follow the linear relationship with dynamic fragility that was proposed by Li and McKenna.
AB - Prior bubble inflation studies have shown strong evidence of rubbery-like stiffening behaviors for several organic and inorganic thin films. The possible origin is still unclear, but recently Ngai et al. [ J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3), 214-224 ] and Li and McKenna [ Macromolecules 2015, 48 (17), 6329-6336 ] proposed that the separation of molecular motions and dynamic fragility are closely related to the observed rubber-like stiffening behavior. In the present work, we report observations from bubble inflation measurements on nanometric thin polyisobutylene (PIB) films that test the correlations suggested by the Ngai coupling model (stiffening is related to the shape parameter describing the α-relaxation) and Li and McKenna (the rubbery stiffening correlates with the dynamic fragility). Mechanical properties and surface tension of nanometric thin PIB films were investigated through strain-stress measurements for film thicknesses ranging from 13 to 126 nm. The tests were performed at room temperature far above the glass transition temperature of PIB. In addition to stiffness and surface tension, rupture strengths were also measured. We find that the stiffness increases with decreasing film thickness and that the surface tension remains constant, independent of the film thickness. The rupture stress is found to increase with decreasing film thickness, whereas the rupture strain decreases with decreasing film thickness. Similar to the prior bubble inflation measurements in polymeric thin films, the thickness dependence of the stiffening followed a power law behavior with film thickness. The observed stiffening behavior agrees with the suggestion from Ngai et al. that the rubbery stiffening should correlate with the separation of the α- and Rouse-mode relaxations. However, unlike prior results for ultrathin polymer films, the stiffening behavior of PIB did not follow the linear relationship with dynamic fragility that was proposed by Li and McKenna.
UR - http://www.scopus.com/inward/record.url?scp=85040012667&partnerID=8YFLogxK
U2 - 10.1021/acs.macromol.7b02009
DO - 10.1021/acs.macromol.7b02009
M3 - Article
AN - SCOPUS:85040012667
VL - 50
SP - 9821
EP - 9830
JO - Macromolecules
JF - Macromolecules
SN - 0024-9297
IS - 24
ER -