Thermal-Regulated Adhesion Enhancement and Fast Switching within the Viscoelastic Glass Transition Zone of a Shape...

The effects of temperature and preload on adhesion of an epoxy-based shape memory polymer (ESMP) were investigated experimentally. The ESMP sheet and polydimethylsiloxane (PDMS) control sample were prepared by mold casting. The adhesion measurements were carried out on a home-built adhesion tester using a hemispherical glass indenter as the counter-surface. The reduced modulus was determined by the Oliver-Pharr method and Hertz theory. The viscoelastic energy dissipation was extracted, and the effective work of adhesion was calculated by the fitting method and JKR theory. In the vicinity of glass transition temperature (T_g), the viscoelastic enhancement factor (1 + f(v, T)) is as high as 955 because of the strong viscoelastic effect of the ESMP sheet. The adhesion strength of the ESMP sheet is about 589 kPa under a relatively smaller contact displacement condition (∼44.6 μm). The strong viscoelastic effect induces more viscoelastic energy dissipation that contributes to the effective work of adhesion and leads to strong preload dependence of the adhesion. The pull-off force F_pull-off is demonstrated to linearly depend on F^1/3E^2/3. In the sharp half glass transition zone (T > T_g), the viscoelasticity and rigidity rapidly decrease with the temperature increasing about 10 °C, leading to a 6-fold reduction in adhesion. The results indicate that the adhesion of the ESMP sheet can be significantly enhanced and meanwhile rapidly switched within the viscoelastic glass transition zone.