On the scaling law of the evolution of lap-shear strength with healing temperature at amorphous polymer−polymer interfaces and surface glass transition

The evolution of lap-shear strength (σ) with healing temperature T _h at symmetric and asymmetric amorphous polymer−polymer interfaces formed of the samples with vitrified bulk has been investigated. It has been found that the square root of the lap-shear strength behaves with respect to healing temperature as σ ^1/2 ~ T _h both at symmetric and asymmetric interfaces. Basing on this scaling law between σ and T _h, the values of the surface glass transition temperature \( \left( {T_{\rm{g}}^{\rm{surface}}} \right) \) have been estimated for a number of amorphous polymers by the extrapolation of the experimental curves σ ^1/2 ~ T _h for symmetric polymer−polymer interfaces and, in some cases, for asymmetric, both compatible and incompatible, polymer−polymer interfaces, to zero strength. A significant reduction in surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}} \) with respect to the glass transition temperature of the polymer bulk \( \left( {T_{\rm{g}}^{\rm{bulk}}} \right) \), reported earlier, has been confirmed by the use of the new proposed approach. The quasi-equilibrium surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}} \) of amorphous polystyrene (PS) has been predicted in the framework of an Arrhenius approach using the plot “logarithm of healing time − reciprocal surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}}\prime \prime \) and the activation energy of the surface alpha-relaxation of PS has been calculated.