The healing process at polymer–polymer interfaces

When two pieces of the same amorphous polymer are brought into contact at a temperature above the glass transition, the junction surface gradually heals until, at very long contact times, it is indistinguishable from bulk polymer. We have developed an analysis of this welding process based on the reptation picture of polymer dynamics due to de Gennes. The theory predicts the number of bridges (pieces of polymer chain) per unit area spanning the original junction surface as a function of time. At fixed time the number of bridges (σ) also depends on the molecular weight (M) of the chains. If the initial contact is between surfaces which have been equilibrated against a gas phase, we find that σ∼t1/2M−3/2. Alternatively, if the contacting surfaces contain many chain ends, such as may be found at brittle fracture surfaces in glassy polymers, we find that σ∼t1/4M−1/4 at short times. The theory may be compared to available measurements on strength development in healing interfaces leading to the conclusion that the model reproduces several aspects of the observed phenomenon.