Diffusion at Polymer/Polymer Interfaces Probed by Rheological Tools

Diffusion at the polymer/polymer interface was probed by small-amplitude oscillatory shear measurements carried out on polystyrene (PS)/polystyrene (PS) sandwich-like assembly as a function of the time of welding in the molten state. It was found that the dynamic complex shear modulus G*(t) at a fixed frequency increases with the time of contact in two time regimes. First G*(t) increases proportionally to t1/2 and then a second regime takes place where G*(t) increases proportionally to t1/4. At longer times, G*(t) tends asymptotically toward G* of pure polystyrene. The results were interpreted in terms of reptation theory and the time of transition between the two scaling law regimes was found to be in agreement with the time needed for the transition from the Rouse mode to the reptation mode. Special attention was given to the initial state of the polymer surfaces before contact by performing experiments on (i) freshly prepared surfaces, (ii) presheared samples, (iii) fractured samples, and (iv) corona-t...