Dynamic Shear Responses of Polymer-polymer Interfaces

Abstract

In multi-component soft matter, interface properties often play a key role in determining the properties of the overall system. The identification of the internal dynamic structures in non-equilibrium situations requires the interface rheology to be characterized. We have developed a method to quantify the rheological contribution of soft interfaces and evaluate the dynamic modulus of the interface. This method reveals that the dynamic shear responses of interfaces in bilayer systems comprising polypropylene and three different polyethylenes can be classified as having hardening and softening effects on the overall system: a interface between linear long polymers becomes more elastic than the component polymers, while large polydispersity or long-chain-branching of one component make the interface more viscous. We find that the chain lengths and architectures of the component polymers, rather than equilibrium immiscibility, play an essential role in determining the interface rheological properties.

Non-Stick Length of Polymer–Polymer Interfaces under Small-Amplitude Oscillatory Shear Measurement

“…In a previous work [ 22 ], we discussed how to determine the dynamic shear modulus of an interfacial layer from the dynamic shear response of the bilayer of two different polymers. The rheological interfacial layer is defined as the region around the interface where the response to the shear deformation is different from that of neighboring bulk layers ( Figure 2 ).…”

“…The rheology of stacked multilayer polymer melts has been used to study the influence of polymer–polymer interfaces. Steady shear flow and dynamic shear measurements parallel to the interface have been used to characterize the interfacial slip [ 17 , 18 , 19 , 20 , 21 , 22 ]. In contrast to the immiscible interface, the shear response of the multilayer film with compatibilized interfaces indicates solid-like behavior of the interphase [ 23 , 24 ].…”

“…The apparent slip or possibly more complex excess response of the interface is supposed to originate from the existence of a finite-volume interphase that is mechanically different from the bulk materials. In the previous work [ 22 ], the dynamic shear modulus of the interphase was estimated by explicitly assuming the thickness of the interphase predicted by the Flory–Huggins theory [ 41 , 42 , 43 ], which is at most several nanometers. However, it is not trivial whether it is appropriate to assume that the thickness of the interphase, whose non-equilibrium response is different from the bulk layers, is equal to the equilibrium thickness.…”