Extensional Viscosity of Immiscible Polymer Multi-Nanolayer Films: Signature of the Interphase

Abstract

The measurement of interfacial mechanical or rheological properties in polymer blends is a challenging task, as well as providing a quantitative link between these properties and the interfacial nanostructure. Here, we perform a systematic study of the extensional rheology of multilayer films of an immiscible polymer pair, polystyrene and poly(methyl methacrylate). We take advantage of multi-nanolayer coextrusion to increase the number of interfaces up to thousands, consequently magnifying the interfacial response of the films. The transient elongational response is compared to an additivity rule model based on the summation of the contribution of each polymer as well as the interfacial one. At low strain rates, the model reproduces the transient extensional viscosity up to strainthinning, while at larger strain rates, the extra stress exceeds the prediction based on constant interfacial tension. This extra contribution is attributed to an interphase modulus on the order of 1−10 MPa, which increases with the strain rate following a power law with an exponent of 1/3. The extensional rheology of multinanolayer films is then an efficient combination to go beyond interfacial tension and quantitatively measure the interfacial rheology of immiscible polymer blends.

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

“…The interdiffusion of miscible polymers has been characterized by dynamic shear measurements [ 27 ], and elongation measurements have been used to measure interfacial tension [ 28 ]. Furthermore, an increased transient elongational viscosity and strain hardening are observed in multilayer film even when the constituent polymers exhibited no strain-hardening behavior, indicating extra stress contribution of the interphase [ 29 , 30 , 31 ]. The Mooney method that was originally developed to characterize the wall slip under steady flow was applied to the interfacial slip [ 32 ].…”