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

Click to copy article linkArticle link copied!

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 strain-thinning, 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 multi-nanolayer films is then an efficient combination to go beyond interfacial tension and quantitatively measure the interfacial rheology of immiscible polymer blends.