Paper Number
VP79 

Session
Pre-recorded Flash Presentations (virtual)

Title
Nonlinear shear rheometry of unentangled polymers

Presentation Date and Time
All Week (Asynchronous) Any Time

Track / Room
Pre-recorded Presentation / Virtual

Authors (Click on name to view author profile)

1. Costanzo, Salvatore (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)
2. Peponaki, Katerina (FORTH, IESL)
3. Alexandris, Stelios (FORTH, IESL)
4. Parisi, Daniele (FORTH, IESL)
5. Grizzuti, Nino (University of Naples Federico II, Chemical, Materials and Industrial Production Engineering)
6. Vlassopoulos, Dimitris (IESL-FORTH and University of Crete)

Author and Affiliation Lines (in printed abstract book)
Salvatore Costanzo¹, Katerina Peponaki², Stelios Alexandris², Daniele Parisi², Nino Grizzuti¹ and Dimitris Vlassopoulos^2
1Chemical, Materials and Industrial Production Engineering, University of Naples Federico II, Naples 80125, Italy; ²IESL-FORTH and University of Crete, Heraklion 71110, Greece

Speaker / Presenter 
Costanzo, Salvatore

Keywords
experimental methods; polymer melts; polymer solutions

Text of Abstract
Decoding the dynamics of polymers in fast flows is a relevant challenge. On the experimental side, fast flows are prone to flow instabilities and require suitable setups to collect reliable data. On the theoretical side, phenomena such as monomeric friction reduction and finite chain extensibility must be considered for understanding nonlinear dynamics. In the past years, many research efforts were devoted to exploring nonlinear dynamics of entangled systems. Elongational data at high Weissenberg number were obtained owing to experimental setups such as the filament stretching rheometer. On the other hand, the cone-partitioned plate rheometry allowed to circumvent effects of edge fracture, and to perform shear start-up experiments at high rates. At the same time, tube-based models were implemented for successfully describing the dynamics of polymer melts and concentrated solutions. Recently, unentangled polymer melts are attracting considerable interest. Unentangled systems are relatively easier to predict, as orientation and stretch occur simultaneously above the Rouse time. However, the data available are scarce because of the associated experimental challenges. For example, in shear flow, the available range of rates for nonlinear tests, comprised between the inverse of the Rouse time and the shear rate at which glassy modes come into play provoking transducer resonance, is quite narrow. Secondly, at high shear rates, instabilities such as edge fracture occur. Matsumyia et al. successfully measured the nonlinear start-up elongational rheology of unentangled melts. In this work we present careful data sets on nonlinear start-up shear experiments on unentangled polystyrene melts. The data are collected by means of cone-partitioned plate setups. The shear thinning behaviour and the validity of the Cox-Merz rule are discussed. Watanabe et al. Macromolecules 2021, 54, 3700-3715; Matsumiya et al. Macromolecules, 2018, 51, 9710-9729; Ianniruberto and Marrucci, Macromolecules, 2020, 53, 4, 1338-1345.