Paper Number
RS2 

Session
Techniques and Methods: Rheometry & Spectroscopy/Microscopy

Title
On the measurement of normal stress differences: Are we making any progress?

Presentation Date and Time
October 11, 2022 (Tuesday) 10:10

Track / Room
Track 6 / Mayfair

Authors (Click on name to view author profile)

1. Thanasis, Athanasiou (FORTH and University of Crete)
2. Vlassopoulos, Dimitris (FORTH and University of Crete)

Author and Affiliation Lines (in printed abstract book)
Athanasiou Thanasis and Dimitris Vlassopoulos
FORTH and University of Crete, Heraklion, Greece

Speaker / Presenter 
Vlassopoulos, Dimitris

Keywords
experimental methods; polymer melts; polymer solutions; rheometry techniques

Text of Abstract
It is known that the measurements of viscometric material functions in viscoelastic materials such as polymer melts and solutions is technically demanding due to the intervention of various instabilities. Over the years, several advances have been made and the level of our understanding is increased. However, several formidable challenges remain. In this talk we summarize the current state-of-the-art and the use of the cone-partitioned plate (CPP) fixture, and present our latest efforts in the direction of measuring N1 and N2. The measurement of N2 is particularly challenging due to its small values and high sensitivity to the radius of the measured specimen, and two CPP-based approaches rely on measuring two loadings or using two partitions, the so-called CPP3 geometry. Earlier attempts were promising but measurements were too involved and with limited temperature control. Our current efforts are focused on a new method to measure the normal forces with CPP3. In this design, a piezoelectric sensor is coaxially mounted on the inner partition and the entire tool mounted onto the rheometer’s temperature control oven. The stiffness of the piezoelectric sensor rules out any force-rebalance complexities while its fast response provides reliable data in the transient regime. We discuss the design and implementation of this simple, robust tool and present encouraging data with entangled polymer solutions and melts, which are compared against literature and available predictions.