Paper Number
AT5 

Session
Advanced Techniques and Methods

Title
Polymer chain stretching during uniaxial deformation: An in-situ, time-resolved SANS study in polymer melts

Presentation Date and Time
February 15, 2017 (Wednesday) 3:35

Track / Room
Track 4 / Sandhill Crane

Authors (Click on name to view author profile)

1. López-Barrón, Carlos R. (ExxonMobil Chemical Company)
2. Richards, Jeffrey J. (NIST Center for Neutron Research)
3. Zeng, Yiming (University of Minnesota, Chemical Engineering and Materials Science)

Author and Affiliation Lines (in printed abstract book)
Carlos R. López-Barrón¹, Jeffrey J. Richards², and Yiming Zeng^3
1ExxonMobil Chemical Company, Houston, TX; ²NIST Center for Neutron Research, Gaithersburg, MD; ³Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN

Speaker / Presenter 
López-Barrón, Carlos R.

Text of Abstract
Understanding the interrelation between stress response and microstructural evolution in polymers during deformation is key for engineering premium products from a bottom-up approach. We use a suite of in-situ probes to investigate different aspects of structure development during uniaxial deformation in semicrystalline polymers and polymer melts. In particular, small-angle neutron scattering (SANS) is a very powerful tool, as it provides information about single chain conformation as well as orientation and alignment induced by external fields such as shear flow or elongation. In this talk, I will present an example of the use of in-situ time-resolved SANS measurements during uniaxial deformation of polymer melts subjected to startup and cessation of uniaxial extensional flow. The fast relaxation of the melts constitutes a challenge for time-resolved SANS measurements. I will discuss the approach we use to overcome such challenges, which include the use of state-of-the-art protocols for stroboscopic SANS data collection in combination with modified commercial rheometers. Our measurements allow us to correlate chain alignment and extensional rheology of a series of bimodal polystyrene blends, which led to the development of a stress-SANS rule in extension. The stress-SANS rule, an analogous to the stress-optical rule, is obeyed at the early stages of stress growth (during flow startup) and at the late stages of stress relaxation (after cessation of flow). The implications of our analysis and the limitations of our method will be discussed in this talk.