Paper Number
SG2 

Session
Self-assembled Systems, Gels and Liquid Crystals

Title
Processing-dependent gelation of aqueous methylcellulose

Presentation Date and Time
February 13, 2017 (Monday) 10:25

Track / Room
Track 3 / White Ibis

Authors (Click on name to view author profile)

1. Nelson, Arif Z. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)
2. Wang, Yushi (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)
3. Margotta, Anthony S. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)
4. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Arif Z. Nelson, Yushi Wang, Anthony S. Margotta, and Randy H. Ewoldt
Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Nelson, Arif Z.

Text of Abstract
We report experimental measurements of the effect of dynamic flow conditions on aqueous methylcellulose, a material that forms a brittle gel at elevated temperatures. We choose to control the applied stress—rather than the applied deformation—during gelation to systematically explore processing-to-structure-to-property relations. Flow makes gelation more difficult, i.e. increases the apparent gelation temperature, and makes the final gel weaker, i.e. decreases both the hot gel elastic modulus and apparent failure stress. In extreme cases, formation of a fully percolated network is inhibited and a soft granular yield-stress fluid is formed. A design space of material properties is generated as a function of concentration and applied stress during gelation. This reveals the possibility of catastrophic inaccuracy when not designing with processing/application conditions in mind. Additionally, our findings of a stress-dependent gel temperature raise questions for other rheological tests that measure gel temperature at finite stress, such as SAOS. Our systematic approach here should serve as a method for verifying any SAOS gelation measurements, namely, to measure gelation as a function of applied stress, and report the limit that stress goes to zero.