Paper Number
SF5 

Session
Surfactants, Foams, and Emulsions

Title
Rheological behavior of amphiphilic block copolymers in oil water mixtures

Presentation Date and Time
October 21, 2019 (Monday) 11:30

Track / Room
Track 5 / Room 306A

Authors (Click on name to view author profile)

1. Qavi, Sahar (New Mexico State University, Department of Chemical and Materials Engineering)
2. Foudazi, Reza (New Mexico State University, Department of Chemical and Materials Engineering)

Author and Affiliation Lines (in printed abstract book)
Sahar Qavi and Reza Foudazi
Department of Chemical and Materials Engineering, New Mexico State University, Las Cruces, NM 88003

Speaker / Presenter 
Qavi, Sahar

Text of Abstract
Self-assembly of block copolymers in the presence of solvents forms ordered mesophase structures, also known as lyotropic liquid crystals (LLCs). Rheological properties of Plurnic block copolymer/water/oil mesophases with lamellar and hexagonal structures are studied. Flow behavior of lamellar and hexagonal mesophases indicates that they have yield stress and the shear banding is possibly present due to the presence of plateau stress in the flow curve of these systems, originated from shear-induced alignment/transition. Applying high strains on these LLCs, induces two relaxation times after cessation of flow, decreases the storage modulus in the whole frequency regime, and decreases the loss modulus in small frequencies with negligible effect at high frequencies. We suggest that at relatively low frequencies, grain boundaries and defects control the rheological behavior of LLCs, while at high frequencies micelles are playing a more important role in the observed rheological behavior. The decrease in moduli is reversible and the system relaxes back to its original elastic modulus at rest. The observed behavior can be attributed to the mesophase alignment, defect formation and/or alignment of defects. Oscillatory experiments show that mesophases have solid-like behavior and exhibit type III non-linear behavior. Mesophases elastic modulus is fitted with a model developed previously by the authors.