Paper Number
FE17
Session
Foams, Emulsions, Surfactants, and Micelles
Title
Magneto-rheology and field-induced ordering in polymer solutions via a mechanism alternate to phase alignment
Presentation Date and Time
October 12, 2021 (Tuesday) 10:40
Track / Room
Track 3 / Meeting Room A-B
Authors
- Suresh, Karthika (University of Illinois Chicago)
- Kresge, Grace V. (University of Minnesota Twin Cities, Chemical Engineering and Materials Science)
- Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)
Author and Affiliation Lines
Karthika Suresh, Grace V. Kresge and Michelle A. Calabrese
Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55414
Speaker / Presenter
Calabrese, Michelle A.
Keywords
micelles; polymer solutions; rheology methods
Text of Abstract
While block copolymers (BCPs) are promising materials due to their tunable structure and functionality, practical methods for processing BCPs with controlled grain size and orientation remain challenging. We recently discovered anomalous rheology and assembly behavior in homopolymer, diblock BCP, and triblock BCP solutions exposed to low intensity (B <0.5 T) magnetic fields, which undergo a disorder-to-order transition after a critical induction time. Prior to magnetization, these solutions are composed of coiled polymers or spherical micelles with no inherent structural anisotropy; we thus attribute this field-induced ordering to a mechanism other than phase alignment, as is traditionally observed in magnetized BCPs. Using magneto-rheology, a three-to-six order of magnitude increase in the suspension modulus is observed upon field application, where the induction time is inversely related to amphiphile molecular weight. Small angle x-ray scattering (SAXS) measurements following magnetization indicate that the observed field-induced phase formation depends on polymer characteristics. Homopolymer solutions like polyethylene oxide and polypropylene oxide exhibit field-induced crystallization, but require long magnetization times (~18 h). Conversely, both diblock and triblock BCPs order rapidly, forming ordered phases including hexagonally-packed cylinders and cubic packings. Unlike in homopolymers, BCPs do not exhibit any signatures of field-induced crystallization. Followup studies using Fourier transform infrared spectroscopy (FTIR) suggest that instead of inducing phase alignment, low intensity magnetic fields alter polymer-solvent interactions in these systems to facilitate structural transitions. Understanding these directed-assembly mechanisms is of significant scientific interest for its potential to enhance assembly with minimal input from external fields, and the potential to discover new structures not accessible through traditional self-assembly routes.