Paper Number
SM31 

Session
Polymers Solutions, Melts, and Blends

Title
Rheological investigation of magnetically induced disorder/order transition in block copolymer micelles

Presentation Date and Time
October 13, 2021 (Wednesday) 10:40

Track / Room
Track 1 / Ballroom 5

Authors (Click on name to view author profile)

  1. Kresge, Grace V. (University of Minnesota Twin Cities, Chemical Engineering and Materials Science)
  2. Suresh, Karthika (University of Illinois Chicago)
  3. Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)

Author and Affiliation Lines (in printed abstract book)
Grace V. Kresge1, Karthika Suresh2 and Michelle A. Calabrese1
1Chemical Engineering and Materials Science, University of Minnesota Twin Cities, Minneapolis, MN 55455; 2University of Illinois Chicago, Chicago, IL 60607

Speaker / Presenter 
Kresge, Grace V.

Keywords
colloids; micelles; polymer solutions

Text of Abstract
Block copolymers (BCPs) have garnered sustained academic and industrial interest due to unparalleled tunability in material properties and widespread applications. Yet, a central obstacle in the application of these materials is controlling self-assembly over long length scales. Directed assembly via magnetic fields is a promising method for improved block copolymer processing but this method has traditionally relied on using large applied fields (> 6 T) or BCPs with anisotropic constituents such as crystalline blocks. We recently discovered anomalous field-induced phase transitions in industrially-relevant amphiphilic block copolymer micelle solutions (20-30 wt%) using weak magnetic fields (B = 0.5 T), which can be used to control their self-assembly and long-range ordering. These solutions exhibit an anomalous transition from a low viscosity fluid (10-2 Pa·s) to an ordered soft solid (105 Pa·s) under weak magnetic fields after a critical induction time. Magnetorheological characterization reveals that the critical induction time is independent of frequency and strain amplitude; however, the maximum achievable induced modulus decreases with increasing strain, suggesting that shear acts antagonistically to the field. Magnetic field intensity, magnetization time, temperature, and solvent highly influence the system kinetics, phases formed, and propensity for relaxation. While BCPs magnetized for short times typically exhibit rapid relaxation upon field cessation, BCPs magnetized for long times or at higher temperatures exhibit little relaxation. These induced structures require substantial cooling or high shear rates to destroy the induced structure which is otherwise stable for hours or days, after which the starting material is fully recovered. These unique magneto-rheological studies reveal new processing methods for tuning ordered BCP micelle phases induced via weak magnetic fields.