Paper Number
SM32 

Session
Polymers Solutions, Melts, and Blends

Title
Magneto-rheology and field-dependent phase separation of aqueous solutions of nanorods and thermo-responsive polymers

Presentation Date and Time
October 13, 2021 (Wednesday) 11:05

Track / Room
Track 1 / Ballroom 5

Authors (Click on name to view author profile)

  1. Neal, Christopher A. (University of Minnesota, Chemical Engineering and Materials Science)
  2. Quan, Michelle C. (University of Minnesota, Chemical Engineering and Materials Science)
  3. Leon, Valeria (University of Texas, Rio Grande Valley, Mechanical Engineering Department)
  4. Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)

Author and Affiliation Lines (in printed abstract book)
Christopher A. Neal1, Michelle C. Quan1, Valeria Leon2 and Michelle A. Calabrese1
1Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455-0331; 2Mechanical Engineering Department, University of Texas, Rio Grande Valley, Edinburg, TX 78539

Speaker / Presenter 
Neal, Christopher A.

Keywords
composites; polymer solutions; suspensions

Text of Abstract
Polymer-particle suspensions composed of anisotropic constituents have great promise for next-generation smart materials requiring fine structural control. Previous work in elastomers has shown that nanoparticles can be introduced into polymers and precisely directed by external forces such as shear and magnetic fields, though work on the mixture of two or more fields is noticeably lacking. Efforts on the magnetic-field directed assembly of polymer solutions has focused on systems that align and/or crystallize under applied magnetic fields. However, Vshikov recently observed that magnetic fields can also decrease solvent quality in semi-crystalline polymer solutions, motivating the present study. The role of magnetic fields on solvent quality and phase transitions in thermo-responsive polymers—which form amorphous phases upon separation from solvent above a certain lower-critical solution temperature (LCST)—has yet to be explored. Here, we investigate the role of magnetic fields on the rheological behavior and phase separation of aqueous poly(N-isopropyl acrylamide), and the impact of silica nanorod addition on altering these properties. Signatures of the LCST transition are examined two-fold: optical signatures are characterized using an in-house turbidity tester with static magnetic field capabilities and rheological signatures are measured via a magneto-rheological device. When silica nanorods are incorporated at low concentrations, the LCST of aqueous poly(acrylamides) shifts towards higher temperatures; the magnitude of this shift upon nanorod addition is dependent on aspect ratio. Both magnetic field application and silica nanoparticle addition complexly impact phase transitions in these polymer solutions, often opposing one another. Interestingly, changes in LCST behavior are most pronounced in thin samples, suggesting that interfacial effects may influence this behavior. This unique field-induced behavior can be exploited to achieve increasingly complex stimuli-responsive polymeric materials.