Paper Number
SC38 

Session
Suspensions and Colloids

Title
Magneto-rheology of thermo-responsive polymer and anisotropic nanoparticle suspensions

Presentation Date and Time
October 12, 2022 (Wednesday) 10:10

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

  1. Neal, Christopher A. (University of Minnesota, Twin Cities, Chemical Engineering and Materials Science)
  2. Quan, Michelle C. (University of Minnesota, Twin Cities, Chemical Engineering and Materials Science)
  3. León, Valeria (University of Texas, Rio Grande Valley, Department of Chemical Engineering)
  4. Chibambo, Nondumiso (University of Minnesota, Twin Cities, Chemical Engineering and Materials Science)
  5. 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 León2, Nondumiso Chibambo1 and Michelle A. Calabrese1
1Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455; 2Department of Chemical Engineering, University of Texas, Rio Grande Valley, Edinburg, TX 78539

Speaker / Presenter 
Neal, Christopher A.

Keywords
colloids; composite rheology; directed systems; gels; polymer solutions; spectroscopy; suspensions

Text of Abstract
Directed assembly of polymer solutions allows for precise control of macroscopic properties such as optical reflectance and flow properties. One method of directed assembly is the introduction of nanoparticles, such as anisotropic hydrophilic silica nanoparticles, that hydrogen bond with aqueous poly(N-isopropyl acrylamide) to encourage network formation and impact phase separation. Magnetic fields have also been shown to impact the assembly of paramagnetic small molecules, nanoparticles, and polymers, but magnetic impacts on diamagnetic polyacrylamides are yet to be examined . Here, we study the application of magnetic fields on anisotropic silica nanoparticles towards their directed assembly in aqueous solutions of poly(N-isopropyl acrylamide) (PNIPAM). Of particular interest are the changes in network formation during PNIPAM phase separation as a function of magnetic field strength and particle concentration. Nanoparticle addition and magnetic field application decrease temperature of phase separation and impact yield stresses and shear thinning behavior—these changes are functions of particle content and applied magnetic field strength. Linear oscillatory temperature ramps suggest magnetic application decreases rheological separation temperature due to decreased preference of PNIPAM-solvent interactions. However, nanoparticles minimize shifts in phase separation temperature from magnetic fields, the nature of which is explained by hydrogen bonding interactions examined with Fourier-transform infrared spectroscopy. Polymer-nanoparticle suspensions that respond to both magnetic fields and temperature can be used in applications requiring complex and rapidly-tunable rheological behavior.