Paper Number
PO27 

Session
Poster Session

Title
Temperature controlled droplet-based extensional rheometry for characterizing thermoresponsive materials

Presentation Date and Time
October 13, 2021 (Wednesday) 6:30

Track / Room
Poster Session / Ballroom 1-2-3-4

Authors (Click on name to view author profile)

  1. Zhang, Diana Y. (University of Minnesota, Chemical Engineering and Materials Science)
  2. Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)

Author and Affiliation Lines (in printed abstract book)
Diana Y. Zhang and Michelle A. Calabrese
Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455

Speaker / Presenter 
Zhang, Diana Y.

Keywords
experimental methods; polymer solutions; rheology methods

Text of Abstract
Understanding the extensional rheology of polymer solutions is essential for determining the sprayability and printability of a wide range of industrially relevant materials such as coatings, printing inks, and agricultural sprays. However, solution extensional rheology remains challenging due to instrumentation constraints. Recently, Dripping-onto-Substrate (DoS) extensional rheometry has enabled the characterization of low viscosity (η0 < 20 mPa∙s), low elasticity (λE < 1 ms) fluids without major pre-deformation, which can disrupt test fluid microstructure. However, to date, DoS measurements have been limited to ambient conditions. In this work, we develop temperature controlled DoS rheometry for the first time and demonstrate its utility by characterizing the temperature-dependent extensional behavior of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Poloxamer 234, P234) in 0.9 M NaF solutions as a model system known to exhibit a pronounced thermal response. To enable heated DoS measurements, we built a custom temperature control chamber in which the nozzle, substrate, and enclosure are heated with custom PID controllers. At room temperature (T = 23 °C), P234 solutions are composed of spherical micelles and exhibit inertiocapillary (IC) behavior in DoS measurements. Above the sphere-to-rod transition temperature (29 °C), the spherical micelles elongate into cylindrical micelles, which continue growing with increasing temperature. Heated DoS measurements of P234 reflect this structural change; as temperature is increased, break up times increase and IC behavior transitions towards viscocapillary behavior. Above 32 °C, the formation and growth of rods also results in elastocapillary behavior. The new temperature control capabilities presented herein add key capabilities to DoS measurements, broadening the range of materials and processing conditions this technique can be used to study.