Paper Number
RS10 

Session
Techniques and Methods: Rheometry & Spectroscopy/Microscopy

Title
Environmentally-controlled dripping-onto-substrate (DoS) extensional rheometry of complex fluids

Presentation Date and Time
October 11, 2022 (Tuesday) 2:30

Track / Room
Track 6 / Mayfair

Authors (Click on name to view author profile)

  1. Lauser, Kathleen T. (University of Minnesota, Chemical Engineering and Materials Science)
  2. Zhang, Diana Y. (University of Minnesota, Chemical Engineering and Materials Science)
  3. Robertson, Ben P. (University of Minnesota, Chemical Engineering and Materials Science)
  4. Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)

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

Speaker / Presenter 
Calabrese, Michelle A.

Keywords
experimental methods; polymer solutions; rheometry techniques; surfactants

Text of Abstract
Injectability, sprayability, and printability in soft materials are dictated by the extensional flow properties. Until recently, the extensional rheology of dilute protein and polymer solutions has been sparsely studied due to experimental limitations; however, capillary-driven thinning of a liquid bridge can be used to accurately measure rheological parameters. To measure scarce materials and low viscosity fluids in truly small volumes, we have developed instrumentation for simultaneous dripping-onto-substrate (DoS) extensional rheometry and surface tension measurements in <10 µL/trial, and developed new sample environments to make measurements over a range of temperatures, humidities, and in organic solvents. Here, we demonstrate the utility of capillary-driven thinning to determine injectability and coatability for two case studies: thermoresponsive, self-assembling polymers and polymers in volatile organic solvents. To measure the temperature-dependent extensional rheology of block copolymer micelle solutions in fine temperature increments, we developed a custom chamber to enable temperature-controlled DoS (TC-DoS). Spherical micelle solutions at ambient conditions exhibit inertiocapillary (IC) thinning, whereas above the sphere-to-rod transition temperature, liquid bridge thinning evolves towards viscocapillary (VC) behavior. With further micelle growth and entanglement at 39 °C, three distinct regimes appear: EC thinning, beads-on-a-string (BOAS) instability formation, and BOAS evolution. For polymer solutions in organic solvents, we employ a new environmental control system to minimize evaporation, and confirm scaling relationships for the first time. We also show that evaporation effects during measurement can depend more on polymer mobility than solvent vapor pressure. These case studies illustrate the utility of environmentally-controlled DoS extensional rheometry for predicting injectability and coatability in a wide range of complex fluids, enabling rapid formulation screening using a single drop.