Paper Number
SM42 

Session
Polymers Solutions, Melts and Blends

Title
Temperature-controlled dripping-onto-substrate (DoS) rheometry of polymer micelle solutions

Presentation Date and Time
October 12, 2022 (Wednesday) 1:50

Track / Room
Track 2 / Sheraton 3

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
flow-induced instabilities; polymer solutions; rheometry techniques; surfactants

Text of Abstract
Measuring solution extensional rheology enables quantitative assessment of solution sprayability, printability, and jettability for applications ranging from coatings to agricultural sprays. More recently, dripping-onto-substrate (DoS) rheometry has become the preferred solution extensional rheology technique over capillary breakup rheometry (CaBER) due to the advantageous low-volume requirement and ability to measure low viscosity (η0 < 20 mPa∙s), low elasticity (λ E < 1 ms), and low surface tension (σ < 35 mN/m) fluids. However, DoS measurements to-date have been limited to ambient conditions while both commercial and custom-built CaBER instruments have been developed to be capable of heated measurements. As such, here we develop a custom instrument chamber to enable temperature-controlled DoS (TC-DoS) measurements, and we examine the temperature-dependent extensional rheology of an aqueous solution of poloxamer 234 (P234) and NaF. Spherical micelle solutions at ambient conditions exhibit inertiocapillary (IC) thinning behavior similar to that of water. Above the sphere-to-rod transition temperature, liquid bridge thinning evolves towards viscocapillary (VC) behavior as micelles elongate and shear viscosity increases. Above 37 °C, the growth of rods into wormlike micelles (WLMs) results in pronounced elastocapillary (EC) thinning behavior. With further WLM growth and entanglement at 39 °C, three distinct elasticity-dominated regimes appear: EC thinning, beads-on-a-string (BOAS) instability formation, and BOAS evolution. Comparisons between DoS measurements of P234 WLMs and prior studies on surfactant WLMs reveal that the step-stretch in CaBER can mask important trends in extensional parameters such as maximum Trouton ratio. These findings reveal the rich temperature-dependent flow behaviors of polymer micelles and emphasize the importance of using minimally-disruptive techniques such as DoS to measure the extensional rheology of microstructured fluids.