Paper Number
TM18                         My Program 

Session
Techniques and Methods: Rheometry, Tribometry, Spectroscopy and Microscopy

Title
Dripping-on-Substrate (DoS) dos and don'ts

Presentation Date and Time
October 22, 2025 (Wednesday) 3:45

Track / Room
Track 7 / Sweeney Ballroom D

Authors (Click on name to view author profile)

  1. Warwaruk, Lucas N. (Massachusetts Institute of Technology, Mechanical Engineering)
  2. Ewoldt, Randy H. (University Of Illinois Urbana-champaign, Mechanical Science and Engineering)
  3. Chris, Macosko (University of Minnesota, Chemical Engineering)
  4. McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Lucas N. Warwaruk1, Randy H. Ewoldt2, Macosko Chris3 and Gareth H. McKinley1
1Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; 2Mechanical Science and Engineering, University Of Illinois Urbana-champaign, Urbana, IL 61801; 3Chemical Engineering, University of Minnesota, Minneapolis, MN 55455

Speaker / Presenter 
Warwaruk, Lucas N.

Keywords
experimental methods; methods; non-Newtonian fluids; polymer solutions; rheometry; techniques

Text of Abstract
Capillarity-driven rheometry techniques are a well-established means of measuring the relaxation time of long-chain polymer solutions. One such technique, known as Dripping-on-Substrate rheometry or DoS, has become a popular method of particular utility for low viscosity solutions [1]. The energy released by a pendant droplet of a complex fluid spreading across a partially-wetting substrate drives rapid formation of a neck, which leads to strong transient extensional flow even in very low viscosity fluids. However, a clear set of guidelines on the capabilities and limitations of DoS rheometry is lacking. In the current technical presentation, we establish the key ``Dos and Don’ts''; of DoS rheometry; discussing critical parameters that influence the quality of the measurements and the accuracy of the resulting estimates of the extensional relaxation time. Dilute solutions of a 2 MDa and 8 MDa polyethylene oxide (PEO) polymer, as well as a 20 MDa polyacrylamide (PAM) polymer, are used as test fluids for probing the role of different experimental control parameters. We develop two instrumental constraints, relating to the spatial and temporal resolution of the DoS setup. Provided these constraints are satisfied, DoS rheometry is able to measure small relaxation times, on the order of 0.1 ms. Such values are markedly smaller than the range of values accessible with other common techniques, such as capillary break-up extensional rheometry (CaBER) [2]; however, care must be taken to ensure that fitting of the elasto-capillary regime covers a sufficiently long duration (in dimensionless time) and that digital video images are recorded at an appropriate acquisition rate and spatial magnification. These instrumental constraints can be combined to provide a figure of merit that allows inter-laboratory comparison of different approaches to capillarity-driven rheometry. [1] Dinic, J., Zhang, Y., Jimenez, L.N. & Sharma, V. 2015 ACS Lett. [2] Rodd, L.E., Scott, T.P., Cooper-White, J.J. & McKinley, G.H. 2000 Appl. Rheol.