Paper Number
PO47 

Session
Poster Session

Title
Evaporation-controlled dripping-onto-substrate (EC-DoS) extensional rheology for CNT/polymer composite coatings

Presentation Date and Time
October 12, 2022 (Wednesday) 6:30

Track / Room
Poster Session / Riverwalk A

Authors (Click on name to view author profile)

1. Robertson, Ben P. (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)
Ben P. Robertson and Michelle A. Calabrese
Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455

Speaker / Presenter 
Robertson, Ben P.

Keywords
experimental methods; colloids; composite rheology; polymer solutions; rheometry techniques; suspensions

Text of Abstract
Carbon nanotube (CNT) composites are promising platforms for developing electrically active hierarchical materials used for electrodes, fuel cells, and separations, but solution processability and coating properties of these materials is limited by the lack of solubility of CNTs in volatile solvents. One approach to producing coatable CNT dispersions is to mix them with conductive, redox-active polymers, but these novel polymers are generally synthesized in-house in small quantities, making large scale coating tests prohibitively consumptive of material. Extensional rheology can be used to predict the deformation and breakup of these dispersions during coating processes like spray coating using small sample volumes, but the low viscosities, short relaxation times, and volatility of these systems leads to challenges in accurate measurement due to inertial instabilities and evaporation effects. To probe these challenging systems, we used a custom evaporation-controlled dripping-onto-substrate (EC-DoS) instrument, creating an atmosphere saturated with solvent vapor around the pendant drop. This instrument was used to measure breakup times and power law exponents of solutions of polymers and CNTs in acetone, which indicate that CNT/polymer dispersions break up more easily than solutions of these polymers alone, and exhibit no detectable elasticity. While the lack of elasticity in these systems is promising for coating applications, the short breakup times indicate that a more viscous cosolvent may be needed to prevent sample loss due to misting. This new instrumentation provides a simple platform for assessing coating properties in a range of volatile dispersions with complex microstructures.