Paper Number
GG60 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
Utilizing rheology to characterize CNT-PDMS gels in the roll coating process

Presentation Date and Time
October 13, 2022 (Thursday) 11:55

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

1. Perera, Himendra (NCSU, Chemical Engineering)
2. Islam, Md Didarul (NCSU, Department of Mechanical and Aerospace Engineering)
3. Ryu, Jong (NCSU, Department of Mechanical and Aerospace Engineering)
4. Khan, Saad A. (North Carolina State University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Himendra Perera¹, Md Didarul Islam², Jong Ryu² and Saad A. Khan^1
1Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27606; ²Department of Mechanical and Aerospace Engineering, NCSU, Raleigh, NC 27606

Speaker / Presenter 
Perera, Himendra

Keywords
experimental methods; composite rheology; gels; rheometry techniques

Text of Abstract
Manufacturing surfaces with periodic microstructures is critical in applications that require drag reduction and superhydrophobicity but is challenging on a large scale. Through forward roll coating, patterns on the surface can be formed through the Saffman Taylor instability, or viscous fingering. Typically, these patterns are fleeting, as surface tension forces flatten the surface. By using a fluid with yield stress, these patterns can be retained long enough for the system to be crosslinked and the microstructure retained. For our system, we utilize a carbon nanotube (CNT)– polydimethylsiloxane (PDMS) gel in loadings from 0.5 to 10 wt. % CNT with different grades of PDMS. The CNT have a large aspect ratio and cause gelling at low loadings, and the PDMS causes deviations from expected viscous fingering behavior as seen in literature. Using dynamic oscillatory shear experiments, we indicated a response consistent with a physically crosslinked material, with G’/G” >1 and both moduli constant with respect to frequency. Yield stress measurements are consistent across multiple techniques, including elastic stress analysis from dynamic oscillatory measurements, creep testing, and stress sweeps. To further explain viscous fingering patterns in the roll coating process, we performed large amplitude oscillatory shear (LAOS) and used MITlaos for analysis. To understand the strain response that occurs near the yield stress, we utilize Lissajous plots. Results indicate that higher loading of CNT increased yield stress but increased the unpredictability of the viscous fingering. This correlation will be explained with results obtained from dynamic oscillatory measurements and results obtained from LAOS analysis.