Paper Number
GS31
Session
Gels and Self-Assembled Systems
Title
Rheological and tribological behavior of soft complex gels
Presentation Date and Time
October 12, 2017 (Thursday) 10:50
Track / Room
Track 4 / Crestone A
Authors
- Farias, Barbara V. (North Carolina State University, Chemical and Biomolecular Engineering)
- Hsiao, Lilian C. (North Carolina State University, Department of Chemical and Biomolecular Engineering)
- Khan, Saad A. (North Carolina State University, Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Barbara V. Farias, Lilian C. Hsiao, and Saad A. Khan
Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC
Speaker / Presenter
Farias, Barbara V.
Text of Abstract
Oil-in-water (o/w) emulsions with polymers and phospholipids are widely used for personal care products due to their thickening and emulsifying properties. However, the underlying mechanism through which this complex emulsion affects rheological and tribological characteristics is not well understood. We investigate systems containing a hydrophobically modified polymer, phospholipids, and o/w emulsions and find that bulk rheology of the studied systems plays a role in frictional behavior. We used dynamic and steady shear experiments to study systems containing the hydrophobically modified polymer and found that their rheological behavior is consistent with concentrated microgel systems. For systems containing phospholipids and polymer, the elastic modulus shows a two-fold increase if compared to systems without phospholipids, leading us to hypothesize that hydrophobic interactions are occurring between the polymer and phospholipids. The yield stress for all the studied systems is similar, except for the o/w emulsion with phospholipids that shows a higher yield stress. In addition, we characterized the tribological behavior using a soft model contact consisting of polydimethylsiloxane (PDMS). In the elastohydrodynamic lubrication regime, which occurs at higher speeds where the contacts are fully separated by a lubricating film, the friction coefficients increase with increasing sample viscosity. Systems containing the polymer and phospholipids showed a lower friction coefficient than Newtonian fluids at the boundary regime, where the contacting asperities dictate the frictional behavior. In order to understand this behavior, adsorption studies with quartz crystal microbalance were performed. The results showed that phospholipids are being adsorbed onto the PDMS surface, with the hydrated heads causing a decrease in the friction coefficients at low entrainment speeds due to a hydration-lubrication mechanism.