Paper Number
PO100 

Session
Poster Session

Title
Rheology of dispersions in the ionic liquid [Bmim][BF4]

Presentation Date and Time
October 8, 2014 (Wednesday) 6:05

Track / Room
Poster Session / Poster

Authors (Click on name to view author profile)

1. Gao, Jingsi (University of Delaware, Department of Chemical and Biomolecular Engineering)
2. Shiflett, Mark B. (DuPont, Central Research and Development)
3. Wagner, Norman J. (University of Delaware, Department of Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Jingsi Gao¹, Mark B. Shiflett², and Norman J. Wagner^1
1Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE; ²Central Research and Development, DuPont, Newark, DE

Speaker / Presenter 
Gao, Jingsi

Text of Abstract
Shear-thickening dispersions of colloidal particles in ionic liquids (ILs) are being developed to improve ballistic, puncture and abrasion resistance for space suits and micrometeorite and orbital debris (MMOD) shielding of spacecraft. ILs are chosen for the solvent phase because of their thermal stability and low volatility. However, simulations and experiments have shown that high ionic strength in ILs effectively shields the electrostatic repulsion between silica particles, leading to significant particle aggregation. In this work we examine the role of solvation forces and solvent structuring as a means to stabilize nanoparticles and colloids in ILs. In particular, stable silica dispersions up to 65 wt % in [Bmim][BF4] are created by chemically coating the surface with 1H, 1H, 9H-hexadecafluoro-1-nonanol, and shear-thickening behavior is observed. A combination of techniques, including rheology, dynamic light scattering (DLS), electron microscopy, and small angle neutron scattering (SANS) are employed to determine the mechanism of colloidal stability. We propose solvation layers are initiated by hydrogen bonds between anion [BF4]- and the fluorinated group on the surface coating, separating and stabilizing the silica particles. Analysis of SANS spectra across a broad range of particle concentrations allows us to quantitatively determine the inter-particle interactions including the thickness of solvation layer. The solvation layer thickness is approximately 5 nm at room temperature and is confirmed by independent rheology and DLS measurements. The addition of water dramatically decreases the IL viscosity but surprisingly, increases the relative viscosity of concentrated suspensions. However, assuming that the water partitions selectively to the particles enables rationalizing this behavior. This work also has potentially important implications for environmental and energy engineering as ILs are candidates for remediation, separation, and recycling of nuclear waste.