Colloidal Interaction in Ionic Liquids: Effects of Ionic Structures and Surface Chemistry on Rheology of Silica Colloidal Dispersions

Abstract

To understand the important factors that dominate colloidal stability in ionic liquids (ILs), rheology of the dispersions of hydrophilic and hydrophobic silica nanoparticles were investigated in ILs with different ionic structures. The dispersion of hydrophilic silica nanoparticles in [BF(4)] anion-based ILs and in an IL containing a hydroxyl group, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([C(2)OHmim][NTf(2)]), showed an intriguing shear thickening response. Nonflocculation of the hydrophilic silica nanoparticles in the [BF(4)] anion-based ILs and in [C(2)OHmim][NTf(2)], where the interparticle electrostatic repulsion appears to be depressed, suggests that an IL-based steric hindrance or solvation force provides an effective repulsive barrier for the colloidal aggregation. On the other hand, the other dispersions presented shear thinning behavior with an increase in shear rates and gelled at relatively low particle concentrations. The elastic modulus (G') of the gels formed by the hydrophilic silica was correlated with the polarity scale, lambda(Cu), of the ILs, indicating that the silica-IL interactions, especially the silica-anion interactions, appear to affect the rheological behavior, even in flocculated systems. All the ILs used in this study can be solidified by the addition of hydrophobic silica particles. The rheological behavior of the silica colloidal dispersions was strongly affected by the ionic structure of the ILs and the surface structure of the silica particles.

New Frontiers in Materials Science Opened by Ionic Liquids

“…In addition, hydrophobic nanoparticles were prepared by grafting poly(MMA) chains on the particle surfaces to understand the peculiar colloidal stability. [84][85][86] The colloidal interaction was investigated using the Derjaguin-Landau-Verway-Overbeek (DLVO) theory, from which it was concluded that bare silica particles cannot be stabilized in ILs. In fact, bare silica particles formed aggregates easily, resulting in gel formation at a small amount of bare silica (2-3 wt %).…”

Thermophysical Properties of Nanoparticle-Enhanced Ionic Liquids (NEILs) Heat-Transfer Fluids

“…12 Few other reports include viscosity measurements of ILs containing small amounts of nanoparticles. [29][30] IL-functionalized multi walled carbon nanotubes have been prepared and added to a neat IL and the viscosity of the resulting nanofluid was lower than the neat IL due to the lubricating properties of carbon nanotubes. 31 The effect of various weight loadings of Al 2 O 3 spheres on the viscosity of the NEIL at elevated temperatures was measured and is reported in Figure 5.…”

Rapid, microwave-assisted thermal polymerization of poly(ethylene glycol) diacrylate-supported ionogels

“…In cases where drying or vacuum treatment steps are employed to remove volatile co-solvents or other gelation reaction byproducts, total gel formation times can be several days. Common ionogel fabrication methods include: use of a co-solvent to blend in a polymer support, 3,5,[20][21][22] initiation of a spontaneous sol-gel reaction to produce an inorganic support, [23][24][25][26] stirring in an assembly of fumed silica particles, [27][28][29] and either UV-initiated [30][31][32][33] or thermally-initiated [34][35][36][37][38][39][40] polymerization/crosslinking of a reactive monomer inside the ionic liquid. Additionally, chemical vapor deposition and alternative polymerization strategies that require on the order of minutes have been reported.…”