TY - JOUR
T1 - Rheology of protic ionic liquids and their mixtures
AU - Smith, J. A.
AU - Webber, Grant B.
AU - Warr, Gregory G.
AU - Atkin, Rob
PY - 2013/11/7
Y1 - 2013/11/7
N2 - The rheological properties of five pure protic ionic liquids (ILs), ethylammonium nitrate (EAN), propylammonium nitrate (PAN), ethanolammonium nitrate (EtAN), ethylammonium formate (EAF), and dimethylethylammonium formate (DMEAF), are characterized and interpreted by considering the effects of both the H-bond network and the solvophobic nanostructure of the liquids. The results demonstrate that these effects are not, however, independent or simply additive. At 20 C, EtAN has the highest zero shear viscosity of 156.1 mPa·s, followed by PAN (89.3 mPa·s), EAN (35.9 mPa·s), EAF (23.1 mPa·s), and DMEAF (9.8 mPa·s). The primary ammonium ILs behave as Newtonian fluids at low shear rates but shear thin at high shear. Fits to the Vogel-Fulcher-Tammann model reveal that nanostructure is not affected appreciably by temperature and that all the ILs studied are of intermediate fragility. The rheology of binary mixtures of these ILs was analyzed and used to demonstrate fundamental differences in the way IL cations and anions interact. IL mixtures containing both nitrate and formate anions resist flow more strongly than the pure liquids, which is a consequence of the difference in hydrogen bonding capacity of the anions. Mixing cations can give rise to complex behavior due to the offsetting effects of hydrogen bonding and solvophobic nanostructure formation.
AB - The rheological properties of five pure protic ionic liquids (ILs), ethylammonium nitrate (EAN), propylammonium nitrate (PAN), ethanolammonium nitrate (EtAN), ethylammonium formate (EAF), and dimethylethylammonium formate (DMEAF), are characterized and interpreted by considering the effects of both the H-bond network and the solvophobic nanostructure of the liquids. The results demonstrate that these effects are not, however, independent or simply additive. At 20 C, EtAN has the highest zero shear viscosity of 156.1 mPa·s, followed by PAN (89.3 mPa·s), EAN (35.9 mPa·s), EAF (23.1 mPa·s), and DMEAF (9.8 mPa·s). The primary ammonium ILs behave as Newtonian fluids at low shear rates but shear thin at high shear. Fits to the Vogel-Fulcher-Tammann model reveal that nanostructure is not affected appreciably by temperature and that all the ILs studied are of intermediate fragility. The rheology of binary mixtures of these ILs was analyzed and used to demonstrate fundamental differences in the way IL cations and anions interact. IL mixtures containing both nitrate and formate anions resist flow more strongly than the pure liquids, which is a consequence of the difference in hydrogen bonding capacity of the anions. Mixing cations can give rise to complex behavior due to the offsetting effects of hydrogen bonding and solvophobic nanostructure formation.
UR - http://www.scopus.com/inward/record.url?scp=84887778055&partnerID=8YFLogxK
U2 - 10.1021/jp407715e
DO - 10.1021/jp407715e
M3 - Article
AN - SCOPUS:84887778055
VL - 117
SP - 13930
EP - 13935
JO - The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical
JF - The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical
SN - 1520-5207
IS - 44
ER -