posted on 2020-03-07, 13:03authored byWeththasinghage
D. Amith, Juan C. Araque, Claudio J. Margulis
Prototypical
ionic liquids (ILs) are characterized by three structural
motifs associated with (1) vicinal interactions, (2) the formation
of positive–negative charge-alternating chains or networks,
and (3) the alternation of these networks with apolar domains. In
recent articles, we highlighted that the friction and mobility in
these systems are nowhere close to being spatially homogeneous. This
results in what one could call mechanical heterogeneity, where charge
networks are intrinsically stiff and charge-depleted regions are softer,
flexible, and mobile. This Letter attempts to provide a clear and
visual connection between frictionassociated with the dynamics
of the structural motifs (in particular, the charge network)and
recent theoretical work by Yamaguchi linking the time-dependent viscosity
of ILs to the decay of the charge alternation peak in the dynamic
structure function. We propose that charge blurring associated with
the loss of memory of where positive and negative charges are within
networks is the key mechanism associated with viscosity in ILs. An
IL will have low viscosity if a characteristic charge-blurring decorrelation
time is low. With this in mind, engineering new low-viscosity ILs
is reduced to understanding how to minimize this quantity.