Nanowetting of Graphene by Ionic Liquid Droplets

Abstract

The behavior of nanodroplets formed by amino acid based 1-ethyl-3-methylimidazolium glycine ionic liquid on graphene sheets was studied using classic molecular dynamics. Nanodroplets of different sizes were analyzed, and the contact angle was inferred. The ion–graphene interaction energy was calculated as a function of droplets size, together with the ions arrangement at the interface. Likewise, wetting of SiO2 and graphene supported on SiO2 by ionic liquid nanodroplets was also analyzed. Graphene wetting by this ionic liquid is discussed in terms of the changes on fluid structure upon adsorption and the mechanism and strength of ion–graphene interactions.

Molecular Dynamics Simulations of the Influence of Drop Size and Surface Potential on the Contact Angle of Ionic-Liquid Droplets

“…The results here contrast with the ones obtained by Herrara et al 38 Firstly, in this work, no consistent drop size dependence on the contact angle was found. Most significantly however, is that the results here show wetting behavior that significantly deviates from a regular drop at a sheet interaction potential of 0.23 kJ mol -1 , whilst Herrara et al 38 reported contact angles of 48 and 80 degrees for drop sizes of 200 and 500 IL pairs respectively whilst using an even more strongly interacting sheet of ε = 0.2929 kJ mol -1 .…”

“…The difference is seen between the energy values in Figure 3. For the interaction potential of 0.23 kJ mol -1 , simulation times in excess of 20 ns were required to reach equilibrium, this is a large increase over that reported by Herrara et al, 38 where less than 5 ns were required with a simulation temperature of 403 K. The differences in time required could possibly be partly explained by the temperature used in this work, 298 K, and it is also the differences in the liquid-liquid interactions between the two IL pairs used may also have played a role. pairs, which is expected due to its smaller size creating shorter diffusion paths for the ions.…”

“…It is very likely due to the different structure of the anions, which results in different adsorption profiles: Although we observe that the first adsorbed layer is enriched with anions, in the case of EMIM-GLY no such effect was observed (on the contrary, cations seem to approach slightly closer to the surface). 38 The size and shape of the ions therefore play an important role on the contact angle, and results obtained for a specific ionic liquid cannot easily be transferred to other systems.…”

“…As with the work by Herrara et al, 38 our IL drop size was also varied. We also changed the graphene sheet properties to examine the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 influence of interaction potential on contact angle.…”

“…[31][32][33][34][35][36][37] There have been few explicit reports of the contact angle between ionic liquids and graphene. Herrara et al 38 performed recent molecular dynamics (MD) simulations of the amino-acid IL 1-ethyl-3-methylimidazolium glycine (EMIM-GLY) and reported 40 degree variation in contact angle with the size of the nano-drops (from 100 to 500 IL pairs) on highly attractive graphene sheets. Taherian et al 39 used MD simulations for an electrowetting study of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF 4 ) ions bridging between graphene surfaces of opposing and fixed coulombic charges.…”