Aqueous, Mixed Micelles as a Means of Delivering the Hydrophobic Ionic Liquid EMIM TFSI to Graphene Oxide Surfaces

Abstract

Most ionic liquids (ILs) are not surface-active and cannot, alone, be directed to assemble at surfacesdespite their potential as nonvolatile structure-directing agents and use as advanced materials in a multitude of applications. In this work, we investigate aqueous systems of common nonionic surfactants (Triton X-100 and Tween 20), which we use to solubilize 1-ethyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide. The resulting solution of mixed micelle leads to spontaneous adsorption of the IL/surfactant complex onto graphene oxide (GO) surfaces, forming a compact film. Adsorption isotherms generated by fluorescence labeling of the IL and surfactant phases are used to quantify the extent of adsorption. While sensitive to the GO dispersion concentration, upwards of 3 g IL/g GO adsorb under dilute conditions. Atomic force microscopy is used to show that the adsorbed layer uniformly distributes as an ∼1 nm thick coating (per GO side) as the system reaches the first plateau of a Langmuir-type isotherm. Adsorption beyond this plateau is possible but leads to thicker (>30 nm), inhomogeneous adsorbed layers. Both micellar size in solution and adsorbed layer thickness reduce upon the addition of IL to the surfactant phase, suggesting significant interactions among the materials and nonideal mixing of the components.

Electrolyte-mediated assembly of graphene-based supercapacitors using adsorbed ionic liquid/non-ionic surfactant complexes

“…, Q max ∼ 1–3 mg IL/mg depending on concentration). 23 According to studies performed on the adsorption of Pluronic (P123 and F127) on GO surfaces, these two surfactants interact with the hydrophobic section of GO using their PPO chain. 30,31 Since rGO is expected to have a larger proportion of more hydrophobic graphene domains compared to GO, it can more efficiently adsorb the surfactant, and therefore, the mixed adsorbate (P123/IL complex).…”

“…The final dispersion was sprayed into liquid nitrogen using a spray bottle to flash freeze the IL/surfactant adsorbed layer onto the surface of the rGO. 23 The resulting frozen slurry was collected and freeze dried to produce a composite powder of mixed rGO/P123/IL (flash freeze drying). At lower concentration of P123 and IL, a flocculent powder was collected.…”

“…The adsorption study was performed using a method reported in our previous study. 23 Briefly, EMImTFSI was labeled using Rhodamine B (Rh B) dye and was added to the aqueous dispersion of P123 ( C P123 = 0.4 mg mL −1 ) using ultrasonication to make different weight ratios of P123/IL = 1, 2, and 3. The emission spectra were collected for the resulting dispersions and set as control.…”

“…These amounts are This journal is © The Royal Society of Chemistry 2023 larger than the adsorbed amounts that we previously reported for similar IL/non-ionic surfactant (Tween 20 and Triton X-100) systems adsorbed to GO prior to reduction (i.e., Q max ∼ 1-3 mg IL/mg depending on concentration). 23 According to studies performed on the adsorption of Pluronic (P123 and F127) on GO surfaces, these two surfactants interact with the hydrophobic section of GO using their PPO chain. 30,31 Since rGO is expected to have a larger proportion of more hydrophobic graphene domains compared to GO, it can more efficiently adsorb the surfactant, and therefore, the mixed adsorbate (P123/IL complex).…”

“…Expanding on this approach, we demonstrated recently that mixing several non-ionic surfactants such as Triton X-100 and Pluronic P123 can, in addition to imparting surface activity to a non-surface active IL, 23,24 have a benecial effect on the C DL measured at the IL/glassy carbon interface. Despite adding these uncharged and effectively electrochemically inert surfactants to the IL, a signicant increase in C DL is observed; For example, over 100% improvement is observed at 40 wt% P123.…”