Imidazolium‐Based Stabilization of Aqueous Multiwall Carbon Nanotube Dispersions

Abstract

Imidazolium bromide, an ionic liquid surfactant acrylate, as well as its homopolymer and various copolymers are demonstrated to be superior dispersing aids for preparing aqueous multiwall carbon nanotube (MWCNT) dispersions. We demonstrate apparent complete exfoliation in water with extinction coefficients at 500 nm of about 60 cm2 mg−1 of MWCNT dispersed, a new lower bound and the highest reported extinction to date. The efficacy or efficiency of dispersion (activated by ultrasonication) is examined in terms of a quotient of extinction and weight ratio of the active monomer and MWCNT. A rank ordering of the results obtained for seven stabilizers based on the same imidazolium bromide monomer provides insights into roles of π‐overlap adsorption onto MWCNT surfaces and how hydrogel properties of some of these polymers provide stability in water at higher concentrations than previously considered feasible for surfactant‐stabilized and polymer‐stabilized MWCNT dispersions. Simple nanocomposite film formation is demonstrated by casting and thermal diffusivity and electrical conductivity properties are examined.

Poly(ionic liquid) composites

“…For example, a poly-(1-vinyl-3-ethylimidazolium bromide) PIL can transfer CNTs from an aqueous to an organic phase by an anion exchange reaction of [Br À ] with [TFSI À ] 45 because of the ''cation-p'' attractive interaction between the imidazolium cation and the CNT surface. 46,47 Similarly, they can stabilize graphene, which contains p-conjugated aromatic rings, 48,49 and switch the surface properties of the graphene sheets from a hydrophilic to a hydrophobic phase by an anion exchange reaction. 50 In the area of developing electrodes for high-performance supercapacitors, PILs attached to the surface of graphene oxide (GO) enhanced the compatibility of GO with the IL electrolyte to enlarge the effective electrode surface area that was accessible to electrolyte ions; as such, the electrode reached a maximum energy density of 6.5 W h kg À1 with a power density of 2.4 kW kg À1 .…”

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

“…The use of IL monomers, PIL-based nanolatexes, PIL-based triblock copolymers, and various linear PILs (homopolymers and copolymers) in stabilizing MWCNTs in water was extended by Texter et al in developing a measure of dispersion efficiency to compare relative efficacies of different stabilizers . This relative efficacy measure is expressed as the quotient ( cm 2 mg MWCNTs − 1 ) / ( g IL monomer g MWCNTs − 1 ) which is an optical absorption coefficient divided by the weight of monomer needed to stabilize a given weight of MWCNTs.…”

“…Both pyrrole and imidazolium bind to sp 2 surfaces by π overlap. PIL-based nanolatexes 66 reported in some of the earliest PIL papers are continuing to prove very effective in producing concentrated nanocarbon dispersions of SWCNTs 67 (1.4% w/ w), MWCNTs 584 (up to 17% w/w 576 and recently 4.8% w/w in water 585 ), hydrothermal carbon, and graphene. 68 The 4% by weight MWCNTs in water dispersions reported years ago were 20× more concentrated than the PPy-Br stabilized dispersions discussed above.…”

“…The use of IL monomers, PIL-based nanolatexes, PIL-based triblock copolymers, and various linear PILs (homopolymers and copolymers) in stabilizing MWCNTs in water was extended by Texter et al in developing a measure of dispersion efficiency to compare relative efficacies of different stabilizers. 584 This relative efficacy measure is expressed as the quotient…”

“…The IL monomer, ILBr, is 1-(11-[acryloyloxy]­undecyl)-3-methyl-imidazolium bromide. Reproduced with permission from Texter et al; ©2019 Wiley and American Oil Chemists Society.…”