Ammonium Laurate Surfactant for Cleaner Deposition of Carbon Nanotubes

Abstract

Experiments probing the properties of individual carbon nanotubes (CNTs) and those measuring bulk composites show vastly different results. One major issue limiting the results is that the procedures required to separate and test CNTs introduce contamination that changes the properties of the CNT. These contamination residues often come from the resist used in lithographic processing and the surfactant used to suspend and deposit the CNTs, commonly sodium dodecyl sulfate (SDS). Here we present ammonium laurate (AL), a surfactant that has previously not been used for this application, which differs from SDS only by substitution of ionic constituents but shows vastly cleaner depositions. In addition, we show that compared to SDS, AL-suspended CNTs have greater shelf stability and more selective dispersion. These results are verified using transmission electron microscopy, atomic force microscopy, ζ-potential measurements, and Raman and absorption optical spectroscopy. This surfactant is simple to prepare, and the nanotube solutions require minimal sonication and centrifugation in order to outperform SDS.

Vial sonication and ultrasonic immersion probe sonication to generate stable dispersions of multiwall carbon nanotubes for physico-chemical characterization and biological testing

“…To evaluate the stability of the dispersions, the particle size distributions were measured after sonication and after a rest period of 1 month. Results reported in Table 3 show no specific differences in the mean length of the MWCNTs between the two preparation methods (using a vial sonicator and probe sonicator) and between the two stock concentrations prepared (0.2 and 1.0 mg/ mL sonicated as described (Table 1)) that remain also stable after 1 month of storage indicating that there is little or no tendency to agglomeration in this time frame (Figure 1 and Table 3) (Hennrich et al 2007;Nilsson et al 2015;Pagani et al 2012;Yu et al 2007). Figure 2 illustrates the variation of the absorbance of the supernatant suspensions with sedimentation time from probe sonication and vial sonicator treatment.…”

“…In the as-synthesised state, CNTs are generally hydrophobic with strong Van der Waals forces along the axis of the tubes which effectively hinder their dispersion in hydrophilic media complicating their use in many practical applications (Hyung et al 2007;Ikeda et al 2006;Krause et al 2009). Different approaches for the dispersion of CNTs can be found in literature (Fujigaya and Nakashima 2015;Nilsson et al 2015;Vaisman et al 2006) such as (i) oxidation of the CNTs surface to increase their dispersibility in water at the expense of modifying some CNTs properties, (ii) covalent functionalization conferring high stability to the CNTs although it may also cause damage which alters their original properties, (iii) noncovalent interactions with polymers or surfactants which better preserve the intrinsic features of the CNTs. This last option is usually performed via sonication treatment in a solution of (a) functionalized polymers resulting in stable polymer wrapping or (b) a low molecular weight surfactant which may be easily washed off causing the formation of CNTs bundles again.…”

“…This last option is usually performed via sonication treatment in a solution of (a) functionalized polymers resulting in stable polymer wrapping or (b) a low molecular weight surfactant which may be easily washed off causing the formation of CNTs bundles again. Among the most common surfactants used, it is possible to find sodium cholate (SC) (Ishibashi and Nakashima 2006), sodium dodecyl sulfate (SDS) (Datsyuk et al 2009;Krause et al 2009;Moore et al 2003;Rastogi et al 2008;Richard et al 2003;Yu et al 2007), sodium dodecylbenzene sulfonate (SDBS) (Klumpp et al, 2006), Triton X (Moore et al 2003;Rastogi et al 2008), ammonium laurate (Nilsson et al 2015), Tween (Datsyuk et al 2009;Moore et al 2003;Rastogi et al 2008), Brij (Moore et al 2003), pluronic (Moore et al 2003;Vaisman et al 2006) and cethyltrimethylammonium bromide (CTAB) (Moore et al 2003) many of which can be toxic to living cells.…”

Beyond Color: The New Carbon Ink

“…Reproduced with permission. [ 196 ] Copyright 2015, American Chemical Society. f,g) Removable/decomposable polymers as stabilizers for SWCNTs.…”

“…reported the use of ammonium laurate as a novel type of surfactant to stabilize SWCNTs. [ 196 ] Importantly, when depositing the SWCNTs on the substrate, the free ammonium laurates do not build up on the surface, as occurs with other common dispersants, such as sodium dodecyl sulfate (SDS), providing cleaner substrate surfaces with much less debris (Figure 14e). This is possibly due to the fact that the low ionic strength of the ammonium laurate solution prevents it from interacting with the substrate surface.…”