277395 Thermophysical and Structural Properties of Electrolyte Solutions Confined in a Carbon Nanotube

Wednesday, October 31, 2012: 9:08 AM
412 (Convention Center )
Daniel W. Siderius1, Jeffrey A. Fagan2 and Vincent K. Shen1, (1)Chemical Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD, (2)National Institute of Standards and Technology, Gaithersburg, MD

Recently, single-wall carbon nanotubes (SWCNT) have found use as sensing materials where, for example, a particular nanotube chirality will bond to certain strands of DNA and, through further electronic measurements, can identify particular base sequences in a DNA strand [1]. When this type of technology has been sufficiently developed, solutions of SWCNTs could, in principle, be used for lab-on-chip biometric applications for gene identification. A key barrier at present is the satisfactory identification of SWCNTs in solution. It is difficult to separate SWCNTs by conventional analytical techniques and most significant progress has only occurred recently [2]. Furthermore, SWCNTs do not readily solubilize in water and a surfactant is typically used to disperse nanotube clusters.

Recent efforts to develop centrifugation techniques that efficiently and reliably separate SWCNTs by chirality have yielded a puzzling result: preliminary measurements have suggested that the density of the surfactant solution in a SWCNT exceeds the bulk density of water by nontrivial amounts for some SWCNT species [3]. If this effect is genuine, it must be a consequence of cation solvation, since the anionic surfactant itself is unable to enter the SWCNT due to size constraints. It is speculated that the alteration of the fluid density is a response to cation-induced restructuring of water in the nanotube.

We address this issue via grand-canonical transition-matrix Monte Carlo simulation, in an effort to eliminate effects that may obscure a clear measurement of the fluid density in experiment. Using the venerable SPC/E model of water [3], we compute solution density as a function of pressure and electrolyte content and compare our results to existing simulations of pure water in SWCNTs [4]. Our results present a clearer view of the phase behavior of electrolyte solutions in SWCNTs which will aid future efforts in reliably separating solutions of SWCNTs.

[1] Tang et al., Nano. Lett., 6:1632 (2006), Tu et al., J. Am. Chem. Soc., 133:12998 (2011)

[2] Fagan et al., Langmuir, 24:13880 (2008), Fagan et al., ACS Nano, 5:3943 (2011)

[3] Berendsen et al., J. Phys. Chem., 91:6269 (1987)

[4] Kyakuno et al., J. Chem. Phys., 134:244501 (2011), Pascal et al., Proc. Natl. Acad. Sci. USA, 108:11794 (2011)

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