The unique structural, optical, and electronic properties of single-walled carbon nanotubes (SWCNTs) lend themselves to a breadth of potential applications. However, a difficulty in realizing widespread use of these materials is the polydispersity of samples in terms of size, chirality, and handedness due to the uncontrolled nature of current synthesis techniques. Numerous separation techniques with related protocols have been developed for use on SWCNTs. Most protocols involve adding surfactants to suspend the tubes in an aqueous media before using techniques such as ion-exchange chromatography (IEX) or aqueous two phase extraction (ATPE) to separate the SWCNTs based on their physiochemical properties. Single-stranded DNA (ssDNA) has proven to be an effective dispersant that exhibits sequence-chirality specific binding behavior. Experimental work has displayed the ability to exploit this specificity to tune the separation for particular nanotube chiralities. However, the mechanism that leads to optimal ssDNA-sequence/ SWCNT-chirality pairs is not understood and the search for further successful pairs requires lengthy trial and error studies. In this study, we use replica exchange molecular dynamics (REMD) simulations to assemble the dispersed ssDNA-SWCNT complexes and then apply free energy perturbation methods to estimate their solvation energy. A novel free energy pathway has been proposed in order to calculate this quantity for such self-assembled systems. Additionally, the structure and dynamics of the solvent shell have been analyzed to better understand the behavior on a molecular level and to provide insight into how ssDNA sequence can play such a large role in the separation. These investigations work towards our ultimate goal of providing better insight into the sequence-chirality specific separation mechanism, and eventually developing a model that allows for the prediction of other pairs leading to the efficient sorting of a desired nanotube chirality.<br/>

Calculation of free-energy of solvation for self-assembled systems: SWCNT-ssDNA hybrids in water/ alcohol mixtures

254th National Meeting (2017)

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