Shielding of Single Walled Carbon Nanotubes by Sodium Dodecyl Sulfate in Aqueous Solution: Molecular Dynamics Study*

Single-walled carbon nanotubes (SWNT) exhibit a temperature dependent near infrared (NIR) exciton spectrum when solvated in water with the help of sodium dodecyl sulfate (SDS) surfactants. Since SWNTs are biocompatible and the NIR spectrum is in transparent window for biological tissue, this represents a potential means for sensing temperature inside cells. Here we seek to investigate a possible mechanism for this temperature dependence: changes in the water coverage of the SWNT as the surfactant structure changes with temperature. Using fully atomistic molecular dynamics simulations we observe for the conditions of our simulation that the SDS structure shield the SWNT effectively, with ~ 70% of water molecules removed from the first two adlayers; this coverage showing a modest temperature dependence. Although we are not able to directly show how this influences the NIR spectrum, this represents a possible pathway since there is a strong influence of the water environment on the excitons in SWNTs.