Enhanced Thermal Conductivity of Water with Surfactant Encapsulated and Individualized Single-Walled Carbon Nanotube Dispersions

In the present work, the effective thermal conductivity of single walled carbon nanotube dispersions in water was investigated experimentally using a transient hot wire technique at room temperature. Single-walled carbon nanotubes (SWNTs) were synthesized using the alcohol catalyzed chemical vapour deposition method [1]. The diameters of the SWNTs were determined using resonant Raman spectroscopy and photoluminescence spectroscopy. Sodium deoxy cholate (SDC), a bile salt was used as the surfactant to prepare the nanofluid dispersion. Nanotube loading of up to 0.3 vol% was used. The maximum enhancement in thermal conductivity was found to be 13.9% at 0.3 vol% loading. Many mechanisms such as particle clustering, Brownian motion, ordered liquid layering were considered to be responsible for the thermal conductivity enhancement in the open literature [2]. Photoluminescence (PL) spectroscopy reveals that majority of the nanotubes were highly individualized when SDC was employed as the surfactant. Based on our PL measurements we conclude that the particle clustering was not the major reason for the thermal conductivity enhancement. The possible mechanisms for the enhancement observed may be attributed to the Brownian motion of the micelles and percolation of the nanotubes to form a tridimensional network. The experimental results were compared with previous findings in the literature and classical theoretical models.