On the Motion of Carbon Nanotube Clusters near Optical Fiber Tips: Thermophoresis, Radiative Pressure, and Convection Effects

Abstract

We analyze the motion of multiwalled carbon nanotubes clusters in water or ethanol upon irradiation with a 975 and 1550 nm laser beam guided by an optical fiber. Upon measuring the velocities of the nanotube clusters in and out of the laser beam cone, we were able to identify thermophoresis, convection and radiation pressure as the main driving forces that determine the equilibrium position of the dispersion at low optical powers: while thermophoresis and convection pull the clusters toward the laser beam axis (negative Soret coefficient), radiation pressure pushes the clusters away from the fiber tip. A theoretical solution for the thermophoretic velocity, which considers interfacial motion and a repulsive potential interaction between the nanotubes and the solvent (hydrophobic interaction), shows that the main mechanism implicated in this type of thermophoresis is the thermal expansion of the fluid, and that the clusters migrate to hotter regions with a characteristic thermal diffusion coefficient D(T) of 9 × 10(-7) cm(2) K(-1) s(-1). We further show that the characteristic length associated with thermophoresis is not that of the nanotube clusters size, O(1) μm, but that corresponding to the microstructure of the clusters, O(1) nm. We finally discuss the role of the formation of gas-liquid interfaces (microbubbles) at high optical powers on the deposition of carbon nanotubes on the optical fiber end faces.

Photomechanical Polymer Nanocomposites for Drug Delivery Devices

“…Experimentally, both mechanisms can be present and thus contribute to the short and long-time release process of fluids contained in the proposed device. Furthermore, bubbles may be generated as well during the heating process due to micro-thermal cavitation thus enhancing the marker solution release process [ 47 ].…”

Negative Thermophoresis in Concentric Carbon Nanotube Nanodevices

“…The discovery and understanding of thermophoresis have provided ample opportunities for applications including thermal precipitation, , particle separation, , drug delivery, energy conversion, , biomolecule manipulation, − and interaction detection, and so forth. Thermophoresis was first discovered in liquids in 1856 by Ludwig, who observed salt diffusing in water against a temperature gradient.…”

“…Thermophoresis in aerosols was first reported in 1870 by Tyndall, who found that dust particles can be pushed away from a heated surface in a dust-filled room. However, in spite of the wide applications − ,− , of thermophoresis in fluids, it was not until more than a century later that thermophoresis at solid–solid interfaces was first predicted. In 2006, Schoen et al , demonstrated via molecular dynamics (MD) simulations that an axial temperature gradient along a single-walled carbon nanotube (SWCNT) would drive a confined nanoparticle to move toward the direction of decreasing temperature.…”

“…Negative thermophoresis in fluids was first noticed in 1967 by Dwyer in a theoretical solution, and the name was coined by Sone . The phenomenon was soon confirmed by a series of numerical calculations. − Very recently, negative thermophoresis in fluid was observed in experiments. ,, However, to this date, the existence of negative thermophoresis in solids still has not been verified in either theoretical or experimental studies, despite its potential applications in nanotechnology.…”

“…29−31 Very recently, negative thermophoresis in fluid was observed in experiments. 11,32,33 However, to this date, the existence of negative thermophoresis in solids still has not been verified in either theoretical or experimental studies, despite its potential applications in nanotechnology.…”