Impedance of Thermal Conduction from Nanoconfined Water in Carbon Nanotube Single-Digit Nanopores

Abstract

There has been recent interest in understanding the transport of nanoconfined fluids through single-digit nanopores (SDNs) or those smaller than 10 nm in diameters, where confinement alters the fluid structure and intermolecular potential. Thermal measurements on such systems are crucial to extracting phase boundaries and the thermodynamic properties of fluids under extreme confinement. In this work, we introduce a metrology approach based on micro-Raman spectroscopy of isolated, free-standing replicates of the identical chirality carbon nanotube suspended over windows between 17 and 200 μm in length to assess spatial variations in axial thermal conduction from segment to segment and upon filling with water. We show that a mathematical heat transfer model based on Fourier's law and diffusive phonon transport can be applied to extract estimates of the thermal conductivity κ. Accounting for nearly a 50% variation among different segments of the same chirality tube, the technique allows revealing the impact of fluid confinement. Our measurements indicate that nanoconfined water enhances acoustic phonon scattering impeding axial transport through SDNs, with a (17,9) carbon nanotube showing a reduction of 10 −3 m K/W. This newfound understanding and thermal measurements on nanoconfined water in carbon nanotube SDNs will advance both theory and experiment of fluids constrained to extreme volumes.

Finely tuned water structure and transport in functionalized carbon nanotube membranes during desalination

“…2c, water molecule forms HBs with both the water molecules in the cross-section and axial direction, generating a hexagonal tube-like HB network. Other studies 69,70 had also reported this hexagonal water structure in (9,9) CNT, which exhibited ice-like behaviour and very low diffusion capability. In OH-(9,9) CNT, the average q between water dipole with z axis is ca.…”

Reorientation of Hydrogen Bonds Renders Unusual Enhancement in Thermal Transport of Water in Nanoconfined Environments

“…The ultrafast transport property in nanoconfined liquid offers a unique opportunity for heat and mass transfer, holding potential to address the bottleneck in the thermal management of high-power density electronic devices with local heat flux up to 10 3 W/cm 2 and concentrated heat sources. , However, the thermal properties of nanoconfined water are controversial because of opposite findings on the confinement effects on phonon activities and thermal conduction. − Specifically, atomistic simulation has revealed that the nanoconfinement can reduce the thermal conductivity of water in a copper channel due to enhanced phonon scattering at the solid–liquid interface, indicated by the redshift of peaks in the vibrational spectrum . In contrast, the thermal conductivity of water confined in a subnanometer graphene channel is increased to twice the bulk value with suppressed phonon scattering .…”

Observation and Isochoric Thermodynamic Analysis of Partially Water-Filled 1.32 and 1.45 nm Diameter Carbon Nanotubes

“…Enhanced flow can be predicted by corrections to Hagen–Poiseuille theory, linking transport results inside isolated carbon nanotubes with less precise but more readily available measurements of membranes and multipore systems. , Thermodynamically, phase boundaries of water inside isolated single-digit carbon nanotubes vary nonmonotonically with confining diameter in ways that cannot be explained by existing theories . Finally, recent advances in fabrication of isolated carbon nanotube systems by segmentation of ultralong carbon nanotubes into shorter segments , allow comparison between filled and empty segments of the same diameter and chirality carbon nanotube.…”

“…24,25 Thermodynamically, phase boundaries of water inside isolated single-digit carbon nanotubes vary nonmonotonically with confining diameter in ways that cannot be explained by existing theories. 19 Finally, recent advances in fabrication of isolated carbon nanotube systems by segmentation of ultralong carbon nanotubes into shorter segments 26,27 allow comparison between filled and empty segments of the same diameter and chirality carbon nanotube. Herein, we observe closed, isolated carbon nanotubes that appear either empty, completely filled with liquid water, or partially water-filled.…”

“…Our study utilizes a previously introduced platform to study isolated, segmented carbon nanotubes (Figure ). ,− Ultralong carbon nanotubes were grown on marked silicon substrates by chemical vapor deposition of methane in hydrogen, using a carbon nanotube solution as a catalyst, as reported previously (Figure a). ,, CNTs were cut by a focused gallium ion beam to produce segments with lengths from 10 to 160 μm (Figure b). CNTs were then characterized by Raman spectroscopy using a 532 nm laser to estimate diameter and determine fluid filling state.…”