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

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.