Observation of extreme phase transition temperatures of water confined inside isolated carbon nanotubes

Abstract

Fluid phase transitions inside single, isolated carbon nanotubes are predicted to deviate substantially from classical thermodynamics. This behaviour enables the study of ice nanotubes and the exploration of their potential applications. Here we report measurements of the phase boundaries of water confined within six isolated carbon nanotubes of different diameters (1.05, 1.06, 1.15, 1.24, 1.44 and 1.52 nm) using Raman spectroscopy. The results reveal an exquisite sensitivity to diameter and substantially larger temperature elevations of the freezing transition (by as much as 100 °C) than have been theoretically predicted. Dynamic water filling and reversible freezing transitions were marked by 2-5 cm shifts in the radial breathing mode frequency, revealing reversible melting bracketed to 105-151 °C and 87-117 °C for 1.05 and 1.06 nm single-walled carbon nanotubes, respectively. Near-ambient phase changes were observed for 1.44 and 1.52 nm nanotubes, bracketed between 15-49 °C and 3-30 °C, respectively, whereas the depression of the freezing point was observed for the 1.15 nm nanotube between -35 and 10 °C. We also find that the interior aqueous phase reversibly decreases the axial thermal conductivity of the nanotube by as much as 500%, allowing digital control of the heat flux.

Liquid Sulfur Impregnation of Microporous Carbon Accelerated by Nanoscale Interfacial Effects

“…Note that using the actual surface free energy of the 1.25 nm tube of −46.23 mJ/m 2 leads to a predicted ΔT m of 30.8 K, which is in very close agreement with the estimate from our MD simulations, and suggests deviation from the macroscopic Gibbs−Thomson equation due to specific molecular interactions at the nanoscale. We also note that the depression of the melting point of nanoencapsulated sulfur is opposite to the recently observed melting point enhancement (ΔT m < 0) for water encapsulated in carbon nanotubes 32 The relative stability of interfacial sulfur molecules decreases with increasing nanopore size, as expected from the geometric arguments cited above, and the overall thermodynamics of the system can be partitioned into adsorbed molecular layers with lower average free energy, and a bulk phase beyond ∼1 nm from the interface. This suggests a scaling law to predict excess interfacial free energy of sulfur molecules in filled carbon nanopores a priori.…”

The Carbon-Water Interface: Modeling Challenges and Opportunities for the Water-Energy Nexus

“…Using membranes with mono--disperse CNTs of inner diameter 2 nm, Holt et al (32) reported water flow rates 2--4 orders of magnitude faster than those predicted by continuum theories, but a few orders of magnitude smaller than those reported by Majumder et al (30), and consistent with MD predictions (14). Experiments on individual CNTs of 0.81 -1.59 nm diameter showed flow enhancement rates below 1000 (33), and sometimes just modest enhancements of water transport through individual CNTs (34). In summary, the experimental data are consistent in showing enhanced water flow through narrow CNTs, but the enhancement factor with respect to continuum fluid dynamics calculations is not uniquely determined.…”

Interaction of HF, HBr, HCl and HI Molecules with Carbon Nanotubes

“…35 Terminal carbon atoms are hydrogenated to saturate their valence. The formulas of the considered (3,3), (4,4), (5,5) and (6,6) carbon nanotubes are : C 36 H 12 , C 48 H 16 , C 60 H 20 and C 72 H 24 respectively. The optimized diameters of the chosen nanotubes are varying from 5.49 Å to 8.23 Å.…”

“…In particular, the confinement processes modifies the properties of the confined molecules in different ways. [16][17][18][19][20] In previous studies, we investigated the local influence of CNT's walls on small molecules H 2 21,22 and F 2 . 23 The former molecule H 2 allowed us to study the effect of the confinement on the electron of the single bond H-H.…”