Water Boiling Inside Carbon Nanotubes: Toward Efficient Drug Release

Abstract

We show using molecular dynamics simulation that spatial confinement of water inside carbon nanotubes (CNTs) substantially increases its boiling temperature and that a small temperature growth above the boiling point dramatically raises the inside pressure. Capillary theory successfully predicts the boiling point elevation down to 2 nm, below which large deviations between the theory and atomistic simulation take place. Water behaves qualitatively different inside narrow CNTs, exhibiting transition into an unusual phase, where pressure is gas-like and grows linearly with temperature, while the diffusion constant is temperature-independent. Precise control over boiling by CNT diameter, together with the rapid growth of inside pressure above the boiling point, suggests a novel drug delivery protocol. Polar drug molecules are packaged inside CNTs; the latter are delivered into living tissues and heated by laser. Solvent boiling facilitates drug release.

Entropy of single-file water in (6,6) carbon nanotubes

“…18,29 Recent experiments by Wu and coworkers 30 indeed showed drying, albeit for tubes of slightly larger diameter (1.4 nm) in which water is not expected to form single-file chains. So the question whether single-file water has larger or smaller entropy than bulk water remains open, both with respect to the differences between different computational results, and with respect to a decisive experimental test.…”

Quasiphase Transition in a Single File of Water Molecules Encapsulated in (6,5) Carbon Nanotubes Observed by Temperature-Dependent Photoluminescence Spectroscopy

“…[30,38] Quantum chemical calculations of water confined in these narrow diameters predict the existence of different ferro-electric groundstate conformations, depending on the model used: the water dipoles, all pointing in the same sense, either form an alternating, sizable angle with the SWCNT axis (classical hydrogen-bonded chains), [30,38,39] or are aligned parallel to the SWCNT axis (bifurcated hydrogen bonds). [14,40] Although the restricted lateral mobility in a single file precludes dis- tinguishing liquid from solid phases, [41] a transition in the orientational order of the water molecules cannot be excluded, for which experimental evidence is still lacking.…”

Why is the nanoscale special (or not)? Fundamental properties and how it relates to the design of nano-enabled drug delivery systems

“…The combination of the different solvents such as water and carbon dioxide under nanoconfinement could provide interesting pressure-activated devices. Heat, light, or electrical conduction could serve to induce the phase transition as the driving force for drug expulsion [162] .…”