Temperature-Induced Hydrophobic-Hydrophilic Transition Observed by Water Adsorption
Hai-Jing Wang,
Xue-Kui Xi,
Alfred Kleinhammes,
Yue Wu*
The properties of nanoconfined and interfacial water in the
proximity of hydrophobic surfaces play a pivotal role in a variety
of important phenomena such as protein folding. Water inside
single-walled carbon nanotubes (SWNTs) can provide an ideal
system for investigating such nanoconfined interfacial water
on hydrophobic surfaces, provided that the nanotubes can be
opened without introducing excess defects. Here, we report a
hydrophobic-hydrophilic transition upon cooling from 22°C
to 8°C via the observation of water adsorption isotherms
in SWNTs measured by nuclear magnetic resonance. A considerable
slowdown in molecular reorientation of such adsorbed water was
also detected. The observed transition demonstrates that the
structure of interfacial water could depend sensitively on temperature,
which could lead to intriguing temperature dependences involving
interfacial water on hydrophobic surfaces.
* To whom correspondence should be addressed. E-mail: yuewu{at}physics.unc.edu
