The structure and dynamics of water confined in quasi one-dimensional and quasi two-dimensional carbon nanostructures is highly intriguing. Being confined in structures with dimensions not much larger than their own size, the water molecules adopt hydrogen-bonded structures distinctly different from those of bulk water, and also various dynamic properties such as phase transitions differ quantitatively.
Water confined in carbon nanostructures
Burkhard Schmidt with Guillermo Pérez-Hernández and Shujuan Li
Cooperation with Shulai Lei, Beate Paulus (Dept. of Chemistry, FU Berlin)
Support by Chinese Scholarship Council and FU Berlin through focus area "Nanoscale"
The narrowest carbon nanotubes (CNTs) known to be water-permeable are (5,5) CNTs (diameter 0.68 nm) where the water molecules arrange in a quasi one-dimensional chain. From (7,7) CNTs (diameter 0.94 nm) onwards, the molecules tend to form ice nanotubes (INTs) which can be found as (chiral) helices or as stacked water polygonal prisms . Moreover, the focus of our work is on the orientation of the water dipoles, with emphasis on the question of ferroelectric, ferrielectric, or antiferroelectric proton ordering. These modifications can be regarded as genuine phases of water with their dependence on temperature, pressure or other simulation details . In other work we have also studied the structure and dynamics of quasi two-dimensional water monolayers confined in nanocapillaries between two layers of graphene where we find rhombic and nearly squre ice phases with characteristic proton ordering patterns .
In contrast to most previous work where the water-carbon interaction is modeled in an essentially empirical way, our work relies on the parametrization of force fields on the basis of the best available ab initio quantum chemical calculations at the CCSD(T) level of theory. In doing so we find that (1) the carbon materials are less hydrophobic than commonly anticipated and (2) that the water-carbon interaction is notably anisotropic , .