11-06/07 :: June/July 2011

nanotimes News in Brief

implantation, and later soft in order to slow down rejection.

http://www.nrp62.ch http://www.am-institute.ch

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Tod A. Pascal, William A. Goddard, and Yousung Jung: Entropy and the driving force for the filling of carbon nanotubes with water, In: PNAS Early Edition, June 27, 2011, DOI:10.1073/pnas.1108073108: http://dx.doi.org/10.1073/pnas.1108073108

Researchers at Korea Advanced Institute of Sci- ence and Technology, Korea; and California In- stitute of Technology, USA, reported in PNAS the entropy, enthalpy, and free energy extracted from molecular dynamics simulations of water con- fined in CNTs from 0.8 to 2.7-nm diameters.

They found for all sizes that water inside the CNTs is more stable than in the bulk, but the nature of the favorable confinement of water changes drama- tically with CNT diameter. Thus they found (i) an entropy (both rotational and translational) stabi- lized, vapor-like phase of water for small CNTs (0.8 to 1.0 nm), (ii) an enthalpy stabilized, ice-like phase for medium-sized CNTs (1.1 to 1.2 nm), and (iii) a bulk-like liquid phase for tubes larger than 1.4 nm, stabilized by the increased translational entropy as the waters sample a larger configurational space. Simulations with structureless coarse-grained water models further reveal that the observed free ener- gies and sequence of transitions arise from the tetra- hedral structure of liquid water. These results offer a broad theoretical basis for understanding water transport through CNTs and other nanostructures important in nanofluidics, nanofiltrations, and desalination. © PNAS

U.S. researchers published in Science an article on carbon-based supercapacitors produced by activation of graphene. Using chemical activation of exfoliated graphite oxide, researchers at University of Texas at Austin (USA), University of Texas at Dallas (USA), Quantachrome Instruments (USA), and Brookhaven National Laboratory (USA) syn- thesized a porous carbon with a Brunauer-Emmett- Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxy- gen and hydrogen content. This sp2-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid elec- trolytes. The processes used to make this carbon are readily scalable to industrial levels. © Science

Yanwu Zhu, Shanthi Murali, Meryl D. Stoller, K. J. Ganesh, Weiwei Cai, Paulo J. Ferreira, Adam Pirkle, Ro- bert M. Wallace, Katie A. Cychosz, Matthias Thommes, Dong Su, Eric A. Stach, Rodney S. Ruoff: Carbon-Based Supercapacitors Produced by Activation of Graphene, In: Science, Vol. 332(2011), No. 6037, June 24, 2011, Pages 1537-1541, DOI:10.1126/science.1200770: http://dx.doi.org/10.1126/science.1200770