Tuesday, July 31, 2007

More of the same

Two papers provide additional evidence of perturbations to water’s structure and properties at interfaces. The long saga about density depletion at hydrophobic surfaces now seems to be settling down in favour of the position that there is indeed a degree of depletion when the surfaces are strongly hydrophobic, but only over angstrom distances. That is supported by the Monte Carlo simulations of Jiri Janacek and Roland Netz (Langmuir 23, 8417; 2007), who see depletion layers 1.5-2 Å thick at ordered hydrocarbon surfaces with contact angles of 110-130 degrees.

And the idea that water confined at the nanoscale between surfaces has greatly enhanced viscosity (see, for example, Li et al., Phys. Rev. B 75, 115415; 2007) is supported in further experiments by Tai-De Li and Elisa Riedo at Georgia Tech, who have investigated water’s nonlinear viscoelastic behaviour using the AFM (www.arxiv.org/abs/ 0707.2521).

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