Because water has a profound effect on the mechanical properties of bulk silica (so-called hydrolytic weakening) it is critical to understand whether there are chemo-mechanical phenomena in nano-scale silica systems. By systematic all-quantum (SIESTA)

1
Science and Software for Predictive Simulation of
Chemo-Mechanical Phenomena in Real Materials
Bartlett, Cheng, and Trickey Univ. of Florida
DMR-0325553 (ITR)
Because water has a profound effect on the
mechanical properties of bulk silica (so-called
hydrolytic weakening) it is critical to
understand whether there are chemo-mechanical
phenomena in nano-scale silica systems. By
systematic all-quantum (SIESTA) and multiscale
(DL_POLY SIESTA via our PUPIL software see
separate nugget) studies, we have found an
unexpected relation between hydration energy and
system strain, both internal and external. At
right is an SiO2 scissor chain with a water dimer
next to it. At far right the chain is coated
with a monolayer of water. Even at zero external
stress, the intrinsic structural strain is
sufficient to spontaneously dissociate water at
sub-picosecond times at room temperature.
Additional external stress speeds up the process
but does not change its fundamental nature. It is
not quenched by adding water notice the high
abundance of H3O and protons in the coated case.
We are investigating whether the phenomenon
occurs in more stable silica nanostructures.
Early indications are favorable.
2
Science and Software for Predictive Simulation of
Chemo-Mechanical Phenomena in Real Materials
Bartlett, Cheng, and Trickey Univ. of Florida
DMR-0325553 (ITR)
Education and Training Simulations with all
quantum and multi-scale techniques require that
the students and postdoctoral associates learn
several different conceptual approaches and the
techniques (mathematical and computa-tional) that
go with them. These results involve the work of
Chao Cao (Ph. D. student of H-P. Cheng), Yao He
(post-doctoral associate of Prof. Cheng), Krishna
Muralidharan (post-doctoral associate of S.B.
Trickey) and Juan Torras (senior postdoctoral
associate with Profs. Trickey and E. Deumens).
Muralidharan has gone to a postdoc at Univ. of
Arizona. Torras has returned to his faculty post
in Catalunya (Spain). The others continue with
the project.
Outreach Student and postdoctoral presentations
were given at APS Annual March Meeting 2006 and
Sanibel Symposium, February 2006. Much of the
work of this ITR project was presented by S.B.
Trickey in a short course (in Spanish) for the
Pontificía Universidad Católica, Santiago Chile,
in November 2005 (picture below), and by Profs.
Trickey and Cheng in four lectures for the PNNL
Workshop on Multiscale Mathematics, May 2006.