Bulk properties
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Water confined within a surfactant bilayer |
The water confined within a surfactant bilayer is studied using different water models via
molecular dynamics simulations. We considered four representative rigid models of water:
the SPC/E and the TIP4P/2005, which are commonly used in numerical calculations and the
more recent TIP4Q and SPC/epsilon models, developed to reproduce the dielectric behaviour of
pure water. The static dielectric constant of the confined water was analyzed as a function
of the temperature for the four models. In all cases it decreases as the temperature increases.
Additionally, the static dielectric constant of the bilayer-water system was estimated through
its expression in terms of the fluctuations in the total dipole moment, usually applied for
isotropic systems. The estimated dielectric was compared with the available experimental data.
We found that the TIP4Q and the SPC/epsilon produce closer values to the experimental data than
the other models, particularly at room temperature. It was found that the probability of finding
the sodium ion close to the head of the surfactant decreases as the temperature increases, thus
the head of the surfactant is more exposed to the interaction with water when the temperature
is higher.
