Structure and Dynamics of Ionic Micelles: MD Simulation
and Neutron Scattering Study
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Abstract
Fully atomistic molecular dynamics
(MD) simulations have been carried
out on sodium dodecyl sulfate (SDS), an anionic micelle, and three
cationic (C<sub><i>n</i></sub>TAB; <i>n</i> =
12, 14, 16) micelles, investigating the effects of size, the form
of the headgroup, and chain length. They have been used to analyze
neutron scattering data. MD simulations confirm the dynamical model
of global motion of the whole micelle, segmental motion (headgroup
and alkyl chain), and fast torsional motion associated with the surfactants
that is used to analyze the experimental data. It is found that the
solvent surrounding the headgroups results in their significant mobility,
which exceeds that of the tails on the nanosecond time scale. The
middle of the chain is found to be least mobile, consolidating the
micellar configuration. This dynamical feature is similar for all
the ionic micelles investigated and therefore independent of headgroup
form and charge and chain length. Diffusion constants for global and
segmental motion of the different micelles are consistent with experimentally
obtained values as well as known structural features. This work provides
a more realistic model of micelle dynamics and offers new insight
into the strongly fluctuating surface of micelles which is important
in understanding micelle dispersion and related functionality, like
drug delivery