Atomistic Potentials for Trisiloxane, Alkyl Ethoxylate,
and Perfluoroalkane-Based Surfactants with TIP4P/2005 and Application
to Simulations at the Air–Water Interface
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Abstract
The mechanism of superspreading,
the greatly enhanced spreading
of water droplets facilitated by trisiloxane surfactants, is still
under debate, largely because the role and behavior of the surfactants
cannot be sufficiently resolved by experiments or continuum simulations.
Previous molecular dynamics studies have been performed with simple
model molecules or inaccurate models, strongly limiting their explanatory
power. Here we present a force field dedicated to superspreading,
extending existing quantum-chemistry-based models for the surfactant
and the TIP4P/2005 water model (Abascal et al. J. Chem. Phys., 2005, 123, 234505). We apply the model to superspreading trisiloxane surfactants and
nonsuperspreading alkyl ethoxylate and perfluoroalkane surfactants
at various concentrations at the air–water interface. We show
that the developed model accurately predicts surface tensions, which
are typically assumed important for superspreading. Significant differences
between superspreading and traditional surfactants are presented and
their possible relation to superspreading discussed. Although the
force field has been developed for superspreading problems, it should
also perform well for other simulations involving polymers or copolymers
with water