posted on 2023-11-13, 18:12authored byMonicka Kullappan, Wes Patel, Manoj K. Chaudhury
While various attempts
have been made to understand the mechanism
of spontaneous emulsification within the scopes of equilibrium and
nonequilibrium thermodynamics, the local processes underlying spontaneous
emulsification still remain elusive. In this research, we investigate
the local processes that involve the transfer of surfactants as well
as water from an aqueous phase to oil, which results in the formation
of a water-in-oil emulsion in the organic phase. Subsequently, these
emulsions invert into the oil-in-water emulsion rather abruptly as
they cross the phase boundary. Studies based on ultraviolet (UV) spectroscopy
and nonequilibrium molecular dynamics simulations indicate that the
crossing of the phase boundary may involve catastrophic explosions
and subsequent assembly of the resulting fragments to other organized
structures. These processes lead to the fluctuation of the component
concentrations below the interface that also becomes evident in the
fast (athermal) diffusion of the emulsion droplets from the interfacial
region farther into bulk water. Spontaneous emulsification is found
to be amplified in mixed solvents, but it can be arrested with additives
that reduce solubility or inhibit the transfer of water and surfactants
in the organic phase.