Though long-lived nanobubbles (NBs)
have been reported
by multiple
researchers, the underlying reason behind their stability is still
obscure. Some of the conjectured reasons include diffusive shielding,
the presence of surface charges, and stability due to contamination.
Still, the stability of NBs against coalescence and Ostwald ripening
is not confirmed. Using molecular dynamics simulations, the present
study aims to understand the stabilization effects due to diffusive
shielding and the presence of an electrical double layer at the surface
of NBs. Accumulation of charges on NBs for different concentrations
of ions is discussed. Also, the collision of equal-sized NBs with
different approach velocities and offset distances is simulated. A
regime map is predicted on the basis of initial approach velocity
and offset distance. The transition in regime obtained upon increasing
the offset distance is discussed, which differs from the collision
characteristics of macroscopic bubbles and drops. The merging of NBs
is initiated through the bridge formation, for which the temporal
evolution rate along with the scaling argument is presented. The stress
terms involved and the corresponding regimes are predicted based on
the fluid properties. For all the cases where merging is observed,
the estimated probability is observed to be low, which suggests the
stability of NBs against coalescence.
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