Effect of Interaction of Nanoparticles and Surfactants on the Spreading Dynamics of Sessile Droplets

While
a body of literature on the spreading dynamics of surfactants
and a few studies on the spreading dynamics of nanocolloids exist,
to the best of the authors’ knowledge, there are no reports
on the effect of presence of surfactants on the spreading dynamics
of nanocolloidal suspensions. For the first time the present study
reports an extensive experimental and theoretical study on the effect
of surfactant impregnated nanocolloidal complex fluids in modulating
the spreading dynamics. A segregation analysis of the effect of surfactants
alone, nanoparticle alone, and the combined effect of nanoparticle
and surfactants in altering the spreading dynamics have been studied
in detail. The spreading dynamics of nanocolloidal solutions alone
and of the surfactant impregnated nanocolloidal solutions are found
to be grossly different, and particle morphology is found to play
a predominant role. For the first time the present study experimentally
proves that the classical Tanner’s law is disobeyed by the
complex fluids in the case of particle alone and combined particle
and surfactant case. We also discuss the role of imbibitions across
the particle wedge in the precursor film in tuning spreading dynamics.
We propose an analytical model to predict the nature of dependency
of contact radius on time for the complex colloids. A detailed theoretical
examination of the governing factors, the interacting forces at the
three phase contact line, and the effects of interplay of surfactants
and the nanoparticles at the precursor film in modulating the spreading
dynamics has been presented for such complex colloids.