2016/07/07 by Joel Koplik, Koplik, Joel, Charles Maldarelli +1
Materials Science · Engineering · #Pickering emulsions and particle stabilization #Material Dynamics and Properties #Phase Equilibria and Thermodynamics
paper · pdf · doi:10.48550/arxiv.1607.02116
Measurements of the surface diffusivity of colloidal spheres translating\nalong a vapor/liquid inter- face show an unexpected decrease in diffusivity, or\nincrease in surface drag (from the Stokes-Einstein relation) when the particles\nsituate further into the vapor phase. However, direct measurements of the\nsurface drag from the colloid velocity due to an external force find the\nexpected decrease with deeper immersion into the vapor. The paradoxical drag\nincrease observed in diffusion experiments has been attributed to the\nattachment of the fluid interface to heterogeneities on the colloid surface,\nwhich causes the interface, in response to thermal fluctuations, to either jump\nor remain pinned, creating added drag. We have performed molecular dynamics\nsimulations of the diffusivity and force experiments for a nanoparticle with a\nrough surface at a vapor/liquid interface to examine the effect of contact line\nfluctuations. The drag calculated from both experiments agree and decrease as\nthe particle positions further into the vapor. The surface drag is smaller than\nthe bulk liquid drag due to the partial submersion into the liquid, and the\nfinite thickness of the interfacial zone relative to the nanoparticle size.\nContact line fluctuations do not give rise to an anomalous increase in drag.\n