Chemical influences on adsorption-mediated self-propelled drop movement

Abstract

We report studies of reactive wetting employing droplets of a nonpolar liquid (decahydronaphthalene) on chemically patterned surfaces. The drops contain an n alkylamine that adsorbs onto surfaces exposing carboxylic acid groups and produces surfaces exposing methyl groups. The change in surface energy that occurs concurrent with the formation of an oriented monomolecular film of alkylamine during this process is sufficient to produce a self-propelled movement of decahydronaphthalene drops on the surface. We employed patterning to direct the movement of the drops on the surface, thereby allowing measurements of the relationships between the macroscopic fluidic behavior of the droplets and microscopic adsorption events. Specifically, we examined the effects of the unbalanced surface-tension force and the influences of adsorbate concentration on drop movement. In this latter case, both kinetic and thermodynamic arguments can be applied to describe the system. We compared the predictions from these two approaches by analyzing data from the present system and those reported by F. Domingues Dos Santos and T. Ondarcuhu [Phys. Rev. Lett. 75(16), 2972 (1975)] that exhibited opposite trends in behavior. The present analysis provides insight into the influence of chemical reaction kinetics on adsorption-mediated drop movement (i.e., reactive wetting).

Mathematical model for self-propelled droplets driven by interfacial tension

“…(8)- (10). Here, we remark that the volume constraint is not complicated in our approach, since the solution with the constraint is proportional to that without it.…”

“…Spontaneous motion driven by inhomogeneity in interfacial tension is an area of study relating to active matter. [5][6][7][8][9][10][11][12][13][14][15][16] For example, alcohol droplets placed on water move spontaneously while exhibiting deformations to their shape. 17,18 Since such systems are relatively simple, it is possible to perform experiments under a broad parameter space; therefore, such a setting provides a preferable experimental framework for investigations of general aspects.…”

Mode Switching and Collective Behavior in Chemical Oil Droplets

“…When chemical potential is physically linked to movement, even in simple systems such an oil droplet in water [1][2][3][4][5][6][7], there is potential for emergent properties. The advantage of using simple chemical systems is that the underlying chemical and physical layers can be elucidated, shedding light…”

Statics and dynamics of a cylindrical droplet under an external body force

“…2 Alternatively, a temperature 3 or wettability gradient 4,5,6 can be applied at the substrate. Forces can also be exerted onto a droplet by immersing it into a sheared, viscous fluid.…”