Thermo-Osmotic Flow in Thin Films

Abstract

We report on the first micro-scale observation of the velocity field imposed by a non-uniform heat content along the solid/liquid boundary. We determine both radial and vertical velocity components of this thermo-osmotic flow field by tracking single tracer nanoparticles. The measured flow profiles are compared to an approximate analytical theory and to numerical calculations. From the measured slip velocity we deduce the thermo-osmotic coefficient for both bare glass and Pluronic F-127 covered surfaces. The value for Pluronic F-127 agrees well with Soret data for polyethylene glycol, whereas that for glass differs from literature values and indicates the complex boundary layer thermodynamics of glass-water interfaces.

Nanoscale Seebeck effect at hot metal nanostructures

“…The novel result concerns the thermoelectric contribution to (35), that is, the first term proportional to the electrolyte Seebeck coefficient S. The remaining term T µ and that e µ are known as thermo-osmosis [5,26], whereas the last one, n µ , is similar to salt osmosis [36,37]. As a main finding of this work, we note that v s does not depend on the electrical conductivity of the particle surface.…”

“…Then s corresponds to the charge per unit area of the surface, which exactly cancels that of the diffuse layer. On the contrary, the main results of the present paper are derived from equation (10), with the outer boundary condition determined by the thermoelectric far-field (5). This implies that σ as defined in (10) contains counterions and thermocharge, and thus does no longer define the surface charge density.…”

“…is zero at the particle surface. With increasing distance, the double-layer potential j s decays and vanishes well beyond the screening length, and the electric field is given by (5). The overall behavior is best displayed in Debye-Hückel approximation,…”

“…In this paper we study how the electrolyte Seebeck effect modifies the electric double layer and drives a creep flow along a surface with non-uniform temperature. The main features are illustrated in figure 1 at the example of a gold-capped Janus particle, but are generally valid for metal nanostructures in contact with water [2][3][4][5][6]. Upon heating the gold cap with a laser, the salt ions move along the temperature gradient, and an excess charge Q T forms at the hot surface, as shown in the middle panel; the corresponding negative ions are at the wall of the container.…”

What Controls Thermo-osmosis? Molecular Simulations Show the Critical Role of Interfacial Hydrodynamics

“…In that context, Ganti et al [32] have explored three different methods to characterize thermo-osmosis using molecular simulations, and they found that all methods yield very similar results. Bregulla et al [33] reported the first microscale observation of the velocity field imposed by a nonuniform temperature and deduced the thermo-osmosis coefficient for different surfaces. Nevertheless, the role of surface wettability and interfacial hydrodynamics have hardly been discussed so far.…”