Switchable imbibition in nanoporous gold

Abstract

Spontaneous imbibition enables the elegant propelling of nano-flows because of the dominance of capillarity at small length scales. The imbibition kinetics are, however, solely determined by the static host geometry, the capillarity, and the fluidity of the imbibed liquid. This makes active control particularly challenging. Here we show for aqueous electrolyte imbibition in nanoporous gold that the fluid flow can be reversibly switched on and off through electric potential control of the solid–liquid interfacial tension, that is, we can accelerate the imbibition front, stop it, and have it proceed at will. Simultaneous measurements of the mass flux and the electrical current allow us to document simple scaling laws for the imbibition kinetics, and to explore the charge transport in the metallic nanopores. Our findings demonstrate that the high electric conductivity along with the pathways for fluid/ionic transport render nanoporous gold a versatile, accurately controllable electrocapillary pump and flow sensor for minute amounts of liquids with exceptionally low operating voltages.

A Switchable and Compressible Carbon Nanotube Sponge Electrocapillary Imbiber

“…This on-off switchable imbibition rate is over 20-fold higher than what can be achieved in oil-preimbibed nanoporous Au (3.5 nL s −1 mm −2 ). [ 8 ] It even compares favorably to the results obtained with nanoporous Au in air under potential control (21-27 nL s −1 mm −2 ) [ 8 ] and the microstructures etched in silicon as capillary pumps (0.7-12 nL s −1 mm −2 ), [ 30 ] respectively. The fast liquid uptaking in CNT sponges may be attributed to their highly conductive 3D network made by stacked CNTs, interconnected fl ow channels throughout the open-porous structure, and especially the ultrahigh porosity.…”

“…For nanoporous Au reported previously, another solvent must be preimbibed in order to diminish the spontaneous fi lling of the electrolyte. [ 8 ] In contrast, empty CNT sponges are amenable to realize on-off switching due to their hydrophobic nature.…”

“…[ 6,7 ] Recently, the electrocapillary effect was utilized to accelerate the liquid fl ow through a conductive media (nanoporous Au) under low operating voltages (e.g., −1 V). [ 8 ] Although on-off switching was demonstrated, the hydrophilic nature of Au required preloading of another solvent (cyclohexane) to prevent spontaneous imbibition of water (in order to completely switch off), which consequently restricted the fl ow rate during the "on" state. In addition, fl exible nanofl uidic systems with tailored pore sizes are highly desired for many applications, and methods such as mechanical actuation of elastomeric pores have already been proposed.…”

Nanoporous Gold by Alloy Corrosion: Method-Structure-Property Relationships

“…10 Dealloying is the removal of the less noble element from a solid solution or intermetallic compound (e.g. Au-Ag, [11][12][13] Au-Cu 13,14 or Au-Al 15,16 ) by selective corrosion.…”

Heterogeneous-surface-mediated crystallization control

“…It can also be noted that, in addition to the trace-detection application demonstrated above, the constructed nanoporous membrane is also promising to serve other purposes such as catalyst supports, nanoelectronic scaffolds, filters for biomolecule purification and switchable fluid/ionic transport. [29][30][31] Furthermore, unique membranes with porous architectures may potentially show superior electrochemical properties. 32 The success in simultaneously tailoring the crystallization efficiency and the morphology of the products on the heterogeneous surface is also of special interest for the control of both bone and tooth formation.…”