Recently, Professor Huiling Duan’s group from Department of Mechanics and Engineering Science, College of Engineering, has made important progress in nanofluidic control by nanoporous material, in collaboration with Professor Joerg Weissmueller and Professor Patrick Huber from Hamburg University of Technology. The research paper has been published online in Nature Communications (Switchable imbibition in nanoporous gold. Nature Communications 5:4237 DOI: 10.1038/ncomms5237. 
http://www.nature.com/ncomms/2014/140701/ncomms5237/full/ncomms5237.html). 
 

Nanofluidic transport exhibits novel interesting properties, spurring different applications in the analysis of the (bio) chemical and physical properties of small numbers of molecules. One issue of interest is the spontaneous imbibition of fluids in bodies with nanoscale dimensions. The capillarity-driven uptake of liquids by porous solids can be experienced in daily life, e.g., when a sponge imbibes water. Given the dominance of capillary forces at small length scales, it provides an elegant and effective way to propel nano-flows and is frequently employed for the synthesis of novel hybrid materials or used in the functionality of nano-devices. 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. 
 

The group’s work first demonstrates 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, they can accelerate the imbibition front, stop it, and have it proceed at will. Simultaneous measurements of the mass flux and the electrical current make it possible to document simple scaling laws for the imbibition kinetics, and to explore the charge transport in the metallic nanopores. Their findings show 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. 

Schematic of experiment setup and electric-switchable control of imbibition in nanoporoud gold
 

The first author of the paper is PhD candidate Yahui Xue from Professor Duan’s group. This paper is supported by Helmholtz-Chinese Scholarship Council, National Science Foundation and Alexander von Humboldt Foundation in Germany under a research group linkage program.