Tailored nanostructured titania integrated on titanium micropillars with outstanding wicking properties

Abstract

A novel wicking material using nanostructured titania grown on high aspect ratio titanium micropillars is demonstrated. High aspect ratio titanium micropillars were micromachined from bulk titanium sheets. Nanostructured titania was then grown on the surface of titanium micropillars by oxidation in aqueous hydrogen peroxide solution followed by thermal annealing. The nanostructured titania formed has an open porous structure with a nanoscale pore diameter and wall thickness. X-ray diffraction and pole figure studies indicate the formation of anatase phase of titania and the absence of a preferred orientation in the porous film. The hybrid nanostructured titania on titanium micropillars has excellent hydrophilic properties with a water capillary speed comparable to or exceeding that of conventional wick materials commonly used in heat pipes for the thermal management of electronic devices.

Superwicking on Nanoporous Micropillared Surfaces

“…In stage I, the power-law fitting gives n L1 = 0.542, 0.548, and 0.563 for the pore depths of 1.5, 5.1, and 7.6 μm, respectively. The kinetics generally follows the power-law relation L ∝ t 1/2 , which is consistent with the droplet wicking shown on traditional hierarchical structures. − In stage II, the slope of the fitting curve increases to n L2 = 0.911, 0.866, and 0.876 for the pore depths of 1.5, 5.1, and 7.6 μm, respectively. The increase in the value of n L from stage I to stage II indicates the more significant effect of the nanoporous layer on the spreading behavior in stage II.…”

“…More recently, hierarchical structures with dual-scaled roughness have been demonstrated to have outstanding wicking speed compared to single-scaled structures. ,− Comparing with the single-scaled structures, the wicking speed for a liquid on hierarchical structures was enhanced significantly. For hierarchically structured surfaces, the power law L = k · t 0.5 has also been found to be valid for the wicking length versus time but with a greater value for the pre-exponential constant k .…”

“…As a result, an additional viscous loss associated with the secondary roughness may be introduced. To date, most superfast wicking phenomena have been realized on hierarchical structures of metallic substrates composing of micrometer-scale primary structures and nanoscale secondary roughness. ,− Recently, the development of advanced silicon-based thermal management technology has brought forward greater requirement of optimized wicking structures for silicon substrates. , In this study, nanopores rather than nanowires are tested as the second level of roughness to the microstructured surface of silicon. We expect that nanopores, as opposed to nanowires, will not narrow the liquid channels so that a droplet may not experience the significant viscous loss associated with the additional roughness.…”

Physics of Fluid Transport in Hybrid Biporous Capillary Wicking Microstructures

“…Because the theoretical limit of the base homogeneous wick is achieved at a contact angle of 0°, this type of hybridization only brings the performance of the hybrid wick closer to the theoretical limit of the base homogeneous wick. Examples of this type of wick include a CuO-coated micropillar array wick, , a carbon-nanotube-coated sintered powder wick, and nanotextured titania micropillar wicks. − …”