Enhanced capillary performance of multiscale microgroove wicks via constructing superhydrophilic TiO₂ nanostructures on wick surfaces

For water-filled titanium ultra-thin flat heat pipes (UTFHPs), superior wick performance is essential to ensure efficient operation and prevent dry-out. In this study, rectangular microgroove wicks were fabricated by electrically assisted micro-rolling, followed by hydrothermal treatment, acid pickling, and calcination to construct TiO₂ nanostructures on the microgroove surfaces. The results show that pure titanium was successively transformed from Na₂Ti₃O₇ to H₂Ti₃O₇ and finally to TiO₂. With increasing NaOH concentration, the TiO₂ morphology evolved from relatively loose structures to denser coverage, while W100–5 exhibited more open and interconnected nanoscale pores. Surface wettability and XPS analyses showed that abundant surface -OH groups on TiO₂ promoted water adsorption and spreading, resulting in excellent hydrophilicity. The capillary rise behavior was characterized by high-speed imaging, and the maximum average wicking velocity and capillary performance parameter (K/R_eff) reached 18.33 mm/s and 3.41 μm, respectively, corresponding to 280% and 741% of those of the untreated wick. Stability tests further showed that the TiO₂ nanostructures and primary microgroove morphology were generally maintained after vacuum storage, ambient aging, and 90 °C water flushing, while the main capillary enhancement effect was retained. The proposed “plastic microforming-chemical modification” strategy enhances the capillary performance of titanium wicks while maintaining the wick thickness within 75–240 μm, showing potential for UTFHPs applications.