Copper capillaries with lubricant-infused walls: fabrication and drag reduction performance

The lubricant-infused surface (LIS) has emerged as a promising drag reduction surface for flow enhancement. At present, there are some applications of LISs in polymer-based microchannels for drag reduction. However, the use of the LIS in metal capillaries or microchannels for drag reduction or flow enhancement is lacking. The present work proposes a method for the fabrication of a LIS on the inner surface of copper (Cu) capillaries to grant them sustainable drag reduction properties. Cu capillaries with an inner superhydrophobic surface (SHS) (contact angle > 160°) are also prepared as a reference for comparison. To test the hydrodynamic performance under different working conditions, we fabricated LIS Cu capillaries with lubricants of varying viscosities, and their frictional factors were experimentally measured with a Reynolds number (Re) ranging from 0 to 1500. The drag reduction of the LIS Cu capillary (32%) is slightly lower than that of the SHS Cu capillary (36%), but the LIS Cu capillary has much better sustainability. The threshold Re for initiating the failure of LIS Cu capillaries is almost three times that of the SHS Cu capillary, and the durability of the LIS Cu capillary under high shear force conditions is also much higher. The superior sustainability of the LIS Cu capillaries is due to the enhanced capillary and Van der Waals (vdW) forces caused by the composite morphology and functional groups applied to the LIS. The present study will provide useful insights for designing robust and sustainable LISs for drag reduction or flow enhancement in Cu capillaries.