**3. Results and Discussion**

### *3.1. SLIPS Characterization*

For all investigated SLIPS, the same nanostructured pseudoboehmite AlOOH coating was used to retain the infused oil [27]. Such coating is made of randomly oriented lamellae (about 200 nm long and few nm thick) separated by 30–50 nm voids which serve as pockets for lubricant retention. The morphology of the, as-prepared, pseudoboehmite coating on aluminum is reported in Figure 1.

**Figure 1.** Scanning electron micrograph of the nanostructured pseudoboehmite layer. Scale bar is reported.

AlOOH coatings were infused with either PFPE or n-hexadecane. Table 1 reports all measured contact angle values for as-fabricated SLIPS.

**Table 1.** Kinematic viscosity of the infused oils at *T* = 40 ◦C and wetting data of related infused surfaces (ACA: Advancing Contact Angle, RCA: Receding Contact Angle, and CAH: Contact Angle Hysteresis; subscript W: Water and subscript H: Hexadecane). Standard deviations are reported as errors. Viscosity values were obtained from the suppliers.


All coatings infused with PFPE displayed excellent amphiphobicity, as both water and n-hexadecane drops did not stick to these surfaces leading to low contact angle hysteresis values. The increase in CAH observed for PFPE-infused SLIPS from Krytox 100 to 107 has already been reported in the literature [28] and is due to the increasing chain length of PFPE molecules, which leads to higher oil viscosity: the recession of water drops on these surfaces is hindered by pinning of their contact line, thus diminishing drop mobility and receding contact angle [29].

Hexadecane-infused SLIPS also showed excellent mobility of water drops, with a CAHW of 3.0◦. Obviously, these surfaces were completely oleophilic as hexadecane drops quickly wetted the surface, therefore it was not possible to measure contact angles with hexadecane.
