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We study the behavior of Janus colloidal particles in the nematic liquid crystal 5CB using polarizing optical microscopy and Landau-de Gennes (LdG) modeling. Different equilibrium orientations of Janus particles and different director field configurations around them are observed, depending on the preparation technique of homeotropic (DMOAP) and planar (Au) hemispheres. Using laser tweezers we measure the interactions between different orientations of Janus nematic colloids, showing a boojum type of interaction in the case of DMOAP/Au capped colloids and dipolar-like attraction for Au/DMOAP capped colloids. We observe a novel type of nematic colloidal particle, called a boojum-ring, characteristic of Au/DMOAP Janus nematic colloids, that is also predicted within the LdG theory for patterned colloidal particles with competing homeotropic and planar surfaces.

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Controlling the surface wettability represents an important challenge in the field of surface functionalization. Here, the wettability of a stainless-steel surface is modified by 30-ns pulses of a Nd:YAG marking laser (λ = 1064 nm) with peak fluences within the range 3.3–25.1 J cm−2. The short- (40 days), intermediate- (100 days) and long-term (1 year) superhydrophilic-to-(super)hydrophobic transition of the laser-textured surfaces exposed to the atmospheric air is examined by evaluating its wettability in the context of the following parameters: (i) pulse fluence; (ii) scan line separation; (iii) focal position and (iv) wetting period due to contact angle measurements. The results show that using solely a short-term evaluation can lead to wrong conclusions and that the faster development of the hydrophobicity immediately after laser texturing usually leads to lower final contact angle and vice versa, the slower this transition is, the more superhydrophobic the surface is expected to become (possibly even with self-cleaning ability). Depending on laser fluence, the laser-textured surfaces can develop stable or unstable hydrophobicity. Stable hydrophobicity is achieved, if the threshold fluence of 12 J cm−2 is exceeded. We show that by nanosecond-laser texturing a lotus-leaf-like surface with a contact angle above 150° and roll-off angle below 5° can be achieved.