Aqueous solution-chemical derived NiAl2O3 solar selective absorbing coatings. 2. Wetting agents and spreading of aqueous solutions on aluminum substrate

► The efficiency of wetting depended on the length of POE chain of the nonionic surfactants. ► The nonionic surfactants with a long POE chain were suitable as the wetting agents. ► The NiAl2O3 coatings containing wetting agents with long POE chain generated a high solar absorptance of 0.81.