Visualization experiments are performed for horizontal mesh-wick flat-plate heat pipes with the evaporator and condenser sections chemically treated to manifest different surface wettabilities. Deionized water is used as the working fluid. The static contact angles (theta(0)s) examined include theta(0,e) = 0 degrees and 13 degrees (untreated) and theta(0.c) = 0 degrees, 13 degrees, 80 degrees and 120 degrees. The measured evaporator resistances are similar for theta(0.e) = 0 degrees and 13 degrees. The condenser resistances for theta(0.c) = 0 degrees are the highest as the liquid in the condenser levels up to the wick top. The condensation for theta(0.c)= 13 degrees or larger exhibits cyclic dropwise condensation on the islands of exposed wire sections. With theta(0) as large as 120 degrees, the water level in the condenser was lowest but numerous large round drops may sustain a while, along with other rapidly growing drops of different sizes, before they rupture and drain away. These large round drops act as heavy thermal barrier so that condenser resistances for theta(0.c) = 80 degrees and 120 degrees are higher than for theta(0,c) = 13 degrees. Hydrophilic treatment on the evaporator fails to enlarge Q(max), because while the capillarity increases slightly from theta(0) = 13 degrees to theta(0) = 0 degrees, the liquid flow is hindered by the deposited nanostructures. Among all the surface conditions tested, the untreated wick (theta(0) = 13 degrees) exhibits the best performances in both and total thermal resistance. (C) 2017 Elsevier Ltd. All rights reserved.