We study the wetting by water of complex "hydropliobic-hydrophilic" Surfaces made of a hydrophobic substrate covered by a hydrophilic polymer brush. Polystyrene (PS) substrates covered with polystyrene-block-poly(acrylic acid) PS-b-PAA diblock copolymer layers were fabricated by Langmuir-Schaefer depositions and analyzed by atomic force microscopy (AFM) and ellipsometry. On bare PS Substrate, we measured advancing angles theta(A) = 93 +/- 1 degrees and receding angles theta(R) = 81 +/- 1 degrees. On PS covered with poorly anchored PS-b-PAA layers, we observed large contact angle hysteresis, theta(A) approximate to 90 degrees and theta(R) approximate to 0 degrees, that we attributed to nanometric scale dewetting of the PS-b-PAA layers. On well-anchored PS-b-PAA layers that form homogeneous PAA brushes, a wetting transition from partial to total wetting occurs versus the amount deposited: both OA and OR decrease close to zero. A model is proposed, based on the Young-Dupre equation, that takes into account the interfacial pressure of the brush Pi, which was determined experimentally, and the free energy of hydration of the polyelectrolyte monomers Delta G(PAA)(hyd), which is the only fitting parameter. With Delta G(PAA)(hyd) approximate to -1300 J/mol, the model renders the wetting transition for all samples and explains why the wetting transition depends mainly oil the average thickness of the brush and weakly oil the length of PAA chains.