On the deflection of the liquid–vapor interface in a wicked heat pipe

•An analytical model to investigate the (non-trivial) variation of the shape of the liquid-vapor interface along the adiabatic section of a heat pipe is developed.•This study pays particular attention to the case where a heterogeneous surface chemical treatment is applied to the wick to achieve an axial wettability gradient.•A key limitation associated with the classical notion of rendering the heat pipe wick uniformly hydrophobic is documented.•The study provides quantitative evidence suggesting that a heterogeneous surface chemical treatment offers performance benefits.