  A theory for wetting of structured solid surfaces is developed, based on the
delta-comb periodic potential. It possesses two matching parameters: the
effective line tension and the friction coefficient on the three-phase contact
line at the surface. The theory is validated on the dynamics of spreading of
liquid zinc droplets on morphologically patterned zinkophilic iron surface by
means of square patterns of zinkophobic aluminum oxide. It is found that the
effective line tension is negative and it has essential contribution to the
dynamics of spreading. Thus, the theoretical analysis shows that the presence
of lyophobic patterns situated on lyophilic surface makes the latter completely
wettable, i.e. no equilibrium contact angle on such surface exists making the
droplet spread completely in form of thin liquid layer on the patterned
surface.
