  We consider a model of bilayer lipid membrane with interdigitation, in which
the lipid tails of the opposite monolayers interpenetrate. The interdigitation
is modeled by linking tails of the hydrophobic chains in the opposite
monolayers within bilayer as a first approximation. A number of thermodynamical
characteristics are calculated analytically and compared with the ones of a
regular membrane without interdigitation. Striking difference between lateral
pressure profiles at the layers interface for linked and regular bilayer models
is found. In the linked case, the lateral pressure mid-plane peak disappears,
while the free energy per chain increases. Within our model we found that in
case of elongation of the chains inside a nucleus of e.g. liquid-condensed
phase, homogeneous interdigitation would be more costly for the membrane's free
energy than energy of the hydrophobic mismatch between the elongated chains and
the liquid-expanded surrounding. Nonetheless, an inhomogeneous interdigitation
along the nucleous boundary may occur inside a ``belt'' of a width that varies
approximately with the hydrophobic mismatch amplitude.
