ABSTRACT
Soft interfaces are a distinctive feature of a large group of membranes in which the most representative group is formed by some biological structures such as proteins, cells and lipid membranes [1-6]. In these membrane systems the hydrophobic groups form, in some sense, a core which is shielded from the aqueous medium by the hydrophilic groups. The latter extend into the water region and create a polar zone whose boundaries are far from being sharp. Actually, the polar zone thickness L is a phenomenological parameter that describes the extent of water and ion penetration into this region of the membrane.
