We discuss the adsorption of a single polyampholyte chain with
degree of polymerization
N carrying Nf charges,
(Nf
+ positive and Nf
-
negative charges) on a charged surface with σ charges
per
unit area. The adsorption is due to the electrostatic polarization
of the polyampholyte chain, which
acquires a dipole moment in the surface electric field. Symmetric
Gaussian polyampholytes with equal
numbers of positive and negative charges adsorb if the surface charge
density σ is larger than
(1/al
B
N)·
(1/f
1/2) (l
B is the
Bjerrum length and a is the bond size). Polyampholyte
chains carrying a charge of the
same sign as the surface can also adsorb if the surface charge is large
enough. For a typical asymmetry
|f
- − f
+| ≈
(f/N)1/2, the adsorption threshold
is σ >
(1/al
B
N
3/4)(1/f
1/4).
The effect of the added salt on the
adsorption is considered. Finally, we determine the adsorption
threshold of a collapsed polyampholyte
globule.