Adsorption of Polyampholytes to Charged Surfaces

The adsorption of flexible polyampholytes to charged surfaces has been investigated. The electrostatic interactions are included in a mean-field manner, while the chain connectivity is treated by Metropolis Monte Carlo (MC) simulations. For large enough surface charge densities, adsorption is found both for neutral polyampholytes and for polyampholytes carrying the same net charge as the surfaces. The simulation results are used to check the reliability of previously proposed analytical theories. The exponents predicted in those scaling relations are not reproduced by MC simulations. The simulations show that the size of the adsorbed polyampholyte initially grows with increasing surface charge density, but for sufficiently charged surfaces it reaches a maximum and starts to decrease. This general behavior is qualitatively captured by scaling arguments. The MC simulations do not bear any evidence for the existence of three disparate regimes where the polyampholyte adsorbs in different conformations.