Polyampholyte Brushes Grafted on the Surface of a Spherical Cavity: Effect of the Charged Monomer Sequence, Grafting Density, and Chain Stiffness

Molecular dynamics simulations are used to study the conformational behaviors of the flexible and semiflexible polyampholytes coated onto the internal surface of a spherical cavity. Dependences of the brush structure and the local conformation of grafted chains on the sequence of charged monomers, the grafting density, and the chain stiffness are addressed. In the range of parameters studied, it was found that a significant transition of the brush structure occurs due to the variation of the charged monomer sequence. As the number of repeat charged monomers increases, both the flexible and semiflexible polyampholyte brushes change to the collapsed conformation. The spherical concave geometry tends to exclude the conformation of chains perpendicular to the grafting surface for the semiflexible case. In addition, we find that most counterions are depleted in the polyampholyte brush due to the strong electrostatic correlation between the oppositely charged monomers.