Responsive behaviors of diblock polyampholyte brushes within self-consistent field theory.

ABSTRACT

Self-consistent field theory (SCFT) calculation has been performed to study the structure and stimuli-responsive behaviors of diblock polyampholyte (PA) brushes. Two kinds of brushes are considered one formed by PA chains consisting of two strong polyelectrolyte blocks (system i) and the other formed by PA chains of a grafted strong acid block and an ungrafted weak base block (system ii). Density profiles and brush thickness are obtained. The chain trajectory (average position of each polymer segment) is also calculated to characterize the conformation of the grafted chains. For system i, the ungrafted blocks loop backward at low salt concentration and extend out at high salt concentration. For system ii, the charge fraction of the annealing block is independent of pH and becomes dependent on it at high salt concentration. As a result, pH has no effect on the brush structure at low salt concentration and takes effect at high salt concentration. That the salt concentration can switch on and off the responses of the PA brush to the pH stimuli may find application in building functional surfaces.