Sequence Effects on the Salt-Enhancement Behavior of Polyelectrolytes Adsorption

Abstract

The comonomer sequence tunes the chain conformation and adsorption, suggesting that sequence design could be used to target the desired properties and morphologies in block copolymer materials. In this work, designing a series of sequence-defined polyelectrolytes (SDPEs), we studied the sequence effect on the salt-enhancement behavior of polyelectrolytes (PEs) adsorption on a negatively charged surface using density functional theory, where the salt-enhancement behavior shows that the adsorption amount (ζ) of PEs on the oppositely charged surface increases with salt concentrations and it cannot be captured by mean-field theories such as self-consistent field theory because of the neglect of electrostatic correlations. Among tapered (T), reversely tapered (R), and alternating (A) sequence-defined PEs, the strength of the salt-enhancement effect of the R-sequence PEs is significantly elevated at a high surface charge density (σb = −0.06 C/m2) because the long middle neutral blocks can form loop conformations. Moreover, R-sequence PEs show the largest adsorption amounts and the strongest salt response of PE adsorptions. Because of similar structural characteristics to the diblock PEs (DPEs), the T-sequence PEs show similar adsorption behavior to DPEs under the conditions with different salt concentrations. The electrostatic attractions between surface and charged blocks are decentralized in A-sequence PE systems, resulting in the smallest adsorption amounts and the weakest salt-enhancement effect and salt response. Additionally, because the decentralization effect of the electrostatic attraction is enhanced with blocks number Nb, the salt-enhancement effect of adsorption amounts is significantly weakened with Nb in R- and A-sequence PE systems.