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 N
b, the
salt-enhancement effect of adsorption amounts is significantly weakened
with N
b in R- and A-sequence PE systems.