Aggregation of polyampholytes: Influence of salt concentration

Area of Science:

• Polymer Physics
• Soft Matter Science
• Computational Chemistry

Background:

• Polyampholytes (PAs) are polymers with both positive and negative charges.
• Their self-assembly behavior is crucial for various applications but sensitive to environmental conditions like salt concentration.
• Understanding sequence-dependent assembly is key to controlling PA properties.

Purpose of the Study:

• To investigate the salt-dependent self-assembly of polyampholytes (PAs).
• To explore how polymer charge sequence influences aggregation behavior under varying salt conditions.
• To compare simulation findings with theoretical predictions from the random phase approximation (RPA).

Main Methods:

• Coarse-grained molecular dynamics simulations with explicit mobile salt ions.
• Theoretical analysis using the random phase approximation (RPA).
• Quantification of aggregation, single-chain dimensions, and structural correlations.

Main Results:

• Aggregation sensitivity to salt is sequence-dependent.
• Blocky PA sequences show non-monotonic salt responses; well-mixed sequences show weaker, monotonic responses.
• High salt concentrations lead to collapse into a single aggregate for all sequences.
• RPA predicts shifts in spinodal lines and reduced microphase instability at higher salt.

Conclusions:

• PA self-assembly and salt sensitivity are strongly influenced by charge sequence.
• Simulation and RPA theory show good agreement regarding salt-induced aggregation and instability.
• The findings provide insights into controlling PA behavior through sequence design and salt concentration.