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This study shows that changing pH can cause flexible diblock polyampholytes to switch between extended and collapsed states in poor solvents. This pH-induced transition is similar to a first-order phase transition.

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Area of Science:

  • Polymer Physics
  • Computational Chemistry
  • Soft Matter Physics

Background:

  • Weak polyelectrolytes exhibit complex conformational behavior influenced by pH and solvent quality.
  • Diblock polyampholytes, with oppositely charged blocks, present unique charge asymmetry upon pH variation.
  • Understanding these behaviors is crucial for designing advanced polymer-based materials.

Purpose of the Study:

  • To investigate the titration and conformational properties of flexible diblock polyampholytes.
  • To explore the effects of pH and solvent conditions on polyampholyte chain conformations.
  • To identify pH-induced transitions between different conformational states.

Main Methods:

  • Grand canonical Monte Carlo simulations were employed.
  • Simulations modeled flexible polyelectrolytes interacting with a pH-controlled reservoir.
  • Analysis focused on conformational changes and free energy landscapes.

Main Results:

  • A discontinuous transition between extended and collapsed states was observed in poor solvents by tuning pH.
  • The transition's first-order-like nature was evidenced by a double-minima free energy distribution.
  • In good solvents, coil-globule transitions at the isoelectric point showed distinct regimes based on electrostatic strength.

Conclusions:

  • Solution pH is a critical factor in controlling diblock polyampholyte conformations, enabling distinct state transitions.
  • The observed pH-induced transitions have implications for stimuli-responsive polymer systems.
  • Diblock polyampholytes exhibit polyelectrolyte-like behavior away from the isoelectric point due to charge repulsion.