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Solid-Liquid-Solution Phases in Poly(diallyldimethylammonium)/Poly(acrylic acid) Polyelectrolyte Complexes at Varying
Chikaodinaka I Eneh1, Kevin Nixon1, Suvesh Manoj Lalwani1
1Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, United States.
Macromolecules
|March 18, 2024
Summary
Temperature significantly impacts polyelectrolyte complexes (PECs), influencing their phase behavior. This study reveals that different PEC phases exhibit distinct upper critical solution temperatures (UCSTs), with precipitates showing higher UCSTs due to kinetic trapping.
Area of Science:
- Polymer Science
- Materials Science
- Physical Chemistry
Background:
- Polyelectrolyte complexes (PECs) are formed by oppositely charged polymers, with their phase behavior influenced by various factors.
- Temperature's role in PEC phase transitions is often overlooked, despite its potential to induce phase separation via critical solution behavior.
- Secondary interactions like hydrogen bonding can further complicate the temperature response of PECs.
Purpose of the Study:
- To investigate the phase behavior of poly(diallylmethylammonium)/poly(acrylic acid) (PDADMA/PAA) complexes under varying conditions.
- To determine the effect of temperature on different phase states of PDADMA/PAA PECs.
- To elucidate the relationship between initial PEC phase state and its temperature-dependent phase transition.
Main Methods:
- Preparation of PDADMA/PAA complexes with controlled ionic strength, mixing ratios, and fixed pH.
- Variable-temperature optical microscopy to observe phase transitions.
- All-atom molecular dynamics (MD) simulations to investigate precipitate behavior.
Main Results:
- PDADMA/PAA PECs exhibited four distinct phases at room temperature: precipitate, coexisting precipitate and coacervate, solid-like gel, and coacervate.
- Upper critical solution temperatures (UCSTs) were identified for transitions to a solution state, varying significantly with the initial phase.
- Solid-like precipitates demonstrated higher UCST values compared to other phases.
Conclusions:
- Temperature is a critical factor influencing the phase behavior of polyelectrolyte complexes.
- The initial phase state of a PEC, particularly precipitates, affects its thermal response due to phenomena like kinetic trapping.
- Understanding temperature-dependent phase behavior is crucial for applications in stimuli-responsive materials, membraneless organelles, and separation technologies.
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