Brittle-to-Ductile Transitions of Polyelectrolyte Complexes: Humidity, Temperature, and Salt.

Area of Science:

• Materials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Polyelectrolyte complexes (PECs) are formed via phase separation and offer sustainable material processing in aqueous solutions.
• Understanding the impact of environmental factors on PEC mechanical properties is crucial for material design.
• Previous studies explored temperature, humidity, and salt concentration, but a universal model is lacking.

Purpose of the Study:

• To investigate the effects of temperature, relative humidity (rH), and salt concentration (C _S) on the mechanical properties of PECs.
• To establish design rules for controlling the mechanical response of PECs.
• To understand the thermodynamics of PEC glass transitions.

Main Methods:

• Formation of PECs from poly(methacrylic acid) and poly(trimethyl aminoethyl methacrylate).
• Systematic variation of temperature, relative humidity (rH), and salt concentration (C _S).
• Mechanical property testing and analysis of glass transition behavior.

Main Results:

• Relative humidity exhibited the most significant influence on PEC mechanical properties.
• Temperature and salt concentration had a lesser impact compared to rH.
• A glass transition line (rH _g/T _g) was identified, dependent on temperature and rH, and tunable with salt.
• Thermodynamic analysis indicated glass transition energies similar to water condensation.

Conclusions:

• Relative humidity is the primary factor governing PEC mechanical properties.
• Water and/or salt can be utilized as efficient, low-energy processing agents for PECs.
• The findings provide a basis for designing PEC materials with tailored mechanical responses for various applications.