pH-Dependent Interfacial Rheology of Polymer Membranes Assembled at Liquid-Liquid Interfaces Using Hydrogen Bonds

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Self-assembly of polymers at liquid interfaces offers a route to create self-healing membranes.
• Controlling the mechanical properties of these membranes is essential for their application.
• Noncovalent interactions, particularly hydrogen bonds, are key to reversible assembly and self-healing.

Purpose of the Study:

• To investigate the interfacial rheological properties of poly(methacrylic acid)-poly(propylene oxide) (PMAA-PPO) polymer membranes.
• To understand how pH influences the mechanical properties and structure of these self-assembled membranes.
• To elucidate the role of noncovalent interactions in controlling membrane behavior.

Main Methods:

• Interfacial rheology measurements using frequency sweeps.
• Assembly of PMAA-PPO polymer membranes at the water-Miglyol interface.
• Systematic variation of pH to control polymer ionization and hydrogen bonding.

Main Results:

• A crossover from viscous to elastic behavior was observed with increasing frequency.
• The crossover elastic modulus decreased with increasing pH, correlating with reduced layer thickness.
• The crossover frequency exhibited an exponential dependence on the PMAA degree of ionization.

Conclusions:

• PPO chains act as noncovalent cross-linkers, bridging PMAA chains.
• The number of propylene oxide units involved in hydrogen bonds dictates the dissociation rate and crossover frequency.
• pH is a critical parameter for tuning the mechanical response and thickness of these self-healing membranes.