Thermodynamics of temperature-sensitive polyether-modified poly(acrylic acid) microgels

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Ionic microgels are versatile materials with tunable properties.
• Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) or Pluronic copolymers influence microgel behavior.
• Understanding temperature-induced structural changes is crucial for microgel applications.

Purpose of the Study:

• To investigate temperature-induced structural changes and thermodynamics of poly(acrylic acid) (PAA) based ionic microgels.
• To compare aggregation behavior in microgels with hydrophobic (L92) versus hydrophilic (F127) Pluronic copolymers.
• To elucidate the role of Pluronic composition in microgel structure and phase transitions.

Main Methods:

• Small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) for structural analysis.
• Differential scanning calorimetry (DSC) for thermodynamic studies.
• Equilibrium swelling techniques to assess microgel volume changes.

Main Results:

• F127-based microgels formed micelle-like aggregates, while L92-based microgels exhibited fractal structures of dense nanoparticles.
• Microgels displayed thermodynamically favorable volume phase transitions due to reversible poly(propylene oxide) (PPO) chain aggregation.
• L92-PAA-EGDMA microgels showed higher hydrophobicity and formed supramolecular structures, unlike F127-PAA-EGDMA microgels.

Conclusions:

• The PPO content in Pluronics significantly dictates microgel aggregation and structure.
• Hydrophobic associations of PPO chains drive the observed volume phase transitions.
• Microgel architecture can be tailored by selecting Pluronic copolymers with varying PPO content for specific applications.