Combined Cononsolvency and Temperature Effects on Adsorbed PNIPAM Microgels

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Poly(N-isopropylacrylamide) (PNIPAM) microgels exhibit volume phase transitions with temperature.
• Cononsolvency effects, where microgels shrink in mixed solvents (water-ethanol), are observed.
• Adsorbed microgels experience compression and altered behavior compared to bulk solutions.

Purpose of the Study:

• Investigate the multiresponsive behavior of PNIPAM microgels adsorbed to interfaces.
• Understand the combined effects of temperature and cononsolvency on adsorbed microgels.
• Elucidate the influence of surface properties and preparation methods on microgel swelling.

Main Methods:

• Atomic Force Microscopy (AFM) to study adsorbed microgel behavior.
• Dynamic AFM measurements for nanorheology studies.
• Microgel deposition on gold and polycation (PAH) coated surfaces.

Main Results:

• Adsorption significantly compresses PNIPAM microgels.
• Surface characteristics and preparation solvent mixtures impact microgel swelling.
• Nanorheology is influenced by polymer density and subtle polymer-solvent interactions.
• Preferential ethanol adsorption drives cononsolvency; hydrogen bond breaking causes temperature-induced shrinking.

Conclusions:

• PNIPAM microgel response is tunable via surface interactions and solvent composition.
• Preferential solvent adsorption and hydrogen bonding are key mechanisms governing microgel behavior.
• Adsorbed PNIPAM microgels offer unique responsive materials for surface-based applications.