Stimuli-Responsive Behavior of PNiPAm Microgels under Interfacial Confinement

Area of Science:

• Polymer Science
• Soft Matter Physics
• Surface Chemistry

Background:

• Microgels exhibit stimuli-responsive volume phase transitions, collapsing from swollen to coiled states.
• The effect of confining interfaces on microgel phase transitions is not well understood.

Purpose of the Study:

• To investigate the impact of an air/liquid interface on the volume phase transition of poly(N-isopropylacrylamide) microgels.
• To elucidate the mechanisms altering microgel behavior at interfaces.

Main Methods:

• Experimental observation of microgel behavior at an air/liquid interface.
• Molecular dynamics simulations to model interfacial interactions.

Main Results:

• The volume phase transition of poly(N-isopropylacrylamide) microgels is largely suppressed at the air/liquid interface.
• Hysteresis in core morphology and interfacial pressure observed during heating and cooling cycles.
• Dangling polymer chains at the interface do not undergo volume phase transition due to surface tension effects.

Conclusions:

• Interfacial confinement fundamentally alters the free energy balance governing microgel volume phase transitions.
• The suppression of the phase transition is attributed to surface tension effects on spread polymer chains.
• Technological applications like emulsion destabilization do not rely on reduced microgel interfacial coverage.