Interactions between a responsive microgel monolayer and a rigid colloid: from soft to hard interfaces

Area of Science:

• Soft matter physics
• Colloid science
• Interface science

Background:

• Poly-N-isopropylacrylamide microgels are model colloids with tunable interactions.
• Microgels form responsive foams and emulsions at liquid interfaces.
• Microgel interactions are sensitive to environmental parameters like temperature and pH.

Purpose of the Study:

• Investigate microgel monolayer interactions with a hard colloid at the air-water interface.
• Determine the influence of temperature and lateral compression on these interactions.
• Understand the transition from soft to hard repulsive interfaces.

Main Methods:

• Utilized the Monolayer Particle Interaction Apparatus to measure force-distance curves.
• Employed silica particles as hard colloid probes.
• Varied temperature and lateral compression (surface pressure) during measurements.

Main Results:

• Observed long-range repulsive forces below the microgel volume phase transition temperature.
• Found that temperature and compression reduce monolayer stiffness.
• Adhesion increased with temperature and decreased with compression.
• Temperature-dependent swelling of aqueous microgel fractions significantly impacted probe interactions.

Conclusions:

• Microgel monolayer properties are modulated by temperature and compression.
• The swelling of microgels in the aqueous phase is a key factor in modulating interface properties.
• A transition from a soft to a hard repulsive interface is driven by these parameters.