Controlling Kinetic Pathways in Demixing Microgel-Micelle Mixtures

Area of Science:

• Colloid science
• Polymer chemistry
• Materials science

Background:

• Poly(N-isopropylacrylamide) (pNIPAM) microgels exhibit temperature-dependent phase behavior.
• Triblock copolymer surfactants (PEO-PPO-PEO) influence microgel interactions.
• Gelation in these systems typically occurs with increasing temperature.

Purpose of the Study:

• Investigate the impact of heating rate on the phase behavior of pNIPAM microgel and PEO-PPO-PEO surfactant mixtures.
• Understand how heating rate influences aggregation mechanisms and final structures.
• Explore the control over competing attraction mechanisms between microgel particles.

Main Methods:

• Systematic variation of heating rates applied to microgel-surfactant mixtures.
• Observation of temperature-dependent phase transitions and aggregation phenomena.
• Analysis of the resulting microstructures formed under different thermal histories.

Main Results:

• Heating rate alters the aggregation mechanism, shifting from depletion at low temperatures to association at high temperatures.
• Two competing attraction mechanisms between microgel particles are identified and controllable via heating rate.
• Rapid heating bypasses demixing, leading to the formation of gel networks instead of phase-separated structures.
• Different final structures, potentially metastable, can be accessed for the same system composition by controlling temperature history.

Conclusions:

• The heating rate is a critical parameter that dictates the aggregation pathway and resulting morphology in pNIPAM microgel and surfactant systems.
• This study reveals a method for kinetic selection of distinct microgel-based structures by manipulating thermal protocols.
• The findings offer new possibilities for controlling the self-assembly of colloidal systems through dynamic thermal stimuli.