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Substrate-Temperature-Driven Microstructural Transitions in Dried Patterns of Microgel Particles
Sanjib Majumder1,2, Madivala G Basavaraj1,2, Dillip K Satapathy1,3,2
1Soft Materials Laboratory, Department of Physics, IIT Madras, Chennai, Tamil Nadu 600036, India.
Langmuir : the ACS Journal of Surfaces and Colloids
|February 24, 2026
Summary
Poly(N-isopropylacrylamide) (PNIPAM) microgels form ordered monolayers at fluid interfaces, enabling colloidal film fabrication. Their temperature-responsive behavior dictates complex deposition patterns, offering tunable material properties.
Area of Science:
- Soft matter physics
- Colloid science
- Materials science
Background:
- Poly(N-isopropylacrylamide) (PNIPAM) microgels are stimuli-responsive colloids with tunable swelling behavior.
- Microgels exhibit distinct kinetics at fluid-fluid interfaces compared to bulk, undergoing flattening and forming ordered monolayers.
- This interfacial behavior offers a route for fabricating colloidal films and patterned structures.
Purpose of the Study:
- To investigate the self-assembly and deposition patterns of PNIPAM microgels during the drying of sessile drops.
- To explore the influence of temperature and initial microgel concentration on the resulting deposit morphologies.
- To understand the role of thermally modulated interfacial behavior in directing microgel self-assembly.
Main Methods:
- Drying of sessile aqueous drops containing PNIPAM microgels on hydrophilic substrates at controlled temperatures.
- In situ monitoring of drop evaporation dynamics using video microscopy and contact angle goniometry.
- Characterization of dried microgel deposit morphologies using atomic force microscopy (AFM).
Main Results:
- PNIPAM microgels adsorb and flatten at the air-water interface, forming ordered monolayers.
- Complex deposition patterns, including uniform films, coffee-ring, and multi-ring patterns, were observed.
- Deposit morphology is dependent on initial microgel concentration and substrate temperature.
- The average height of dried microgels increases with substrate temperature.
- Spatial heterogeneity in microgel height suggests thermally modulated interfacial behavior directs self-assembly.
Conclusions:
- PNIPAM microgels can be patterned into diverse structures by controlling drying conditions and temperature.
- Temperature plays a crucial role in modulating microgel interfacial activity and self-assembly during evaporation.
- This study demonstrates a method for fabricating tunable colloidal films using temperature-responsive microgels.
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