Photo-, thermally, and pH-responsive microgels.

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Stimuli-responsive microgels are crucial for advanced materials.
• Poly(N-isopropylacrylamide) (PNIPAM) microgels show thermal responsiveness.
• Spiropyran (SP) photochromes offer light-induced property changes.

Purpose of the Study:

• To synthesize and characterize novel photo-, thermally, and pH-responsive microgels.
• To integrate spiropyran photochrome into PNIPAM-allylamine copolymer microgels.
• To investigate the combined stimuli-responsive behavior of the new microgels.

Main Methods:

• Copolymerization of N-isopropylacrylamide and allylamine.
• Functionalization of microgels with carboxylic acid-bearing spiropyran via amide bonding.
• Characterization using dynamic light scattering and UV-visible spectroscopy.

Main Results:

• Synthesized PNIPAM-SP microgels exhibit photo-, thermal-, and pH-responsiveness.
• Visible light irradiation induced spiropyran isomerization, reducing particle size.
• PNIPAM-SP microgels showed a broadened thermal transition range and reversible photoisomerization.
• Microgels self-assembled into crystalline lattices in aqueous suspension.
• pH changes affected the swelling capability due to amine group residues.

Conclusions:

• Successfully developed multifunctional PNIPAM-SP microgels with tunable properties.
• Demonstrated reversible photochromic behavior and stimuli-responsive volume phase transitions.
• The integration of SP enhanced the responsiveness and broadened the thermal transition of PNIPAM microgels.
• These microgels show potential for applications in smart materials and colloidal systems.