Inverse opal pH sensors with various protic monomers copolymerized with polyhydroxyethylmethacrylate hydrogel

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Developing advanced colorimetric sensors for environmental monitoring is crucial.
• Hydrogel-based materials offer unique swelling properties sensitive to external stimuli like pH.
• Inverse opal structures provide photonic properties for visual detection.

Purpose of the Study:

• To synthesize and characterize novel pH-sensitive inverse opal hydrogel colorimetric sensors.
• To investigate the pH-dependent optical responses of hydrogels incorporating acidic and basic vinyl monomers.
• To explore the potential of these sensors for visual pH indication.

Main Methods:

• UV-initiated photopolymerization of vinyl monomers (acrylic acid, vinylphosphonic acid, vinylimidazole, DMAEMA) with HEMA.
• Fabrication of inverse opal hydrogels via opal templating and template removal.
• Characterization of pH-induced color changes through optical diffraction measurements.
• Analysis of monomer ionization and hydrogel swelling behavior in response to pH variations.

Main Results:

• Four inverse opal hydrogel sensors exhibiting distinct pH-dependent color shifts (green to red) were successfully fabricated.
• Sensors with acidic monomers (AA, VPA) showed red-shifts with increasing pH due to deprotonation.
• Sensors with basic monomers (VI, DMAEMA) displayed opposite color changes with decreasing pH due to protonation.
• Diprotic VPA sensor showed two-step spectral shifts, and copolymerization extended the pH sensing range.

Conclusions:

• Inverse opal hydrogels functionalized with acidic or basic monomers serve as effective colorimetric pH sensors.
• The observed optical responses correlate with the ionization states of the incorporated monomers.
• These tunable hydrogel sensors offer a promising platform for visual pH monitoring with potential applications in various fields.