Tuning the stop bands of inverse opal hydrogels with double network structure by controlling the solvent and pH

Polyacrylic acid (PAA) and polyacrylamide (PAAm) double network (DN) hydrogels with high mechanical strength (about 1.5 MPa) are obtained when two kinds of monomer solutions of 4 M AA with 5 mol% crosslinker and 4 M AAm with 0.1 mol% crosslinker are used for the optimal preparation. Their high mechanical strength can be maintained even at high water content (above 50%) and at external stimuli (solvent and pH). This optimized DN hydrogel is used to develop the PAA/PAAm inverse opal hydrogel with DN structure by twice infiltration–polymerization and colloidal templating. Its photonic stop band can be tuned by controlling the solvent and pH. It first shows a small red-shift (about 20 nm), and then a large blue-shift (about 180 nm) with the increased ethanol content. For pH response, the DN inverse opal hydrogel has a large stop-band shift of about 140 nm when the pH increases from 1.2 to 5.6. Moreover, the DN inverse opal hydrogel also shows rapid recovery ability without hysteresis phenomenon in strong acidic environment, good reproducibility and durability. The interaction between the independently crosslinked PAA network and PAAm network plays a significant role in determining the response performance.

Graphical abstractPAA and PAAm double network (DN) hydrogels with high mechanical strength are used to develop PAA/PAAm DN inverse opal hydrogels showing good stop-band tunability by controlling the solvent and pH.Figure optionsDownload full-size imageDownload high-quality image (146 K)Download as PowerPoint slideResearch highlights► PAA and PAAm double network (DN) hydrogels show high mechanical strength (above 1 MPa). ► PAA/PAAm DN inverse opal hydrogels show good stop-band tunability by controlling the solvent and pH. ► The response performances depend on the DN structure.