Synergistic Thermoresponsive Optical Properties of a Composite Self-Healing Hydrogel

Abstract

A fast (30 s) thermoresponse and rapid (30 min) self-healing were achieved by noncovalently incorporating a small fraction of poly(N-isopropylacrylamide) (PNI-PAM) nanogels (≤0.18 wt %) into a benzyl methacrylate-cooctadecyl methacrylate-co-methacrylic acid (BOMA-16) polymer matrix. The PNIPAM serves as the thermoresponsive component while the BOMA-16 provides self-healing via hydrophobic associations. The PNIPAM/BOMA-16 composite showed tunable lower critical solution temperature and up to 95% more visible light modulation (ΔT) than the same concentration of PNIPAM by itself. Conversely, the PNIPAM nanogels (≤0.18 wt %) served as reinforcements and increased the storage modulus of the PNIPAM/BOMA-16 hydrogel by up to 2.7 times relative to a BOMA-16 hydrogel. Using different analytical techniques, we show that the synergistic thermoresponsive light modulation is due to a hydrophilic−hydrophobic phase transition and clustering of the PNIPAM nanogels facilitated by the BOMA-16. The synergistic optical effect is also observed for mixtures of PNIPAM and other polyelectrolytes.

Thermoresponsive Three‐Stage Optical Modulation of a Self‐Healing Composite Hydrogel

“…The dramatic increase in diameter might be result from the aggregation of the PNIPAM nanogels, and the presence of PAH hydrogels might even accelerate the aggregation process. As mentioned by Owusu‐Nkwantabisah and co‐workers, the synergistic thermoresponsive optical property of the polyelectrolytes and PNIPAM nanogels is due to the electrostatic effect . Since PAH hydrogels also have strong ion bonds, it is reasonable to conclude that such electrostatic synergistic effect might also occur in PAH/PNIPAM composite hydrogels.…”

“…Furthermore, when the temperature increases above the LCST of PNIPAM nanogels (55 °C), the nanogels start to aggregate, leading to form holes in PAH/PNIPAM composite hydrogels that are larger than holes seen in pure PAH, as shown in Figure a 3 ,b 3 . The possible synergistic effect makes the aggregation more obvious . Thus, the aggregated particles cooperating with the phase separation of PAH result in the decrease of transmittance again.…”

“…PNIPAM nanogels were prepared according to a procedure in previous literature . Briefly, 440 mL of deionized water, 900 mg of (0.0698 mol) of NIPAM, 150 mg of (0.001 mol) MBAA, and 450 mg (0.001 mol) of sodium diisooctyl succinate were added into a 500 mL three‐neck flask subsequently.…”

“…Recently, Kodak Research Laboratories successfully incorporated a small amount of PNIPAM nanogels into a self‐healing polymer matrix. This resulted in a rapid thermoresponse, with the matrix transitioning from a transparent state to an opalescent state within ≈30 s. This response resulted from the nonassociative electrostatic interaction between the PNIPAM nanogels and the bulk polymer . Although the PNIPAM nanogels achieved the rapid thermoresponse, only a single stage of optical transition is presented.…”

Bimetallic ions synergistic cross‐linking high‐strength rapid self‐healing antibacterial hydrogel

“…The original hydrogel was cut in half with a blade. Then, the two separated hydrogel surfaces were again in contact . To assess the healing efficiency, the tensile length of original hydrogel and the self‐healed hydrogel were measured.…”