There are many strategies and efforts to develop nanocomposite gels for wide applications that display desirable strength and properties, such as self-healing. Self-healable laponite-poly(N-isopropylacrylamide) hydrogels were prepared by gamma-ray radiation employing stepwise processes that provide gelation without any chemicals for crosslinking and initiation. Self-healable properties were achieved similar to that of typical gels crosslinked using crosslinkers and initiators. The main factor of the property is the homogeneous distribution of laponite particles, based on comparisons of samples prepared using three synthetic strategies. Three types of laponite-PNIPAM hydrogels were successfully pre-pared and characterized. Lap/NIPAM/γ-ray gel, Lap/γ-ray/NIPAM, and Lap/NIPAM/KPS gels were characterized by cross-sectional structures, nanostructures, mechanical properties, swelling characteristics, and self-healing ability. For the Lap/NIPAM/γ-ray gel, the directly γ-ray-irradiated monomers were polymerized at the same time in all directions, causing many chemical crosslinks and short intercrosslinking lengths. Thus, they have an irregular structure and do not provide good performance in areas such as self-healing. Alternatively, the Lap/γ-ray/NIPAM and Lap/NIPAM/KPS gels, which were initiated from the surface of the laponite, had long PNIPAM chains between laponite particles. Their uniform structure is responsible for the self-healing behavior because the regular finite distances lead to spatial conjunction to make interactions. Lap/γ-ray/NIPAM gels have dense structures compared to Lap/NIPAM/KPS gels, and their dense crosslinking of Lap/γ-ray/NIPAM gels contributed to the uniformity even in the swollen states. The uniformity of the networks was evaluated with mesoscopic structures associated with large inhomogeneities and nanostructures described with interparticle distances at different swelling ratios. The results indicate that the stepwise process of the radiation method generates dense networks with uniform structures, which leads to self-healing ability. Consequently, we suggest that gelation by gamma-ray irradiation can provide better properties via effective chemical controls.

Self-healable laponite-poly(N-isopropylacrylamide) hydrogels prepared by gamma-ray irradiation

ACS Spring Meeting 2021

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