Abstract
The scope of hydrogel applications can be greatly expanded by the improvement of mechanical properties. However, enhancement of nanocomposite hydrogels (NC gels) has been severely limited because the size of crosslinking nanoparticles is too large, at least in one dimension. Here we report a new strategy to synthesize non-aggregated spherulite nanoparticles, with diameters <5 nm, in aqueous solution, and their enhancement to hydrogel. The stress and stretch ratio at rupture of our NC gel are 430 and 121 KPa with only 40-p.p.m. nanoparticle content. The NC gel containing 200-p.p.m. nanoparticles can revert to 90% of its original size after enduring 100-MPa compressive stress. Our results demonstrate that the suppression of nanoparticle size without aggregation helps to establish a super stretchable and high-toughness hydrogel network at very low inorganic content.
Highlights
The scope of hydrogel applications can be greatly expanded by the improvement of mechanical properties
Either a large surface area or aggregation of the nanoparticles leads to uneven dispersion of the crosslink points, which greatly limits the property enhancement of the nanocomposite hydrogels (NC gels)
The number of crosslink points in all these NC gels are restricted in the largest functional area (42,800 nm[2]; Supplementary Table 1) of the particles, resulting in the aggregation of the crosslink points within the NC gel, which greatly limits the enhancement of mechanical properties
Summary
The scope of hydrogel applications can be greatly expanded by the improvement of mechanical properties. Either a large surface area or aggregation of the nanoparticles leads to uneven dispersion of the crosslink points, which greatly limits the property enhancement of the NC gels. With sizes of 4800 nm in at least one dimension, clay has a concentration threshold (at least 1 wt%) for improving the strength of NC gels[5,6,7,8,9] Such a high content of nanoparticles in the NC gels leads to residual and transparency problems. Hydrogel enhanced by exfoliated montmorillonite layers can be stretched up to 118 times of the initial length, but the maximum stress is limited to 100 KPa 10); and for hydrogels with a stress 4200 KPa enhanced by high-content clay nanoparticles, the stretch ratio at rupture is o10 CNS has a swelling ratio of 250, a maximum stretch ratio of 121, and a stress up to 430 KPa, which are B5, 14 and 4 times higher than those of poly(N-isopropylacrylamide)/clay NC gel with 3 wt% clay[5]
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