As high-water absorption and high-water retention polymers

hydrogels are widely used in many fields such as smart materials

water absorption materials

drug delivery

slow release

skin dressings

and biomedicine. However

the traditional hydrogels like polyacrylamide (PAAm) have the limitation of low mechanical strength and poor stability

which greatly limits the development of hydrogels. The commonly used methods to increase the strength of hydrogels include the construction of double-network structure hydrogels

the introduction of chemical groups to modify hydrogels

the introduction of nanoparticles to form nanocomposite hydrogels

and so on. In this work

the mechanical properties of PAAm hydrogels are mainly improved by introducing hydrophilic silica (SiO2) nanoparticles. The results show that SiO2 nanoparticles

as multi-functional crosslinking agents

are physically adsorbed or chemically bonded into the hydrogel matrix to enhance the 3D network structure of the hydrogel. In addition

hydrogen bonds formed between the silicon hydroxyl group on the surface of SiO2 nanoparticles and the amide group on the polymer chain

which increases the crosslinking density of the hydrogel and greatly improves the compression performance. The SiO2 nanoparticles are hydrophilic

which will increase the water absorption of the composite hydrogel and increase the swelling rate

but the swelling rate will decrease due to the limitation of the three-dimensional mesh of the hydrogel. The energy storage modulus of composite hydrogels will gradually increase due to the denser three-dimensional mesh structure

but the loss modulus will increase due to the increase of internal structure friction

but also because of the denser mesh

the increase of loss modulus will be limited. In general

the addition of SiO2 nanoparticles has a certain significance for improving the viscoelasticity of hydrogels.