The relationship between the cross-linking density and the water absorption capacity of polymer-based superabsorbent materials is generally inverse. As the cross-linking density increases, the water absorption capacity of the superabsorbent material decreases.Polymer-based superabsorbent materials, such as hydrogels, are composed of long-chain polymers that are cross-linked to form a three-dimensional network structure. The cross-linking density refers to the number of cross-linking points per unit volume or mass of the polymer network. These cross-linking points provide the structural integrity and mechanical strength to the material.The water absorption capacity of superabsorbent materials is mainly attributed to the presence of hydrophilic functional groups such as -OH, -COOH, and -CONH2 in the polymer chains and the porous structure of the network. When the material comes into contact with water, these hydrophilic groups form hydrogen bonds with water molecules, causing the polymer network to swell and absorb water.When the cross-linking density is low, the polymer chains have more freedom to move and expand, allowing the material to absorb more water. The pores within the network are also larger, providing more space for water molecules to enter and be retained. As a result, the water absorption capacity is higher.However, as the cross-linking density increases, the polymer chains become more restricted in their movement, and the pores within the network become smaller. This reduces the ability of the material to swell and absorb water, leading to a decrease in water absorption capacity. Additionally, a higher cross-linking density can also reduce the number of available hydrophilic groups for hydrogen bonding with water molecules, further decreasing the water absorption capacity.In summary, there is an inverse relationship between the cross-linking density and the water absorption capacity of polymer-based superabsorbent materials. Optimizing the cross-linking density is crucial for achieving a balance between the mechanical strength and water absorption capacity of these materials for various applications.