水凝胶力学性能如何优化？MBAA交联度与无机盐改性协同机制

2.2.2 Mechanical Properties Mechanical properties are key indicators of hydrogel materials. As the amount of MBAA increases, the elongation at break of the hydrogel shows a decreasing trend (Figure 2a). The reason is that the increase in crosslinking degree (the molar ratio of MBAA to AAm, C(×10^-4)) restricts the mobility of molecular chains, leading to a decrease in material ductility. The tensile strength of acrylamide hydrogels initially increases and then decreases with the increase in MBAA content (Figure 2b). The possible reason is that as the MBAA content increases, the crosslinking degree rises, gradually increasing the tensile strength. However, when the MBAA content exceeds the optimal value, the excessively high crosslinking degree leads to shorter network segments, making it difficult for stress to be effectively distributed, thus causing the material to become brittle and the tensile strength to decrease. Similarly, the toughness of acrylamide hydrogels also shows an initial increase followed by a decrease with the increase in MBAA content (Figure 2b,c). The possible reason is that when the MBAA content is moderate, the hydrogel network has a certain degree of crosslinking while still retaining some mobility of chain segments. Under external force, the molecular chains can absorb energy through elastic deformation and limited plastic slip, resulting in better toughness. However, when the MBAA content is too high, the hydrogel network structure becomes more dense, restricting molecular chain movement and preventing long-distance slip and rearrangement. Therefore, the toughness of the hydrogel decreases. With the increase in MBAA content, the crosslinking density of the hydrogel network gradually increases, making the network structure tighter and more resistant to deformation under external force, thus increasing the elastic modulus (Figure 2c). In summary, when the crosslinking degree is 3.95×10^-4, the hydrogel exhibits a moderate elastic modulus (0.178±0.018 MPa), maximum tensile strength (0.310±0.042 MPa), and toughness (2.89±0.64 MJ/m³). Additionally, compared to pure hydrogels, the addition of inorganic salts generally maintains the elastic modulus of the hydrogels, and the tensile strength and elongation at break show an overall upward trend, although there is a slight decrease in the tensile strength of P-HG-0.5, P-HG-1, Y-HG-0.1, Y-HG-0.5, I-0.5, and the elongation at break of Y-HG-0.1 and Y-HG-0.5 (Figure 2d,e,f). The 100-cycle tensile loading-unloading curves for P-HG-1, Y-HG-1, Sr-HG-1, and I-HG-1 are shown in Figure 2g,h,i. The starting points of subsequent cycles after the first cycle are all shifted positively along the strain axis, indicating the presence of cumulative residual strain. However, the cyclic residual strain and hysteresis loop area decrease with each cycle. This suggests that after the initial cycles, the material undergoes adaptive structural adjustments, and its network structure gradually stabilizes into a fatigue-resistant elastoplastic state.