Fig. 4.

Adhesion of the poly(cation-adj-π) gels under seawater. a Force–displacement curves of the physical P(ATAC-adj-PEA) gel adhered to a negatively charged glass substrate in 0.7 M NaCl solutions. The insert is a schematic diagram of the tack test. b Photographs illustrating the bulk deformation of the physical P(ATAC-adj-PEA) gel during retraction from the glass substrate. The diameter and thickness of the gel were 15 mm and 1.6 mm, respectively. c Adhesion values of P(ATAC-adj-PEA) gels with different amounts of chemical crosslinkers MBAA to the glass substrates in 0.7 M NaCl solutions. d Photographs showing a P(ATAC-adj-PEA)-0.1 gel adhered to a 0.49-kg glass block in seawater and then lifted it up out of the seawater to the air. e Adhesion behaviors of P(ATAC-adj-PEA)-0.1 hydrogels to a variety of substrates with different types of surface charges and hydrophobicity in 0.7 M NaCl solution. The result marked by asterisk indicates that the fracture occurred in the bulk of the substrate hydrogel, but not at the interface. The error bars indicate the standard deviation (n = 5)