Fig. 5

Effects of surfactant and temperature on adhesion. a The pre-hydrolysis trialkoxysilane on the elastomer chains is hydrophobic, and is hard to stick into the hydrogel. b The surfactant moves to the hydrogel–elastomer interface, and helps the trialkoxysilane on the elastomer chains hydrolyze and condensate. c When too much surfactant is added into the hydrogel, the surfactant–polymer complex covers the relatively hydrophobic coupling agent, which slows down the condensation reaction. d We use a matrix of peeling tests to study how the surfactant affects the amount of the coupling agent in the elastomer needed for strong adhesion. Bonding is considered successful if the peeling test causes a fracture inside the hydrogel, rather than on the hydrogel–elastomer interface. The default recipe uses 10 mmol/l SDS. e Higher temperature speeds up the bonding and reduces the amount of required coupling agent in the elastomer