In Situ Adhesive and Crack Detectable Polyurea Adhesive at Extremely Low Temperatures

Adhesives that can in situ adhere to substrates and long-term maintain robust adhesion at extremely low temperatures are highly desired in fields such as aerospace, polar regions, and biological industries. Unfortunately, developing such adhesives has been a daunting task so far, as most polymers tend to freeze in such an environment, leading to poor interfacial wetting, serious deformation, and significant fragileness. To address this challenge, a series of poly(dimethylsiloxane)-based polyurea adhesives were synthesized through a non-isocyanate route. This adhesive exhibited exceptional segmental dynamics and toughness at extremely low temperatures, as demonstrated by the continuous evolution of ordered and disordered hydrogen bonds associated with C═O until the test limit of −170 °C and unprecedented bendability in liquid nitrogen (LN, −196 °C). It could adhere firmly and reversibly to various substrates in LN, achieving an in situ adhesion strength of as high as 1.6 MPa on steel. Evenly important, this adhesive exhibited outstanding long-term tolerance in LN with an ultrahigh adhesion strength of 18.3 MPa after 30 days of immersion. Surprisingly, long-persistent phosphorescence lasting for ∼7s was also observed in LN. This study reduced the adhesion temperature of adhesives to −196 °C while enhancing the in situ adhesion strength in LN to the MPa level.