MECHANISMS OF CRITICALITY IN ENVIRONMENTAL ADHESION LOSS
Christopher C. White, Kar T. Tan, Donald L. Hunston, Kristen L. Steffens, Deborah S. Jacobs, Bulent Akgun, Vogt D. Bryan
Moisture attack on adhesive joints is a long-standing scientific and engineering problem. A particularly interesting observation is that when the moisture level in certain systems exceeds a critical concentration, the bonded joint shows a dramatic loss of strength. Through many investigations on this phenomenon, the joint interface has been shown to play a dominant role; however, why there is a critical concentration of moisture and what role is played by the properties of the bulk adhesive have not been adequately addressed. Moreover if the interface is crucial to the observed effect, information about the local water content near the interface should be more important to elucidating the mechanisms of criticality than the bulk water concentration in the adhesive since the two are known to be different. To gain a detailed picture of this criticality, we have combined a fracture mechanics approach to determine joint strength with neutron reflectivity, which provides data on the moisture distribution near the interface. A well-defined model system, silica glass substrates bonded to a series of polymers based on poly(n-alkyl methacrylate), was utilized to probe the role of the adhesive in a simple example. By substituting alkyl chains of different length, the molecular structure of the polymer can be systematically changed to vary the chemical and physical properties of the adhesive over a relatively wide range. Our findings suggests that the loss of adhesion is dependent on a combination of a build-up of the local water concentration near the interface, interface swelling stresses resulting from water absorption, and water induced weakening of the interfacial bonds.
, Tan, K.
, Hunston, D.
, , K.
, Jacobs, D.
, Akgun, B.
and Bryan, V.
MECHANISMS OF CRITICALITY IN ENVIRONMENTAL ADHESION LOSS, ACS Applied Materials and Interfaces, [online], https://doi.org/10.1039/c4sm02725f
(Accessed August 10, 2022)