Role of salt on adhesion of an epoxy/aluminum (oxide) interface in aqueous environments

Abstract

Joints held by polymeric adhesives are commonplace in many engineered products, but normal service can require exposure to environmental conditions that present a significant challenge for maintaining the structural integrity of the interface. In particular, aqueous environments can wreak havoc on the joint strength. Here, a mechanistic approach is used to understand the difference in the debonding behavior of an epoxy/aluminum (oxide) interface when exposed to deionized (DI) water and aqueous sodium chloride by correlating macroscopic failure with the sorption of salt and water into the adhesive and its nanoscale distribution. For the epoxy‐aluminum system examined here, the presence of sodium chloride increases the resistance to crack growth in comparison to DI water. The debonding appears to be controlled by water near the buried interface. Salt water decreases the solubility of water in the epoxy and decreases the concentration of water near the buried interface, but the concentration of salt that enters the epoxy is below the detection limit. Thus, even if ions cannot penetrate or sorb into the adhesive, the presence of salt can significantly alter the water distribution within the adhesive and ultimately the strength of the joint. POLYM. ENG. SCI., 56:18–26, 2016. © 2015 Society of Plastics Engineers

Hygroscopic compounds in spider aggregate glue remove interfacial water to maintain adhesion in humid conditions

“…Our SFG observations of pristine aggregate glue together with results obtained for model polyacrylic acid polymer suggest the sequestration of interfacial liquid-like water by the hygroscopic LMMCs, thus explaining the cohesive failure of Larinioides cornutus aggregate glue at high humidity. Tan et al reports similar observations with synthetic adhesives, where the osmotic pressure effect of sodium chloride in water improves the adhesion underwater 50 . Thus, hygroscopic LMMCs and glycoproteins team-up in sequestering interfacial water at high humidity, thereby overcoming a fundamental limitation of conventional synthetic adhesives.…”

Role of Hygroscopic Low Molecular Mass Compounds in Humidity Responsive Adhesion of Spider’s Capture Silk

“…Inorganic LMMCs interact with adhesive proteins produced by marine organisms such as oysters, as well as in glycoprotein function in synovial fluids . Synthetic systems such as hydrogels, electrospun fibers, polymer brushes, membranes, and more recently adhesive joints have also been shown to alter function on the basis of interaction of LMMCs with macromolecular structures such as polymers. These studies further support the hypothesis that LMMCs in the glue interact directly with glycoproteins and the water uptake can be modulated by this interactions and the differences in water uptake between Tetragnatha and other three species could reflect the differences in the chemical composition of glycoproteins instead .…”

Quantifying Fluorogenic Dye Hydration in an Epoxy Resin by Noncontact Microwave Dielectric Spectroscopy

“…Experimental characterization of moisture uptake often focuses on the effects of moisture on polymer matrix relaxation, the extent of water molecule immobilization, and the water droplet shape in relation to the cumulative hydration level. Characterization methods include dielectric and infrared (IR) spectroscopies, − positron annihilation, nuclear magnetic resonance reflectometry, neutron reflectivity, , and fluorogenic dye sensors among other modalities, each having specific strengths and limitations. For example, methods based on neutron reflectivity are capable of assessing the size of the interfacial zone in the direction transverse of the substrate to within several angstroms, yet such scattering measurements are limited to thin polymer films supported on flat substrates with topological surface imperfections smaller than the method resolution.…”