Anomalous moisture diffusion in an epoxy adhesive detected by magnetic resonance imaging

Abstract

Non-Fickian or anomalous diffusion is frequently observed when the absorption of moisture by a polymer is being studied. Different models have been presented in the literature that can accurately predict the trends of the weight-gain curves. However, it is not always clear which of these models yield good predictions of moisture distribution. This article presents a timeresolved moisture distribution study of an epoxy sample immersed in deuterated water (D 2 O) at 708C over a period of 2.5 months. The moisture distribution was measured during that period with a novel high-resolution magnetic resonance imaging technique that is well adapted to the imaging of thin plates. The experimental results showed that the concentration of D 2 O at the surface of the sample increased with time, even after 2.5 months. These results were used to evaluate the performance of several standard diffusion models. Although this study is phenomenological, it appears that a model featuring time-varying boundary conditions yields the best representation of moisture absorption for these samples.

Moisture degradation of open-faced single lap joints

“…The uncontaminated and contaminated cases do not appear significantly different in terms of absorbed moisture. In turn, the above mentioned curves can be satisfactorily fitted by the Fickian model [13] for one-dimensional diffusion:…”

“…The first, obviously, is assessing the diffusion of water in the joint, which can affect both the adhesive bulk and the interfaces. Almost all studies regard Fick's law of diffusion as a starting point [1][2][3][11][12][13][15][16][17][18], but several researchers find that the process is non-Fickian and adopt more sophisticated laws, for instance dual-Fickian or Langmuir's [6,10,13,15,16,18]. A related aspect is the effect of water on the adhesive, which causes plasticization and swelling [2][3][4]6,8,11,[15][16][17].…”

“…Although the subject has been investigated since long, it is still extensively studied at present [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Effect of hot-humid exposure on static strength of adhesive-bonded aluminum alloys

“…Previous studies revealed that if the exposure was over a significant period of time, the joint strength gradually declined [6] which was closely related to the water absorption of the adhesive-bonded joints [7,8]. Many studies [9e12] on effect of hot-humid exposure on the strength of the adhesive-bonded aluminum alloys showed that the hot-humid exposure significantly decreased the strengths of the adhesivebonded aluminum joints.…”

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

“…The samples are removed periodically to measure their mass and/or volume changes for a given amount of time, from weeks to years 10,[13][14][15][16][17] . The hygrothermal test may be followed by mechanical testing, i.e., residual static/fatigue strength/fracture mechanics testing [17][18][19] , which only gives information on the effect of hygrothermal stimulus on the mechanical responses of materials. Test data may be fitted to diffusion models of varying complexity, from simple Fickian diffusion to models that include dependency on concentration, stress, temperature, reversible physical aging/plasticization and irreversible chemical reactions.…”