Use of Self-assembled Monolayers at Variable Coverage to Control Interface Bonding in a Model Study of Interfacial Fracture: Pure Shear Loading

Kent, Michael S.; Yim, Hyungshin; Matheson, Aaron J.; Cogdill, C.; Nelson, Gerald C.; Reedy, E.D.

doi:10.1080/00218460108029605

Cited by 15 publications

(25 citation statements)

References 23 publications

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“…15 We note that we were unable to directly locate the initiation site. The results presented below suggest strongly that the napkin-ring test measures the nominal far field shear stress required for a crack to initiate.…”

Section: B Methodsmentioning

confidence: 88%

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Using self-assembling monolayers to study crack initiation in epoxy/silicon joints

et al. 2004

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The effect of the density and in-plane distribution of interfacial interactions on crack initiation in an epoxy-silicon joint was studied in nominally pure shear loading. Well-defined combinations of strong (specific) and weak (nonspecific) interactions were created using self-assembling monolayers. The in-plane distribution of strong and weak interactions was varied by employing two deposition methods: depositing mixtures of molecules with different terminal groups resulting in a nominally random distribution, and depositing methyl-terminated molecules in domains defined lithographically with the remaining area interacting through strong acid-base interactions. The two distributions lead to very different fracture behavior. For the case of the methyl-terminated domains (50 m on a side) fabricated lithographically, the joint shear strength varies almost linearly with the area fraction of strongly interacting sites. From this we infer that cracks nucleate on or near the interface over nearly the entire range of bonded area fraction and do so at nearly the same value of local stress (load/bonded area). We postulate that the imposed heterogeneity in interfacial interactions results in heterogeneous stress and strain fields within the epoxy in close proximity to the interface. Simply, the bonded areas carry load while the methyl terminated domains carry negligible load. Stress is amplified adjacent to the well-bonded regions (and reduced adjacent to the poorly bonded regions), and this leads to crack initiation by plastic deformation and chain scission within the epoxy near the interface. For the case of mixed monolayers, the dependence is entirely different. At low areal density of strongly interacting sites, the joint shear strength is below the detection limit of our transducer for a significant range of mixed monolayer composition. With increasing density of strongly interacting sites, a sharp increase in joint shear strength occurs at a methyl terminated area fraction of roughly 0.90. We postulate that this coincides with the onset of yielding in the epoxy. For methyl-terminated area fractions less than 0.85, the joint shear strength becomes independent of the interfacial interactions. This indicates that fracture no longer initiates on the interface but away from the interface by a competing mechanism, likely plastic deformation and chain scission within the bulk epoxy. The data demonstrate that the in-plane distribution of interaction sites alone can affect the location of crack nucleation and the far-field stress required.

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Section: B Methodsmentioning

confidence: 88%

“…15 (After publication, an error was discovered in the calculation of the joint shear strength values. This curve has the same qualitative features as that reported previously for the case of incomplete SAMs of OTS, where the coverage of OTS was varied continuously from 0 to 100% area fraction.…”

Section: B Mixed Monolayersmentioning

confidence: 99%

Using self-assembling monolayers to study crack initiation in epoxy/silicon joints

et al. 2004

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“…This is so because as soon as a fraction of adhesive chains are bound to the substrate the fracture energy reaches its maximum values. The bound chains pull all the other in the neighbourhood and the 'cooperative effect' produces the same resistance independently of R. Measurement on silica wafer covered with a layer of octadecyl trichloro silane [45] or a metallic surface covered with silicon oil [46] indicate that at a value of 20% of the maximum anchorage the adhesive bond reaches its maximum resistance . If mechanical tests do not see the variation in anchorage density, the evolution of the bond in humid environment is very sensitive to it, as water condenses in the voids between the sites of anchoring.…”

Section: The Fake Of Fracture Energy Measured In Ambient Conditionsmentioning

confidence: 99%

Some recent progress in adhesion technology and science

Cognard

2005

Comptes Rendus. Chimie

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“…At the lower limit of 0% bromine-terminated chains, which corresponds to a SAM surface coating with 100 percent methyl-terminated chains, the molecular work of separation has a value near 0.05 J/m 2 (Kent, Yim, et al 2001). The interactions in this case are weak (van der Waals forces), and the molecular work of separation equals the reversible work of adhesion.…”

Section: Ii231 Surface Interactionsmentioning

confidence: 99%

Physical Basis for Interfacial Traction-Separation Models

Moody¹

2002

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Many weapon components contain interfaces between dissimilar materials where cracks can initiate and cause failure. In recent years many researchers in the fracture community have adopted a cohesive zone model for simulating crack propagation (based upon traction-separation relations) Sandia is implementing this model in its ASCI codes. There is, however, one important obstacle to using a cohesive zone modeling approach. At the present time traction-separation relations are chosen in an ad hoc manner. The goal of the present work is to determine a physical basis for Traction-Separation (T-U)relations. This report presents results of a program aimed at determining the dependence of such relations on adhesive and bulk properties. The work focused on epoxy/solid interfaces, although the approach is applicable to a broad range of materials. Asymmetric double cantilevered beam and free surface film nanoindentation fracture toughness tests were used to generate a unique set of data spanning length scales, applied mode mixities, and yield (plastic) zone constraint. The crucial roles of crack tip plastic zone size and interfacial adhesion were defined by varying epoxy layer thickness and using coupling agents or special self-assembled monolayers in preparing the samples. The nature of the yield zone was probed in collaborative experiments run at the Advanced Photon Source. This work provides an understanding of the major phenomena governing polymer/solid interfacial fracture and identifies the essential features that must be incorporated in a T-U based cohesive zone failure model. We believe that models using physically based T-U relations provide a more accurate and widely applicable description of interface cracking than models using ad hoc relations. Furthermore, these T-U relations provide an essential tool for using models to tailor interface properties to meet design needs.

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Use of Self-assembled Monolayers at Variable Coverage to Control Interface Bonding in a Model Study of Interfacial Fracture: Pure Shear Loading

Cited by 15 publications

References 23 publications

Using self-assembling monolayers to study crack initiation in epoxy/silicon joints

Using self-assembling monolayers to study crack initiation in epoxy/silicon joints

Some recent progress in adhesion technology and science

Physical Basis for Interfacial Traction-Separation Models

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