Elastic-Modulus-Dependent Macroscopic Supramolecular Assembly of Poly(dimethylsiloxane) for Understanding Fast Interfacial Adhesion

Moisture poses a significant threat to the reliability of microelectronic assemblies and can be attributed as being one of the principal causes of many premature package failures. It is a multi-dimensional concern in electronic packaging, having an adverse effect on package reliability by changing both the mechanical properties and interfacial adhesion of the microelectronic assembly. In this paper, a study has been conducted to evaluate the moisture-induced degradation of both the elastic modulus of a commercially available no-flow underfill and the interfacial adhesion of the underfill to a copper alloy substrate. Three different levels of moisture preconditioning, 85C/50%RH, 85C/65%RH, and 85C/85RH%, were implemented in this study. Diffusion coefficient test specimens were constructed to experimentally measure the moisture diffusivity into the underfill resin and obtain the moisture saturation concentration for each level of moisture preconditioning. Flexural bend test specimens were made to characterize the effect of moisture on the elastic modulus of the underfill adhesive. Last, interfacial fracture toughness specimens with prefabricated interface cracks were used in a four point bending test to quantify the effect of moisture on interfacial fracture toughness. The results of this study will aid in the development of more robust microelectronic assemblies, demonstrating how both the elastic modulus and interfacial toughness change as a function of moisture concentration.

Download Full-text

Understanding the influence of silicone elastomer properties on wedge-shaped microstructured dry adhesives loaded in shear

Journal of The Royal Society Interface ◽

10.1098/rsif.2018.0551 ◽

2018 ◽

Vol 15 (146) ◽

pp. 20180551 ◽

Cited By ~ 8

Author(s):

Aiva Simaite ◽

Brigitte Temple ◽

Mohammad Amin Karimi ◽

Vahid Alizadehyazdi ◽

Matthew Spenko

Keyword(s):

Elastic Modulus ◽

Interfacial Adhesion ◽

Biomedical Applications ◽

Normal Direction ◽

Stick Slip ◽

Flat Surfaces ◽

Work Of Separation ◽

Dry Adhesives ◽

Normal Adhesion ◽

Interfacial Adhesion Strength

Anisotropic, gecko-inspired, microstructured adhesives are one of the most promising solutions for many applications in robotics and biomedical applications that require controllable adhesives to grip flat surfaces. In such adhesives, normal adhesion is negligible when loaded solely in the normal direction, but becomes available when the adhesive is loaded in shear first. However, much remains to be learned regarding the friction and failure mechanisms of microstructures loaded in shear. In response, we analysed the load–displacement profiles of wedge-shaped microstructured adhesives comprised of nine different silicone elastomers and their mixtures loaded in shear. The results show that the friction profile depends on at least three factors related to material properties: interfacial adhesion strength in the normal direction (work of separation), elastic modulus and the sample's imperfections (e.g. contamination, misalignment and moulding errors). Moreover, the work of separation influences the maximum friction load such that for materials with the same elastic modulus, the strongest interfacial adhesion yields the lowest friction force. To explain this, we suggest that strongly adhering materials will lead to a macroscopic frictional sliding of the array rather than previously reported stick-slip behaviour.

Download Full-text

The 3-Dimensional Molecular Structure of the Actin Filament Revisited

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119223 ◽

1985 ◽

Vol 43 ◽

pp. 480-481

Author(s):

U. Aebi ◽

R. Millonig ◽

H. Salvo

Keyword(s):

Actin Filament ◽

Supramolecular Assembly ◽

Specimen Preparation ◽

X Ray Diffraction ◽

Single Filament ◽

X Ray ◽

3 Dimensional ◽

Filament Diameter ◽

Preparation Conditions ◽

Apparent Diameter

To date, most 3-D reconstructions of undecorated actin filaments have been obtained from actin filament paracrystal data (for refs, see 1,2). However, due to the fact that (a) the paracrystals may be several filament layers thick, and (b) adjacent filaments may sustantially interdigitate, these reconstructions may be subject to significant artifacts. None of these reconstructions has permitted unambiguous tracing or orientation of the actin subunits within the filament. Furthermore, measured values for the maximal filament diameter both determined by EM and by X-ray diffraction analysis, vary between 6 and 10 nm. Obviously, the apparent diameter of the actin filament revealed in the EM will critically depend on specimen preparation, since it is a rather flexible supramolecular assembly which can easily be bent or distorted. To resolve some of these ambiguities, we have explored specimen preparation conditions which may preserve single filaments sufficiently straight and helically ordered to be suitable for single filament 3-D reconstructions, possibly revealing molecular detail.

Download Full-text

Morphological behavior of compatibilized ternary blends prepared by mechanical mixing

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100151830 ◽

1993 ◽

Vol 51 ◽

pp. 1200-1201

Author(s):

S.D. Smith ◽

R.J. Spontak ◽

D.H. Melik ◽

S.M. Buehler ◽

K.M. Kerr ◽

...

Keyword(s):

Interfacial Adhesion ◽

Diblock Copolymers ◽

Ternary Blends ◽

Mechanical Mixing ◽

Design Considerations ◽

Covalently Bonded ◽

Homopolymer Blends ◽

Emulsifying Agent ◽

Surface Active ◽

Low Entropy

When blended together, homopolymers A and B will normally macrophase-separate into relatively large (≫1 μm) A-rich and B-rich phases, between which exists poor interfacial adhesion, due to a low entropy of mixing. The size scale of phase separation in such a blend can be reduced, and the extent of interfacial A-B contact and entanglement enhanced, via addition of an emulsifying agent such as an AB diblock copolymer. Diblock copolymers consist of a long sequence of A monomers covalently bonded to a long sequence of B monomers. These materials are surface-active and decrease interfacial tension between immiscible phases much in the same way as do small-molecule surfactants. Previous studies have clearly demonstrated the utility of block copolymers in compatibilizing homopolymer blends and enhancing blend properties such as fracture toughness. It is now recognized that optimization of emulsified ternary blends relies upon design considerations such as sufficient block penetration into a macrophase (to avoid block slip) and prevention of a copolymer multilayer at the A-B interface (to avoid intralayer failure).

Download Full-text

Effect Of Elevated Temperatures On Complete Concrete Deformation Diagrams

Promyshlennoe i Grazhdanskoe Stroitel stvo ◽

10.33622/0869-7019.2019.11.09-14 ◽

2019 ◽

pp. 9-14

Keyword(s):

Experimental Data ◽

Elastic Modulus ◽

Elevated Temperatures ◽

Peak Load ◽

Relative Deformation ◽

Deformation Characteristics ◽

Compression Tests ◽

Strain Behavior ◽

Different Temperatures ◽

Deformation Diagrams

The analysis of the previous results of the study on concrete stress-strain behavior at elevated temperatures has been carried out. Based on the analysis, the main reasons for strength retrogression and elastic modulus reduction of concrete have been identified. Despite a significant amount of research in this area, there is a large spread in experimental data received, both as a result of compression and tension. In addition, the deformation characteristics of concrete are insufficiently studied: the coefficient of transverse deformation, the limiting relative compression deformation corresponding to the peak load and the almost complete absence of studies of complete deformation diagrams at elevated temperatures. The two testing chambers provided creating the necessary temperature conditions for conducting studies under bending compression and tension have been developed. On the basis of the obtained experimental data of physical and mechanical characteristics of concrete at different temperatures under conditions of axial compression and tensile bending, conclusions about the nature of changes in strength and deformation characteristics have been drawn. Compression tests conducted following the method of concrete deformation complete curves provided obtaining diagrams not only at normal temperature, but also at elevated temperature. Based on the experimental results, dependences of changes in prism strength and elastic modulus as well as an equation for determining the relative deformation and stresses at elevated temperatures at all stages of concrete deterioration have been suggested.

Download Full-text

Effective elastic modulus of peristatic bar with periodically distributed damage

International Journal for Multiscale Computational Engineering ◽

10.1615/intjmultcompeng.2018022670 ◽

2018 ◽

Cited By ~ 1

Author(s):

Valeriy Buryachenko

Keyword(s):

Elastic Modulus ◽

Effective Elastic Modulus

Download Full-text

Supramolecular Assembly of U(IV) Clusters and Superatoms

10.26434/chemrxiv.11860065 ◽

2020 ◽

Author(s):

Ian Colliard ◽

Gregory Morrosin ◽

Hans-Conrad zur Loye ◽

May Nyman

Keyword(s):

Quantum Dots ◽

Supramolecular Assembly ◽

Emergent Properties ◽

Organic Media ◽

Body Centered Cubic ◽

Cluster Anions ◽

Charge Balance ◽

Interpenetrating Networks ◽

Hierarchical Assembly ◽

Two Parameters

Superatoms are nanometer-sized molecules or particles that can form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in superlattices of quantum-dots, p-block clusters, and fullerenes. Here, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters; acidity and the countercation. In acid, larger LnIII (Ln=La-Ho) link hexamer (U6) oxoclusters into body-centered cubic frameworks, while smaller LnIII (Ln=Er-Lu &Y) promote linking of fourteen U6-clusters into hollow superclusters (U84 superatoms). U84 assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations, and U6-clusters. Divalent transition metals (TM=MnII and ZnII), with no added acid, charge-balance and promote the fusion of 10 U6 and 10 U-monomers into a wheel–shaped cluster (U70). Dissolution of U70 in organic media reveals (by small-angle Xray scattering) that differing supramolecular assemblies are accessed, controlled by TM-linking of U70-clusters.

Download Full-text