Interfacial Adhesion Mechanism Research Articles

Surface Characteristics of Rare Earth Treated Carbon Fibers and Interfacial Properties of Composites

Abstract Effect of rare earth treatment on surface physicochemical properties of carbon fibers and interfacial properties of carbon fiber/epoxy composites was investigated, and the interfacial adhesion mechanism of treated carbon fiber/epoxy composite was analyzed. It was found that rare earth treatment led to an increase of fiber surface roughness, improvement of oxygen-containing groups, and introduction of rare earth element on the carbon fiber surface. As a result, coordination linkages between fibers and rare earth, and between rare earth and resin matrix were formed separately, thereby the interlaminar shear strength (ILSS) of composites increased, which indicated the improvement of the interfacial adhesion between fibers and matrix resin resulting from the increase of carboxyl and carbonyl.

Influence of rare earth treatment on interfacial properties of carbon fiber/epoxy composites

In this work, the effect of soaking and irradiating in praseodymium nitrate solution on the surface physicochemical properties of carbon fibers and interfacial properties of composites has been investigated, and the interfacial adhesion mechanism of treated carbon fiber/epoxy composite was analyzed. It was found that both of immersion and irradiation lead to an increase of fiber surface roughness, improvement of oxygen-containing groups, enhancement of disorder degree and introduction of praseodymium element on carbon fiber surface. As a result, the coordination linkage between fibers, praseodymium ion and matrix is formed and the interlaminar shear strength (ILSS) of composites is increased, due to the improvement of interfacial adhesion between fibers and matrix resin. Moreover, γ-ray irradiation treatment is superior to immersion treatment in promoting interfacial properties owing to the increase of carboxyl and carbonyl.

Interfacial adhesion mechanisms in incompatible semicrystalline polymer systems

AbstractThe mechanism of adhesion at semicrystalline polymer interfaces between isotactic polypropylene (iPP) and linear low‐density polyethylene (PE) was studied with transmission electron microscopy (TEM) and an asymmetric‐double‐cantilever‐beam test. From the TEM images, both the interfacial width and the lamellar thickness of the polymers were extracted. During annealing, the interfacial width increased with the annealing temperature, and this indicated the accumulation of amorphous polymers at the interface. The interfacial strength, determined from the critical fracture energy (Gc), also increased with the annealing temperature and reached a maximum above the melting temperatures of iPP and PE, whereas the smallest Gc value was obtained below the melting temperatures of the two materials. A mechanism of interfacial strengthening was proposed accounting for the competition between the interdiffusion of PE and crystallization of iPP. As the annealing temperature increased, the rates of PE diffusion and iPP crystallization increased. Although the crystallization of iPP hindered the interdiffusion of PE, both the interfacial width and the fracture energy increased with the temperature, and this indicated that PE interdiffusion dominated iPP crystallization. Below the critical temperature, the fracture surfaces of both iPP and PE were smooth, and chain pullout dominated the fracture mechanism. Above the critical temperature, iPP crystallization still hindered the interdiffusion, and crazes could be seen on the iPP side. Above the melting temperatures of the two materials, ruptured surfaces could also be seen on the PE side, and crazing was the fracture mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2667–2679, 2004

Effects of titania content and plasma treatment on the interfacial adhesion mechanism of nano titania-hybridized polyimide and copper system

Effects of titania content and plasma treatment on the interfacial adhesion mechanism of nano titania-hybridized polyimide and copper system

Effects of titania content and plasma treatment on the interfacial adhesion mechanism of nano titania-hybridized polyimide and copper system

Nano-titania (TiO 2) incorporated into polyimide (PI) matrix can significantly enhance the adhesion strength for PI/TiO 2 hybrid film and copper system. Surface modifications by various plasma treatments (Ar, Ar/N 2 and Ar/O 2) were also applied in this study to improve the adhesion strength. The Ar/N 2 plasma treatment is regarded as the more effective way in promoting the adhesion strength. The maximum adhesion value of 9.53 N/cm was obtained for the PI/TiO 2–1 wt% hybrid film with Ar/N 2 plasma treatment. It is enhanced about 10 times as large as pristine PI. Furthermore, by Ar/O 2 plasma treatment, a weak boundary of copper oxide was formed at the interlayer between PI/TiO 2 hybrid film and copper which decreases the adhesion strength. The effects of plasma treatment and content of nanosized TiO 2 on the adhesion strength between PI/TiO 2 hybrid film and copper system were studied. Atomic force microscope and contact angle analyses were used to measure the changes in surface morphology and surface energy as a result of plasma treatment. Besides, the interfacial states of peeled-off polymer side and copper side were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Based on the result of XPS spectra, the peeled-off failure mode between PI/TiO 2 hybrid film and copper was proposed in this study.

Influence of polymeric surfactants on the properties of drug-loaded PLA nanospheres

Different dextran derivatives containing various grafted hydrophobic groups (phenoxy, P; hexyl, C 6 or decyl, C 10) were synthesized and their applicability as emulsion stabilizers in the preparation of poly(lactic acid) (PLA) nanospheres by an o/w emulsion/evaporation technique was investigated. The effect of dextran modification on particle size, surface charge and stability was evaluated. Differential scanning calorimetry (DSC) studies suggested that the mechanism of interfacial adhesion between immiscible dextran and PLA chains depend on the nature of the hydrophobic grafted groups. However, all dextran layers behaved similarly in terms of stability and in preventing protein adsorption. The encapsulation of lidocaine in PLA nanoparticles was not possible when using phenoxy–dextran as an emulsion stabilizer in the preparation of particles. Conversely, particles with drug-loading varying from about 7 to 18% (w/w) were obtained in the presence of alkyl–dextrans. The polysaccharide layer at the surface of PLA particles did not significantly change the in vitro release of lidocaine, compared with that obtained with drug-loaded uncoated PLA nanoparticles. The partition coefficient of lidocaine between PLA and water and the drug diffusion in the matrix were found to control the release pattern of lidocaine from nanoparticles.

Adhesion and toughening mechanisms at underfill interfaces for flip-chip-on-organic-substrate packaging

The flip chip-on-organic-substrate packaging technology utilizes a particulate reinforced epoxy as the underfill (UF) to adhere the chip to the package or board, Although the use of underfill encapsulation leads to improved reliability of flip-chip solder interconnections, delamination at various interfaces becomes a major concern for assembly yield loss and package reliability. In spite of their importance, the adhesion and fracture behaviors of the underfill interfaces have not been investigated until recently. Considerable controversy exists over the effects of underfill formulation and the adhesion and toughening mechanisms of the interfaces. The present work focuses on investigating the effects of several key variables on the interface adhesion strengths for UF/chip and UF/organic substrate systems. These variables are underfill organosilane content, filler particle content, rubber particle content, surface morphology and chemistry of the chip and organic substrates. The approach of this study is to measure the effect of these variables on the interfacial fracture energy using the double-cantilever-beam (DCB) techniques. The results demonstrate that the underfill interfacial adhesion and fracture characteristics are controlled by several distinct but competing mechanisms, such as formation of primary bonds, crack-pinning by glass fillers, debonding of glass filler from epoxy matrix (defect formation), and cavitation and shearing induced by rubber particles. Fundamental understanding of the interfacial adhesion and toughening mechanisms can provide guidance for developing new processes and materials to enhance interfacial adhesion and reliability.

Relationship of hierarchical structure to mechanical properties

AbstractThe mechanical properties in complex systems are explained based on the hierarchical structures present in the system. Hierarchical structures designed for specific mechanical responses are best exemplified by examples from biology. Collagen, a main component in soft connective tissues, is organized into hierarchical structures in the form of tendons or intervertebral discs as examples. Understanding these structures is vital in relating the structures to the intended properties. This approach is also used to characterize organic/inorganic natural composites such as human bone, reindeer antler and nacre. Another example of a hierarchical structure in biology with excellent mechanical properties is that of cellulose, when organized into wood. The importance of hierarchical structures also applies to synthetic polymers for a clearer understanding of the structure‐property relationships. Solid‐state biaxially oriented polypropylene has excellent tensile and impact properties, which are explained by the hierarchical structure induced during the processing. Thermotropic liquid crystalline polymers develop a hierarchical structure during injection molding that influence the final properties. Furthermore, the impact modification of polycarbonate is more easily understood when the system is explained in a hierarchical manner. It is also now possible to create or force hierarchical structures in synthetic polymers by microlayering technology. Several systems are outlined in which a hierarchical structure is created to enhance specific properties. SAN, a brittle polymer, can be microlayered with PC to create tough materials due to the scale, interaction and architecture of the microlayered composite. Another example is the effect of microlayered composite of PC/SAN on the interfacial adhesion mechanisms. Furthermore, toughening mechanisms in filled microlayers are examined based on the hierarchical structure.

Interfacial Adhesion Strength between Fibers of Liquid Crystalline Polymer and Thermoplastic Matrix

The interfacial shear stress between fibers of liquid crystalline polymer (LCP) and various thermoplastics was evaluated using a single fiber composite test. Several ductile polymers such as polycarbonate (PC), polyethersulfone (PSF), and polyetherimide (PEI) were employed as a matrix polymer. The effects of matrix properties, welding time and welding temperature on the interfacial shear stress were examined. The interfacial shear stress increased abruptly at the initial welding time and became an equilibrium value, which implies that the wetting approached the equilibrium with increasing welding time. The equilibrium interfacial shear stress, τ decreased in the order of PSF/LCP, PEI/LCP, and PC/LCP. The debonding occurred at the interface and the plastic deformation of the matrix was not observed in the case of PC/LCP. However, the plastic deformation of the matrix near the interface was observed in the case of PSF/LCP. Through the measurement of polarity and compressive pressure, the polar interaction and compressive pressure were found to be the main interfacial adhesion mechanisms between LCP fibers and thermoplastic matrices.

A study on interfacial adhesion of poly(vinylidene fluoride) with substrates in a multilayer structure

AbstractThe peel force of a PVDF/3‐APS/Si joint and a PVDF/3‐APS/Al joint can reach the same level by treating the Si substrate with ⩾ 0.3% 3‐aminopropyltriethoxy silane (3‐APS) solution and treating the aluminum substrate with NH3 solution (pH 10.5) first and then with ⩾ 3% 3‐APS solution. Scanning electron micrographs show that the interfacial adhesion mechanisms of PVDF/3‐APS/Si joints and PVDF/3‐APS/Al joints are different. In the peel test, the PVDF [poly(vinylidene fluoride)] break surfaces from PVDF/3‐APS/Si joints reveal striations on the surface and less plastic deformation. The significant plastic deformation of the PVDF at the break surface may result from the deeper interpenetration of 3‐APS with PVDF in the PVDF/3‐APS/Al joint than in the PVDF/3‐APS/Si joint. The peel force of PVDF film/substrate joint depends on many factors: film thickness, peel rate, concentration of coupling agent, the treatment time of the coupling agent on the substrate, and the substrate pretreatment.

The fibre/matrix interphase and the adhesion mechanism of surface-treated Twaron R aramid fibre

In order to optimize the adhesion to an epoxy matrix, Twaron R aramid fibre requires a pretreatment with an epoxy/hardener solution. The chemical composition of the pretreated fibre surface was analysed using X-ray photoelectron spectroscopy and static imaging secondary ion mass spectrometry. To this end model epoxy monomers were synthesized and use was made of a fluorine-labelled hardener. The effects of processing steps such as ageing of the pretreatment solution and curing of the epoxy/hardener at the fibre surface have been systematically analysed. Our results show that polar interactions between the aramid and epoxy molecules play a dominant role in the interfacial adhesion mechanism. There is evidence to suggest that the epoxy layer introduced onto the surface of the Twaron R filaments is inhomogeneous as a result of the processing conditions.

Interfacial adhesion and toughening mechanisms in an alloy of polycarbonate/polyethylene

Interfacial adhesion and toughening mechanisms in an alloy of polycarbonate/polyethylene (PC/PE) are investigated using transmission electron microscopy. In contrast to the general speculation, it is found that the PE particles strongly adhere to the PC matrix. The toughening mechanisms in the PC/PE blend are found to be debonding of the PC/PE interface, which relieves the triaxial tension in front of the crack tip, followed by shear banding of the PC matrix. Possible causes for such an unexpected strong interfacial adhesion between PC and PE are discussed. Also, the importance of the cavitational strength of the toughener phase in toughness optimization is addressed.