hesion at the fiber matrix interface of composite specimens is often ascribed to the following factors (Sharpe and Drzal): (1) mechanical interlocking, (2) physicochemical interactions, (3) chemical bonding, and (4) mechanical deformation of the fiber-matrix interphase region. As noted by Drzal, the interphase region is a complicated three-dimensional construction consisting of the bulk adherend, adherend surface layer, adsorbed material, polymer surface layer, and bulk adhesive. Hence, early models of adhesion were ineffective since they oversimplified the composition and nature of the fiber-matrix interface.Although silane coupling-agents deposited by self-assembled monolayer (SAM) technology have no current industrial relevance, this technology provides a methodology for compressing the three-dimensionality of the interphase region in glass-fiber reinforced composites. Using this technology, the roughness of the glass surface induced by the industrial water-deposition process can be minimized and the contribution of adsorbed material in the interphase region is eliminated. Despite similar contact angles, interfacial adhesion was found to be higher for non-bonding silane coating agents deposited by the water-deposition process. Atomic force microscopy indicates that the surface rugosity for water-deposited coatings is greater than SAM coatings. Hence, these results support mechanical interlocking as the primary stress-transfer mechanism for water-deposited non-bonding silane coatings.Interfacial adhesion for a 100 % bonding amine interface was found to be significantly higher using the SAM technology. Although both types of interfaces exhibited debonding with matrix crack formation during fiber fracture, the matrix cracks were larger for the interface formed with the water-deposited silane coating. As a result, the specimen failure rate was highest with the water-deposited silane coated specimens. Preliminary evaluation of the E-glass/epoxy/amine based composite data indicates that the model for adhesion proposed by Nardin and Ward in 1987 for polyethylene based composites may provide a framework for independently evaluating the contribution to adhesion of the first three factors delineated by Sharpe and Drzal.
Citation: Adhesion Society
Pub Type: Journals
adhesion, interface strength, self-assembled monolayer, silane coupling agent, single fiber fragmentation test