A Reliable Method to Measure the Adhesive Force with a Tiny Amount of Adhesive Material

A new method is proposed and developed to measure adhesive forces by use of the force-distance curve of a micro cantilever with an extremely small amount of testing material such as adhesive proteins. The contact area should be well-controlled at a reasonable value. Even though the area is desired to be as small as possible, a contact region of several micrometers by several micrometers is adopted in order to avoid obtaining meaningless measured values and uncertainty in the contact areas. An AFM cantilever is used after having been modified with a micro glass bead to enlarge the contact area for adhesion. A glass plate with micro-scale circular patterns is fabricated from a glass wafer by micro-machining processes in order to control precisely the contact area in adhesion tests. In the proposed method the adhesive materials are directly applied to the bead attached at the AFM cantilever before it is applied on the top area of the truncated cone on the fabricated glass plate. The developed method is applied to measure the adhesive forces of Cell-Tak® (which is a commercial extracted mussel adhesive) and recombinant Mgfp-5 (which is a recombinant mussel adhesive protein) and the statistical credibility of the measured adhesive force data is enormously improved as a result.     

Force spectrum of a few chains grafted on an AFM tip: Comparison of the experiment to a self-consistent mean field theory simulation

A simulation model based on self-consistent mean field theory (SCMFT) has been developed to inspect the approaching process of the polymer chain grafted AFM tip to a substrate. The effects of various controlling parameters, such as grafting position, chain number, chain length, as well as solvent- and substrate-chain interactions, on the force curve were investigated. Real force spectroscopy of AFM tips modified by poly(ethylene glycol) (PEG) chains interacting with the fresh mica has been recorded, and several typical types of the force curves that correspond to the different states of the grafting chain were assorted. The simulations fit the experimental results well, providing a strong support to the model.     

The Use of Peel Ply as a Method to Create Reproduceable But Contaminated Surfaces for Structural Adhesive Bonding of Carbon Fiber Reinforced Plastics

In the fabrication of fiber-reinforced plastics materials peel plies are commonly used as an additional layer on top of the laminates to sponge up the surplus resin and to create an activated surface for adhesive bonding or coating by peel ply removal. In theory, the peel ply removal results in a new and uncontaminated fracture surface that is activated by polymer chain scission. The peel ply method is often presented as being a good surface treatment for structural bonding.

In this study carbon fiber-reinforced plastics (Hexcel® 8552/ IM7) were produced by the use of five different peel plies and a release foil made of polytetrafluorethylene (PTFE). The peel plies themselves and the surfaces on the CFRP created by peeling were examined by scanning electron microscopy (SEM), x-ray photo electron spectroscopy (XPS), energy-dispersive x-ray spectroscopy (EDX), infrared (IR) spectroscopy, atomic force microscopy (AFM), and contact angle measurements to characterize the surfaces produced. Furthermore, the bond strength of lap shear and floating roller peel samples was determined with and without additional plasma treatment. For bonding, a room temperature-curing two-component-epoxy adhesive (Hysol® 9395) was used to prove the applicability of different peel plies for structural adhesive bonding under repair conditions.     

A Method of Determining the Contact Area Between a Particle and Substrate Using Scanning Electron Microscopy

A new technique for determining the contact radius between a micrometer size particle and a contacting substrate using scanning electron microscopy has been developed. The Contact Area Measurement (CAM) technique, which is especially suited for small surface-force-induced contact radii, involves evaporating a thin, uniform coating of a conductive material, such as aluminum, over a sample comprised of particles on a substrate while the sample is rotated slowly. The sample is examined before and after particle removal to determine both the radii of the particle and its respective contact. Where the particle contacted the substrate, no metal deposition occurred. The resulting differences in the secondary electron emissions provide a contrast mechanism that the SEM can image. The CAM technique is shown to be useful in examining rigid particles on rigid substrates, where the inherent contacts are small, making measurements difficult, and for examining irregularly-shaped particles and contact areas.