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Surface energy

When investigating a bonding problem at work, I made this picture of a water droplet resting on a carbon fiber and epoxy resin laminate, to measure the contact angle, which is an indicator of surface energy.

water droplet on a carbon-fiber epoxy laminate

This particular laminate turns out to have a low surface energy; it does not attract the water droplet very much. This is what causes trouble when you try to bond materials like this. There will be little adhesion between the glue and the substrate.

The picture was made using the "digital macro" mode of my Canon Digital IXUS 970 IS, which works surprisingly well.