Читать книгу Sticking Together - Steven Abbott - Страница 34

If you are a gecko, surface energy adhesion is ideal. If you want repositionable hooks on your wall, surface energy adhesion can sometimes work. If you want to fix something at home and you aren't going to put unexpected peel loads onto it and if you can find a liquid glue that rapidly changes to a solid, then surface energy adhesion works OK.

If we recall that surface energies change, across most relevant materials, only by a factor of 2.5 across most relevant materials, then we cannot get a 10× increase by increasing the surface energy. This means that we need some very different science to help us. We will find that there are two very different approaches to strong adhesion, one of which relies on having weak adhesives!

Before we start exploring strong adhesion, we need to understand how to determine whether adhesion is strong or not. We already have a hint that this is not an easy matter. The two strong men found that the adhesion was strong, then the little girl showed that it wasn't.

In most adhesion science books, the question of measuring adhesion is kept until later, because it is assumed that measurement is something rather straightforward. My view is the other way around. We cannot understand what makes strong adhesion without understanding that there is no objective way to measure it! Very quickly we will find that the force needed to separate the same samples of pure rubber, held together by surface energy, can vary by more than 1000× depending on how the force is applied.