Glue and Skin

name         Max D.
status       student
grade        6-8
location     HI

Question -   How does glue stick to skin? Is there a way to
create a glue that sticks to everything else but not skin? how?
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Max,

Most glues work on the principle that a fluid is able to fit into 
the microscopic cracks and crevices of a surface. This fluid, under 
the action of oxygen, heat, or some other molecule will then form 
more chemical bonds and harden. Think of a bunch of rubber bands. As 
a loose grouping, the rubber bands can penetrate into small holes, 
or fit themselves into tight spaces (the microscopic cracks on the 
surface of what it is you are trying to glue together). However, let 
us say you then took a flame or a heat gun to the rubber bands so 
that the pieces melted into each other. Now, because the bands are 
linked to each other, they do not move as much. But if these pieces 
of rubber were initially already partly found in cracks and 
crevices, than they will be very difficult to pull out since they 
are no longer as mobile once they have been melted together.

So the problem is that skin is very much a rough surface, full of 
crevices and cavities in which the fluid glue can penetrate. Once 
the glue hardens, the individual molecules of the glue bond to each 
other, then the hardened glue is difficult to remove from the 
crevices in the skin where it penetrated.

It might be possible to develop a glue that works on a different 
principle. A glue could be made that would dissolve the surface of 
the object(s) that has to be glued together. Then, when the glue 
evaporates, the dissolved material will harden once again but the 
two pieces will be penetrating into each other. The glue can then be 
made such that it does not dissolve skin, but can dissolve some 
other material. This is not economically feasible however as one 
would have to develop a glue that can dissolve a wide variety of 
objects (otherwise it would have limited use) while making sure that 
it does not dissolve skin. Both because it is difficult to find such 
a substance, and because it would have to be tailored to the 
specific object to be glued - I don't think it would be a 
commercially successful product.

Greg (Roberto Gregorius)
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Glue sticks to skin (or any other material) if it forms some 
sort of chemical bond to the material. This bond may be strong or 
weak depending upon the chemical nature of the glue and the material.
One way to prevent the glue from sticking to the material is to 
apply a thin layer of a coating that either does not stick to the 
glue, or to the skin, or both. In the case of skin, a thin layer of 
Vaseline, or mineral oil works well. Even some water based hand 
creams also prevent sticking to the skin. You may have noticed that 
if you try to apply a piece of adhesive tape to skin that is 
"sweaty" that it won't stick. The principle is the same, but the 
weak sticking layer is oil from your skin. You can use any "weak 
sticking" film of any sort. For example, the Teflon "goop" plumbers 
apply to pipe threads so that the pipe will not freeze up over time 
is the same principle.
   So the choice of the glue is less important that the barrier 
film applied to the skin. Some examples: epoxy, Elmer's glue, and 
"Crazy" glue all stick to skin very aggressively -- as well to most 
other materials except maybe polyethylene. So the strategy for 
keeping the glue from sticking to skin is to apply a lotion or 
cream before exposing the skin to the glue. Note: it doesn't take 
much to do the job, just a couple of drops rubbed into the skin 
very thoroughly.

Vince Calder
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