"Bruce Sterling - Superglue (2)" - читать интересную книгу автора (Sterling Bruce)

ingredients to design glues with well-defined specifications:
qualities such as shear strength, green strength, tack, electrical
conductivity, transparency, and impact resistance. But when it
comes to actually describing why glue is sticky, it's a different
matter, and a far from simple one.

A good glue has low surface tension; it spreads rapidly and
thoroughly, so that it will wet the entire surface of the substrate.
Good wetting is a key to strong adhesive bonds; bad wetting leads
to problems like "starved joints," and crannies full of trapped air,
moisture, or other atmospheric contaminants, which can weaken the
bond.

But it is not enough just to wet a surface thoroughly; if that
were the case, then water would be a glue. Liquid glue changes
form; it cures, creating a solid interface between surfaces that
becomes a permanent bond.

The exact nature of that bond is pretty much anybody's guess.
There are no less than four major physico-chemical theories about
what makes things stick: mechanical theory, adsorption theory,
electrostatic theory and diffusion theory. Perhaps molecular strands
of glue become physically tangled and hooked around irregularities
in the surface, seeping into microscopic pores and cracks. Or, glue
molecules may be attracted by covalent bonds, or acid-base
interactions, or exotic van der Waals forces and London dispersion
forces, which have to do with arcane dipolar resonances between
magnetically imbalanced molecules. Diffusion theorists favor the
idea that glue actually blends into the top few hundred molecules of
the contact surface.

Different glues and different substrates have very different
chemical constituents. It's likely that all of these processes may have
something to do with the nature of what we call "stickiness" -- that
everybody's right, only in different ways and under different
circumstances.

In 1989 the National Science Foundation formally established
the Center for Polymeric Adhesives and Composites. This Center's
charter is to establish "a coherent philosophy and systematic
methodology for the creation of new and advanced polymeric

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adhesives" -- in other words, to bring genuine detailed scientific
understanding to a process hitherto dominated by industrial rules of
thumb. The Center has been inventing new adhesion test methods
involving vacuum ovens, interferometers, and infrared microscopes,
and is establishing computer models of the adhesion process. The