Bruce Sterling - Superglue.pdf - Bruce Sterling - margozap

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Bruce Sterling

bruces@well.sf.ca.us

LITERARY FREEWARE: NOT FOR COMMERCIAL USE

From THE MAGAZINE OF FANTASY AND SCIENCE FICTION, June 1993.

F&SF, Box 56, Cornwall CT 06753 $26/yr USA $31/yr other

F&SF Science Column #7:

SUPERGLUE

This is the Golden Age of Glue.

For thousands of years, humanity got by with natural glues like

pitch, resin, wax, and blood; products of hoof and hide and treesap

and tar. But during the past century, and especially during the past

thirty years, there has been a silent revolution in adhesion.

This stealthy yet steady technological improvement has been

difficult to fully comprehend, for glue is a humble stuff, and the

better it works, the harder it is to notice. Nevertheless, much of the

basic character of our everyday environment is now due to advanced

adhesion chemistry.

Many popular artifacts from the pre-glue epoch look clunky

and almost Victorian today. These creations relied on bolts, nuts,

rivets, pins, staples, nails, screws, stitches, straps, bevels, knobs, and

bent flaps of tin. No more. The popular demand for consumer

objects ever lighter, smaller, cheaper, faster and sleeker has led to

great changes in the design of everyday things.

Glue determines much of the difference between our

grandparent's shoes, with their sturdy leather soles, elaborate

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stitching, and cobbler's nails, and the eerie-looking modern jogging-

shoe with its laminated plastic soles, fabric uppers and sleek foam

inlays. Glue also makes much of the difference between the big

family radio cabinet of the 1940s and the sleek black hand-sized

clamshell of a modern Sony Walkman.

Glue holds this very magazine together. And if you happen to

be reading this article off a computer (as you well may), then you

are even more indebted to glue; modern microelectronic assembly

would be impossible without it.

Glue dominates the modern packaging industry. Glue also has

a strong presence in automobiles, aerospace, electronics, dentistry,

medicine, and household appliances of all kinds. Glue infiltrates

grocery bags, envelopes, books, magazines, labels, paper cups, and

cardboard boxes; there are five different kinds of glue in a common

filtered cigarette. Glue lurks invisibly in the structure of our

shelters, in ceramic tiling, carpets, counter tops, gutters, wall siding,

ceiling panels and floor linoleum. It's in furniture, cooking utensils,

and cosmetics. This galaxy of applications doesn't even count the

vast modern spooling mileage of adhesive tapes: package tape,

industrial tape, surgical tape, masking tape, electrical tape, duct tape,

plumbing tape, and much, much more.

Glue is a major industrial industry and has been growing at

twice the rate of GNP for many years, as adhesives leak and stick

into areas formerly dominated by other fasteners. Glues also create

new markets all their own, such as Post-it Notes (first premiered in

April 1980, and now omnipresent in over 350 varieties).

The global glue industry is estimated to produce about twelve

billion pounds of adhesives every year. Adhesion is a $13 billion

market in which every major national economy has a stake. The

adhesives industry has its own specialty magazines, such as

Adhesives Age andSAMPE Journal; its own trade groups, like the

Adhesives Manufacturers Association, The Adhesion Society, and the

Adhesives and Sealant Council; and its own seminars, workshops and

technical conferences. Adhesives corporations like 3M, National

Starch, Eastman Kodak, Sumitomo, and Henkel are among the world's

most potent technical industries.

Given all this, it's amazing how little is definitively known

about how glue actually works -- the actual science of adhesion.

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There are quite good industrial rules-of-thumb for creating glues;

industrial technicians can now combine all kinds of arcane

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

Center's corporate sponsors -- Amoco, Boeing, DuPont, Exxon,

Hoechst Celanese, IBM, Monsanto, Philips, and Shell, to name a few of

them -- are wishing them all the best.

We can study the basics of glue through examining one typical

candidate. Let's examine one well-known superstar of modern

adhesion: that wondrous and well-nigh legendary substance known

as "superglue." Superglue, which also travels under the aliases of

SuperBonder, Permabond, Pronto, Black Max, Alpha Ace, Krazy Glue

and (in Mexico) Kola Loka, is known to chemists as cyanoacrylate

(C5H5NO2).

Cyanoacrylate was first discovered in 1942 in a search for

materials to make clear plastic gunsights for the second world war.

The American researchers quickly rejected cyanoacrylate because

the wretched stuff stuck to everything and made a horrible mess. In

1951, cyanoacrylate was rediscovered by Eastman Kodak researchers

Harry Coover and Fred Joyner, who ruined a perfectly useful

refractometer with it -- and then recognized its true potential.

Cyanoacrylate became known as Eastman compound #910. Eastman

910 first captured the popular imagination in 1958, when Dr Coover

appeared on the "I've Got a Secret" TV game show and lifted host

Gary Moore off the floor with a single drop of the stuff.

This stunt still makes very good television and cyanoacrylate

now has a yearly commercial market of $325 million.

Cyanoacrylate is an especially lovely and appealing glue,

because it is (relatively) nontoxic, very fast-acting, extremely strong,

needs no other mixer or catalyst, sticks with a gentle touch, and does

not require any fancy industrial gizmos such as ovens, presses, vices,

clamps, or autoclaves. Actually, cyanoacrylate does require a

chemical trigger to cause it to set, but with amazing convenience, that

trigger is the hydroxyl ions in common water. And under natural

atmospheric conditions, a thin layer of water is naturally present on

almost any surface one might want to glue.

Cyanoacrylate is a "thermosetting adhesive," which means that

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(unlike sealing wax, pitch, and other "hot melt" adhesives) it cannot

be heated and softened repeatedly. As it cures and sets,

cyanoacrylate becomes permanently crosslinked, forming a tough

and permanent polymer plastic.

In its natural state in its native Superglue tube from the

convenience store, a molecule of cyanoacrylate looks something like

this:

CH2=C

COOR

The R is a variable (an "alkyl group") which slightly changes

the character of the molecule; cyanoacrylate is commercially

available in ethyl, methyl, isopropyl, allyl, butyl, isobutyl,

methoxyethyl, and ethoxyethyl cyanoacrylate esters. These

chemical variants have slightly different setting properties and

degrees of gooiness.

After setting or "ionic polymerization," however, Superglue

looks something like this:

CN CN CN

| | |

- CH2C -(CH2C)-(CH2C)- (etc. etc. etc)

| | |

COOR COOR COOR

The single cyanoacrylate "monomer" joins up like a series of

plastic popper-beads, becoming a long chain. Within the thickening

liquid glue, these growing chains whip about through Brownian

motion, a process technically known as "reptation," named after the

crawling of snakes. As the reptating molecules thrash, then wriggle,

then finally merely twitch, the once- thin and viscous liquid becomes

a tough mass of fossilized, interpenetrating plastic molecular

spaghetti.

And it is strong. Even pure cyanoacrylate can lift a ton with a

single square-inch bond, and one advanced elastomer-modified '80s

mix, "Black Max" from Loctite Corporation, can go up to 3,100 pounds.

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Bruce Sterling - Superglue.pdf

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