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.
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
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
(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:
CN
/
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.
This is enough strength to rip the surface right off most substrates.
Unless it’s made of chrome steel, the object you’re gluing will likely
give up the ghost well before a properly anchored layer of Superglue
will.
Superglue quickly found industrial uses in automotive trim,
phonograph needle cartridges, video cassettes, transformer
laminations, circuit boards, and sporting goods. But early superglues
had definite drawbacks. The stuff dispersed so easily that it
sometimes precipitated as vapor, forming a white film on surfaces
where it wasn’t needed; this is known as “blooming.” Though
extremely strong under tension, superglue was not very good at
sudden lateral shocks or “shear forces,” which could cause the glue—
bond to snap. Moisture weakened it, especially on metal-to-metal
bonds, and prolonged exposure to heat would cook all the strength
out of it.
The stuff also coagulated inside the tube with annoying speed,
turning into a useless and frustrating plastic lump that no amount of
squeezing of pinpoking could budge — until the tube burst and and
the thin slippery gush cemented one’s fingers, hair, and desk in a
mummified membrane that only acetone could cut.
Today, however, through a quiet process of incremental
improvement, superglue has become more potent and more useful
than ever. Modern superglues are packaged with stabilizers and
thickeners and catalysts and gels, improving heat capacity, reducing
brittleness, improving resistance to damp and acids and alkalis.
Today the wicked stuff is basically getting into everything.
Including people. In Europe, superglue is routinely used in
surgery, actually gluing human flesh and viscera to replace sutures
and hemostats. And Superglue is quite an old hand at attaching fake
fingernails — a practice that has sometimes had grisly consequences
when the tiny clear superglue bottle is mistaken for a bottle of
eyedrops. (I haven’t the heart to detail the consequences of this
mishap, but if you’re not squeamish you might try consulting The
Journal of the American Medical Association, May 2, 1990 v263 n17
p2301).
Superglue is potent and almost magical stuff, the champion of
popular glues and, in its own quiet way, something of an historical
advent. There is something pleasantly marvelous, almost Arabian
Nights-like, about a drop of liquid that can lift a ton; and yet one can
buy the stuff anywhere today, and it’s cheap. There are many urban
legends about terrible things done with superglue; car-doors locked
forever, parking meters welded into useless lumps, and various tales
of sexual vengeance that are little better than elaborate dirty jokes.
There are also persistent rumors of real-life superglue muggings, in
which victims are attached spreadeagled to cars or plate-glass
windows, while their glue-wielding assailants rifle their pockets at
leisure and then stroll off, leaving the victim helplessly immobilized.
While superglue crime is hard to document, there is no
question about its real-life use for law enforcement. The detection
of fingerprints has been revolutionized with special kits of fuming
ethyl-gel cyanoacrylate. The fumes from a ripped-open foil packet of
chemically smoking superglue will settle and cure on the skin oils
left in human fingerprints, turning the smear into a visible solid
object. Thanks to superglue, the lightest touch on a weapon can
become a lump of plastic guilt, cementing the perpetrator to his
crime in a permanent bond.
And surely it would be simple justice if the world’s first
convicted superglue mugger were apprehended in just this way.
“Creation Science”
In the beginning, all geologists and biologists were creationists.
This was only natural. In the early days of the Western scientific
tradition, the Bible was by far the most impressive and potent source
of historical and scientific knowledge.
The very first Book of the Bible, Genesis, directly treated
matters of deep geological import. Genesis presented a detailed
account of God’s creation of the natural world, including the sea, the
sky, land, plants, animals and mankind, from utter nothingness.
Genesis also supplied a detailed account of a second event of
enormous import to geologists: a universal Deluge.
Theology was queen of sciences, and geology was one humble
aspect of “natural theology.” The investigation of rocks and the
structure of the landscape was a pious act, meant to reveal the full
glory and intricacy of God’s design. Many of the foremost geologists
of the 18th and 19th century were theologians: William Buckland,
John Pye Smith, John Fleming, Adam Sedgewick. Charles Darwin
himself was a onetime divinity student.
Eventually the study of rocks and fossils, meant to complement
the Biblical record, began to contradict it. There were published
rumblings of discontent with the Genesis account as early as the
1730s, but real trouble began with the formidable and direct
challenges of Lyell’s uniformitarian theory of geology and his disciple
Darwin’s evolution theory in biology. The painstaking evidence
heaped in Lyell’s Principles of Geology and Darwin’s *Origin of
day in the scientific community.
But convincing the scientific community was far from the end
of the matter. For “creation science,” this was only the beginning.
Most Americans today are “creationists” in the strict sense of
that term. Polls indicate that over 90 percent of Americans believe
that the universe exists because God created it. A Gallup poll in
1991 established that a full 47 percent of the American populace
further believes that God directly created humankind, in the present
human form, less than ten thousand years ago.
So “creationism” is not the view of an extremist minority in our
society — quite the contrary. The real minority are the fewer than
five percent of Americans who are strictly non-creationist. Rejecting
divine intervention entirely leaves one with few solid or comforting
answers, which perhaps accounts for this view’s unpopularity.
Science offers no explanation whatever as to why the universe exists.
It would appear that something went bang in a major fashion about
fifteen billion years ago, but the scientific evidence for that — the
three-degree background radiation, the Hubble constant and so forth
— does not at all suggest why such an event should have happened
in the first place.
One doesn’t necessarily have to invoke divine will to explain
the origin of the universe. One might speculate, for instance, that
the reason there is Something instead of Nothing is because “Nothing
is inherently unstable” and Nothingness simply exploded. There’s
little scientific evidence to support such a speculation, however
, and
few people in our society are that radically anti-theistic. The
commonest view of the origin of the cosmos is “theistic creationism,”
the belief that the Cosmos is the product of a divine supernatural
action at the beginning of time.
The creationist debate, therefore, has not generally been
between strictly natural processes and strictly supernatural ones, but
over how much supernaturalism or naturalism one is willing to
admit into one’s worldview.
How does one deal successfully with the dissonance between
the word of God and the evidence in the physical world? Or the
struggle, as Stephen Jay Gould puts it, between the Rock of Ages and
the age of rocks?
Let us assume, as a given, that the Bible as we know it today is
divinely inspired and that there are no mistranslations, errors,
ellipses, or deceptions within the text. Let us further assume that
the account in Genesis is entirely factual and not metaphorical, poetic
or mythical.
Genesis says that the universe was created in six days. This
divine process followed a well-defined schedule.
Day 1. God created a dark, formless void of deep waters, then
created light and separated light from darkness.
Day 2. God established the vault of Heaven over the formless watery
void.
Day 3. God created dry land amidst the waters and established
vegetation on the land.
Day 4. God created the sun, the moon, and the stars, and set them
into the vault of heaven.
Day 5. God created the fish of the sea and the fowl of the air.
Day 6. God created the beasts of the earth and created one male and
one female human being.
On Day 7, God rested.
Humanity thus began on the sixth day of creation. Mankind is
one day younger than birds, two days younger than plants, and
slightly younger than mammals. How are we to reconcile this with
scientific evidence suggesting that the earth is over 4 billion years
old and that life started as a single-celled ooze some three billion
years ago?
The first method of reconciliation is known as “gap theory.”
The very first verse of Genesis declares that God created the heaven
and the earth, but God did not establish “Day” and “Night” until the