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World Scientific Book - 9in x 6in
Chapter 1
Introduction: Physics in the World of
Giant Molecules
Molecules are supposed to be small, aren’t they? Quite apart from anything
else, even the very word molecule comes from a Latin phrase that literally
means “a tiny mass of something”. Nevertheless, what would you say about
a molecule about 1 meter long? Or another one that weighs almost 1
kilogram? There are many molecular giants of the kind. They are called
polymers; perhaps you have heard this word. Thus, our book is about
polymers. The world of polymers.
The world of polymers. . . Are polymers really so diverse and numerous
that they make up a whole world? Is this not an exaggeration?
Well, what are polymers? The first things that come to mind may be
plastic bags, and other common plastics. You may also think of rubber and
all its products. Then, synthetic fibres and fabrics, as well as natural ones,
of course. In fact, the list is endless: for example, cellulose (which makes
up both timber and paper), the shell of a space probes traveling to Venus
or Mars, and artificial valves implanted into a human heart. . . Polymers are
used for all sorts of purposes. Huge quantities of them are made these days
throughout the world. In fact, the volume of polymers produced already
exceeds that of metals (although metals still win by weight).
The applications alone are a good enough reason to study polymers.
This is just the same as with semiconductors, for example. However, it is
not only their applications that make polymers so fascinating. The greatest
incentive to do polymer science is life itself. Even a schoolchild knows these
days that our so called “genetic blueprint” (that is, what one is born to
be, a dog or a cat, a boy or a girl, and what color of skin, hair, and eyes
one is to have, etc.) is contained in molecules of a special polymer, DNA
(deoxyribonucleic acid). Modern biology regards a living cell as a kind of
factory, finely tuned, and controlled by DNA. Meanwhile, all the working
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GIANT MOLECULES - Here, There, and Everywhere (Second Edition)
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Giant Molecules: Here, There, and Everywhere
devices in this factory (be they chemical, electrical, mechanical, optical, or
whatever) are based on another type of polymer called proteins. In addition
to this, polymers make hooves and horns, hair, and lots more!
It is not just that polymers are found in abundance in nature, they
actually play a crucial role. So M.D. Frank-Kamenetskii was not really
joking when he called his popular book on DNA “The Most Important
Molecule” (Ref. [45] in the list at the end of the book).
You may say, “All right, I believe you, polymers are important. Perhaps
one can even talk about the world of polymers if one wants. But why
physics?” Good question. We shall try to answer it in a minute, but before
that let’s make one more comment.
We would hate to sound like totally boring people who believe in doing
only useful things. In fact, sometimes it is a good idea just to pursue
whatever takes your fancy! At least, it works very well in scientific research.
After all, it is seldom clear from the start what use you can make of a
discovery or idea. What is fortunate is that good scientists usually have
well developed “taste”: what they like and want to do, tends to be also
useful.
Well, let’s go back to the question. Why study the physics of polymers?
We can now give one good reason. It is merely very interesting! And
it has a lot to offer. Beautiful effects, fundamental analogies with other
areas, and clear physical principles explaining complex phenomena. These
are just what we shall try to give a feel for in this little book. As for
various applications, there are other people who can write a better story
on those. Chemists could talk with confidence about synthetic polymers.
And molecular biologists know a lot about biological polymers. However,
even in these areas, physicists have no reasons to feel too much out of place.
Without physics, one can hardly reach a proper understanding of polymer
chemistry or molecular biology. This is why all polymer scientists know
the physics of polymers, and all use it to some extent in their work. Quite
often the combination proves very fruitful.
There was even a period, in the 1940s and 1950s, when polymer physics
was developed mainly by professional chemists. The most notable among
them was Paul Flory (1908–1982), an American physical chemist who went
down in scientific history chiefly due to his pioneering work in polymer
physics. He received a Nobel prize for this in 1974.
However, science tends to become more and more specialized. So it
is not surprising that polymer physics has eventually grown into an independent field of research. This was helped by some eminent physicists,
GIANT MOLECULES - Here, There, and Everywhere (Second Edition)
© World Scientific Publishing Co. Pte. Ltd.
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August 19, 2010
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Introduction: Physics in the World of Giant Molecules
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3
such as I.M. Lifshitz in Russia, S.F. Edwards in England, and P.G. de
Gennes in France, who in the middle of the 1960s turned towards the study
of polymers. They revealed basic analogies between problems in polymer
physics and some of the most burning and tantalizing questions of general
physics. Polymers emerged on to the pages of the world’s main physics
journals and at major international conferences. Rather rapidly, a harmonious system of simple models and qualitative ideas formed about the basic
physical properties of polymers at a molecular level. All these concepts
have been used successfully both in physical chemistry and in molecular
biology. This brought also some terminology simplification. For example,
we shall frequently follow physics tradition and call the units of polymer
chain “monomers,” not the “monomer units,” as chemists prefer.
If you know about the physics of polymers you will understand why
they are so widely used in everyday life and in industry, as well as how they
work in biology.
GIANT MOLECULES - Here, There, and Everywhere (Second Edition)
© World Scientific Publishing Co. Pte. Ltd.
http://www.worldscibooks.com/materialsci/7199.html