Excluded volume

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The concept of excluded volume was introduced by Werner Kuhn in 1934 and applied to polymer molecules shortly thereafter by Paul Flory.

[edit] In liquid state theory

In liquid state theory, the 'excluded volume' of a molecule is the volume that is inaccessible to other molecules in the system as a result of the presence of the first molecule^[1].

[edit] In polymer science

In polymer science, excluded volume refers to the idea that one part of a long chain molecule can not occupy space that is already occupied by another part of the same molecule^[2]. Excluded volume causes the ends of a polymer chain in a solution to be further apart (on average) than they would be were there no excluded volume. The recognition that excluded volume was an important factor in analyzing long-chain molecules in solutions provided an important conceptual breakthrough, and led to the explanation of several puzzling experimental results of the day. It also led to the concept of the theta point, the set of conditions at which an experiment can be conducted that causes the excluded volume effect to be neutralized. At the theta point, the chain reverts to ideal chain characteristics^[3]. The long-range interactions arising from excluded volume are eliminated, allowing the experimenter to more easily measure short-range features such as structural geometry, bond rotation potentials, and steric interactions between near-neighboring groups. Flory correctly identified that the chain dimension in polymer melts would have the size computed for a chain in ideal solution if excluded volume interactions were neutralized by experimenting at the theta point.

[edit] References

1. ^ Hill T. L., An Introduction to Statistical Thermodynamics,Dover Publications, New York, 1986, p 288
2. ^ Hill T. L., An Introduction to Statistical Thermodynamics,Dover Publications, New York, 1986, p 225
3. ^ Rubinstein M., Colby R. H., Polymer Physics, Oxford University Press, New York, 2003, p 49