Paul Flory
From Wikipedia, the free encyclopedia
| Born | June 19, 1910 Sterling, Illinois |
|---|---|
| Died | September 9, 1985 Big Sur, California |
| Nationality |  American |
| Field | Chemist |
| Institution | DuPont, Stanford University |
| Alma mater | Manchester College and Ohio State University |
| Academic advisor | Herrick L. Johnston |
| Known for | Polymers |
| Notable prizes |  Nobel Prize for Chemistry (1974) |
Paul John Flory (June 19, 1910 – September 9, 1985) was an american chemist who was known for his prodigious volume of work in the field of polymers, or macromolecules. After graduating from Elgin High School in Elgin, Illinois in 1927, Flory received a bachelor's degree from Manchester College in 1931 and a Ph.D. from the Ohio State University in 1934. His first position was at DuPont with Wallace Carothers. He was a leading pioneer in understanding the behavior of polymers in solution.
Among his accomplishments are an original method for computing the probable size of a polymer in good solution, the Flory-Huggins Solution Theory, and the derivation of the Flory exponent, which helps characterize the movement of polymers in solution. He introduced the concept of excluded volume. 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. 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. (As a visual aid, consider a tightly wound spring. If each coil could occupy the same space, the spring would be shorter than the real-world situation where each coil must occupy its own unique space.) Excluded volume interactions between distant segments of a molecule have a dominant effect and for this reason excluded volume is called a long range effect. 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. This 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 - 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.
His contributions to the field of polymer science are best summarized in his classic 1953 text, Principles of Polymer Chemistry, where he provided a comprehensive account of experimental and theoretical results proven in his day. While the field of polymers has expanded considerably, the text continues to be highly useful in understanding several key concepts and for didactic reasons.
He was awarded the Nobel Prize in Chemistry in 1974 "for his fundamental achievements, both theoretical and experimental, in the physical chemistry of the macromolecules." His Nobel Lecture discusses many of the above concepts and is available online.
Contents |
[edit] The Flory convention
In modeling the position vectors of atoms in macromolecules it is often necessary to convert from Cartesian coordinates (x,y,z) to generalized coordinates. The Flory convention for defining the variables involved is usually employed. For an example, a peptide bond can be described by the x,y,z positions of every atom in this bond or the Flory convention can be used. Here one must know the bond lengths li, bond angles θi, and the dihedral angles φi. Applying a vector conversion from the Cartesian coordinates to the generalized coordinates will describe the same three-dimensional structure using the Flory convention.
[edit] See also
[edit] Books
- (1953) Principles of Polymer Chemistry (George Fisher Baker Non-Resident Lec). Cornell University Press. ISBN 0-8014-0134-8.
- (1969) Statistical Mechanics of Chain Molecules. Interscience. ISBN 0-470-26495-0. Reissued 1989. ISBN 1-56990-019-1.
- (1985) Selected Works of Paul J. Flory. Stanford Univ Press. ISBN 0-8047-1277-8.
