notes_section_3-chain_dynamics - CHM 5511 Spring 2010...

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CHM 5511 – Spring 2010 Section 3 – Chain Dynamics and Chain Flexibility LECTURE 1 Polymer Conformations Chain flexibility Review trans and gauche (g + and g - ) states, Rotational energy diagrams Actual polymer conformation is a potential energy plot U(theta) as f(theta) Use butane as an example of polyethylene Rotational Isomeric Approximation Only need to consider minima Energy differences are from non-bonded interactions So what is reality? For butane/hexane, 3 rotational isomers Ca. 80% t, 10 % each g + , and g - Plot U(theta) as f(theta) – RI NRG diagram Number of rotational isomers (N RI ) N RI = 3 n-3 where n = # carbon atoms RI half life is ca. 10 -10 secs, since vibrations occur in 10 13 – 10 14 Hz, have about 1,000 to 10,000 vibrations for each rotational state. Chain end-to-end distance (R) (model with hexane) When all trans – use projection of the bonds Equation (1) Note how rotations bring chain ends closer (R is smaller) Extended chain vs. collapsed chain. Various models developed from most fundamental to most practical/real The Ideal Chain (Rubinstein Chapter 2) Has no interactions between monomer units Real chains can have attractive or repulsive interactions
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This note was uploaded on 05/29/2011 for the course CHM 5511 taught by Professor Graham during the Spring '11 term at University of Florida.

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notes_section_3-chain_dynamics - CHM 5511 Spring 2010...

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