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Ferrochirality: a simple theoretical model of interacting, dynamically invertible, helical polymers, 2. Molecular field approach: supports and the details
Ist Teil von
Macromolecular theory and simulations, 1995-01, Vol.4 (1), p.1-43
Ort / Verlag
Zug: Hüthig & Wepf Verlag
Erscheinungsjahr
1995
Link zum Volltext
Quelle
Wiley Online Library Journals
Beschreibungen/Notizen
Using a molecular field approach, the effect of interaction between reversibly invertible, helical polymers is investigated theoretically. The helices are modelled by nearest‐neighbour statistical thermodynamics. If the interaction energy between two helices of common handedness is lower than that of oppositely handed ones, a critical temperature Tc exists, below which the system spontaneously must leave the racemic state, though there is no contact to any chiral centre or force. This is analogous to the second‐order phase transition of ferromagnets. The critical point increases with molecular weight and optical persistence of the helices. At the critical point the system is highly sensitive to any chiral influence. Doping with 1 ppb of a chiral additive leads to a relative optical rotation of order 10−3 at the critical point. This corresponds to an intrinsic energy difference of left‐ to right‐handed monomeric units of only 10−8 J/mol. The cooperative effects in chirally doped nematic poly(hexyl isocyanate) (PHIC) can be easily described without using the improbable assumption that the supramolecular cholesteric arrangement with an axis‐to‐axis rotation of only 0,001° must be the reason for the collective helix sense preference in this system. On the other hand, if the chain‐to‐chain interaction is transmitted through this supermolecular twist, the structure of the equations is altered slightly only and critical behaviour must be expected as well.