Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 351187
Title On the escape transition of a tethered Gaussian chain; exact results in two conjugate ensembles
Author(s) Skvortsov, A.M.; Klushin, L.I.; Leermakers, F.A.M.
Source Macromolecular Symposia 237 (2006)1. - ISSN 1022-1360 - p. 73 - 80.
Department(s) Physical Chemistry and Colloid Science
Publication type Refereed Article in a scientific journal
Publication year 2006
Keyword(s) polymer-chain - force microscope - compression
Abstract Upon compression between two pistons an end-tethered polymer chain undergoes an abrupt transition from a confined coil state to an inhomogeneous flower-like conformation that is partially escaped from the gap. In the thermodynamic limit the system demonstrates a first-order phase transition. A rigorous analytical theory of this phenomenon for a Gaussian chain is presented in two ensembles: a) the H-ensemble, in which the distance H between pistons plays the role of the control parameter, and b) the conjugate f-ensemble in which the external compression force f is the independent parameter. A loop region for f(H) with negative compressibility exists in the H-ensemble, while in the f-ensemble H(f) is strictly monotonic. The average lateral forces taken as functions of H (or H, respectively) have distinctly different behavior in the two ensembles. This result is a clear counterexample of the main principles of statistical mechanics stating that all ensembles are equivalent in the thermodynamic limit. Another theorem states that the thermodynamic potential as a function of volume must be concave everywhere. We demonstrated that the exact free energy in the H-ensemble contradicts this statement. Inapplicability of these fundamental theorems to a macromolecule undergoing the escape transition is clearly related to the fact that phase coexistence in the present system is strictly impossible. This is a direct consequence of the tethering and the absence of global translational degrees of freedom of the polymer chain
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