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You are here: Home Events Prof. Roland Netz "A Highly Stretched Polymer in Water is an Energetic, not an Entropic Spring"

Prof. Roland Netz "A Highly Stretched Polymer in Water is an Energetic, not an Entropic Spring"

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Theoretical Bio- and Soft Matter Physics, Freie Universität Berlin

What
  • Seminar
When Nov 23, 2017
from 01:15 PM to 02:00 PM
Where Physikalische Chemie
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In many applications, a polymer’s elastic response against conformational deformations is key to its function. According to textbook knowledge, a polymer reacts to the stretching of its end-to-end separation by an increase in entropy that is due to the reduction of available molecular conformations. This is why polymers are commonly called entropic springs. By a combination of single-molecule force spectroscopy experiments with molecular dynamics simulations in explicit water, we show that PEG in fact turns from an entropic into an energetic spring at moderate stretching. The thermodynamic analysis of our simulation trajectories reveals that the conformational entropy price of chain stretching is compensated by the entropy gain associated with the release of water molecules forming double hydrogen bonds with the PEG backbone in the low-stretching state. As a consequence, the stretching response of PEG is predominantly of energetic, not of entropic, origin and caused by the release of strongly energetically bound water upon stretching. These findings not only challenge a basic notion of polymer science but also constitute a case example that sheds light on the antagonistic interplay of conformational solute and solvent degrees of freedom.

 

invited by Prof Thorsten Hugel and Prof. Günter Reiter

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