Title Self-Organization caused by a natural balance of forces
Date 26.06.2017
Number 53346
Abstract Matter orgonizes itself due to the balance of interaction energies and the degrees of freedom of the constituting porticles or molecules. The pictures taken from a computer simulation show a tree-like branched molecule (dendrimer) which is composed of two different species (monomers). The hydrophobic branched interior (disployed in yellow) has grown from a central monomer (red) in two directions. The hydrophilic chains (displayed in blue) are attached to the ends of the branched structure. Because of this architecture, the inner part of the macromolecule acts similar to a mechanical spring. If the temperature is high, the spring is soft and the chains can distribute rather freely into space. This illustrates a fundamental principle in nature: Every system tends to realize the maximum possible number of alternatives under the given constraints. This is called the principle of entropy in physics. For polymers, there exists a particular form of entropy, which is related to the variety of possible arrangements of monomers in space due to the high flexibility of the molecular chains. It is called conformational entropy and is the origin of the particular material properties of polymers such as rubber elasticity. If the temperature of the dendrimer is now lowered, the branched part of the molecule shrinks like a hard spring (higher surface tension due to the attraction of the hydrophobic monomers) and forces the <br />hydrophilic chains to come tightly together (thus reducing their conformational entropy). For each value of the temperature, typical distributions (conformations) of the molecule dominate. If the temperature is changed stepwise, the dendrimer undergoes transitions from one preferred state to another, which corresponds to the optimal state at the present temperature. Since the changes of state are only caused by the change of the environment, and are not due to energetic processes of the molecule itself, it is called self-organization.<br /><br />To understand materials and their applications it is of great importance to investigate the changes in structure and properties of large, well-defined molecules (polymers). This is the research area of theoretical physicists at the Institute Theory of Polymers at the Leibniz-lnstitute of Polymer Research Dresden.
Publisher PLASMA - International Art & Science Magazine
Identifier 0
Citation PLASMA - International Art & Science Magazine 3 (2017) 74-77
Authors Sommer, J.-U. ; Wengenmayr, M. ; Lordick, D.

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