MOLECULAR MECHANISMS, OPERATING AT THE SEGMENTAL SCALE, THAT TRANSPORT MASS AND MOLECULAR ROTATION THROUGH A POLYMER CRYSTAL

Darrell H. Reneker
Department of Polymer Science, The University of Akron, Akron, OH 44325-3909

Crystals of linear polymers, such as polyethylene, provide a framework for mechanisms that move along the polymer chain, translating and rotating the segments of the molecule through which the mechanism moves. On a nanometer scale, we can produce crystals in the form of folded chain lamellae or fibers in which the polymer chains are fully extended. Spherulites and other interesting structures can be produced on a micron scale.

These structures, which are general features of the morphology of polymer solids, can not only supports biomolecular motors and nanomachines, but also transmit the useful motions of the nanomachines over useful distances. The motions of the molecular mechanisms are coupled to strain fields that are present in the polymer crystal. This means that micron scale strain fields can cause the mechanisms to operate, or conversely, an integrated effect of the thermodynamical motions of several mechanisms can be a change in the strain field in the sample.

The mechanisms can carry special chemical groups attached to the polymer chain to a location where the chemical group can react, even though the reactive groups are initially separated by distances of around 10 nanometers.

The mechanisms of interest are examples of what, in crystal physics and metallurgy, are called crystallographic defects. Dislocations provide an example. A dislocation can be described as a defect in the translational symmetry of a crystal. In polymer crystals, crystallographic defects involving only one chain are particularly interesting. At the single chain scale, dislocations, defects in the helical symmetry called dispirations, and defects in the rotational symmetry called disclinations, are all energetically feasible, and each is capable of performing certain potentially useful functions.

This presentation will provide information about naturally occurring structures associated with the crystallization of linear polymers, and the motions of polymer molecules within the crystals, that are of potential use in the design of molecular nanomachines.