Molecular chain orientation in supercontracted and re-extended spider silk

The dragline silk from Nephila clavipes was studied by wide angle X-ray dif fraction in its original state, after supercontraction to L/L-o = 0.46, and during re-extension to its original length L-o. The fibers were carefully dried before each exposure. The molecular orientation in the crystalline re gions is found to follow the simple predictions of affine deformation, indi cating that the crystals act as inert rigid filler particles. The crystals retain considerable orientation after supercontraction, when non-crystallin e orientation is weak. This shows that crystallization occurs after orienta tion as the ber forms. The oriented amorphous material, treated as a phase of constant volume fraction, also follows affine deformation. These results do not contain any indication of a special structure in the protein fiber. (C) 1999 Elsevier Science B.V. All rights reserved.