DOI: 10.1209/epl/i2001-00305-x


Europhys. Lett., 54 (2) , pp. 269-274 (2001)

Defect-mediated creep of structured materials

R. H. Colby¹, L. M. Nentwich², S. R. Clingman³ and C. K. Ober<sup>3

1</sup>  Materials Science and Engineering, Pennsylvania State University University Park, PA 16802, USA
²  James Franck Institute, University of Chicago - Chicago, IL 60637, USA
³  Materials Science and Engineering, Cornell University - Ithaca, NY 14853, USA

(Received 28 July 2000; accepted in final form 13 February 2001)

Abstract
Low-stress creep measurements on a nematic liquid crystal polymer indicate that it is a viscoelastic solid, with a modulus of 100 dynes/cm² and a yield stress of 50 dynes/cm². Both smectics and nematics are viscoelastic solids at very low stress levels, with a modulus that is related to their defect texture. At stress levels somewhat above the yield stress, there is a yielding regime where the deformation rate and defect spacing are power laws in the applied stress. We understand these power laws using the ideas developed long ago by Orowan for the motion of line defects in crystalline solids. The exponents of these power laws are different for nematics and smectics, but the nematic universality class also appears to apply to superplastic metals and ceramics.

PACS
83.80.Xz - Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
61.30.Jf - Defects in liquid crystals.
62.20.Fe - Deformation and plasticity (including yield, ductility, and superplasticity).


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