THERMODYNAMIC STABILITY ANALYSIS OF LIQUID-CRYSTALLINE POLYMER FIBERS

Classical theories of liquid-crystalline materials are used to develop a new model that describes the thermodynamic stability of nematic liq uid-crystal cylindrical fibers that arise in the fabrication of in-sit u liquid crystal polymer (LCP) composites. The thermodynamic model ide ntifies the new contributions to elastic storage due to the nematic or ientational order present in LCP fibers. It is shown that the addition al nematic surface and bulk elastic storage mechanisms tend to promote fiber stability when compared with isotropic fibers. The theory predi cts that elastic storage due to orientational deformations within the fiber may be able to overcome the classical capillary (Rayleigh) insta bility present in isotropic fibers. The parametric conditions that lea d to fiber stability are smaller fibers, low interfacial tensions, and large nematic elastic constants. Nevertheless, using estimates typica l of the actual in situ LCP-polymer composites, it is found that LCP f ibers are unstable and will break up, in agreement with existing exper imental studies on the stability of liquid-crystalline polymer fibers in a thermoplastic elastomeric matrix when subjected to annealing at h igh temperatures.