Contrasting roles of layered structures in the molecular assembly of liquid crystal matrices on the viscoelastic properties of microparticle/liquid crystal composite gels leading to rigidification and destabilization

Abstract: We investigated the effects of the nematic and smectic A (SmA) phase structures of liquid crystalline matrices on the viscoelastic properties of microparticle/liquid-crystal composite gels. The storage (G′) and loss (G″) moduli of the gels were largely increased in gels containing SmA matrices with a layered molecular assembly. However, the critical strain at which the gel state transformed into the sol state by the application of mechanical strain showed no significant changes with variation in the liquid crystal phase of the matrix. These results indicate that the introduction of a layered molecular assembly could be effective for rigidification of composite gels, while maintaining their critical strains. However, the composite gels tended to show a metastable state when SmA matrices were used because G′ and G″ of the gels were close to each other in the entire frequency region. This behavior was in contrast to the gels with nematic matrices, which showed a larger value in G′ than that in G″. The metastable state of gels with SmA matrices was also reflected in the frequency dependence of G′ and in the deterioration of the recovery of the gel state after mechanical breakdown. [Copyright &y& Elsevier]