Stress–strain behavior in main chain liquid crystalline elastomers: effect of crosslinking density and transverse rod incorporation on “Poisson's ratio”

Abstract

Abstract Stress–strain results are reported for two series of smectic C main chain liquid crystalline elastomers (MCLCEs). The structural variable in one series is crosslink density; in the other, transverse rod content. With increasing crosslinker content, the LCEs exhibit increased modulus, a shorter polydomain‐to‐monodomain (P–M) plateau, and a lower elongation at break. Increasing transverse rod content leads to lower clearing temperatures and lower modulus. For each series, stress–strain measurement was made simultaneously with Poisson's ratio determination. For the variable crosslinker series, typical behavior showed the Poisson's ratio increased at small strain, rose to a maximum about 50% strain, then decreased with greater strain. For the transverse rod series, typical behavior also showed the Poisson's ratio increased at small strain, rose to a maximum about 50% strain, then decreased with greater strain. In both series, the maximum in the Poisson's ratio corresponded to the onset of the P–M transition. Possible deformation mechanisms are presented.