Sub-stripe pattern formation in liquid crystal elastomers: Experimental observations and numerical simulations

We report on some new experimental observations of pattern formation during stretching experiments of nematic liquid crystal elastomers (LCEs). We observe stretching-induced formation of the well-known stripe domains. However, we also observe additional periodic modulations inside the stripes, with a smaller and very regular period. The wavelength of this fine modulation increases with temperature and shows a critical behavior near the phase transition, which is unexpected. We compare the experimental observations with results from numerical simulations of the stretching experiments. The mathematical model we use is obtained through a second order expansion of the Warner and Terentjev free-energy density for nematic LCEs. Our theory is suitable to describe small deformation and large director rotation. Using measured material parameters, our numerical simulations show an extremely fine modulation of the director in very good agreement with experimental results.