Polarization patterning in ferroelectric nematic liquids via flexoelectric coupling.

The recently discovered ferroelectric nematic liquids incorporate to the functional combination of fluidity, processability and anisotropic optical properties of nematic liquids, an astonishing range of physical properties derived from the phase polarity. Among them, the remarkably large values of second order optical susceptibility encourage to exploit these new materials for non-linear photonic applications. Here we show that photopatterning of the alignment layer can be used to structure polarization patterns.

Cross-differential dynamic microscopy.

We demonstrate the use of a dual-camera-equipped microscope for the study of the wavevector-dependent dynamics of soft matter. Contrary to the standard differential dynamic microscopy (DDM) in which a series of digital video images is acquired with a single camera at a constant frame rate, we use two randomly triggered cameras to acquire two sequences of images of the same region in the sample. From the two data sets we calculate cross-image differences and Fourier analyze them as a function of time delay between the two images.

Nematic fluctuations and semisoft elasticity in swollen liquid-crystal elastomers.

Dynamic light scattering (DLS) experiments were performed on stretched sheets of liquid crystal elastomers (LCEs) swollen with a nematic solvent with different swelling ratios. We show that the obtained stress-strain curve and DLS data can still be explained with the concepts of semisoft elasticity. The stress-strain curve shows a typical semisoft response with a threshold strain and a plateau region where stress increases only a little with the applied strain.

Nematic fluctuations and semisoft elasticity in liquid-crystal elastomers.

We give a detailed theory of nematic fluctuations in liquid-crystal elastomers (LCEs) and calculate relaxation rates as obtained by dynamic light scattering (DLS). In ideal LCEs, a nematic state is formed by a spontaneous orientational symmetry breaking of an isotropic state, manifesting itself in an existence of a coupled director-shear soft mode (Goldstone mode). The relaxation rate of the soft mode (a pure bend and a pure splay mode) goes to zero in a long-wavelength limit.

Strain dependence of the nematic fluctuation relaxation in liquid-crystal elastomers.

Dynamic light scattering on a nematic liquid-crystal elastomer was performed as a function of deformation perpendicular to the director and along the director. We show that the relaxation rate of the nematic director fluctuations increases with strain along the director, as expected from the theory of semisoft elasticity. Deformation applied perpendicular to the director, on the other hand, decreases the relaxation rate to a very small value at the onset of the soft elastic response, revealing the existence of a dynamic soft mode.

Observation of a soft mode of elastic instability in liquid crystal elastomers.

In monodomain liquid crystal elastomers a symmetry-breaking locked-in anisotropy causes a semisoft elastic response characterized by a plateau in the stress-strain curve. We show by dynamic light scattering performed as a function of deformation that the relaxation rate of the nematic director fluctuations decreases with strain to a very small value at the onset of the soft elastic response, revealing the existence of a dynamic soft mode. The results are in complete agreement with the theory of semisoft elasticity and allow us to determine all the constants of the model.