We investigate the mesogen reorientation behavior of thin films of liquid crystal elastomers (LCEs) under uniaxial elongation (z-axis) normal to their initial homeotropic alignment (x-axis). The stress−strain relation is characterized by three regions:  (I) a small-strain regime exhibiting a linear relationship, (II) a moderate-strain region with a quasi-plateau stress, and (III) a large-strain region where the stress again increases. The Poisson's ratio μ yz is strain-dependent:  μ yz ≈ 0.17 in region II, whereas in regions I and III, μ yz ≈ 0.5 in accordance with that of incompressible isotropic elastomers. The considerably small μ yz in region II is a consequence of the suppression of the transverse shrinkage in the y-direction (corresponding to the director rotation axis) during elongation. Such a deformation mode is considerably closer to pure shear than uniaxial stretching. The infrared dichroism measurement reveals that the mesogen primarily rotates within the x−z plane toward the z-direction in region II, whereas no further mesogen realignment takes place in region III. These results indicate that the director−rotation process is featured by a quasi-plateau stress and a pure shearlike deformation. The orientation order of the mesogens in the fully reoriented state is comparable to that in the unloaded state. The complete unloading, even after stretching up to region III, recovers the original homeotropic alignment.

Dynamic nuclear polarization (DNP) at low temperature (1.2 K) and high magnetic field (3.3 T) was applied to a contrast variation study in small-angle neutron scattering (SANS) focusing on industrial rubber materials. By varying the scattering contrast by DNP, time-of-flight SANS profiles were obtained at the pulsed neutron source of the Japan Proton Accelerator Research Complex (J-PARC). The concentration of a small organic molecule, (2,2,6,6-tetramethylpiperidine-1-yl)oxy (TEMPO), was carefully controlled by a doping method using vapour sorption into the rubber specimens. With the assistance of microwave irradiation (94 GHz), almost full polarization of the paramagnetic electronic spin of TEMPO was transferred to the spin state of hydrogen (protons) in the rubber materials to obtain a high proton spin polarization (P H ). The following samples were prepared: (i) a binary mixture of styrene-butadiene random copolymer (SBR) with silica particles (SBR/SP); and (ii) a ternary mixture of SBR with silica and carbon black particles (SBR/SP/CP). For the binary mixture (SBR/SP), the intensity of SANS significantly increased or decreased while keeping its q dependence for P H = À35% or P H = 40%, respectively. The q behaviour of SANS for the SBR/SP mixture can be reproduced using the form factor of a spherical particle. The intensity at low q ($0.01 Å À1) varied as a quadratic function of P H and indicated a minimum value at P H = 30%, which can be explained by the scattering contrast between SP and SBR. The scattering intensity at high q ($0.3 Å À1 ) decreased with increasing P H , which is attributed to the incoherent scattering from hydrogen. For the ternary mixture (SBR/SP/CP), the q behaviour of SANS was varied by changing P H . At P H = À35%, the scattering maxima originating from the form factor of SP prevailed, whereas at P H = 29% and P H = 38%, the scattering maxima disappeared. After decomposition of the total SANS according to inverse matrix calculations, the partial scattering functions were obtained. The partial scattering function obtained for SP was well reproduced by a spherical form factor and matched the SANS profile for the SBR/SP mixture. The partial scattering function for CP exhibited surface fractal behaviour according to q À3.6 , which is consistent with the results for the SBR/CP mixture.

The temporal resolution of X-ray tomography, using a synchrotron radiation X-ray source, has been improved to millisecond order in recent years. However, the sample must be rotated at a speed of more than a few thousand revolutions per minute, which makes it difficult to control the environment around the sample. In this study, a high-speed rotation device has been developed, comprising two synchronized coaxial motors movable along the direction of the axis, which can stretch or compress the rotating sample. Using this device, tomograms of breaking rubber were successfully obtained at a temporal resolution of 10 ms.

We reveal that the swelling and shrinking of monodomain nematic elastomers in solvents exhibit unusual kinetics owing to the presence of shape and volume variation modes with markedly different rates. A change in the degree of nematic order caused by temperature (T) jumps drives a spontaneous macroscopic deformation along the director as well as a change in the chemical potential of the solvent inside the gel. The former yields an almost instantaneous shape variation, whereas the latter induces a slow volume variation governed by the diffusion of polymer networks, such as the swelling of isotropic gels. The markedly different rates of these two modes yield unique kinetics of swelling and shrinking: (1) a pronounced over-or undershoot of the gel dimensions is observed in the direction where the effect of shape variation on the dimensions counters that of the volume variation, and (2) a large dimensional change (more than 50% of the total change) occurs immediately after the T-jumps in the direction along which the effects of the two modes on the dimensions harmonize.