Swelling and Shrinking Dynamics of Nematic Elastomers Having Global Director Orientation

Abstract

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.