Model for photoresponsive nematic elastomers

We study the equilibria of a photoresponsive nematic elastomer ribbon within a continuum theory that builds upon the statistical mechan- ics model put forward by Corbett and Warner [Phys. Rev. E 78, 061701 (2008)]. We prove that the spontaneous deformation induced by illumination is not monotonically dependent on the intensity I. The ribbon’s deflection first increases with increasing I, as expected, but then decreases and abruptly ceases altogether at a critical value Ie of I. Ie , which is enclosed within a hysteresis loop, marks a first-order shape transition. Finally, we find that there is a critical value of the ribbon's length, depending only on the degree of cross- linking in the material, below which no deflection can be induced in the ribbon, no matter how intense is the light shone on it.