Liquid-crystalline elastomers

Abstract. Changing the orientational order in liquid-crystal elastomers leads to internal stresses and changes of the sample shape. When this effect is induced by light, due to photoisomerization of con-stituent molecular moieties, the photomechanical actuation results. We investigate quantitatively how the intensity and the polarization of light affect photoactuation. By studying dissolved, as well as covalently bonded azo-dyes, we determine the changes in absorption and the response kinetics. For the first time we compare the response of aligned monodomain, and randomly disordered polydomain nematic elastomers, and demonstrate that both have a comparable photoresponse, strongly dependent on the polarization of light. Polarization-dependent photoactuation in polydomain elastomers gives an unambiguous proof of its mechanism since it is the only experiment that distinguishes from the associated thermal effects. PACS. 78.20.Hp Piezo-, elasto-, and acoustooptical effects; photoacoustic effects – 61.41.+e Polymers, elastomers, and plastics – 82.35.Ej Nonlinear optics with polymers – 83.80.Va Elastomeric polymers Liquid-crystal elastomers (LCE) are remarkable ma-terials that combine physical properties of liquids and solids in a unique way. LCE are rubbers whose constituent molecules are orientationally ordered. The resulting cou