Synthesis of Elastomeric Liquid Crystalline Polymer Networks via Chain Transfer

Materials capable of complex shape changes have broad reaching applications spanning biomimetic devices, componentless actuators, artificial muscles, and haptic displays. Liquid crystal elastomers (LCE) are a class of shape programmable materials which display anisotropic mechanical deformations in response external stimuli. This work details a synthetic strategy to quickly and efficiently prepare LCEs through the usage of chain transfer agents (CTA). The polyacrylate materials described herein exhibit large, reversible shape changes with strains greater 475%, rivalling properties observed in polysiloxane-based networks. The approach reported here is distinguished in that the materials chemistry is readily amenable to surface alignment techniques. The facile nature of the materials chemistry and the compatibility of these materials with directed self-assembly methods could further enable paradigm shifting end uses as designer substrates for flexible electronics or as actuating surfaces

Electrical Control of Shape in Voxelated Liquid Crystalline Polymer Nanocomposites

Liquid crystal elastomers (LCEs) exhibit anisotropic mechanical, thermal, and optical properties. The director orientation within an LCE can be spatially localized into voxels [three-dimensional (3-D) volume elements] via photoalignment surfaces. Here, we prepare nanocomposites in which both the orientation of the LCE and single-walled carbon nanotube (SWNT) are locally and arbitrarily oriented in discrete voxels. The addition of SWNTs increases the stiffness of the LCE in the orientation direction, yielding a material with a 5:1 directional modulus contrast. The inclusion of SWNT modifies the thermomechanical response and, most notably, is shown to enable distinctive electromechanical deformation of the nanocomposite. Specifically, the incorporation of SWNTs sensitizes the LCE to a dc field, enabling uniaxial electrostriction along the orientation direction. We demonstrate that localized orientation of the LCE and SWNT allows complex 3-D shape transformations to be electrically triggered. Initial experiments indicate that the SWNT–polymer interfaces play a crucial role in enabling the electrostriction reported herein

High Performance Graded Rainbow Holograms via Two-Stage Sequential Orthogonal Thiol–Click Chemistry

Orthogonal, sequential “click” reactions were implemented to yield novel polymeric substrates with the ability to record holographic data. The base-catalyzed thiol–acrylate Michael “click” reaction was implemented to yield a writable, stage 1 polymeric substrate with glass transition temperatures (<i>T</i>_g) ranging from 0 to −26 °C and rubbery storage moduli (<i>E</i>′) from 11.1 to 0.3 MPa. The loosely cross-linked matrix also contained a novel high refractive index monomer 9-(2,3-bis­(allyloxy)­propyl)-9<i>H</i>-carbazole (BAPC) that did not participate in the thiol–Michael reaction but allowed for large index gradients to be developed within the network upon subsequent exposure to coherent laser beams and initiation of the radical-mediated thiol–ene reaction. The holographic gratings were recorded with 96% diffraction efficiency and ca. 2.4 cm/mJ of light sensitivity in 2 s under a 405 nm exposure with an intensity of 20 mW/cm². Subsequent to pattern formation, via a thiol–allyl radical “click” photopolymerization initiated by flood illumination of the sample, holographic materials with high <i>T</i>_g, high modulus, diffraction efficiency as high as 82%, and refractive index modulation of 0.004 were obtained. Graded rainbow holograms that displayed colors from blue to red at a single viewing angle were readily formed through this new technique