A stimuli-responsive material is synthesized that combines the actuation potential of liquid-crystalline elastomers with the anisotropic magnetic properties of ellipsoidal iron oxide nanoparticles. The resulting nanocomposite exhibits unique shape-memory features with magnetic information, which can be reversibly stored and erased via parameters typical of soft materials, such as high deformations, low stresses, and liquid-crystalline smectic-isotropic transition temperatures.
We combine tensile strength analysis and X-ray scattering experiments to establish a detailed understanding of the microstructural coupling between liquid-crystalline elastomer (LCE) networks and embedded magnetic core-shell ellipsoidal nanoparticles (NPs). We study the structural and magnetic re-organization at different deformations and NP loadings, and the associated shape and magnetic memory features. In the quantitative analysis of a stretching process, the effect of the incorporated NPs on the smectic LCE is found to be prominent during the reorientation of the smectic domains and the softening of the nanocomposite. Under deformation, the soft response of the nanocomposite material allows the organization of the nanoparticles to yield a permanent macroscopically anisotropic magnetic material. Independent of the particle loading, the shape-memory properties and the smectic phase of the LCEs are preserved. Detailed studies on the magnetic properties demonstrate that the collective ensemble of individual particles is responsible for the macroscopic magnetic features of the nanocomposite.
Five-fold symmetric substituted corannulene derivatives that display liquid-crystalline behavior and organogelation properties were prepared by coupling of N-azidoethyl long-chain fatty acid amides to sym-pentabutynyl corannulenes via dipolar cycloaddition chemistry.
New mesogens presenting smectic A (SmA) phases and capable of hosting lithium salts are designed. The mesogens comprise a vinyl-functionalized spacer to allow further reaction to the polymer backbone, an aromatic core and ethylene oxide chains, able to coordinate lithium ions. Copolymerizing these monomers with a suitable crosslinker yields the first lithium containing liquid crystalline elastomers (LCEs). The SmA structure where the ethylene oxide chains are microphase separated in layers is fixed by the crosslinking and permanent macroscopic orientation is obtained. Diffusion and conductivity measurements of the monomer sample show a large anisotropy of the ion mobility (100 for the cation and 400 for the anion). In the elastomer the anisotropy of the lithium mobility is comparable to that in the monomers.
Remotely controlled actuation with wireless sensorial feed‐back is desirable for smart materials to obtain fully computer‐controlled actuators. A light‐controllable polymeric material is presented, in which exposure to light couples with a change in magnetic properties, allowing light signal conversion into non‐volatile magnetic memory. The same material can serve, additionally, both as actuator and transducer, and allows the monitoring of its two‐way elastic shape‐changes by magnetic read‐out. In order to tune the macroscopic magnetic properties of the material, both the reorientation of i) shape anisotropic ferrimagnetic nano‐spindles and ii) a mechanically and magnetically coupled liquid‐crystalline elastomer (LCE) matrix are controlled. These materials are envisioned to have great potential for the development of innovative functional objects, for example, computer‐controlled smart clothing, sensors, signal encoding, micro‐valves, and robotic devices.
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