Strain-induced macroscopic magnetic anisotropy from smectic liquid-crystalline elastomer–maghemite nanoparticle hybrid nanocomposites† Johannes M. Haberl, a Antoni S´ anchez-Ferrer, a Adriana M. Mihut,‡ b Herv´ e Dietsch,§ b Ann M. Hirt c and Raffaele Mezzenga * a 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. Introduction Liquid-crystalline elastomers (LCEs) combine the anisotropic properties of liquid crystals with the entropy elasticity of polymer networks, and give rise to various anisotropic properties such as the spontaneous macroscopic shape change at the phase tran- sition 1 which is associated with property changes, similar to shape-memory alloys. 2 Several studies have shown a broad application potential for LCEs in smart actuators and sensors. 3–5 Nanocomposites of LCEs have been used to further expand the resulting applications beyond the traditional limits imposed by organic materials. In this context, LCE nanocomposites with MoO 3x nanowires 6 or carbon black 7 have been introduced as conductive actuators. Gold nanoparticles were incorporated to enhance the thermo-mechanical response of such composites. 8 Moreover, to improve infrared and terahertz activity, carbon nanotubes were embedded into the matrix 9 and the composites were used as contactless strain sensors for infrared light. 10,11 Further efforts have also been made in the design of mechan- ically adaptive polymer nanocomposites, which change the tensile strength behaviour as a function of an external stim- ulus. 12,13 For example, in magnetic hybrid elastomers 14 and gels, 15 that were synthesized in the presence of an applied magnetic eld to achieve chainlike-organized magnetic parti- cles, mechanical experiments showed that a magnetic eld coupled to the modulus of the material. Special interest was also devoted to the improvement of inductive activation of magnetic shape-memory nanocomposites and a “triple-shape effect” in recovery was achieved. 16 In a monodomain LCE nanocomposite, inductive heating of incorporated magnetite particles was used to heat the matrix beyond its transition temperature and to create an entropy-driven reversible actuator. 17 Magnetic domains without superparamagnetic relaxation were crucial for such success. 18 In our recent work, we presented the integration of covalently bonded ellipsoidal maghemite nanoparticles into a smectic LCE nanocomposite to build wireless strain sensors with a magnetic read-out of deformation. 19 Smectic LCEs with layered mesogen structures were related to shape-memory properties, 20 and similar behaviour was used to store magnetic information in the material, which enabled the very desirable feature of controlling magnetic properties using parameters typical of so materials. 19 The present study aims for an improvement of the under- standing of the effects arising from nanoparticles incorporation into LCE host matrices. The incorporation of nanoparticles into a ETH Z¨ urich, Department of Health Science and Technology, 8092 Z¨ urich, Switzerland. E-mail: raffaele.mezzenga@hest.ethz.ch; Fax: +41-44-632-16-03; Tel: +41-44-632- 91-40 b Adolphe Merkle Institute and Fribourg Center for Nanomaterials, University of Fribourg, 1723 Marly, Switzerland c ETH Z¨ urich, Department of Earth Science, 8092 Z¨ urich, Switzerland † Electronic supplementary information (ESI) available: Fig. ESI-1: polarized optical microscopy images, Fig. ESI-2–4: supplementary X-ray data, Fig. ESI-5: FORC diagrams. See DOI: 10.1039/c3nr01016c ‡ Present Address: Physical Chemistry, Department of Chemistry, Lund University, 22100 Lund, Sweden. § Present Address: BASF SE, Formulation Platform, 67056 Ludwigshafen am Rhein, Germany. Cite this: Nanoscale, 2013, 5, 5539 Received 26th February 2013 Accepted 8th April 2013 DOI: 10.1039/c3nr01016c www.rsc.org/nanoscale This journal is ª The Royal Society of Chemistry 2013 Nanoscale, 2013, 5, 5539–5548 | 5539 Nanoscale PAPER Published on 18 April 2013. Downloaded by ETH-Zurich on 14/06/2013 14:30:33. View Article Online View Journal | View Issue