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Synthesis and characterization of electromechanically active composites of mesogenic elastomers and electrically active nanoparticles

Final Activity Report Summary - ELACEM (Synthesis and characterization of electromechanically active composites of mesogenic elastomers and electrically active nanoparticles)

The proposed project focused on the preparation and characterization of the chemical and physical properties of a new type of advanced materials, obtained by combining Liquid Crystalline Elastomers and ferroelectric or dielectric nanoparticles, as well as nanowires. The organic part of the new composites is constituted by mesogenic elastomers, formed by mesogenic units attached to a crosslinked polysiloxane backbone through flexible spacers in order to form a side-chain elastomeric network [1]. The mesogenic units used in this work are azo-compounds or/and standard nematic mesogens, showing by themselves different degrees of orientational or/and positional ordering. The second component of the new composites, which were the subject of this project, is based on new nanoparticles and nanowires, showing peculiar shape and dimension distribution, optical and physical properties. The most interesting aspect is related to the ferroelectric and dielectric properties of these inorganic compounds [2], which are very promising for potential applications in constructing nanoscaled electronic and opto-electronic devices. In particular, Lead Titanate Ferroelectric Nanoparticles and Molibden Oxide Nanowires have been used in this research. All new materials prepared in the framework of this project have been synthesized by using the Finkelmann procedure [3] in order to get Liquid Single Crystalline Elastomeric (LSCE) films with different dimensions and thickness. Selectively deuterated samples, with Deuterium on the mesogenic or crosslinking units, were also prepared. Differently from recent studies, in which the nanoparticles or nanotubes were inserted in the elastomeric matrix after the preparation of the LSCEs throughout a «reprocessing» of the elastomeric materials [4], in this work a new strategy consisting of a single step preparation has been tested. The composite materials prepared with this procedure have been characterized by using different techniques in order to check the chemical composition, the thermo-mechanical properties, mesophasic behavior, the local ordering and homogeneity of the prepared samples. The physical and chemical properties investigated so far on the prepared composite samples indicate that inserting individual nanoparticles in a liquid crystalline elastomeric environment is possible without destroying the elastomeric network, retaining its typical elastic, mechanical and orientational properties, even though it should be noticed that in this research the percentage of nanoparticles, or nanowires, was controlled to be sensibly low (less than 5% in weight). Macroscopic and collective properties of these composite materials have been detected by means of thermo-elastic investigations, while microscopic methods, such as AFM, SEM and TEM, have been used to check the distribution of the inorganic components in the elastomeric matrix. Nuclear Magnetic Resonance methods were useful to get information about the local orientational properties of these materials, by looking directly to the elastomeric matrix through the Deuterium nucleus [5]. More detailed NMR investigations are in progress to study the structure and dynamic properties of both the liquid crystal and crosslinker units, as well as the influence of application of external stimuli (electric field and temperature on the samples containing the ferroelectric nanoparticles and UV illumination and temperature on the samples containing the azo-compound mesogenic units). References: [1] M. Warner, E. M. Terentjev, Liquid Crystal Elastomers, Oxford University Press, Oxford, 2003. [2] T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, K. Niihara, Languimir, U14U, 3160, 1998. [3] H. Finkelmann, H. J. Kock, G. Rehage, Makromol. Chem. Rapid Commun., 2, 317, 1981. [4] M. Chambers, B. Zalar, M. Remskar, H. Finkelmann, S. Zumer, Appl. Phys. Lett., 89, 243116, 2006. [5] A. Lebar, Z. Kutnjak, S. Zumer, H. Finkelmann, A. Sanchez-Ferrer, B. Zalar, Phys. Rev. Lett., 94, 197801, 2005.