Photophysics, photochemistry and solar energy conversion with tris(bipyridyl)ruthenium(II) and its analogues

A number of materials have been explored for their use as artificial muscles Among these, dielectric elastomers (DEs) appear to provide the best combination of properties for true muscle-like actuation DEs behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied Materials combining very high energy densities, strains, and efficiencies have been known for some time To date, however, the widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications

Advances in dielectric elastomers for actuators and artificial muscles.

This review collects recent developments in the field of liquid crystalline elastomers (LCEs) with an emphasis on their use for actuator and sensor applications. Several synthetic pathways leading to crosslinked liquid crystalline polymers are discussed and how these materials can be oriented into liquid crystalline monodomains are described. By comparing the actuating properties of different systems, general structure-property relationships for LCEs are obtained. In the final section, how these materials can be turned into usable devices using different interdisciplinary techniques are described.

Liquid Crystalline Elastomers as Actuators and Sensors

In this article, we reexamine and extend a relationship proposed earlier between entanglement density and chain dimensions in polymer melts The power-law equation presented in the earlier work, relating the entanglement molecular weight Me, melt chain density ρ, and the packing length p is tested with additional polymer species Now included are additional polydienes and their hydrogenated derivatives, the isotactic forms of polypropylene and polystyrene, the essentially syndiotactic form of poly(methyl methacrylate), along with poly(tetrafluoroethylene), poly(vinylmethyl ether), various poly(methacrylates), and polymeric sulfur We find that within experimental uncertainties, Me/ρ and p are related through an equation (Me/ρ = 218p3) that is insensitive to temperature (25°C ≤ T ≤ 380°C) and which seems to be universal for flexible Gaussian chains in the melt state © 1999 John Wiley & Sons, Inc J Polym Sci B: Polym Phys 37: 1023–1033, 1999

Chain dimensions and entanglement spacings in dense macromolecular systems

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat-panel displays, their intrinsic ability to self-organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid-crystalline materials as organic semiconductors, which are solvent-processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli-responsive macroscopic shape change of cross-linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid-crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.

Liquid-crystalline ordering as a concept in materials science: from semiconductors to stimuli-responsive devices.

Backbone anisotropy and the structure of the mesophases of a series of side-chain liquid crystal polymers have been studied in the bulk by neutron scattering. The backbone conformation is obtained by small-angle neutron scattering on mixtures of hydrogenous polymers with deuteriated backbones. The components of the radius of gyration parallel, R ⊥ and perpendicular, R ∥ to the magnetic field are determined as a function of temperature for both the nematic phase and the smectic phase. It is shown that the polymer backbone is deformed in both phases. When the polymer exhibits only a nematic phase, it adopts a prolate conformation, where the average backbone direction is more or less parallel to the aligned mesogenic groups. Upon transition from the smectic phase to a nematic phase, the backbone in the nematic phase assumes a slightly oblate shape. This tendency towards oblate shape is due to the smectic fluctuations which are always present in such nematic phases. The exentricity of the oblate back...

On the structure and the chain conformation of side-chain liquid crystal polymers

The anisotropy of the conformation of two kinds of comblike liquid crystal polymers, a polymethacrylate and a polymethylsiloxane has been measured in the nematic and smectic phases by small angle neutron scattering (SANS). The global sizes (parallel and perpendicular to the director) of one labelled chain and their temperature dependence have been determined.

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Conformational anisotropy of liquid crystalline side chain polymers : a small angle neutron scattering study

The backbone conformation of a liquid crystalline side-chain polyacrylate was studied by Small Angle Neutron Scattering (SANS) in the isotropic, nematic, smectic A and re-entrant nematic phases. A transition from an oblate backbone conformation (observed in the nematic and in the smectic A phases) to a prolate conformation (observed in the re-entrant nematic phase) is clearly demonstrated.

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Backbone conformation study of a side chain polyacrylate through a re-entrant polymorphism

A small angle neutron scattering study of a mesomorphic side chain polyacrylate in the nematic phase shows that the backbone adopts a prolate conformation. This observation is discussed in relation to the previous determinations of backbone anisotropy in the nematic phase of other side chain polymers. On the basis of the comparison with these previous determinations and also with the results obtained on other related systems, the assumption is made that, provided that the spacers are long enough, the natural tendency of the backbones is to adopt a prolate shape in any nematic phase devoid of smectic fluctuations.

Neutron scattering study and discussion of the backbone conformation in the nematic phase of a side chain polymer

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Evidence for a jacketed nematic polymer F. Hardouin, S. Mery, M. Achard, L. Noirez, P. Keller

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P. Keller

Papers

On the structure and the chain conformation of side-chain liquid crystal polymers

Conformational anisotropy of liquid crystalline side chain polymers : a small angle neutron scattering study

Backbone conformation study of a side chain polyacrylate through a re-entrant polymorphism

Neutron scattering study and discussion of the backbone conformation in the nematic phase of a side chain polymer

Evidence for a jacketed nematic polymer