Over the 100 years since its discovery, liquid crystals have been the intriguing subject for both academia and industries. The textbook of de Gennes The Physics of Liquid Crystals published in 1974 is still the bible for many LC researchers, but new subjects unmentioned in the book have also risen for these years. This chapter describes the story of the recent developments and the future perspectives in physics of liquid crystals, especially focusing on the contributions by Japanese research groups for the last decade.

Physics of Liquid Crystals

Dealloying is a common corrosion process during which an alloy is 'parted' by the selective dissolution of the most electrochemically active of its elements. This process results in the formation of a nanoporous sponge composed almost entirely of the more noble alloy constituents. Although considerable attention has been devoted to the morphological aspects of the dealloying process, its underlying physical mechanism has remained unclear. Here we propose a continuum model that is fully consistent with experiments and theoretical simulations of alloy dissolution, and demonstrate that nanoporosity in metals is due to an intrinsic dynamical pattern formation process. That is, pores form because the more noble atoms are chemically driven to aggregate into two-dimensional clusters by a phase separation process (spinodal decomposition) at the solid-electrolyte interface, and the surface area continuously increases owing to etching. Together, these processes evolve porosity with a characteristic length scale predicted by our continuum model. We expect that chemically tailored nanoporous gold made by dealloying Ag-Au should be suitable for sensor applications, particularly in a biomaterials context.

/pdf/evolution-of-nanoporosity-in-dealloying-1vysl3gdw0.pdf

Evolution of nanoporosity in dealloying

Shape-memory polymers (SMPs) have attracted significant attention from both industrial and academic researchers due to their useful and fascinating functionality. This review thoroughly examines progress in shape-memory polymers, including the very recent past, achieved by numerous groups around the world and our own research group. Considering all of the shape-memory polymers reviewed, we identify a classification scheme wherein nearly all SMPs may be associated with one of four classes in accordance with their shape fixing and recovering mechanisms and as dictated by macromolecular details. We discuss how the described shape-memory polymers show great potential for diverse applications, including in the medical arena, sensors, and actuators.

http://research.vuse.vanderbilt.edu/srdesign/2009/group8/Papers/shape%20memory%20polymers%20review%20article.pdf

Review of progress in shape-memory polymers

Fundamentals, processes and applications of high-permittivity polymer–matrix composites

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.

Mechanisms for converting electrical energy into mechanical energy are essential for the design of nanoscale transducers, sensors, actuators, motors, pumps, artificial muscles, and medical microrobots. Nanometre-scale actuation has to date been mainly achieved by using the (linear) piezoelectric effect in certain classes of crystals (for example, quartz), and 'smart' ceramics such as lead zirconate titanate. But the strains achievable in these materials are small--less than 0.1 per cent--so several alternative materials and approaches have been considered. These include grafted polyglutamates (which have a performance comparable to quartz), silicone elastomers (passive material--the constriction results from the Coulomb attraction of the capacitor electrodes between which the material is sandwiched) and carbon nanotubes (which are slow). High and fast strains of up to 4 per cent within an electric field of 150 MV x m(-1) have been achieved by electrostriction (this means that the strain is proportional to the square of the applied electric field) in an electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer. Here we report a material that shows a further increase in electrostriction by two orders of magnitude: ultrathin (less than 100 nanometres) ferroelectric liquid-crystalline elastomer films that exhibit 4 per cent strain at only 1.5 MV x m(-1). This giant electrostriction was obtained by combining the properties of ferroelectric liquid crystals with those of a polymer network. We expect that these results, which can be completely understood on a molecular level, will open new perspectives for applications.

Giant lateral electrostriction in ferroelectric liquid-crystalline elastomers

Ferroelectricity and thus piezoelectricity are well known features of low molar mass chiral smectic C (Sc*) liquid crystals. We present a new technique to orientate macroscopically the director as well as the smectic layers of a Sc*-polymer network by applying a suitable mechanical field. The uniform orientation of the network film is checked by X-ray diffraction. According to the phase symmetry electromechanical measurements indicate the existence of a polar axis of the network and the direct as well as the inverse piezoelectric effect is demonstrated.

Piezoelectricity of mechanically oriented SC*-elastomers

Ferroelectric liquid crystalline elastomers (FLCEs) form a novel class of materials, in which the properties of macroscopically oriented ferroelectric liquid crystals can be combined with those of elastomers. The (direct and the inverse) piezoelectric effect in these systems is measured and analyzed on a molecular level. Backed also by x-ray measurements, a model is suggested that interprets the observed piezoelectricity caused by electrically or mechanically induced motions of smectic layers which are inclined with respect to the sample surface. The strength of the observed electromechanical effects compares well with (or exceeds) that of classical piezoelectric materials like barium titanate, lead zirconate titanate or poled polymers like poly(vinylidene fluoride), making FLCEs an interesting candidate for applications in microsystems technology.

Direct and inverse electromechanical effect in ferroelectric liquid crystalline elastomers

The direct and inverse piezoelectricity in single crystal ferroelectric liquid crystalline elastomers was measured by means of purpose-made experimental setups. As expected the observed effects depended strongly on temperature and the strength of the applied alternating electric field; additionally they could be strongly enhanced by a superimposed direct current electric field. The latter resulted from a molecular amplification of the polarization vector of the single smectic layers by inducing a rotational bias of the lateral distribution of the polar groups of the mesogens. This resulted in a pronounced magnification of the (macroscopic) piezoelectric effect. Backed also by X-ray measurements, a model is suggested, which interprets the observed piezoelectricity as caused by a field-induced change of the inclination of the tilted smectic layers. The strength of the observed electromechanical effects compares well with or exceeds that of classical materials, such as barium titanate or lead–zirconate–titanate or the polymer polyvinylidene fluoride. © 1998 John Wiley & Sons, Ltd.

Piezoelectricity in ferroelectric liquid crystalline elastomers

An ultra-stable Michelson interferometer is described which enables to measure periodic displacements (of a mirror in one interferometer arm) with a resolution of less than 100 fm. This setup is employed to measure the (linear) inverse piezoelectric and the (quadratic) electrostrictive effect in macroscopically oriented ferroelectric liquid crystalline elastomers (FLCE). A pronounced temperature dependence of the electromechanical effects is observed. Superposition of a DC-bias field leads to a strong enhancement of the inverse piezoelectric effect being well comparable in its strength with classical piezoceramics (BaTiO3, PZT, etc.). The molecular mechanisms of the observed effects are discussed.

The inverse electromechanical effect in mechanically oriented S * C -elastomers examined by means of an ultra-stable Michelson interferometer

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