Current developments in the field of thermotropic chiral-nematic liquid crystals as sensors are discussed. These one dimensional photonic materials are based on low molecular weight liquid crystals and chiralnematic polymeric networks. For both low molecular weight LCs and polymer networks, real-time and time integrating sensors have been realized. The response mechanism is either based on a change of helical twisting power of the dopant upon exposure to an analyte, or due to physical swelling, with a change of order in the liquid crystalline phase upon uptake of the analyte, causing the pitch to change.Sensors that respond to organic and water vapour, amines, water CO 2 , O 2 , metal ions, pH, strain and temperature have been reported.

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A humidity-responsive bilayer actuator has been developed that consists of an oriented polyamide-6 substrate and a liquid-crystalline polymer coating. The oriented substrate acts as an alignment layer for the liquid crystal. The liquid-crystalline polymer consists of a supramolecular network having hydrogen-bonded entities that, after activation with an alkaline solution, exhibit deformation in response to a change in humidity. The bending behavior of the bilayer actuator was analyzed, showing a large response to a change in the humidity.

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A theoretical framework is presented to describe the optical properties of polarizers produced by tensile deformation of semicrystalline polymers containing dichroic dyes. In the model it is assumed that orientation of both the host polymer and guest molecule occurs in the f f i e mode. The development of optical anisotropy with Orientation is described using an aggregate model. The theory is employed to evaluate the optical Characteristics of the polarizers, i.e., dichroic ratio, order parameter, polarizing efficiency, and single-piece transmittance. Good agreement is observed between theoretical predictions and experimental data produced in this work on oriented linear polyethylendSudan Red polarizing films. It is shown that the model is useful to estimate the limiting polarizing efficiency and single-piece transmittance of the polarizing films at hand. IntroductionSeveral processes exist for the production of polymeric sheet polarizers, chiefly for use in the visible wavelength range.i-9 These polarizers are widely employed in, for instance, liquid-crystalline display applications. In most of the aforementioned processes, semicrystalline polymers, such as poly(viny1 alcohol) and polyolefins, are oriented by tensile drawing at temperatures close to, but below, the melting temperature of the p~l y m e r ; l -~ dichroic chromophores are introduced in the oriented films either by chemical modification of the polymer or by incorporation of dichroic dyes in the films prior to or

Highly transparent, ultradrawn high-density polyethylene (HDPE) films were successfully prepared using compression molding and solid-state drawing techniques. The low optical transmittance (<50%) of the pure drawn HDPE films can be drastically improved (>90%) by incorporating a small amount (>1 wt %/wt) of specific additives to HDPE materials prior to drawing. It is shown that additives with relatively high refractive index result in an increased optical transmittance in the visible light wavelength which illustrates that the improvement in optical characteristics probably originates from refractive index matching between the crystalline and noncrystalline regions in the drawn films. Moreover, the optically transparent drawn HDPE films containing additives maintain their physical and mechanical properties, especially their high modulus and high strength, which make these films potentially useful in a variety of applications, such as high-impact windows.

A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange. The relaxation behavior of the embossed film can be fully described using a Kelvin–Voigt model, which reveals that the influence of temperature on the generation of colors is much stronger than that of time, thereby producing stable multiple colors.

action by mixing two micellar solutions containing the reactants. The coprecipitation takes place by mixing two micellar solutions having the same water content, w = [H 2 O]/[AOT]: 0.1 M Na(AOT) containing Na 2 Te and a mixed micellar solution containing Cd(AOT) 2 [46] and Na(AOT). An excess of cadmium ions is used in the synthesis (x = [Cd 2+ ]/[Te 2± ] = 2). The overall concentrations of Na 2 Te and Cd(AOT) 2 in micellar solution were 1.5 10 ±4 and 3´10 ±4 M, respectively. The relative volume of each solution varied. CdTe nanocrystals were formed a few seconds after these two degassed micellar solutions were mixed. The syntheses were performed with droplets of various sizes.Procedure I: On addition of dodecanethiol to the micellar solution, a selective surface reaction between the thio derivative and the cations took place. The coated particles were then extracted from the micellar solution and the surfactant used to form the colloidal dispersion was removed by addition of degassed ethanol. The coated particles precipitated. After centrifugation, the substrate was removed. The coated particles are in powder form and they are stable in air. The coated particles were then redispersed in a mixture of two solvents (isopentane/methylcyclohexane, 3V/V) forming an optically clear glass at low temperature. The coated particles dispersed in solution were stable for a short period (7 days). When they were kept for longer, the stability of the particles changed markedly. In contrast, in powder form, the particles are stable for several months.Procedure II. This was the same as procedure I except that after the two micellar solutions had been mixed, the particles were kept in micellar solution under nitrogen for 48 h. Then dodecanethiol was then added and the particles extracted as before.Remark: When syntheses were performed in the presence of excess telluride (x = [Cd 2+ ]/[Te 2± ] = 1/2), CdTe nanoparticles were formed. However, after dodecanethiol addition and during the washing process, a black precipitate appeared, due to the formation of tellurium oxide. It was then impossible to separate the CdTe nanoparticles from TeO 2 aggregates.