Novel ferroelectric liquid crystals based on optically active Preliminary communication propargylic alcohols

Some new calamitic chiral mesogens (2,5-diphenyl-1,3,4-thiadiazoles, 2,5-diphenylpyrimidines and a biphenylyl benzoate) incorporating the 1-alkylpropynyl moiety have been synthesized as enantiomerically enriched materials (ee c. 87%) and/or as racemates. Their liquid crystalline properties were studied by polarizing microscopy, differential scanning calorimetry and electro-optical investigation. Thereby it was found that most of the new compounds exhibit smectic C phases. The spontaneous polarization (Ps) of the optically active materials was measured to be around 10 nCcm-2.     

Preliminary communication Optical investigation of the Goldstone mode in free-standing films of ferroelectric smectic C* phases

An optical method for investigating the dynamics in free-standing films of ferroelectric liquid crystals in the range 10 to 105 Hz by means of optical reflectivity is presented. The experimental results were obtained in the linear-response regime applying electric a. c. fields of strengths less than 16 V cm 1. By measuring the magnitude and phase of the dynamic reflectivity, a relaxation process was found at frequencies near 1 kHz originating from the Goldstone mode.     

Preliminary communication Low frequency dielectric relaxation in the smectic C* phase of a ferroelectric liquid crystal

Dielectric measurements were made on the ferroelectric liquid crystal Felix 018/100 manufactured by Hoechst, Germany, over the temperature range 30 to 65degreeC (smectic C* phase), frequency range 0.1Hz to 100kHz, with bias voltages of 0, 1, 3 and 10 V, and in a dielectric cell with a spacing of 4 times the helical pitch. Plots of the dielectric loss versus log (frequency) show the usual monotonic increase in the loss with decreasing frequency, as well as the usual loss peak at approximately 1kHz. Plots of the log (dielectric loss) against log (frequency) at low frequencies, have slopes varying from -0.75 to -0.89 when the temperature increases from 30 to 65degreeC. Following the suggestion of Scaife, transforming the complex permittivity data to the complex polarizability of a sphere of unit radius in a vacuum, and plotting the loss polarizability against log (frequency), shows two distinct and separate loss peaks. The sums of the two loss peaks appear to be independent of temperature and bias voltage, even though both depend on these variables.     

Dispersion and filler network structure of fibrillar silicates in elastomers

The dispersion and filler network of fibrillar silicate (FS) in elastomers were studied. The results showed that a good dispersion of FS in matrix during mechanical blending in unvulcanized composites contributed to a strong FS filler network, different from that of traditional reinforcing fillers. Meanwhile, the filler re-aggregation during vulcanization caused by the overlapping and intertwining of FS further strengthened the filler network. The factors including Mooney viscosity and molecular polarity of elastomer, type and amount of silane coupling agents used for filler modification, that may influence the filler network, were studied. Our study helps us to understand the mechanism for the formation of filler network of FS in elastomers and provides guidance for the preparation of high performance FS/elastomer composites.     

Effects of phase separation on network and viscoelastic properties in SBS thermoplastic elastomers

Stress relaxation of poly(styrene-b-butadiene-b-styrene) thermoplastic elastomers is studied in dependence of molecular weight and degree of hydrogenation in the temperature range between ?30° and +80 °C. The influence of these parameters on the structure of the physical network and the degree of partial mixing in the domain boundary is investigated by separating the stress-relaxation modulus into a viscoelastic term and an equilibrium network modulus calculated from the relaxation-time spectrum. The temperature dependence of the one-second relaxation modulus is quantitatively described by use of a modified Kerner model for the simulation of the viscoelastic term. The modification allows the estimation of the volume fraction of interfacial material and its correlation to the parameters which govern phase separation.     

Preliminary communication Induction of the smectic phase in comb-shaped liquid crystalline ionogenic copolymers by hydrogen bond formation

Using a radical copolymerization of 4-(4-cyanobiphenyl-4-yloxy)butyl acrylate and acrylic acid, a number of new liquid crystalline ionogenic copolymers capable of hydrogen bonding were synthesized. The formation of hydrogen bonds results in an invariant temperature interval of existence for the LC state (up to 52mol% of acrylic acid) and a rather sudden replacement of the nematic phase by the SmA phase with increase in content of acrylic acid ( 35 mol%) in copolymers.     

New mechanism of the formation of superconductive ferromagnetic structures in elastomers without conjugation in the backbones

A quantum-mechanical model of charge condensation is proposed for non-conjugated polar elastomers It was found that the stability of the bi- and multi-polaron state may be achieved if the dielectrical permeability of the matrix is high enough. It is shown that the multi-electron unit, called as superplaron, should have a linear structure and possess ferromagnetic properties. The one-dimensional character of the conductivity of a superpolaron leads to the formation of electron pairs and to the appearance of high temperature superconductivity of superpolarons. A lot of experimental data confirms the real existance of superconductivity at some polar elastomers at 300 K.     

Measurement of the pyroelectric response and of the thermal diffusivity of microtomized sections of 'single crystalline' ferroelectric liquid crystalline elastomers

The pyroelectric response and the thermal properties of microtomized sections of 'single-crystalline' ferroelectric liquid crystalline elastomers (FLCE) have been investigated. The microtomized sections were manufactured in the thickness range from 20 to 100 mum. The roughness of the surfaces due to the cutting process was investigated with an alpha-stepper and found to be in the range of about 5 mum. The thermal diffusivity of the elastomer at different temperatures was determined by placing the sample on a pyroelectric substrate and measuring the pyroelectric signal of the substrate under appropriate conditions. From the pyroelectric current spectra, information about the spatial distribution of the polarization could be deduced. It was found to be constant except in a range also about 5 mum near the surface. From the combination of this result and that of the alpha-stepper measurements, the conclusion is drawn that the molecular orientation at the surface is destroyed due to the cutting process. The magnitude of the spontaneous polarization was calculated from the pyroelectric measurements at different temperatures, making use of the thermal diffusivity values.     

Measurement of the pyroelectric response and of the thermal diffusivity of microtomized sections of 'single crystalline' ferroelectric liquid crystalline elastomers

The pyroelectric response and the thermal properties of microtomized sections of 'single-crystalline' ferroelectric liquid crystalline elastomers (FLCE) have been investigated. The microtomized sections were manufactured in the thickness range from 20 to 100 mum. The roughness of the surfaces due to the cutting process was investigated with an alpha-stepper and found to be in the range of about 5 mum. The thermal diffusivity of the elastomer at different temperatures was determined by placing the sample on a pyroelectric substrate and measuring the pyroelectric signal of the substrate under appropriate conditions. From the pyroelectric current spectra, information about the spatial distribution of the polarization could be deduced. It was found to be constant except in a range also about 5 mum near the surface. From the combination of this result and that of the alpha-stepper measurements, the conclusion is drawn that the molecular orientation at the surface is destroyed due to the cutting process. The magnitude of the spontaneous polarization was calculated from the pyroelectric measurements at different temperatures, making use of the thermal diffusivity values.     

Electric field induced structure formation in free standing ferroelectric films

Abstract

Free standing ferroelectric films in a rotating electric field have been investigated. Depending upon the applied voltage and the period of the field rotation different structure formations could be observed. At high fields, a homogeneous orientation is obtained. In the case of very low fields, a schlieren texture results. Under special conditions, a stable ring system appears. The dynamics of these rings have been studied. The dependence of the structure formation on the relation between the impulse length of the applied field and the reorientation time is discussed.     

Electric field induced structure formation in free standing ferroelectric films

Free standing ferroelectric films in a rotating electric field have been investigated. Depending upon the applied voltage and the period of the field rotation different structure formations could be observed. At high fields, a homogeneous orientation is obtained. In the case of very low fields, a schlieren texture results. Under special conditions, a stable ring system appears. The dynamics of these rings have been studied. The dependence of the structure formation on the relation between the impulse length of the applied field and the reorientation time is discussed.     

Theory of light-induced deformation of azobenzene elastomers: influence of network structure

Azobenzene elastomers have been extensively explored in the last decade as photo-deformable smart materials which are able to transform light energy into mechanical stress. Presently, there is a great need for theoretical approaches to accurately predict the quantitative response of these materials based on their microscopic structure. Recently, we proposed a theory of light-induced deformation of azobenzene elastomers using a simple regular cubic network model [V. Toshchevikov, M. Saphiannikova, and G. Heinrich, J. Phys. Chem. B 116, 913 (2012)]. In the present study, we extend the previous theory using more realistic network models which take into account the random orientation of end-to-end vectors of network strands as well as the molecular weight distribution of the strands. Interaction of the chromophores with the linearly polarized light is described by an effective orientation potential which orients the chromophores perpendicular to the polarization direction. We show that both monodisperse and polydisperse azobenzene elastomers can demonstrate either a uniaxial expansion or contraction along the polarization direction. The sign of deformation (expansion/contraction) depends on the orientation distribution of chromophores with respect to the main chains which is defined by the chemical structure and by the lengths of spacers. The degree of cross-linking and the polydispersity of network strands do not affect the sign of deformation but influence the magnitude of light-induced deformation. We demonstrate that photo-mechanical properties of mono- and poly-disperse azobenzene elastomers with random spatial distribution of network strands can be described in a very good approximation by a regular cubic network model with an appropriately chosen length of the strands.     

Effect of gel network on pattern formation in the ferrocyanide-iodate-sulfite reaction

Stationary patterns have been researched experimentally since the discovery of the Turing pattern in the chlorite-iodide-malonic acid (CIMA) reaction and the self-replicating spot pattern in the ferrocyanide-iodate-sulfite (FIS) reaction. In this study, we reproduced the pattern formation in the FIS reaction by using poly(acrylamide) gels. Gels with different swelling ratios were prepared to use as a medium. The effect of the swelling ratio was compared with the effect of thickness. It was found that the swelling ratio greatly influenced pattern formation. Oscillating spot patterns appeared at high swelling ratios, and lamellar patterns appeared at a low swelling ratio. Self-replicating spot patterns appeared in between the two areas. The front velocities, which were observed in the initial stage of pattern formation, depended on the swelling ratio. Furthermore, this dependence obeys the free volume theory of diffusion. These results provide evidence that the change in front velocities is caused by a change in diffusion. Pattern formation can be controlled not only by thickness but also by swelling ratio, which may be useful for creating novel pattern templates.     

TMA characterization of urethane elastomers,with the structure varying from chain to network

TMA has been used to investigate the thermomechanical behaviour of six series of elastomers in connection with their chemical constitution and physical structure. The elastomers, were synthesized from an NCO-terminal pre-polymer, based on oligo (ethylene adipate), 1,4-butanediol and 2,4-toluylene diisocyanate, by curing with systems of two agents: a bifunctional one (1,4-butanediol, bistethylene glycol)terephthalate, or monoethanolamine), and a trifunctional one (1,1,1-trimethylolpropane or diethanolamine). The TMA results are presented as due to the superposition of the chemical cross-linking and the physical network, formed through microphase segregation. The TMA suggests that diethanolamine unexpectedly acts as a chain extender, rather than a cross-linking agent.     

Preliminary communication Nematic-substrate repulsion in the nematic-isotropic phase coexistence region

Observations of two types of nematic droplet in the nematic-isotropic phase coexistence region are reported. One type contains topological defects and is free to move within a thin, homeotropically treated cell; the other is defect free and appears to be pinned at the substrates. The freely moving droplet represents an apparently new liquid crystal-substrate repulsion, which depends on the director alignments at the substrate and at the surface of the nematic droplet.     

On the stereochemistry of allylmetal-aldehyde condensations. Preliminary communication

The stereochemical course of the intramolecular allylsilane-aldehyde condensation of 1a has been investigated. A modest preference for the product arising from a synclinal orientation of double bonds was observed with Lewis-acid catalysts. Cyclization induced by fluoride ion resulted in stereochemical reversal.     

A chemical circular communication network at the nanoscale

In nature, coordinated communication between different entities enables a group to accomplish sophisticated functionalities that go beyond those carried out by individual agents. The possibility of programming and developing coordinated communication networks at the nanoscale—based on the exchange of chemical messengers—may open new approaches in biomedical and communication areas. Here, a stimulus-responsive circular model of communication between three nanodevices based on enzyme-functionalized Janus Au–mesoporous silica capped nanoparticles is presented. The output in the community of nanoparticles is only observed after a hierarchically programmed flow of chemical information between the members.

A community of three nanodevices communicates through a hierarchically programmed circular flow of chemical information between members.