Smectic Liquid Crystalline Elastomers Research Articles

Rheology of Smectic Liquid Crystalline Elastomers with Dynamic Covalent Bonds

Rheology of Smectic Liquid Crystalline Elastomers with Dynamic Covalent Bonds

Synthesis and characterisation of novel chiral smectic liquid crystalline elastomers containing menthol dimer-type side chain

ABSTRACTA series of siloxane-based chiral smectic liquid crystalline elastomers (ChSLCEs) formed by a dimer-type smectic monomer (M1), a dimer-type chiral smectic monomer (M2) and a smectic cross-linker (CL) were reported. M1 and M2 were both new liquid crystals with dimer structures, and their chemical structures and purities were characterised by Fourier transform infrared spectra and 1H NMR. The thermal stability and mesomorphism of monomers, cross-linker and ChSLCEs were examined by different analytical techniques. The results showed both monomers exhibited excellent smectic properties. The combination of different smectic phases from the two liquid crystalline side chains endowed the obtained ChSLCEs with good chiral smectic properties. The effect of different dosages of cross-linkers on the mesomorphic properties of the elastomers was also examined. The temperature ranges of mesophase-isotropic phases was narrowed with increasing addition of the cross-linkers according to the differential scanning calorimetry. All of the ChSLCEs exhibited good thermal stability from thermal gravity analysis results. The effective cross-link densities of ChSLCEs were calculated according to the swelling experiments to give the fact that the molecular weights between the cross-linking points decrease with the increase of the cross-linkers. Novel achiral smectic monomer (M1), chiral smectic monomer (M2), and an achiral smectic crosslinking agent (CL) have been synthesized to form a series of side chain chiral smectic liquid crystalline elastomers (ChSLCEs) LCE1-LCE7 by graft copolymerization with the poly(methylhydrogeno)siloxane backbone

1B20 キラルスメクティック液晶エラストマーにおけるX線構造解析と電気力学的性質(化学・材料)

1B20 キラルスメクティック液晶エラストマーにおけるX線構造解析と電気力学的性質(化学・材料)

Preparation and Properties of a Main-Chain Smectic Liquid-Crystalline Elastomer with Shape-Memory Ability

This article presents the preparation of a smectic liquid-crystalline elastomer from a main-chain polybibenzoate with cross-linkable methacrylate groups incorporated at the ends of the polymeric chains. The advantage of this functionalization is that it can be thermally cross-linked in the bulk state without initiator. Rheological experiments have established that temperatures around 20–30 °C above the isotropization point were found to be the most appropriate for the preparation of the network, leading to excellent sheets with a superior cross-linking yield, and prepared in relatively short curing times. The DSC and X-ray diffraction experiments indicate that the network retains the liquid crystalline ability (with a slightly smaller order than that of the linear polymer). The shape-memory behavior of the network has been determined from the well-known cyclic thermomechanical experiments. It follows that the investigated network shows a rather remarkable shape-memory behavior, with considerably good shap...

Electrically Induced Twist in Smectic Liquid-Crystalline Elastomers.

As an approach for electrically controllable actuators, we prepare elastomers of chiral smectic-A liquid crystals, which have an electroclinic effect, i.e., molecular tilt induced by an applied electric field. Surprisingly, our experiments find that an electric field causes a rapid and reversible twisting of the film out of the plane, with a helical sense that depends on the sign of the field. To explain this twist, we develop a continuum elastic theory based on an asymmetry between the front and back of the film. We further present finite-element simulations, which show the dynamic shape change.

Synthesis and characterization of chiral smectic side-chain liquid crystalline elastomers containing nematic and chiral mesogens

A novel series of siloxane-based chiral smectic side-chain liquid crystalline elastomers containing nematic and chiral mesogens were fabricated through synthesis involving a one-step hydrosilication reaction via a liquid crystalline crosslinking agent containing smectic and nematic phases.

Controlled Shape Memory Behavior of a Smectic Main-Chain Liquid Crystalline Elastomer

A smectic main-chain liquid crystalline elastomer (LCE), with controlled shape memory behavior, is synthesized by polymerizing a biphenyl-based epoxy monomer with an aliphatic carboxylic acid curing agent. Microstructures of the LCEs, including their liquid crystallinity and cross-linking density, are modified by adjusting the stoichiometric ratio of the reactants to tailor the thermomechanical properties and shape memory behavior of the material. Thermal and liquid crystalline properties of the LCEs, characterized using differential scanning calorimetry and dynamic mechanical analysis, and structural analysis, performed using small-angle and wide-angle X-ray scattering, show that liquid crystallinity, cross-linking density, and network rigidity are strongly affected by the stoichiometry of the curing reaction. With appropriate structural modifications it is possible to tune the thermal, dynamic mechanical, and thermomechanical properties as well as the shape memory and thermal degradation behavior of LCEs.

Strain-induced macroscopic magnetic anisotropy from smectic liquid-crystalline elastomer–maghemite nanoparticle hybrid nanocomposites

We combine tensile strength analysis and X-ray scattering experiments to establish a detailed understanding of the microstructural coupling between liquid-crystalline elastomer (LCE) networks and embedded magnetic core-shell ellipsoidal nanoparticles (NPs). We study the structural and magnetic re-organization at different deformations and NP loadings, and the associated shape and magnetic memory features. In the quantitative analysis of a stretching process, the effect of the incorporated NPs on the smectic LCE is found to be prominent during the reorientation of the smectic domains and the softening of the nanocomposite. Under deformation, the soft response of the nanocomposite material allows the organization of the nanoparticles to yield a permanent macroscopically anisotropic magnetic material. Independent of the particle loading, the shape-memory properties and the smectic phase of the LCEs are preserved. Detailed studies on the magnetic properties demonstrate that the collective ensemble of individual particles is responsible for the macroscopic magnetic features of the nanocomposite.

Calorimetric Investigation of the Isotropic to Smectic-A Phase Transition of Smectic Liquid-Crystalline Elastomers

A high-resolution calorimetric study has been performed in the vicinity of the isotropic to smectic-A phase transition of smectic liquid crystalline elastomers. The transition is weakly first order for both investigated samples. Nevertheless, different features have been observed when the crosslinking density is changed, such as substantial broadening of the transition and decrease of the involved latent heat. The latter is sluggishly released in a range of few K.

First liquid single crystal elastomer containing lactic acid derivative as chiral co-monomer: Synthesis and properties

For the first time new type of liquid single crystal elastomers forming the chiral smectic A* (SmA*) phase has been prepared using chiral lactic acid derivative as a co-monomer. The synthesis and the basic characterization of the ferroelectric liquid crystalline co-monomer based on differential scanning calorimetry and small/wide-angle X-ray scattering are reported and discussed. The monomer possesses the paraelectric SmA* and the ferroelectric SmC* phases over a broad temperature range. The preparation of new smectic liquid crystalline elastomers together with characterization of their mesomorphic and structural properties is also reported. New elastomers possess the orthogonal paraelectric SmA* phase over 50 K broad temperature range.

Shear Deformation and Ferroelectricity in Chiral SmC* Main-chain Elastomers

Ferroelectric smectic main-chain liquid crystalline elastomers were synthesized and subjected to simple shear deformation to achieve reorientation of the layer structure and the formation of a macroscopic spontaneous polarization. The phase behavior and structural parameters of these elastomers are investigated and discussed. A shear-induced splitting of the X-ray scattering intensity distribution is found. A splitting of the sample in domains of two director orientations that couple differently to the shear deformation is proposed. The smectic layers also move at different affinities depending on their initial orientation. The smectic layer spacing was found to be nearly constant even though the smectic tilt angle changes significantly. The realignment of the smectic layers indicates a migration process, where depending on their original orientation the layer normals are leaving or entering the X-ray scattering plane. The spontaneous polarization was found to be linearly dependent on the dopant concentra...

Elongation Behavior of a Main-Chain Smectic Liquid Crystalline Elastomer

We have prepared a polydomain smectic liquid crystalline (LC) elastomer by introducing 2 mol % 1,3,5-benzenetricarboxylic acid as a cross-linker into a main-chain BB-5 polyester. The elastomer designated as BB-5/E2 forms isotropic and smectic CA (SmCA) LC phases in order of decreasing temperature similarly to the un-cross-linked BB-5 polyester. BB-5/E2 in the isotropic liquid phase shows a typical rubberlike elasticity, whereas that in the SmCA phase shows a characteristic elongation behavior accompanying a polydomain−monodomain transition: the initial strain up to 100% orients the smectic layer with its normal parallel to the elongation direction, and the further elongation does not change the layer orientation and results in permanent deformation. The corresponding stress−strain curve shows a quasi-plateau, which is a so-called “soft stress plateau”, over a wide strain region from 100% to 450%. These indicate that the polymer chains folded in the oriented smectic LC elastomer at a strain of 100% are str...

Order and strain in main-chain smectic liquid-crystalline polymers and elastomers

Order and strain in main-chain smectic liquid-crystalline polymers and elastomers

Order and strain in main-chain smectic liquid-crystalline polymers and elastomers

The layer correlations in main-chain smectic liquid-crystal polymer and elastomer systems have been studied using high-resolution X-ray scattering. In contrast to side-chain smectic polymers, in main-chain systems the polymer chains are oriented parallel to the layer normal. As a result they couple directly to the lamellar structure and any polymer defect is translated into layer distortions. For the homopolymers the resulting X-ray lineshapes are well described by Lorentzians. This is interpreted as an average of algebraically decaying order in domains with dimensions of hundreds of nm and a wide dispersion of sizes. The elastomers show much broader peaks than the correponding polymers. This is attributed to strong non-uniform strain within the finite-size domains due to defects of the layer structure.

Mechanical manipulation of molecular lattice parameters in smectic elastomers

Smectic liquid crystalline elastomers (SLCE) represent unique materials that combine a 1-D molecular lattice arrangement and orientational order with rubber-elasticity mediated by a polymer network. Such materials may exhibit large thermo-mechanical, opto-mechanical and electro-mechanical effects, due to the coupling of macroscopic sample geometry and microscopic structural features. It is shown that the molecular layer dimensions in the smectic phases can be influenced reversibly by macroscopic strain of the material. We present a microscopic model on the basis of experimental results obtained by mechanical dilatation measurements, optical interferometry, X-ray scattering, (13)C NMR, FTIR and polarizing microscopy data. The model gives an explanation of the controversial results obtained in different types of smectic elastomers.

Synthesis and characterization of a series of smectic liquid crystalline elastomers

AbstractA series of new smectic and cholesteric liquid crystalline elastomers was prepared by graft polymerization of mesogenic monomer with the chiral and nonmesogenic crosslinking agent using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance spectra (1H‐NMR). The mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction measurements (XRD). M1 showed smectic (SB, SC, SA) and nematic phases during the heating and the cooling cycles. Polymer P0 and elastomer P1 exhibited smectic B phase, elastomers P2–P5 showed smectic A phase, P6 and P7 showed cholesteric phase, and P8 displayed stress‐induced birefringence. The elastomers containing less than 15 mol % M2 displayed elasticity and reversible phase transition with wide mesophase temperature ranges. Experimental results demonstrated that the glass transition temperatures decreased first and then increased; melting temperatures and the isotropization temperatures and the mesophase temperature ranges decreased with increasing content of crosslinking unit. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 498–506, 2005

Study of smectic elastomer films under uniaxial stress

We study the mechanical properties of free-standing films of smectic liquid crystalline elastomers. Macroscopically ordered elastomer films of submicrometer thickness are prepared from freely suspended smectic A polymer films by photo crosslinking. The deformation characteristics depend criticically on the sample composition, in particular on the density of mesogenic side chains at the siloxane backbone. In materials where the siloxane backbone is only partially substituted (dilute systems), a uniaxial stretching of the films in the layer plane is accompanied by a shrinkage of the smectic layers. This layer shrinkage is to only a minor extent achieved by the induction of a molecular tilt. We conclude that the layer compression modulus (enthalpic contribution to elasticity) in such materials is very weak. In materials with a fully substituted backbone (homopolymers), the smectic layer thickness is preserved under uniaxial stress in the layer planes.

Electromechanics of a Chiral Smectic C Elastomer: Measurement of Complex Piezoelectric Constant through Successive Phase Transformations

AbstractSummary: Piezoelectric properties of a chiral smectic liquid crystalline elastomer are investigated by means of dynamic electromechanical measurements. We have confirmed that the piezoelectric constant is fairly large in the chiral smectic C (SmC*) phase. A relaxation of the piezoelectric constant is observed in the frequency dispersion curve of a director orientated elastomer obtained by a uniaxial deformation. The temperature dependence of the relaxation frequency in the smectic phases is nicely fitted to the Vogel‐Fulcher‐Tammann law, because the dynamics observed here is closely related to the glass transition phenomena. A resonance instead of a relaxation is recognized in the case of a biaxial deformed elastomer in which both layer and director are oriented to their preferred directions. In addition, the piezoelectric constant of the biaxially deformed elastomer possessing a macroscopically spontaneous polarization is smaller than that of the uniaxially deformed elastomer with no net spontaneous polarization. We discuss the mechanism of polarization generation in the electromechanical response of the SmC* elastomers, and also consider the emergence of the resonance in the biaxial deformed elastomer.Geometry of sample deformation.imageGeometry of sample deformation.

X-Ray Diffraction Studies on the Phase-Transformational Behavior of a Smectic Liquid-Crystalline Elastomer Composed of Chiral Mesogens

Structural changes through successive phase transformations of a chiral smectic liquid-crystalline elastomer are investigated by X-ray scattering technique. In uniaxially deformed elastomers, the smectic layer seemingly tilts even in the SmA phase, in which an in-plane chevron structure formed in the tilted smectic phase. On the basis of an analysis of the layer reflection peaks, the layer correlation length in the tilted smectic phases is shorter than that in the non-tilted SmA phase, though smectic layers in the tilted smectic phases are better ordered than those in SmA. Experimental arrangement for X-ray measurements of the uniaxially deformed elastomer in the tilted smectic phase at room temperature.

2B04 X線回折によるスメクティック液晶エラストマーのSmA-SmC^*相転移挙動の研究(化学・材料)

2B04 X線回折によるスメクティック液晶エラストマーのSmA-SmC^*相転移挙動の研究(化学・材料)