Thermomechanical properties of tri-functionally crosslinked liquid single crystal elastomers (original) (raw)
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Journal of The Physical Society of Japan, 2007
We study the relation between the shape anisotropy changes, Δα, and the optical birefringence, Δ n, of dry and swollen rigid bi-functionally (8.0 mol %, 8A2) and flexible tri-functionally [5 mol % (5V3) and 7 mol % (7V3)] cross-linked liquid single crystal elastomers (LSCEs) as a function of temperature. 4-n-pentyl-4-cyanobiphenyl (5CB) is used as the solvent. Plotting Δα as a function of Δ n, a linear dependence is observed for all LSCE samples. This indicates that Δα results from the liquid crystal ordering. The largest Δα (˜0.2 at T=30 °C) is observed in dry 8A2, which has a large frozen-in orientational order (FOO). The swollen samples show much smaller Δα, ˜0.03--0.05, because of a smaller modulus elasticity after the swelling process.
Thermal and Mechanical Properties of New Main-Chain Liquid-Crystalline Elastomers
Mol. Cryst. Liq. Cryst., 2009
New Main-Chain Liquid-Crystalline Elastomers (MCLCEs) were synthesised based on reacting vinyloxy-terminated mesogens under hydrosilylation conditions with a flexible crosslinker. These main-chain systems showed smectic and nematic mesophases and their anisotropic properties were mechanically and thermally analysed as a function of the crosslinking density. Due to the suitable chemistry used in this work low crosslinking densities have been achieved (2.5mol-%) with low soluble content (5%). For the first time, the degree of crosslinking could be adjusted and nematic or smectic MCLCEs with tuneable thermal and mechanical properties were obtained.
Japanese Journal of Applied Physics, 2007
Here, we study the influence of cross-linking density, X, on the swelling, thermal and electric field response of trifunctionally cross-linked liquid single crystal elastomers (V3 LSCEs) swollen with low molecular weight liquid crystals, 4-n-pentyl-4cyanobiphenyl (5CB). The cross-linker concentrations are X 3V3 ¼ 3:3 mol %, X 5V3 ¼ 5 mol %, and X 7V3 ¼ 7 mol %. LSCE networks are characterized by frozen-in orientation order, P. X c is a constitutional critical point for LSCE networks. When X < X c (P ¼ 0), there are no shape changes and a nematic-isotropic transition takes place at T NI . When X > X c (P > 0), supercritical behavior prevails over a range of temperatures, ÁT s . Taking ÁT s / ðX À X c Þ 1=2 , we find a critical cross-linking density, X c % 3%, for V3 LSCEs. 5CB diffuses ?n into V3 similar to isotropic gels with typical times, ?n in minutes, that decreases with increasing ðX À X c Þ. Swelling with reorientation effects is initiated by 5CB propagating into V3 followed by relaxation of the front profile with ð2Þ ? (twist), and ð13Þ k (splay-bend) that both increase nearly parabolically with increasing ðX À X c Þ. Front speeds are 50% faster in 5V3 than in 7V3 but no fronts were observed in 3V3. Compared to dry V3 LSCE volumes, V d , the swollen volumes, V s , increased as X ! X c : V s =V d $ ðX À X c Þ À0:27 reducing the frozen-in orientational order at X toX X ¼ XðV d =V s Þ. The maximum electromechanical effect found in swollen V3 was MAX $ ðX X ÀX X c Þ withX X c $ 0:25%. The size of the effect is much smaller than observed in 8A2 which has a larger P. For 7V3 the effect is about 4 times smaller and for 5V3, it is an order of magnitude smaller.
Study of the optical, thermal, and mechanical properties of nematic liquid crystal elastomers
Journal of Information Display, 2016
In the present study, the optical, thermal, and mechanical properties of liquid crystal elastomers (LCEs) were investigated using various techniques. The presence of functional groups in LCE was studied using Fourier transform infrared spectroscopy. The phase transition temperatures were confirmed via polarizing optical microscopy and Fabry-Perot scattering studies. The differential thermal analysis was used for investigating the thermal behavior. A dynamic mechanical analysis was used to study the mechanical properties of LCE. The significant mechanical changes with a considerable reversible effect were observed for this soft material. The changes in the mechanical shape with the temperature are attributed to the change in the phase of the LCE material.
Thermal Characterisation of Thermotropic Nematic Liquid-Crystalline Elastomers
Liquid Cryst., 2016
Nematic liquid-crystalline elastomers (LCEs) are weakly cross-linked polymeric networks that exhibit rubber elasticity and liquid-crystalline orientational order due to the presence of mesogenic groups. Three end-on side-chain nematic LCEs were investigated using real-time synchrotron wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and thermogravimetry (TG) to correlate the thermal behaviour with structural and chemical differences among them. The elastomers differed in cross-linking density and mesogen composition. Thermally reversible glass transition temperature, Tg, and nematic-to-isotropic transition temperature, Tni, were observed upon heating and cooling. By varying the heating rate, Tg 0 and Tni 0 were determined at zero heating rate. The temperature dependence of the orientational order parameter was determined from the anisotropic azimuthal angular distribution of equatorial reflections seen during real-time WAXS. Results show that the choice of cross-linking unit, its shape, density, and structure of co-monomers, all influence the temperature range over which the thermal transitions take place. Including multi-ring aromatic groups as cross-linkers increased the effective stiffness of the cross-linking, resulting in a higher glass transition temperature. The nematic-to-isotropic transition temperature increased in the presence of multi-ring aromatic structures, as either cross-linkers or mesogens, particularly when the multi-ring structures were larger than the low-molar-mass mesogen common to all three samples.
Mechanical Properties of New Main-Chain Liquid-Crystalline Elastomers
Solid State Sci., 2010
New Main-Chain Liquid-Crystalline Elastomers (MCLCEs) were synthesized based on reacting vinyloxy-terminated mesogens under hydrosilylation conditions with a flexible crosslinker. These main-chain systems showed smectic and nematic mesophases and their anisotropic properties were mechanically and thermally analysed as a function of the crosslinking density. Due to the suitable chemistry used in this work low crosslinking densities have been achieved (2.5 mol-%) with low soluble content (5%). For the first time, the degree of crosslinking could be adjusted and nematic or smectic MCLCEs with tuneable thermal and mechanical properties were obtained.
Chemical Physics Letters, 2003
We experimentally measured the birefringence of a liquid single crystal elastomer (LSCE) swollen with a low molecular weight liquid crystal (LMWLC), 5CB, by polarizing microscopy as a function of temperature. The optical intensity of swollen LSCE shows significant intensity changes at temperatures T NI , T A and T B that indicates a variety of different transitions. A temperature T NI is known as the apparent nematic-isotropic transition for outside LMWLC, T A and T B are interpreted as the nematic-isotropic transition for LMWLC inside the LSCE and for the swollen LSCE, respectively.
Synthesis and Characterization of Liquid Crystal Elastomer
2015
The thermal and mechanical properties of Liquid Crystal Elastomers (LCEs) were characterized using various techniques for understanding of their physical behavior. The material used for investigation was synthesized by us, using Finklemann procedure, with proper cross linking density in nematic phase. The material is found to have unique coupling between anisotropicorder of liquid crystal component and elasticity of polymer network. The chemical structures were confirmed by Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM). Fabry Perot Scattering Studies (FPSS), Thermo gravimetric Analysis (TGA) and Differential Scanning Calorimatory (DSC) were used to study thermal properties. The mechanical properties were studied using force sensor. Our investigation shows that this synthesized Liquid Crystal Elastomer has ability of spontaneous change as a function of temperature and mechanical force, which shows it as a unique class of soft material.
Liquid-Crystalline Elastomers: Thermally and Optically Effected Ordering
International Meeting on Information Display, 2005
The nature of the phase transition in nematic liquid crystalline elastomer is investigated using NMR and calorimetry. The balance between ordering and disordering effects of the polymer network is identified as crucial for the behavior of the order parameter near the phase transition. The change from supercritical to critical regime with adding low molecular weight liquid crystal to the elastomer is proven.