Effects of magnetic fields on flexural properties of a longitudinal polymer liquid crystal

We have placed a copolymer of poly(ethylene terephthalate + 0.6 mole fraction of p-hydroxybenzoic acid) in magnetic fields up to 1.8 Tesla, heated it to the molten state (at several temperatures in the range 240–315 °C) and cooled to the room temperature under the field to maintain the orientation so acquired. Then the extent of the orientation has been determined with an anisotropy parameter a based on the ultrasound critical–angle reflectometry (UCR); the parameter is calculated from the ratio of the maximum velocity to the minimum velocity of the reflected wave at critical incidence angles at which total internal reflection occurs. A significant orientation effect is found. As expected, anisotropy increases with time, magnetic field strength and to a lesser extent with the temperature. Large changes in the extent of the anisotropy are connected to phase transitions determined before. The Freederickscz transition is observed. The influence of the orientation effect on the mechanical properties of samples has been established by flexural tests. The strengthening observed has been explained using an extension of the statistical–mechanical theory of Flory in terms of channeling of flexible sequences in the polymer liquid crystals (PLC) and changes in phase structures under the magnetic field. The strengthening effect depends strongly on the presence, size and distribution of liquid crystal (LC) islands in the material. The islands act similarly as dispersoids in other types of materials. Maxima of the strengthening effect with respect to the alignment are found and related to the size of LC-rich islands in the structure. Electronic Publication     

Effect of organoclay platelets on morphology and properties of LLDPE/EMA blends

Blends of linear low density polyethylene (LLDPE) and ethylene-co-methyl acrylate (EMA) and their nanocomposites with two types of modified montmorillonite (organoclay) were explored in order to achieve an improved balance between stiffness and toughness. The nanocomposites were prepared in a HAAKE RHEOMIX at three different mixing sequences. The compression molded nanocomposites were utilized to evaluate the morphology and the properties like mechanical, dynamic mechanical and thermal. The results reveal that the morphology and the properties of the nanocomposites are dependent on the blending sequence as well as the type of nanoclay used. The addition of organoclay slightly increases the tensile modulus for all the nanocomposites. On the other hand, a drastic improvement of the impact strength was observed when the organoclay located at the dispersed EMA phase. The effects of clay concentration on the properties of the nanocomposites were also studied. The optimum dispersion as well as property was found for the nanocomposite at 5 wt% of the nano clay.     

Improvement of ternary recycled polymer blend reinforced with date palm fibre

This paper investigates the study and preparation of date palm fibre reinforced recycled polymer blend composites. This is the first paper which describes the recycled polymer ternary blends of (1) recycled low density polyethylene (RLDPE), (2) recycled high density polyethylene (RHDPE) and (3) recycled polypropylene (RPP). The date palm fibre reinforced composites (C_D00) were prepared by maintaining constant weight% of fibre of 20 wt% without any fibre treatment. Maleic anhydride (MA) was used as the compatabilizer (1 and 2 wt%) and the effect of compatabilizer on the blend matrix composites was studied. The mechanical, thermal, morphological properties, water absorption and chemical resistance properties were evaluated for these composites and also studied for pure blend matrix (C₀₀). Date palm fibre improved the tensile strength and hardness of recycled polymer blend matrix. Further improvement was achieved with 1% MA (C_D1), which showed that 1% MA treated composites (C_D1) had higher tensile strength, modulus and hardness properties. Thermal stability and water absorption were improved by 1% MA. These improvements were demonstrated at the nanoscale level by the decrease in roughness appearing in Atomic Force Spectroscopic Microscopy analysis indicating that flow is better under this concentration. The SEM analysis also showed that the fibre matrix adhesion improved by adding 1 wt% (C_D1) of MA. The melting and crystallisation temperatures of the blends did not change with the addition of date palm fibre and MA, indicating that the additives did not influence the melting and crystallisation properties of the composites. The chemical resistance test results showed that these composites are resistance to all chemicals but more weight gain observed in solvents. 2 wt% of MA (C_D2) caused poor adhesion between the polymer chains and fibres as well as polymer chain scission.     

Influence of melt processing induced orientation on the morphology and mechanical properties of poly(styrene-b-ethylene/butylene-b-styrene) block copolymers and their composites with graphite

The effect of orientation induced during the manufacturing process on the self-assembled morphology and mechanical properties of poly(styrene-b-ethylene/butylene-b-styrene) block copolymer (SEBS), maleated SEBS (SEBS-MA) and their composites with graphite was examined in this paper. The roll milling process induced higher stiffness along the rolling direction, emphasized by the increase of Young’s modulus with 645% in this direction relative to the perpendicular one and the increase of storage modulus at room temperature with one order of magnitude. The addition of graphite particles diminished the anisotropy of static and dynamic mechanical properties but contributed to the increase of the total energy absorbed till break. The different self-assembled morphologies and degree of order observed by polarized optical microscopy (POM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) in SEBS and SEBS-MA explained some of the differences in their static and dynamic mechanical behavior. For the first time the anisotropy was emphasized by the different glass transition values obtained on the two stretching directions.     

Assessment of rheological and mechanical properties of nanostructured materials based on thermoplastic olefin blend and organoclay

This work aims to assess rheological and mechanical properties of thermoplastic olefin (TPO) nanocomposites reinforced by organo-modified montmorillonite (OMMT). In this regard, TPO/OMMT nanocomposites were produced via melt compounding and characterized in terms of OMMT content and processing parameters. The main objective of the work is to determine the optimum OMMT content and processing parameters. Both dynamic oscillatory and steady shear measurements revealed that a very good degree of OMMT dispersion occurs in the case of nanocomposite containing 3 wt.% OMMT which was also verified by X-ray diffractometry and transmission electron microscopy. Mechanical properties were studied through tensile and impact tests. It was found that as the OMMT content increases, tensile modulus and tensile strength are increased but impact strength is reduced. The optimum properties were observed at 3 wt.% OMMT which is in conformity with the rheological analysis results. As the main processing variables in melt compounding, the effect of mixing time and rotor speed on mechanical properties of TPO nanocomposites were studied and correlated to their rheological properties. It was concluded that using an intermediate mixing time and rotor speed would be more appropriate to achieve desirable mechanical properties.     

Morphological control and polarization switching in polymer dispersed liquid crystal materials and devices

Liquid crystals dispersed in polymer systems constitute novel class of optical materials. The precise control of the liquid crystal droplet morphology in the polymer matrix is essentially required to meet the prerequisites of display device. Experiments have been carried out to investigate and identify the material properties and processing conditions required for the precise control of the droplet morphology of the dispersed liquid crystal systems. Polarization switching has been studied. Aligned liquid crystal dispersed systems showed higher polarization over unaligned ones.     

Photorefractivity in polymer dissolved liquid crystal composites composed of low-molecular-weight nematic liquid crystals and copolymer comprising mesogenic side groups

This paper describes the photorefractive effect of the liquid crystalline composite materials comprising low-molecular-weight nematic liquid crystals (L-LC), copolymer with mesogenic side groups and a small amount of photosensitizer. Copolymers with four kinds of mesogenic side groups were investigated with respect to the compatibility between the L-LC and the copolymer and the photorefractivity of the composites. Two of them could be miscible with L-LC and the composite exhibited LC phase even though the copolymer itself did not show a LC phase. High gain coefficients (> cm^K1) under the low applied dc electric field (<1V/mm) was observed when the composites showed a mesophase without any macroscopic phase separation.     

Effect of frequency on dielectric properties of liquid crystal doped with side-chain liquid crystalline polymer

The frequency and applied bias voltage dependence of the dielectric properties and dielectric anisotropy of liquid crystal (LC) doped with side-chain liquid crystalline polymer (SLCP) mixture have been investigated using the admittance spectroscopy method (C–V and G/ω–V) in the frequency range of 10 kHz to 10 MHz at room temperature. The liquid crystal used in this experiment is E63. The doping material used in this study is SLCP and its concentration is ensured 1 wt % in E63. Dielectric constant (?′), dielectric loss (?), dielectric loss tangent (tan δ) and real and imaginary parts of electrical modulus (M′ and M″) of the E63/SLCP mixture was also calculated. Moreover, dielectric anisotropy (Δ?) as a function of frequency was obtained. Results show that the values of the all dielectric parameters are strong functions of frequency and applied bias voltage. After a critical frequency, dielectric anisotropy has negative values according to p/n type changing.     

聚合物网络稳定液晶光栅的制备与特性研究

将光敏预聚物单体与向列相液晶按一定比例混合,注入液晶盒;采用光掩模法,在紫外灯照射下,使混合物产生定域光聚合反应,形成聚合物网络稳定液晶光栅。利用光学显微镜和He-Ne激光器进行测试,实验检测结果表明,该光栅具有周期性的栅结构,且衍射效率具有先增大后减小电场调制特性,并利用折射率调制机理对该现象进行分析。     

Morphology and photophysical properties of polymer thin films dispersed with dye nanoparticle

We prepared nanoparticles of an organic dye, acridine orange (AO), dispersed in poly(methacrylic acid) (PMA) films by spin-coating the solution of the two components. The surface of the AO/PMA films became bumpier with increasing AO concentration (c_AO). The absorption and fluorescence spectra of AO/PMA films exhibited a marked dependence on c_AO at low c_AO (c_AO < 2.1 × 10^− 1 mol kg^− 1), and were independent of c_AO at high c_AO (c_AO > 2.1 × 10^− 1 mol kg^− 1). The peak shift of fluorescence spectra with changing c_AO was as large as ∼ 100 nm.     

Multifunctional properties of high volume fraction aligned carbon nanotube polymer composites with controlled morphology

Advanced composites, such as those used in aerospace applications, employ a high volume fraction of aligned stiff fibers embedded in high-performance polymers. Unlike advanced composites, polymer nanocomposites (PNCs) employ low volume fraction filler-like concepts with randomly-oriented and poorly controlled morphologies due to difficult issues such as dispersion and alignment of the nanostructures. Here, novel fabrication techniques yield controlled-morphology aligned carbon nanotube (CNT) composites with measured non-isotropic properties and trends consistent with standard composites theories. Modulus and electrical conductivity are maximal along the CNT axis, and are the highest reported in the literature due to the continuous aligned-CNTs and use of an unmodified aerospace-grade structural epoxy. Rule-of-mixtures predictions are brought into agreement with the measured moduli when CNT waviness is incorporated. Waviness yields a large (10×) reduction in modulus, and therefore control of CNT collimation is seen as the primary limiting factor in CNT reinforcement of composites for stiffness. Anisotropic electron transport (conductivity and current-carrying capacity) follows expected trends, with enhanced conductivity and Joule heating observed at high current densities.     

Effects of polymer viscosity on the polymerization switching and electro-optical properties of unaligned liquid crystal/UV curable polymer composites

Polymer dispersed ferroelectric liquid crystal composite films consisting of varying polymer viscosities were prepared by polymerization induced phase separation (PIPS) technique. It was found that polymer viscosity influences the polarization switching and optical responses. A polymer dispersed ferroelectric liquid crystal film of low polymer viscosity shows faster switching, however a higher optical transmission at ~ 70% was observed in a higher polymer viscosity film.     

Effects of morphology and concentration of CuS nanoparticles on alignment and electro-optic properties of nematic liquid crystal

Nanopartides (NPs) with flower-like and frame morphologies were synthesized from CuS,a remarkable transition-metal sulfide.We introduced two kinds of CuS NPs into a nematic liquid crystal (LC) 4-cyano-4'-n-pentylbiphenyl (5CB) and investigated the morphology-and concentration-dependent alignment and electro-optic (E-O) effects of CuS NPs on 5CB.A trace amount of flower-like CuS NPs induced a uniform homeotropic orientation of LC molecules;this is attributable to the obtained desirable compact nanosheet structure.Moreover,both flower-like and frame CuS NPs induced a remarkable improvement in the E-O properties of 5CB,and the flower-like CuS/5CB system exhibited a better performance.The doped CuS NPs in the LC host suppressed the shielding effect and strengthened the electric field,resulting in outstanding E-O properties.At a doping concentration of 0.05 wt.％,CuS NPs were well-dispersed and achieved the optimum E-O performance.This study provides a novel method for inducing a uniform orientation and enhanced E-O properties of LC molecules by doping with extraordinary CuS NPs,leading to potential applications in establishing flexible LC displays.     

Graphical modeling and computer animation of tensile deformation in polymer liquid crystals (PLCs)

We create polymer liquid crystals (PLCs) on a computer and subject them to constant-force tensile deformations. Molecular dynamics simulation procedure is used and graphical models and animations of crack formation and propagation as a function of time are generated. Special attention is given to realistic rigid LC island geometry and the island spatial distribution in the material. Internal fracture processes can now be easily studied. As a result of the numerous animations recorded, clear patterns in PLC crack initiation and propagation emerge. With the help of the animations, the structure of PLCs may be understood without having to resort to costly laboratory experimentation. Received: 25 September 2000 / Reviewed and accepted: 26 September 2000     

Influence of P3HT concentration on morphological, optical and electrical properties of P3HT/PS and P3HT/PMMA binary blends

Poly(3-hexylthiophene) (P3HT) has interesting optoelectronic properties and a wide variety of applications such as solar cells and O-FET devices. It is a soluble conductive polymer but their mechanical properties are poor and its conductivity is unstable in environmental condition. With the finality of overcome these disadvantages, P3HT binary blends with two insulating polymers, polystyrene (PS) and polymethylmetacrilate (PMMA), have been synthesized by direct oxidation of 3-hexylthiophene with FeCl₃ as oxidant inside the insulator polymers. Molecular weight and polydispersity of P3HT polymer were measured by size exclusion chromatography and the degree of regioregularity by ¹H RMN. P3HT/PS and P3HT/PMMA thin films were prepared by spin-coating technique from toluene solution at different P3HT concentrations. The doped films were obtained by immersion during 30 s in a 0.3 M ferric chloride (FeCl₃) solution in nitromethane. A classical percolation phenomenon was observed in the electrical properties of the binary blends, it was smaller than 4 wt.% of P3HT in the blend. Atomic force microscopy and confocal microscopy showed a phase-separated morphology. Variation in the surface morphology of the blends was observed, which was a function of the polymer concentration and the type of insulator polymer used in the blends. The insulator polymer was segregated on the surface of the films and showed pit and island-like topography. The pit and island size changed as a function of the polymer concentration. Optical absorption properties as a function of the P3HT concentration in the undoped and doped state were analyzed. In doped state, the bipolaron bands in the PS/P3HT and PMMA/P3HT blends were observed from a P3HT concentration of 1 wt.% and 3 wt.%, respectively. Finally, the polymers were analyzed by thermogravimetric analysis and infrared spectroscopy.     

Characteristics of di- and tri-block copolymers: polymer disperse liquid crystal display

In the reported work the block copolymers are used in the polymer disperse liquid crystal (PDLC) films. The present work has been performed to investigate the effect of block copolymer addition and block ratios on the PDLC characteristics. From our experimental finding, addition of block copolymer in PDLC shows variation in droplet size, electro-optical properties, extent of phase separation, and phase transition temperature. These finding indicate the alteration in solubility parameters of solutions with the addition of block copolymers. Moreover, the tri-block copolymer shows enlarge droplet size, enhancement in the degree of phase separation, and predict improvement in electro-optical properties, as compared to di-block copolymer. Similarly upon such comparison, the study suggests the tri-block copolymer have a relative lower molecular interaction with the liquid crystal molecules.     

Processing and characterization of functionally graded materials through mechanical properties and glass transition temperature

Functionally graded materials (FGMs) were prepared by construction based layering method through dispersion of carbon nanoparticles in the styrene butadiene rubber matrix. The gradation of material property i.e., ‘glass transition temperature’ was brought in the nanocomposite by varying the concentration of process oil. Glass transition temperature (T_g) of FGMs was varied from − 56 to − 80 °C along the span of 3 mm thick sheet. The gradation of oil in FGMs also changes other properties like tensile strength, elongation at break, modulus, etc. Tensile strength and modulus at 100% drops down while elongation at break continuously increases while moving from one end to other end along the sheet thickness. Thermal analysis of FGMs verifies the compositional changes as well as the change in T_g along the thickness.     

Synthesis and effect of polyphosphazenes on the thermal,mechanical and morphological properties of poly(etherimide)/thermotropic liquid crystalline polymer blend

Effect of functionalized polyphosphazene as compatibilizer in melt-compounded polyetherimide (PEI)/liquid crystalline polymer (LCP) blend has been investigated in details. DMTA study showed the variation in glass transition temperature (T_g) in presence of polyphosphazene having different funtionalization. Superior thermal stability of polyphosphazene aided composites is exhibited from thermo-gravimetric analysis. From dielectric measurements it was clear that polyphosphazene-aided PEI/LCP blend can act as low dielectric material as well as high dielectric material depending on the nature of pendant group used. Scanning electronic microscopic observation revealed that the addition of small amount of polyphosphazene results in a decrease in average disperse domain sizes of LCP phase leading to improved filler-matrix adhesion.     

Morphology,interfacial and mechanical properties of polylactide/poly(ethylene terephthalate glycol) blends compatibilized by polylactide-g-maleic anhydride

Polylactide/poly(ethylene terephthalate glycol) (PLA/PETG 80/20 wt) blends compatibilized with polylactide-g-maleic anhydride (PLA-g-MAH) were prepared by melt blending and the rheological, morphological and mechanical properties of the blends were studied. PLA/PETG (80/20 wt) blend formed a typical sea-island morphology, while upon compatibilization, the size and size distribution of the dispersed phase decreased significantly and the 3 wt% PLA-g-MAH compatibilized blend exhibited the smallest phase size and the narrowest distribution of the dispersed particles. The interfacial tension between PLA and PETG was determined from the morphological characteristics and the viscoelastic response of PLA/PETG blends via using two emulsion models. A minimum for PLA/PETG blend containing 3 wt% PLA-g-MAH was observed from both Palierne model and G–M model. The elongation-at-break increased by ∼320%, from 6.9% for PLA to 28.7% for the blend containing 3 wt% PLA-g-MAH without significant loss in the tensile modulus and tensile strength.