Polarized Optical Micrographs Research Articles

Optical Properties of Cholesteric Liquid Crystal Elastomer Film

A series of liquid crystal elastomer (LCE) films (ABC films) were prepared by polymerization of polymethylhydrosiloxane (PMHS), liquid crystal (LC) monomer cholesterol 4-(allyloxy) benzoate (MB) and cross-linking agent 4'-(undec-10-enoyloxy)-[1,1'-biphenyl]-4-yl dodec-11-enoate (MC) . The chemical structures and LC properties of the monomers and polymers were characterised by Fourier Transform Infrared Spectrometer (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), polarized optical micrograph (POM) and X-ray diffractometer (XRD). MB is a cholesteric LC and MC is a smectic LC. The ABC films are cholesteric LCEs. The temperature at which 5% weight loss occurred for the ABC films are around 300 °C. The glass transition temperature of ABC films increases with the increase of LC monomer MB content. The ABC films have a strong absorption around 200-330nm in the ultraviolet (UV) region, and the absorption range does not change with temperature.

Effect of Composition on the Crystallization, Water Absorption, and Biodegradation of Poly(ε-caprolactam-co-ε-caprolactone) Copolymers.

Poly(ester amide)s have aroused extensive research interest due to the combination of the degradability of polyester and the higher mechanical properties of polyamide. In this work, a series of poly(ε-caprolactam-co-ε-caprolactone) (P(CLA-co-CLO)) copolymers with different compositions were synthesized by anionic copolymerization. The structure, crystallization behavior, water absorption, and biodegradation behavior of these copolymers were investigated by means of nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized optical micrographs (POM). The results indicated that the composition of P(CLA-co-CLO) copolymers can be adjusted by the molar feed ratio. The PCL blocks decreased the crystallization rate of PA6 blocks but had little effect on the melting behavior of PA6, while the crystallized PA6 acted as a heterogeneous nucleating agent and greatly improved the crystallization rate of PCL. Moreover, the introduction of PCL blocks greatly reduced the water absorption of P(CLA-co-CLO) copolymers and endow them a certain degree of degradability.

Tuning the mechanical properties and degradation properties of polydioxanone isothermal annealing.

Polydioxanone (PPDO) is synthesized by ring-opening polymerization of p-dioxanone, using stannous octoate as the catalyst. The polarized optical micrograph (POM) shows thes pherulite growth rate of PPDO decreases with an increase in the isothermal crystallization temperature. PPDO is compression-molded into bars, and PPDO bars are subjected to isothermal annealing at a range of temperatures (Ta = 50, 60, 70, 80, 90, and 100 °C), and correspond to three different annealing times (ta = 1h, 2h, 3h). The effect on PPDO is investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). With an increase in Ta and ta, the grain size and the degree of crystallinity also increase. Meanwhile, the tensile strength is significantly improved. The PPDO bars (90 °C, 2 h) reach the maximum crystallinity (57.21%) and the maximum tensile strength (41.1 MPa). Interestingly, the heat treatment process does not result in serious thermal degradation. It is observed that the hydrolytic degradation of the annealed PPDO is delayed to some extent. Thus, annealed PPDO might have potential applications, particularly in the fields of orthopedic fixation and tissue engineering.

Spectroscopic, dielectric and nonlinear current–voltage characterization of a hydrogen-bonded liquid crystalline compound influenced via graphitic nanoflakes: An equilibrium between the experimental and theoretical studies

Herein, we investigate a hydrogen-bonded liquid crystal compound, namely 4-(Heptyloxy) benzoic acid (7OBA), and its composites by dispersing Graphene and reduced graphene oxide (rGO) flakes into an optimized concentration. The pristine 7OBA and its composites are characterized by different instrumental techniques like polarized optical microscopy, differential scanning calorimetry (DSC), dielectric, UV-visible, and Fourier-transform infrared (FTIR) spectroscopy. DSC thermograms of the 7OBA composites evince the down-shift in the smectic C−nematic and nematic−isotropic phase transition temperatures. The polarized optical micrographs (POMs) of composites reveal the homogeneous distribution of graphene and rGO flakes in the 7OBA compound without any aggregation. The π-π* transitions in phenyl ring of 7OBA compound and π-π* transitions in CC bonds of graphitic materials are superimposed to each other providing an enhanced UV absorbance nearly at 255 nm for the composites. The presence of graphene and rGO enhances the tan δ and electrical conductivity of the composites, whereas dielectric anisotropy, Δϵ, reduces as a function of temperature in comparison to the pristine 7OBA compound. The sign inversion of Δϵ has been observed for the 7OBA/rGO composite which has been explained via dipole−dipole interactions. The I−V behavior of the pristine 7OBA compound yields the ohmic I−V curve with a non-zero current at 0 V attributing to the pseudocapacitance effect, whereas, after the dispersion of graphene and rGO flakes, nonlinear diode like I−V curves having a hundred times larger conduction current were obtained. Furthermore, the molecular interactions have been analyzed by the FTIR which confirms the formation of hydrogen bonding in the 7OBA/rGO composite. At last, these experimental findings are compared with the simulated results by DFT. The experimental and theoretical simulations are commensurable to each other. The studied composites have shown their vital applications in nonlinear electronics.

Synthesis and Characterization of Chiral azo LCPs

Precursor polymer MP series were synthesized by 4-allyloxybenzoic acid cholesteryl ester (M) and 4- hydroxyphenyl 4- (propionyloxy) benzoate (P). We obtained novel themotropic side-chain liquid crystal polymer MPZ series by esterification between MP series and 4-((4-ethoxyphenyl) diazenyl) benzoic acid (Z). Differential scanning calorimetry (DSC) was used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by polarized optical micrograph (POM), DSC and X-Ray. MP series exhibited yellow, green, blue and purple Grandjean textures. MPZ series also showed colorful Grandjean textures. They exhibited thermotropic liquid crystal properties in a broad mesogenic region.

Fabrication of pixelated polarizer array and its application in polarization enhancement

Pixelated polarizer array can be used in the real-time measurement of Stokes parameters. In this paper, pixelated polarizer array based on the aluminum nano-grating is designed and fabricated, and the fabrication technology is electron beam exposure technology. The size of each unit is 7.4 μm, and the polarization directions of each adjacent 2×2 units in the polarizer array are 0, π/4, π/2, and 3π/4. The period, duty cycle, depth and surface type of the grating are 140 nm, 0.5, 100 nm and rectangle type, respectively. The scanning electron micrographs of the pixelated polarizer array show that there is no disconnection, cross and pollution on the fabricated metal nano-grating lines. The nano-grating lines are straight and uniform in thickness, and the surface type of the grating is ideal rectangular type. The polarization optical micrographs show that the pixelated polarizer array has good polarization characteristics. The maximum polarization transmissivity can reach 79.3%, and the extinction ratio can arrive at 454. Furthermore, the pixelated polarizer array is integrated with the charge coupled devise chip, and the Stokes parameters can be calculated from one frame, then the degree of linear polarization and angle of linear polarization can be obtained. Thus, the polarization enhancement of image is achieved, which can be used in the anti-stealth and recognition.

Graft Copolymeriztion of Glycidyl Methacrylate/Styrene onto Polypropylene in Solid State

Radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) powder was studied in this research. The reaction temperature was below the melting point of PP so that the reaction was carried out in solid state. Styrene (St) acting as electron donor compounds was used as grafting comonomer and xylene was used as interfacial agent to swell the PP powder. The effects of monomer and comonomer concentration on the graft degree were investigated. The FT-IR spectra of the grafted PP demonstrated that GMA and St were grafted onto PP backbone successfully and the polarization optical micrographs showed that the grafted chains acted as nucleating agent and speeded up the crystallization process.

侧链密度对聚酰亚胺取向膜性能的影响

4-dodecyloxy-phenyl-4′,4″-diaminotriphenylamine(DPDTA) containing triphenylamine were successfully synthesized.Polyimides(PIs) containing triphenylamine units in the main chain were synthesized with the co-condensation of DMMDA,DPDTA and aromatic dianhydride 4,4′-oxydiphthalic anhydride(ODPA) by thermal imidization.The structures of the PIs were confirmed by FT-IR.The alignment behavior of PIs as liquid crystal alignment layers was also examined with polarized optical micrograph(POM).The properties of the PIs were characterized by TGA,UV-Vis and DSC etc.It was found that side chain density of PIs had important influence on properties of liquid crystal alignment film.Before rubbing,PI containing 25% DPDTA could induce uniform vertical alignment and a pretilt angle of 89.7°.The liquid crystal was not aligned on the surface of PI film which contained 10% DPDTA without the rubbing treatment.After the rubbing process,the pretilt angle of liquid crystal was 2.4,when PI film contained 25% DPDTA and the pretilt angle of liquid crystal was 1.8°,when PI contained 10% DPDTA.The transmittances of the PIs in 500～800 nm wavelengths are more than 80%,and their glass transition temperatures are above 230 ℃.

Synthesis and crystallization behavior study of syndiotactic polystyrene-g -isotactic polypropylene (sPS-g -iPP) graft copolymers

Based on coordination polymerization mechanism only, novel stereoregular graft copolymers with syndiotactic polystyrene main chain and isotactic polypropylene side chain (sPS-g-iPP) were synthesized via two steps of catalytic reactions. First, a chain transfer reaction was initiated by a chain transfer complex composed of a styrene derivative, 1,2-bis(4-vinylphenyl)ethane, and hydrogen in propylene polymerization mediated by rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2 and MAO, which gave iPP macromonomer bearing a terminal styryl group (iPP-t-St). Then the iPP-t-St macromonomers of varied molecular mass were engaged in syndiospecific styrene polymerization over a typical mono-titanocene catalyst (CpTiCl3/MAO) under different conditions to produce sPS-g-iPP graft copolymers of varied structure. With an effective purification process, well-defined sPS-g-iPP copolymers were obtained, which were then subjected to differential scanning calorimetry (DSC) and polarized optical micrograph (POM) studies. The graft copolymers were generally found with dual melting and crystallization temperatures, which were ascribable respectively to the sPS backbone and iPP graft. However, it was revealed that the two segments displayed largely different melting and crystallization behaviors than sPS homopolymer and the precursory iPP-t-St macromonomer. Consequently, the graft copolymer exhibited much distinctive crystalline morphologies when compared with their individual components. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

Montmorillonite particle alignment and crystallization and ion-conducting behavior of montmorillonite/poly(ethylene oxide) nanocomposites

This study investigates the polarization filler effects of montmorillonite on the crystal morphology and ionic conductivity of poly(ethylene oxide) solid electrolytes. Direct-current (DC) electric field was applied during the synthesis of the PEO/montmorillonite nanocomposite to induce the alignment of the montmorillonite particles between the electrodes. Differential scanning calorimetry (DSC), polarized optical micrograph (POM), X-ray diffraction (XRD) and thermogravimetry analysis (TGA) revealed that the montmorillonite particles were well dispersed and aligned in the nanocomposites through the application of the electric field. The electric field created higher ionic conductivity ( ρ) as the anisotropic clay mineral particles provided an ion conducting channel parallel to the electric field in the PEO matrix of low crystallinity.

Thermal properties and liquid crystallinity of side-chain azobenzene copolymer containing pendant polyhedral oligomeric silsequioxanes

Vinylated polyhedral oligomeric silsesquiox- ane (POSS-M) was prepared by the reaction of POSS containing amine groups with acrylic acid. Azobenzene liquid crystalline copolymer (LCP-POSS) was then syn- thesized with 6.0 mol% POSS-M and 94.0 mol% acrylate monomer containing azobenzene liquid crystalline moiety (Azo-M) by free-radical copolymerization. Homopolymer of Azo-M (LCP) was also synthesized under the same conditions. Their thermal properties and liquid crystallinity were characterized by Thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), Wide-angle X-ray diffraction experiments (XRD) and polarized optical micrographs (POM). The results showed that LCP-POSS has higher thermal stability and glass transition tempera- ture than pure LCP due to the incorporation of the rigid cage-like POSS. Especially, LCP-POSS exhibits enantio- tropic smectic and nematic liquid crystalline behaviors, its smectic-nematic transition temperature (TSN) and nematic-isotropic transition temperature (TNI) are higher than those of pure LCP, which may promote and extend its applications on stimuli-responsive materials and devices.

Influence of nucleating agent on the formation and enzymatic degradation of poly(butylene adipate) polymorphic crystals

The effects of nucleating agent multimethyl-benzilidene sorbitol (TM6) on crystallization and morphology of poly(butylene adipate) (PBA) with polymorphic crystal structures were studied by means of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical micrographs (POM). In addition to the heterogeneous nucleation, TM6 changes the formation conditions of PBA polymorphic crystals. The addition of TM6 is favorable for the formation of PBA α-form crystals, resulting in the morphological changes from spherulites to interpenetrated fibrils. The influences of TM6 on enzymatic degradation of PBA were studied in terms of the morphological change and weight loss. The results indicate that the α-form crystals induced by TM6 show much slower degradation rate. This work provides an efficient method to control the polymorphic crystal structure and further to regulate the biodegradation rate of polymer materials through modulating the homogeneous and heterogeneous nucleation modes by adding nucleating agents.

Local liquid crystal alignment on patterned micrograting structures photofabricated by two photon excitation direct laser writing

The authors demonstrate local alignment of nematic liquid crystal through the fabrication of local micrograting structures by curing an ultraviolet curable material via a two-photon excitation laser-lithography process. A local twisted-nematic region was prepared using one rubbed and one fabricated micrograting surface and the resulting cell was observed with a polarizing optical microscope. The polarization optical micrographs of the locally fabricated region suggest that liquid crystal molecules align parallel to the grating structure and that local alignment is achieved. We evaluate the anchoring energies of the fabricated microgratings by the torque balance method.

Micro-segregated layer structures generated by liquid crystalline dimers possessing an oligo(ethylene glycol) spacer and two terminal alkyl chains

Liquid crystalline dimers consisting of two rodlike cores, two terminal alkyl chains and an oligo(ethylene glycol) spacer were synthesized. Their phase behaviors and structures were investigated by polarized optical micrograph (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). These liquid crystalline dimers generated unconventional smectic layer structures in which the alkyl and oligo(ethylene glycol) chains micro-segregated in the chain layers.

Single-crystalline polytetrafluoroethylene-like nanotubes prepared from atmospheric plasma discharge

Atmospheric plasma polymerization of perfluorohexane was investigated in this letter. A large quantity of single-crystalline polytetrafluoroethylene (PTFE)-like nanotubes were formed on a simultaneously deposited film at room temperature without any catalysts or templates. The outer diameter of the nanotubes varied from 60 to 1200 nm with a maximum aspect ratio up to 100:1. Transmission electron microscopy and x-ray diffraction results indicated a single crystal close-packed hexagonal (cph) structure in the nanotubes. Polarization optical micrographs of the nanotubes showed their thermal stability comparable to PTFE. It is suggested that the plasma filament played a key role in the rapid formation of the nanotubes. This atmospheric plasma discharge synthesis can serve as a common method for nanofabrication of many other single-crystalline polymer systems.

NONISOTHERMAL CRYSTALLIZATION KINETICS AND MECHANICAL PROPERTIES OF PP/NANO-SiO2 COMPOSITES

The nonisothermal crystallization kinetics of polypropylene (PP)/nano-SiO2 composites was studied by means of differential scanning calorimetry (DSC). The modified Avrami theories by Jeziorny, Ozawa, and Mo were used to analyze the data of DSC. The results showed that both the Jeziorny and Mo methods could describe this system very well, but the Ozawa analysis failed. The activation energy was evaluated by the Kissinger method. It was found that the crystallization activation energy of PP was higher than that of PP/nano-SiO2 composites. The determined results of mechanical properties showed that the addition of nano-SiO2 increased the mechanical properties of the PP. Micrographs of Polarized optical micrograph (POM) further demonstrated that nano-SiO2 could toughen the PP.

Crystallization and morphology of starch-g-poly(1,4-dioxan-2-one) copolymers

The thermal transition, crystallization and spherulitic morphology of starch-g-poly(1,4-dioxan-2-one) copolymers were studied by means of differential scanning calorimetry (DSC) and polarized optical micrographs (PM). It is found that the graft structures of copolymers have obvious effects on the thermal and crystallization behaviors. Because there were more defect sites in the crystalline phase originating from the short grafted chains of poly(1,4-dioxan-2-one) (PPDO), the crystal structure of the copolymers was much less perfect than that of PPDO. PM revealed that the spherulitic morphology of the graft copolymers depended on graft structures and crystallization temperatures. From the single polarized micrograph of the graft copolymers it was observed clearly that the starch segments acted as nucleation sites. The Avrami equation was used to analyze the overall isothermal crystallization of the graft copolymers. Avrami exponents were almost constant at crystallization temperatures Tc ranging from 45 to 60°C. Both the PM observation and the DSC investigation (crystallization rate constant, K values) indicated that the graft copolymers crystallize faster than pure PPDO, especially at higher crystallization temperatures.

Morphology and electro‐optic responses of poly(methyl methacrylate)/nematic liquid crystal composite films: Effect of the polymer molecular weight

AbstractThe director configuration, state of liquid crystal (LC) phase aggregation, and the electooptic properties of thin polymer films of poly(methyl methacrylate) (PMMA) containing nematic liquid crystal have been studied. Measurements included scanning electron micrograph (SEM), polarized optical micrographs (POM), and transmittance response of the film with the applied electric AC voltage and frequency. Two types of PMMA with significantly different molecular weight (Mw) were used, and the effects of polymer molecular weight on morphology and electro‐optic properties of the composite films were examined. © 1995 John Wiley & Sons, Inc.