Liquid Crystalline Textures Research Articles

Synthesis of liquid crystalline polymers from polyethylene terephthalate and 4‐acetoxybenzoic acid: A kinetic study

AbstractLiquid crystalline polymers (LCPs) have been synthesized from polyethylene terephthalate (PET) and 4‐acetoxybenzoic acid (OB) through melt step‐growth polymerization. The presence of liquid crystalline texture is first examined using optical polarizing microscopy. The thermal durability of the developed systems is studied through thermogravimetric analysis. The kinetics of the polymerization processes is analyzed. The effectiveness of three catalysts commonly used in polyesterification is investigated. The effect of reaction temperature is also examined. The progress of polycondensation reactions over time takes a nonlinear behavior of slight sigmoidal shape, irrespective of whether or not the reaction is catalyzed. Simple second and third order equations, along with a nonlinear model, are used to determine the kinetic parameters characterizing these reactions. The rate of reaction is enhanced when the reaction temperature is increased. Overall, second‐order kinetics well describes the polymerization reactions when the data set is divided into two regions. Antimony trioxide induces a more visible enhancement to the rate of reaction, compared to zinc acetate and sodium acetate. The presence of a catalyst generally increases the reaction activation energy. This indicates that entropy factors outweigh the increase in activation energy and drive the catalyzed reactions to completion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis of Thermotropic Polyurethanes Containing Biphenylnate and Imide Units and their Mesophase Behavior

A series of novel liquid crystal polyurethanes containing biphenylnate and imide units were synthesized through the polyaddition reaction of 4,4′-Bis-(2-hydroxyhexoxy)biphenyl (BP2), 2,4-toluenediisocyanate (2,4-TDI) with N,N′-bis(2-hydroxyhexyl)-dicarboxyimide (BHDI) by altering the molar ratio of BP2 and BHDI. The effects of structure difference molar ratio between BP2 and BHDI on the liquid crystalline behavior and thermal stability were studied. Results showed that all of the polyurethane polymers exhibited thermotropic nematic liquid crystalline textures in the range of 160~190°C. The melting temperatures (Tm) and the thermal stability increased with increasing BHDI content.

In‐Plane Liquid Crystalline Texture of High‐Performance Thienothiophene Copolymer Thin Films

AbstractPoly(2,5‐Bis(3‐alkylthiophen‐2‐yl)thieno[3,2‐b]thiophenes (pBTTTs) are a new class of solution‐processable polymer semiconductors with high charge carrier mobilities that rival amorphous silicon. This exceptional performance is thought to originate in the microstructure of pBTTT films, which exhibit high crystallinity and a surface topography of wide terraces. However, the true lateral grain size has not been determined, despite the critical impact grain boundaries can have on the charge transport of polymer semiconductors. Here a strategy for determining the lateral grain structure of pBTTT using dark‐field transmission electron microscopy (DF‐TEM) and subsequent image analysis is presented. For the first time, it is revealed that the in‐plain pBTTT crystal orientation varies smoothly across a length scale significantly less than one micrometer (e.g., with only small angles between adjacent diffracting regions). The pBTTT polymers thus exhibit an in‐plane liquid crystalline texture. This microstructure is different from what has been reported for small molecule semiconductors or polymer semiconductors such as poly(3‐hexyl thiophene) (P3HT). Even though films processed differently exhibit different apparent domain sizes, they exhibit similar charge carrier hopping activation energies because they possess similar low densities of abrupt grain boundaries.

Supramolecular Liquid Crystalline π-Conjugates: The Role of Aromatic π-Stacking and van der Waals Forces on the Molecular Self-Assembly of Oligophenylenevinylenes

Here, we report a unique design strategy to trace the role of aromatic π-stacking and van der Waals interactions on the molecular self-organization of π-conjugated building blocks in a single system. A new series of bulky oligophenylenevinylenes (OPVs) bearing a tricyclodecanemethylene (TCD) unit in the aromatic π-core with flexible long methylene chains (n = 0-12 and 16) in the longitudinal position were designed and synthesized. The OPVs were found to be liquid crystalline, and their enthalpies of phase transitions (also entropies) showed odd-even oscillation with respect to the number of carbon atoms in alkyl chains. OPVs with an even number of methylene units in the side chains showed higher enthalpies with respect to their highly packed solid structures compared to odd-numbered ones. Polarized light microscopic analysis confirmed the formation of cholesteric liquid crystalline (LC) phases of fan shaped textures with focal conics in OPVs with 5 ≤ n ≤ 9. OPVs with longer alkyl chains (OPV-10 to OPV-12) produced a birefringence pattern consisting of dark and bright ring-banded suprastructures. The melting temperature followed a sigmoidal trend, indicating the transformation of molecular self-organization in OPVs from solid to ring-banded suprastructures via cholesteric LC intermediates. At longer alkyl chain lengths, the van der Waals interactions among the alkyl chains became predominant and translated the mesogenic effect across the lamellae; as a consequence, the lamellae underwent twisted self-organization along the radial growth direction of the spherulites to produce bright and dark bands. Scanning electron microscope (SEM) analysis of cholesteric LC and ring-banded textures strongly supported the existence of twisted lamellae in the OPVs with ring-banded textures. Variable temperature X-ray diffraction analysis confirmed the reversibility of the molecular self-organization in the solid state and also showed the existence of the higher ordered lamellar structure in ring-banded OPVs. Photophysical characterizations such as excitation, emission, and time resolved fluorescence decay measurements were employed to trace molecular self-organization in their liquid crystalline phases. The emission spectra of the OPV samples showed odd-even oscillation in their emission wavelengths with respect to the length of alkyl chains. Highly packed even-OPVs showed more blue shift compared to that of less crystalline odd-OPVs. Time dependent fluorescence decay of OPVs followed a biexponential fit, and their lifetimes (τ(1) and τ(2) values) revealed that the decay is faster for odd-OPVs compared to even-OPVs. Among all the OPVs, the τ(2) values for OPV-8 and OPV-12 were found to be much higher, indicating their high luminescent characteristics. In a nut shell, bulky liquid crystalline OPV chromophores were cleverly utilized, for the first time, to probe the aromatic π-stacking versus van der Waals interactions on the molecular self-organization of π-conjugated system.

Synthesis and Properties of Thermotropic Liquid Crystalline Polyesters with Flexible Polymethylene Spacer

Polymethylene bis(p-hydroxybenzoates) were prepared from methyl p-hydroxybenzoate and different diols by melted transesterification reaction. Three liquid crystalline polyesters were synthesized from terephthaloyl dichloride and polymethylene bis(p-hydroxybenzoates). Its structure, morphology and properties were characterized by Ubbelohde viscometer, Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), polarized optical microscopy (POM) with a hot stage, and wide-angle X-ray diffraction (WAXD). Results indicated that the intrinsic viscosities were between 0.088 and 0.210 dL/g. Optical microscopy showed that the TLCP has a highly threaded liquid crystalline texture and a high birefringent schlieren texture character of nematic phase and has wider mesophase temperature ranges for all polyesters. DSC analysis were found that the melting point (Tm), isotropic temperature (Ti) of TLCPs decreased and the temperature range of the liquid crystalline phase became wider with increased number of methylene spacers in the polyester. The WAXD results showed that TLCPs owned two strong diffraction peaks at 2θ near 19° and 23°.

Synthesis and Characterization of Thermotropic Liquid Crystalline Polyesters/Glass Fiber by <i>In Situ</i> Process

Liquid crystalline polyesters containing central biphenylene moiety in the mesogenic unit with ester linkages to the different lengths of flexible spacers were synthesized using melt polycondensation reaction. Glass fiber, as a reinforce, was meltpolymerized with 4-acetoxybenzoic(ABA),4,4＇-diacetoxybiphenyl and terephthalic acid(TA) to make TLCPs with a good mechanical properties. All the obtained compounds were characterized by conventional spectroscopic methods. The thermal behavior of the polymers has been characterized using polarized optical microscopy and differential scanning calorimetry. The effect of monomer structure and mechanical properties has been investigated on the prepared polyesters and is also compared with that of the analogous polyester by other processing mode. Optical microscopy showed a highly threaded liquid crystalline texture to a high birefringent Schlierene texture characteristic of the nematic phase for all polyesters. DSC experiments were also found in accord with mesophase formation. The melting points of polymers having a central 4,4’-biphenyldicarboxylate residue have two broad endotherms. The glass transition temperature values of polyesters are not effect by the glass fiber. According to the SEM result showed that the composite had strong fiber-matrix adhesion. From the mechanical test result, it showed that TLCP are reinforced by rigid fiber further improvement of properties depending on fiber content, fiber fabric construction, fiber type. The mechanical properties of GF/TLCP had been improved greatly as the content of glass fiber was increased,but GF/TLCP mechanical properties do not improve remarkably as glass fiber content more than 30wt%.The effect of copolymerization with added glass fiber in synthesis process is compared with that of the anlogous homopolyesters by other processing mode. Our finding shows that the copolymers exhibit reduced technical process and maintained mechanical properties.

The physicochemical properties and chemical composition of trehalose lipids produced by Rhodococcus erythropolis 51T7

This study analyzed the chemical and physical properties of a biosurfactant synthesized by Rhodococcus sp. 51T7. The biosurfactant was a trehalose tetraester (THL) consisting of six components: one major and five minor. The hydrophobic moieties ranged in size from 9 to 11 carbons. The critical micelle concentration (CMC) was 0.037 g L −1 and the interfacial tension against hexadecane was 5 mN m −1. At pH 7.4 the glycolipid CMC/critical aggregation concentration (CAC) was 0.05 g L −1 and at pH 4 it was 0.034 g L −1. A phase diagram revealed effective emulsification with water and paraffin or isopropyl myristate. A composition of 11.3–7.5–81.8 (isopropyl myristate–THL–W) was stable for at least 3 months. The HLB was 11 and the phase behaviour of the glycolipid revealed the formation of lamellar and hexagonal liquid-crystalline textures.

Synthesis and characterization of fluorene‐based rod–coil liquid crystal polymers

AbstractA series of fluorene‐based rod–coil liquid crystal polymers with different lengths of the coil segments on backbones were designed and synthesized by a palladium‐catalyzed Suzuki coupling‐reaction. The thermal stability, the UV–Vis absorption and fluorescence spectra in chloroform solution and thin film, the electrochemical properties, thermal behavior, and morphology of these rod–coil polymers were investigated. The thermal stability of these polymers steadily decreased on increasing the length of the coil segments on the backbone; their optical and electrochemical properties did not exhibit noticeable dependence on the weight fraction of the coil segments. However, the shoulder emission and the full width at the half‐maximum (FWHM) in PL spectra of the films increased, whereas the oxidation onset potentials and the corresponding HOMO energy levels decreased with the increase in the weight fraction of the coil segments, which was assigned to microphase separation and formation of folded chain conformation as the weight fraction of the coil segments increased. These polymers displayed a characteristic liquid crystalline texture. The variation of the weight fraction of the coil segments obviously affected the thermal behavior and morphology of these rod–coil polymers. Copyright © 2008 John Wiley & Sons, Ltd.

Liquid Crystalline Phase Behavior of High Molecular Weight DNA: A Comparative Study of the Influence of Metal Ions of Different Size, Charge and Binding Mode

The ability of Li(+), Na(+), K(+), Rb(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Cu(2+), Cd(2+), Al(3+), V(4+), Hg(2+), Pd(2+), Au(3+), and Pt(4+) to provoke liquid crystalline (LC) phases in high molecular weight DNA was investigated. The alkali and alkaline earth metal ions provoked typical cholesteric/columnar structures, whereas transition metal ions precipitated DNA into solid/translucent gel-like aggregates. Heavy metal ions reduced viscosity of DNA solution, disrupting rigid, rod-like DNA structure necessary for LC textures. Three-layer quantum mechanical-molecular mechanical (QM/MM) studies of Li(+), Na(+), K(+), Mg(2+), and Ca(2+) binding DNA fragment suggested several possible binding modes of these ions to the phosphate groups. The dianion mode of metal binding, involving the phosphate groups of both strands of DNA, allowed for higher DNA binding affinity of the alkaline earth metal ions. These results have implications in understanding the biological role of metal ions and developing DNA-based sensors and nanoelectronic devices.

Lyotropic liquid crystal preconcentrates for the treatment of periodontal disease

The aim of our study was to develop water-free lyotropic liquid crystalline preconcentrates, which consist of oils and surfactants with good physiological tolerance and spontaneously form lyotropic liquid crystalline phase in aqueous environment. In this way these preconcentrates having low viscosity can be injected into the periodontal pocket, where they are transformed into highly viscous liquid crystalline phase, so that the preparation is prevented from flowing out of the pocket due to its great viscosity, while drug release is controlled by the liquid crystalline texture. In order to follow the structure alteration upon water absorption polarization microscopical and rheological examinations were performed. The water absorption mechanism of the samples was examined by the Enslin-method. Metronidazole-benzoate was used as active agent the release of which was characterized via in vitro investigations performed by means of modified Kirby–Bauer disk diffusion method. On the grounds of the results it can be stated that the 4:1 mixture of the investigated surfactants (Cremophor EL, Cremophor RH40) and oil (Miglyol 810) formed lyotopic liquid crystalline phases upon water addition. Polarization microscopic examinations showed that samples with 10–40% water content possessed anisotropic properties. On the basis of water absorption, rheological and drug release studies it can be concluded that the amount of absorbed water and stiffness of lyotropic structure influenced by the chemical entity of the surfactant exerted major effect on the drug release.

Liquid crystalline phases from polymer functionalised semiconducting nanorods

The orientation of semiconducting nanomaterials is a hot topic in optoelectronic applications. Liquid crystallinity offers the potential to orient inorganic anisotropic nanorods, if they can be solubilised sufficiently as realised by polymer functionalisation. In this work we functionalised TiO2, SnO2, ZnO and CdTe nanorods with PMMA, PS and PDEGMEMA (poly(diethylene glycol monomethyl ether) methacrylate) diblock copolymers containing anchor groupsvia grafting-to. The block copolymers were synthesised by RAFT polymerisation (PDI ≈ 1.2) via reactive ester diblock copolymers, which were functionalised later with anchor units polymer-analogously. The surface coverage of the nanorods (determined by TGA) is dependent on the block lengths and ratios and maximal coverage is found for short anchor unit blocks. Stable dispersions are obtained for these hairy rod hybrids and they form liquid crystalline phases at suitable concentrations in organic solvents as well as in oligomeric and polymeric matrices like oligo-PEG, oligo-PS and polymeric PDEGMEMA. Liquid crystalline textures are found in polarised microscopy images. Clearing temperatures were found to be between 60 and 230 °C depending on the length of the nanorods and the organic matrix.

Preparation and Liquid Crystalline Properties of Spherical Cellulose Nanocrystals

A novel kind of spherical cellulose nanocrystal (SCNC) suspension was prepared by hydrolysis of microcrystalline cellulose with a mixture of sulfuric acid and hydrochloric acid under ultrasonic treatment. The mechanism of SCNC formation and the liquid crystalline properties of their suspensions were investigated. A suspension of spherical particles was usually inclined to form crystallization colloids rather than liquid crystals at high concentration. However, a SCNC suspension with high polydispersity (49%) was observed to form the liquid crystalline phase, and the liquid crystalline textures changed with increasing concentration. This observation offers an approach to the liquid crystal formation of highly polydisperse spherical nanoparticles.

Synthesis and characterization of thermotropic liquid crystalline polyesters with biphenyl unit in the main chain

Two new series of liquid crystalline polyesters containing central biphenylene moiety in the mesogenic unit with ester and ether linkages to the different lengths of flexible spacers (series I and II, respectively) were synthesized using melt polycondensation reaction. All the obtained compounds were characterized by conventional spectroscopic methods. The copolymer compositions were obtained from 1H NMR. The thermal behavior of the polymers has been characterized using polarized optical microscopy and differential scanning calorimetry. The effect of monomer structure and methylene spacer length has been investigated on the prepared polyesters and is also compared with that of the analogous polyester having central phenylene unit. Optical microscopy showed a highly threaded liquid crystalline texture to a high birefringent Schlierene texture characteristic of the nematic phase for all polyesters. DSC experiments were also found in accord with mesophase formation. The melting points and isotropization temperature values of series I polymers having a central 4,4′-biphenyldicarboxylate residue were significantly higher than those of the series II having a central 4,4′-biphenol moiety due to different molecular geometry. The glass transition temperature values of series I polyesters are also higher than those for series II because of increased chain rigidity. The effect of copolymerization on liquid crystallinity has been studied on the prepared copolymers from equimolar mixture of monomer with different lengths of spacers (n=4, 6) and it is compared with that of the analogous homopolyesters. Our finding shows that the copolymers exhibit reduced melting point and extended liquid crystalline range.

Biomimetic PAMAM-Poly(Benzyl L-Glutamate) Amphiphiles with Multi- Armed Architecture: Synthesis, Physical Properties and Self-Assembled Nanoparticles

Biomimetic poly(amidoamine)-poly(benzyl L-glutamate) (PAMAM-PBLG) amphiphiles with multi-armed architecture were synthesized by the ring-opening polymerization (ROP) of beta-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) using primary amine-terminated PAMAM dendrimer as the macroinitiator. Both (1)H NMR and (13)C NMR demonstrated that all the primary amines of PAMAM participated in initiating the ROP of BLG-NCA monomer, and the chain length of PBLG can be adjusted linearly by the molar ratio of BLG-NCA monomer to PAMAM. These multi-armed PAMAM-PBLG amphiphiles exhibited both alpha-helix and beta-sheet conformations similar to linear analogues, while their multi-armed architecture could enhance the secondary conformation content of PBLG segments. Meanwhile, the PAMAM-PBLG amphiphiles showed weaker liquid crystalline textures than the linear analogues. Moreover, spherical nanoparticles could be generated by direct injection of these PAMAM-PBLG solutions into distilled water, and their average size (38 - 275 nm) could be adjusted through the multi-armed architecture, the PBLG composition, and the concentration of the amphiphiles. These nanoparticles were stable in aqueous solution for up to 64 days at room temperature and 16 days at 37 degrees C. Consequently, this will provide a convenient method not only to synthesize multi-armed polypeptides amphiphiles, but also to generate biodegradable and biocompatible nanoparticles with adjustable size for drug/gene release.

Synthesis of multi‐block copolymer and its compatibilization to the blends of poly(ether ether ketone) with thermotropic liquid crystalline polymer

AbstractA multiblock copolymer (BCP) containing amorphous poly(aryl ether ketone) (PAEK) and thermotropic liquid crystalline polymer (TLCP) segments was synthesized. The chemical structure and properties of BCP were characterized by fourier‐transform infrared spectrometer (FTIR), differential scanning calorimeter (DSC), gel permeation chromatograms (GPC), thermogravimetry analysis, polar light microscope (PLM), and solubility test respectively. BCP can dissolve in chloroform because of soluble PAEK block bonded with TLCP block, which was insoluble. The peak of the original PAEK oligomer was no more present in the GPC traces of the block copolymer. These facts indicated that polymer synthesized should be copolymers of the two components rather than blends. A single Tg at 138.1°C and broad melting endotherm at 315.7°C can be observed. The liquid crystalline texture of BCP showed uniformity in the view after heat treated for 10 min above its Tm under PLM. Ternary blends of poly(ether ether ketone) (PEEK)/TLCP/BCP were prepared by extrusion and characterized by DSC. DSC results showed that the crystallization temperature of PEEK phase in the blends shifted higher with the addition of TLCP. Wide angle X‐ray diffraction investigations indicated that the crystalline structure of PEEK was not disturbed by blending or compatibilizing. Scanning electron microscope and mechanical tests confirmed the compatibilizing effect of BCP. Reduction in dispersed phase TLCP size was observed when 2 phr by weight of compatibilizer was added to the blend. Measurement of the tensile properties showed increased elongation as well as improved modulus and strength to some extent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Matrix-molecule induced chiral enhancement effect of binary supramolecular liquid crystals

Chiral enhancement effects associated with supramolecular liquid crystalline structures are studied, using a complex of achiral molecules (4,4′-bipyridine, 4Bpy) and chiral cholesteric liquid crystalline molecules (3-cholesteryloxycarbonylpropanoic acid, C4) as the model system. Non-mesogenic achiral molecule 4Bpy is used as the matrix element. The chiral enhancement of the supramolecular liquid crystalline structures can be revealed by circular dichroism (CD) and helical twisting power measurements. It is interesting that CD spectra of the complex exhibited an appreciably enhanced chiral property in comparison with that of the pure chiral cholesteric C4 molecules at room temperature. The helical pitch measurements by the Grandjean–Cano method also confirm the chiral enhancement effect. In addition, polarizing optical microscopy (POM) measurements indicate that the addition of matrix molecules leads to the explicit expression of the chiral liquid crystalline texture, i.e. twisted grain boundary (TGBA*) phase, at the liquid crystal temperature. Differential scanning calorimetry (DSC) and variable-temperature X-ray diffraction measurements further confirm the existence of the TGBA* phase. The binary supramolecular assembly structures are investigated by scanning tunneling microscope (STM) and the formation of hydrogen bonds between the chiral mesogens and the achiral matrix molecules can be directly observed. The variable-temperature Fourier transform infrared (FTIR) results further demonstrate that the hydrogen bonds persist until 168 °C. These results indicate that the introduction of a bifunctional aromatic base such as bipyridine could lead to self-assembled supramolecular architectures with discernible enhancements of chiral properties.

Helical Morphologies of Thermotropic Liquid-Crystalline Chiral Schiff-Based Rod−Coil Amphiphiles

A series of Schiff-based rod−coil molecules possessing thermotropic liquid-crystalline (LC) character have been prepared whereas a sugar-based moiety was introduced to the chain end of the molecules so as to create chiral amphiphiles for self-assembly. The self-assembly of the chiral Schiff-based rod−coil amphiphiles gave rise to a variety of specific LC textures. A banded morphology under polarized light microscopy (PLM) can be observed; the appearance of the banded texture is strongly dependent upon the length of hydrophobic tail that determines the twisting power of self-assembled hierarchical superstructures with helical sense. As a result, the banded spherulites are identified as quaternary helical morphology with a collection of the tertiary chiral structures (i.e., helical twists) so as to give regular extinction in PLM attributed to zero-birefringence effect. Consistent with the observation of helical morphologies, the occurrence of chiral smectic C (SmC*) phase can only be found in samples with enough alkoxyl chain length, suggesting the existence of strong correlation for morphological evolution from molecular level to macroscopic object with the formation of SmC*. A hypothetic model about the bilayer structure within the SmC* structure is thus given to elucidate the morphological evolution. Consequently, the self-assembly of the chiral amphiphiles with thermotropic LC character represents the mechanism for the chirality transfer in different length scales.

Photophysical properties and morphology of fluorene‐alt‐benzene based conjugated polymers

AbstractA series of fluorene‐alt‐benzene based conjugated main chain polymers attached chemically with different lengths of alkyl side chains on phenylene rings were designed and synthesized by a palladium catalyzed Suzuki coupling reaction. The UV‐vis absorption and fluorescence spectra, thermal stability of spectral property, phase transition behavior and morphology of the synthesized polymers were investigated. With increasing the length of the alkyl side chain, the UV and fluorescence spectra exhibit obvious blue shift compared with those of the unsubstituted polymer. The alkyl substitution improves the thermal stability of the spectra due to the steric hindrance of the alkyl side chains and thus the effective separation of the main chain backbones. The phase transition behavior is closely related to the length of alkyl side chains attached on the phenylene rings. The annealed polymer films display characteristic nematic liquid crystalline texture. Transmission electron microscopy (TEM) observations indicate that solvent‐cast thin deposits of all the polymers show typical fibrillar morphology. Copyright © 2006 John Wiley & Sons, Ltd.

P2-064: Long-term cognitive and behavioral response, and liquid crystalline states of brain mitochondrial membrane in estrogen-treated mice exposed to low-dose radiation in utero

Estrogen has been recently shown to play a neuroprotective role apart from popular view of its functions in human reproduction. In our research, we focused on the long–term membrane effects of estrogen on brain mitochondria and correlated these findings with its beneficial effects on cognitive and behavioral skills. Using an in utero radiation model of mice, the liquid crystalline (LC) organization of mitochondrial membrane from 60–day old mice was investigated by analyzing the self–organized LC textures, thermotropic transitions, and measured its lateral mobility. Various behavioral and cognitive tests were done. The organization of brain mitochondrial membranes of adult mice irradiated in utero at 17 dpc exhibited a decrease in unit texture size from 11.2–16.68 μm in control mouse to 5.58–11.12 μm in 1.0 and 1.5 Gy–irradiated mice. The ability of lyotropic LC domains to undergo intermediary phase changes and aggregate into more complex structures, e.g. coarse mosaic and pseudoisotropic textures, was ablated in the fetally–irradiated mice and this was not reversed even with post–natal treatment of 25 μg estradiol s.c. on day 5. Interestingly, estradiol treatment increased mitochondrial membrane fluidity in irradiated mice based on the calculated lateral diffusion coefficients from the quantum ratio, I' (excimer intensity)/I (monomer intensity) with 1–pyrene dodecanoic acid as probe. The effects of estradiol on lateral diffusion are not dependent on the radiation dose used and the sex. The biophysical data is consistent with the cognitive skills and behavioral patterns of the mice. Our results provide new insights on the molecular mechanisms of how estrogen acts in dampening neurodegeneration from a concurrent biophysical and behavioral perspective.

The photophysical properties and morphology of fluorene-alt-benzene based conjugated polymer

A series of fluorene-alt-benzene based conjugated main chain polymers chemically attached with alkyl side chains of different lengths on phenylene rings were designed and synthesized by a palladium catalyzed Suzuki coupling reaction. The UV-vis absorption and fluorescence spectra, thermal stability of spectral property, phase transition behavior and morphology of the synthesized polymers were investigated. With increasing the length of the alkyl side chain, the UV and fluorescence spectra exhibit an obvious blue shift compared with those of the unsubstituted polymer. The alkyl substitution improves the thermal spectral stability of the polymers due to the steric hindrance of the alkyl side chains, thus leading to efficient separation of the main chain backbones. The phase transition behavior is closely related to the length of the alkyl side chains attached on the phenylene rings. The annealed films of the polymers display characteristic nematic liquid crystalline texture. TEM observations indicate that solvent-cast thin deposits of all the polymers show typical fibrillar morphology.