Mesomorphic Phase Research Articles

Impact of BaTiO(3) nanoparticles on pretransitional effects in liquid crystalline dodecylcyanobiphenyl.

The pretransitional behavior of dodecylcyanobiphenyl (12CB) (isotropic-smectic-A-solid mesomorphism) with d=50nmBaTiO(3) nanoparticles (NPs) linked to the cubic phase was monitored via temperature studies of dielectric constant. Tests were carried out in the isotropic, liquid crystal mesomorphic, and solid phases. For each phase transition the same value of the critical exponent α∼0.5 was obtained, including nanocolloids. All phase transitions show the weakly discontinuous nature. The temperature metric of the discontinuity ΔT notably decreases when adding nanoparticles. The addition of nanoparticles first decreases the dielectric constant by approximately 50% in comparison with pure 12CB, but already for a concentration ∼x=0.4% NP an increase over 50% takes place. It is notable that for the latter concentration unique hallmarks of the pretransitional effect emerge also for the solid-mesophase transition. All these indicate the important impact of nanoparticles on multimolecular mesoscale fluctuations.

Mesomorphism dependence on molecular rigidity and flexibility

ABSTRACTA novel homologous series of mesogens was synthesized and studied with a view to understanding and establishing the relations between molecular structure and liquid crystal properties. Eleven members of the series were synthesized. Mesogenic behavior commences from the C6 member and continues up to the C14 member. The rest of the members, C1 to C5 and C16, are non-mesogenic. Mesogenic homologues (C6 to C14) are enantiotropically nematogenic. Textures of nematic phase are threaded or Schlieren. Transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. Analytical and structural data confirm the molecular structures of homologues. Thermal stability for nematic phase is 198.0°C. Mesomorphic phase length ranges from 11.0°C to 50.0°C. Cr-I/N and N-I transition curves of a phase diagram behave in normal manner from C1 to C12 members, and higher members C14 and C16 deviated from normal behavior. Mesogenic properties of present novel ester series are compared with the structurally similar series. Odd-even effect is missing for the N-I transition curve. Thus, the present series is partly nematogenic without exhibition of smectic property whose transition temperatures vary between 153°C and 210°C.

Mesomorphism dependence on heterocyclic end group

ABSTRACTAn ester homologous series containing a heterocyclic end group was synthesized and studied with a view to understanding and establishing the effect of molecular structure on liquid crystal behavior. The novel series consists of 13 homologues. All members of the series are enantiotropically smectogenic without exhibition of nematogenic character. The textures of smectogenic homologues are of the type smectic A or C. The transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. The Sm-I transition curve in a phase diagram behaves partly in an abnormal manner with the exhibition of an odd-even effect. The average thermal stability for smectic is 141.45°C and the mesomorphic phase length ranges from 8.1 °C to 30.3 °C. Analytical and spectral data confirm the molecular structures. The liquid crystal properties of present series are compared with the structurally similar known homologous series.

Random Copolymers from Polyamide 11 and Polyamide 12 by Reactive Extrusion: Synthesis, Eutectic Phase Behavior, and Polymorphism

Random copolymers from polyamide 11 (PA11) and polyamide 12 (PA12) were obtained from the parent homopolymers by transamidation reactions during high-temperature reactive extrusion. Concomitantly, the product molecular weight increased by postcondensation reactions. With both species being crystallizable, eutectic phase behavior was observed and explained in terms of the Flory theory for random copolymer melting. Close to the eutectic composition, both species crystallize in a competitive mode, which induces mesomorphic phase formation. Although the crystal centers most likely remain PA11 or PA12 pure, it is argued that foreign comonomer units might be tolerated at the crystal borders, at least for PA11 crystals. To understand the copolymer crystallization behavior in general, large amounts of rigid amorphous material need to be created alongside the crystallites. Because of their low melting point and since the crystallinity and mechanical performance typical of the parent homopolymers are preserved, ran...

Mesomorphism dependence on terminal end groups

ABSTRACTA novel homologous series of liquid crystals (LC) 4-(4′-n-alkoxy cinnamoyloxy)-4′′-bromobenzylbenzoate was synthesized and studied with a view to understanding and establishing the relation between LC properties and the molecular structure. The novel series comprises 11 members, and all the members exhibit mesomorphism as enantiotropic smectic. None of the homologues are nematogenic, even in the monotropic condition. Transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. The textures of smectic phase are of the type A or C. The transition curves Sm-I and Cr-Sm behave in a normal manner in the phase diagram. An odd-even effect is exhibited by the Sm-I transition curve. Thermal stability for smectic is 102.6°C. Mesomorphism commences from the very first member of the series. The series is entirely smectogenic and of middle-order melting type whose mesomorphic phase length ranges from 7.4°C to 60.9°. Analytical and spectral data confirmed the molecular structures of homologues. The mesomorphic properties of the present series are compared with structurally similar homologous series.

Recent development on the theory of polymer crystallization

In this paper, the history and the recent development of polymer crystallization have been reviewed briefly. After introducing the conventional Hoffman-Lauritzen theory, the recent new experimental results, especially on X-ray scattering, have been summarized. Some new models of crystallization have been reviewed, such as Strobl's mesomorphic phase model, Olmsted's spinodal-assisted crystallization theory, and Muthukumar's molecular modeling of polymer crystallization.

Sorption and selective chromatographic properties of isomer-selective composite sorbent based on a eutectic mixture of nematic liquid crystals and perbenzoylated β-cyclodextrin

Mesomorphic, sorption, and selective properties of a three-component sorbent based on a mixture of nematic (N) liquid crystals of 4-methoxy-4′-ethoxyazoxybenzene (MEAB) and 4,4′-diethoxyazoxybenzene (azoxyphenetol, AOP) of an eutectic composition and heptakis-(2,3,6-tri-O-benzoyl)-β-cyclodextrin (Bz-β-CD) are studied. For 30 organic compounds of different classes with linear and cyclic molecular structures, including optical isomers of limonene, pinene, camphene, and butanediol-2,3, thermodynamic functions are determined for their gas-phase sorption using a three-component MEAB-AOP-Bz-β- CD sorbent (62: 28: 10 wt %). It is found that the investigated sorbent possesses high structural selectivity (αp/m = 1.128–1.059, 100–130°C, N) and moderate enantioselectivity (1.07–1.02) within a broad temperature range (95–170°C) including both mesomorphic and isotropic phases of the sorbent. It is shown that the enantioselectivity of the sorbent is apparent under conditions of both increasing retention when a chiral Bz-β-CD additive is introduced into the MEAB–AOP system (limonenes, pinenes, camphenes) and decreasing retention (butanediols-2,3).

Nanostructure and Transport Properties of Proton Conducting Self-Assembled Perfluorinated Surfactants: A Bottom-Up Approach toward PFSA Fuel Cell Membranes

A comprehensive study of commercially available and newly synthesized proton conducting perfluorinated sulfonic acid (PFSA) surfactants and polymeric systems is reported, specially designed in a bottom-up search to improve the basic understanding of PFSA polymers used as benchmark electrolytes in fuel cells. Hydration-dependent mesomorphous phases are formed by the self-assembly of these molecules in water. The impact of the hydrophobic chain length, the density of charge, the molecular architecture on the nanostructure, and the dynamics of confined water were studied by combining small-angle X-ray scattering, quasielastic neutron scattering, and pulsed-field gradient NMR. We introduce a hydration-dependent structural parameter, dw (mean size of water domains), that allows to establish the structure–transport relationship in PFSA materials. This multiscale study reveals that (i) the dynamical behavior of confined protons and water molecules are rather insensitive to the topology of the host matrix and (ii...

Study of Liquid Crystal Behavior and Dependence on Additional Central Bridge of Ester Homologous Series

A novel homologous series of esters was synthesized and studied with a view to understanding and establishing the effects of molecular structure on liquid crystal (LC) properties. The series consists of 11 members, and all exhibit enantiotropically the smectogenic mesophase. The nematogenic mesophase is totally absent. The textures of smectic phases are of the type A or C. The Sm-I transition curve of the phase diagram behaves in abnormal manner. The average Sm-I thermal stability is 124.53°C with mesomorphic phase length between 6.5°C and 52.3°C and is of a middle-ordered melting type. LC properties of the novel series are compared with a structurally similar other known series. Analytical and spectral data of the homologous match the molecular structure.

Synthesis and Study of Molecular Structure and Its Relation to Liquid Crystal Behavior in a Novel Azoester Series

A novel liquid crystal (LC) homologous series of 12 azoesters was synthesized and evaluated, and nine members of the series exhibited enantiotropically or monotropically nematogenic LC behavior. Smectogenic character is totally absent. The methoxy, tetradecyloxy, and hexadecyloxy homologues are non-liquid crystals (NLC). Textures of nematic phase are threaded, or schlieren. The solid–isotropic/nematic and N-I or vice versa transition curves behave in normal manner. The N-I transition curve exhibits an odd-even effect. The average thermal stability for nematic is 113.25°C. Mesomorphic phase length ranges from 21 to 35°C. The textures of nematic mesophase and transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. Analytical and spectral data confirm the molecular structures of homologues. The LC behavior of the present novel series is compared with a structurally similar known series. The present series is predominantly nematogenic with the absence of smectic property, and is of a middle-ordered melting type.

Mesomorphism Dependence on Terminal and Lateral Polar Groups in the Nonlinear Novel Azoester Series

The synthesis of a novel azoester homologous series was carried out with a view to understanding and establishing the effect of molecular structure on liquid crystal (LC) behavior of a substance. The novel series consists of eleven homologs, and all are enantiotropically nematogenic without exhibition of any smectic property. Transition and melting temperatures, textures of LC were determined by an optical polarizing microscope equipped with a heating stage. The textures of the nematic phase are threaded or Schlieren. Transition curves of a phase diagram behave in normal manner. The nematic-isotropic transition curve exhibits an odd-even effect. Analytical and spectral data support and confirm the structures of the homologues. Average thermal stability for the nematic is 137.2°C. The mesomorphic phase length ranges from 15°C to 50°C. LC behavior of the novel series is compared with a structurally similar known homologous series. The novel azoester homologous series is entirely nematogenic without exhibition of smectogenic character and of a middle-ordered melting type.

Simultaneous Synchrotron WAXD and Fast Scanning (Chip) Calorimetry: On the (Isothermal) Crystallization of HDPE and PA11 at High Supercoolings and Cooling Rates up to 200 °C s(-1).

An experimental setup, making use of a Flash DSC 1 prototype, is presented in which materials can be studied simultaneously by fast scanning calorimetry (FSC) and synchrotron wide angle X-ray diffraction (WAXD). Accumulation of multiple, identical measurements results in high quality, millisecond WAXD patterns. Patterns at every degree during the crystallization and melting of high density polyethylene at FSC typical scanning rates from 20 up to 200 °C s(-1) are discussed in terms of the temperature and scanning rate dependent material crystallinities and crystal densities. Interestingly, the combined approach reveals FSC thermal lag issues, for which can be corrected. For polyamide 11, isothermal solidification at high supercooling yields a mesomorphic phase in less than a second, whereas at very low supercooling crystals are obtained. At intermediate supercooling, mixtures of mesomorphic and crystalline material are generated at a ratio proportional to the supercooling. This ratio is constant over the isothermal solidification time.

Lyotropic model membrane structures of hydrated DPPC: DSC and small-angle X-ray scattering studies of phase transitions in the presence of membranotropic agents

Multibilayer structures of hydrated phospholipids, often considered as model biological membranes, are, from the physical viewpoint, lyotropic liquid crystalline systems undergoing temperature-induced mesomorphic phase transitions. Effects of silver nitrate and urocanic acid on lyotropic phase states of hydrated L-α-dipalmitoylphosphatidylcholine (DPPC) have been studied by small-angle X-ray scattering and differential scanning calorimetry (DSC). Both methods show increase of the main phase-transition temperature (Tm) of hydrated DPPC upon introduction of AgNO3 or urocanic acid, decrease of pre-transition temperature (Tp) in the presence of urocanic acid and its increase in the presence of AgNO3. Thus, urocanic acid widened the ripple-phase temperature region. Silver nitrate caused the appearance of an additional high-temperature peak on DSC thermograms, evidencing phase separation in the system. Both agents caused minor effects on DPPC lipid bilayer repeat distance (D) in gel phase, but resulted in noticeable increase of D in the liquid crystal phase with temperature as compared to undoped DPPC structures.

Mesomorphic and luminescence properties of side chain cholesteric liquid crystalline polymers containing Eu(III) and Tb(III) ions

Luminescent cholesteric liquid crystalline polymers consisting of the lanthanide ions covalently attached to cholesteric polysiloxanes are prepared. Cholesteric liquid crystalline monomer and 4-(allyloxy)benzoic acid grafted to poly(methylhydrogeno)siloxane is used as one of the precursors for the preparation of the lanthanide-containing cholesteric liquid crystalline polymers. The chemical structures of the monomers are characterised by Fourier transform infrared, 1H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing <3 mol% of the lanthanide ions reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. The introductions of the lanthanide ions do not change the liquid crystalline state of polymer systems; on the contrary, the polymers are enabled with the significant luminescent properties. With the lanthanide ions contents ranging between 1 and 3 mol%, luminescent intensity and luminescent lifetimes of polymers gradually increased. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase.

Dependence of Liquid Crystalline Behaviors on Molecular Flexibility

A novel homologous series of thermotropic liquid crystal (LC) has been synthesized with a view to understand and establish the effect of molecular structure on liquid crystal behaviors of a series. The present LC series consist of twelve homologues (C1 to C16); whose mesomorphic properties commence from octyloxy (C8) homologue of a series. C8, C10 and C12 members of a series are monotropic smectic and C14, C16 members are enantiotropically smectogenic. C1 to C7 homologues are nonmesomorphic. Nematogenic property is totally absent. Transition and melting temperatures are determined by an optical polarizing microscopy equipped with a heating stage. Textures of smectic mesophases are focal conic three or two dimensional networking of the type A or C. Cr-I/Sm and Sm-I or I-Sm transition curves behaved in normal manner. Analytical and spectral data confirms the molecular structures of homologues. Thermal stability of smectogenic mesophase is 100.6 oC and mesomorphic phase length is very short (12.9 °C to 15.3 oC). LC properties of a present novel series are compared with the structurally similar homologous series. Present series is partly smectogenic and partly non mesomorphic with poor degree of mesomorphism and middle ordered melting type without exhibition of nematogenic behavior.

Advanced Vibrational Microspectroscopic Study of Conformational Changes within a Craze in Poly(ethylene terephthalate)

Crazes constitute one of the most common failure mechanisms in polymers. They act as fracture precursors, severely degrading the mechanical properties of the material. Thus, a deep understanding of the chain rearrangement occurring inside crazes is of utmost fundamental and practical importance. We have employed synchrotron infrared microspectroscopy (SIRMS) and Raman microspectroscopy to investigate the conformational changes inside micron-sized crazes in poly(ethylene terephthalate), PET. A promotion of the full-extended chain conformational structure at the expense of mainly the trans amorphous mesomorphic phase along with an increase in crystallinity of around 4% has been found. These results differ from what we observed across the deformation neck during PET cold drawing, where no promotion of the all-trans crystalline conformation occurred for slow drawing speeds at temperatures well below the glass transition. Our results show the tremendous capabilities of advanced vibrational microspectroscopy te...

Nonlamellar Phases in Cationic Phospholipids, Relevance to Drug and Gene Delivery.

Lipid aggregates have been used as drug carriers for several decades. Recently, nonlamellar liquid crystalline lipid systems have attracted attention as possible drug-delivery vehicles because of their unique nanostructure and physicochemical properties. Here we summarize data on the nonlamellar phase-forming propensity of the cationic phosphatidylcholines (cationic PCs). The class of cationic PCs has been specifically designed and explored for the purpose of nonviral gene delivery. These lipids were found to comprise an attractive cationic lipid class because they are biodegradable, have low toxicities, and in a number of cases, display high transfection activity. Lipids of this class form a variety of polymorphic and mesomorphic phases-lamellar and nonlamellar, depending on the structure of their hydrocarbon chains and especially on the third hydrocarbon chain used to alkylate the PC phosphate group and convert the zwitterionic PC headgroup into a cation. Here we characterize the phase behavior and transfection activity of eight cationic PCs that have been identified as forming nonlamellar phases-inverted hexagonal and cubic. We then demonstrate that those cationic PCs that also form nonlamellar lipoplexes are notably less efficient gene nanocarriers in comparison with the cationic PCs forming lamellar phase lipoplexes.

Dependence of Liquid Crystalline Behaviors on Molecular Flexibility

A novel homologous series of thermotropic liquid crystal (LC) has been synthesized with a view to understand and establish the effect of molecular structure on liquid crystal behaviors of a series. The present LC series consist of twelve homologues (C1 to C16); whose mesomorphic properties commence from octyloxy (C8) homologue of a series. C8, C10 and C12 members of a series are monotropic smectic and C14, C16 members are enantiotropically smectogenic. C1 to C7 homologues are nonmesomorphic. Nematogenic property is totally absent. Transition and melting temperatures are determined by an optical polarizing microscopy equipped with a heating stage. Textures of smectic mesophases are focal conic three or two dimensional networking of the type A or C. Cr-I/Sm and Sm-I or I-Sm transition curves behaved in normal manner. Analytical and spectral data confirms the molecular structures of homologues. Thermal stability of smectogenic mesophase is 100.6 oC and mesomorphic phase length is very short (12.9 °C to 15.3 oC). LC properties of a present novel series are compared with the structurally similar homologous series. Present series is partly smectogenic and partly non mesomorphic with poor degree of mesomorphism and middle ordered melting type without exhibition of nematogenic behavior.

A Comparative Study of Mesomorphism in Symmetric and Nonsymmetric Dimers

A homologous series consisting of 12 homologue symmetrical dimers, viz., bis(4-n-alkoxy benzoyloxy) 2,2-diphenyl propanes was synthesized, studied, and evaluated to establish the relation between molecular structure and mesomorphic properties on comparative basis with nonsymmectric dimers. The methoxy to pentyloxy homologue dimers, the novel symmetric series, are nonmesogenic. Mesomorphism commences from the hexyloxy homologue as smectic and nematic. The hexyloxy to decyloxy dimers possess smectogenic character with nematogenic character and the dodecyloxy to hexadecyloxy homologue dimers exhibit nematogenic character without the exhibition of smectogenic character. All the mesogenic homologues are enantiotropic mesomorphs. The smectic and nematic thermal stability of series is 129.0°C and 147.7°C, respectively, and mesomorphic phase length varies between 18°C for the hexadecyloxy homologue and 56°C for the heptyloxy homologue.

Determination of Local Packing Structure of Mesomorphic Form of Isotactic Polypropylene by Solid-State NMR.

Understanding the local packing structures of a disordered mesomorphic phase is a challenging issue in polymer characterization. In this work, 13C-13C through-space interactions, as well as a molecular dynamics analysis based on the reorientation of chemical shift anisotropy (CSA), were proposed for the evaluation of the local packing structure of the mesomorphic form of isotactic polypropylene (iPP). 13C-13C double quantum (DQ) buildup curves of 13C 15% CH3 selectively labeled iPP and spin-dynamics simulations demonstrated that the local packing structures in the mesomorphic form were very similar to the packing in the β phase. Moreover, centerband only detection of exchange (CODEX) NMR proved that the correlation time ⟨τc⟩ of the overall stem dynamics in the mesomorphic form followed the same Arrhenius line observed for the β phase, but it deviated from that for the α phase. Based on both structural and dynamic results, it was concluded that the local packing structure in the mesomorphic form was exceedingly close or the same as that of the β phase.