Phases In Binary Mixtures Research Articles

Sequential Epitaxial Organization of Poly(9,9-di-n-octyl-2,7-fluorene) in an Eutectic System

The phase diagram of a binary eutectic system of poly(9,9-di-n-octyl-2,7-fluorene) (PFO) and hexamethylbenzene (HMB) has been established via onset melting temperatures. Upon homogeneous mixing, the growth of PFO nematic phase in binary mixtures exhibits both lyotropic and thermotropic features. During cooling, a smectic phase of PFO developed epitaxially on the surface of prior-developed HMB crystals, establishing layer stacking via the packing of side chains. Upon the annealing at 120 °C, further epitaxial organization of PFO smectic packing on HMB crystalline substrate results in the growth of β crystalline. Both smectic and β phases of PFO yield characteristic ultraviolet (UV) absorption at 434 nm wavelength and photoluminescence at the wavelength of 441 nm. While HMB crystals were sublimated prior to the annealing treatment, α crystalline form developed instead through the transformation of smectic packing. The UV absorption and fluorescence of α form are relatively shorter wavelengths. As attributing the rise of energy bandgaps to the effect of backbone conformation, organization of less coplanar backbones within α crystalline form is proposed as a result of the lack of epitaxial effect. After the growth of smectic phase via the monotropic behavior of PFO in eutectic mixture, the following routes of phase transformation upon annealing hence unveiled the growth mechanisms of both α and β crystalline forms of PFO.

Degeneracy lifting due to thermal fluctuations around the frustration point between anticlinic antiferroelectric SmCA*and synclinic ferroelectric SmC*

In the binary mixture phase diagram of MC881 and MC452, the borderline between anticlinic antiferroelectric SmC(A)(*) and synclinic ferroelectric SmC(*) becomes apparently parallel to the temperature ordinate axis at the critical concentration r(c). The free energy difference between SmC(A)(*) and SmC^{*} is extremely small in a wide temperature range near r(c). In such circumstances, by observing Bragg reflection spectra due to the director helical structure and electric-field-induced birefringence, we have observed the continuous change from SmC(A)(*) to SmC(*) for r</~r(c) and the gradual growth of the full-pitch band over 5 °C or more in the apparent SmC(*) temperature region for r>/~r(c). These intriguing phenomena have been explained, successfully at least in the high-temperature region, by a thermal equilibrium between the synclinic and anticlinic orderings and the resulting Boltzmann distribution for the ratio between them; the thermal equilibrium is considered to be attained in a nonuniform defect-assisted way through solitary waves moving around dynamically. We have also discussed qualitatively an important role played by the effective long-range interlayer interactions in the low-temperature region.

Induced Reentrant Smectic-A Phase in Binary Mixtures of Liquid Crystals

We report the results of our studies on the optical and thermal properties of the mixture of cholesteryl chloride (ChCl) and sodium dodecyl sulphate/water (SDS/water), which exhibits very interesting liquid crystalline mesophases, such as cholesteric (N∗) phase and induced reentrant smectic-A phase, sequentially when the specimen is cooled from its isotropic liquid phase. Different liquid crystalline phases observed in the mixture were studied using DSC, X-ray, and optical microscopic techniques. The pitch of the cholesteric phase and the temperature variation of optical anisotropy have also been discussed.

Research on the Thermo Physical Properties of Lauric Acid-Capric Acid Binary Mixture Phase Change Materials

Lauric acid(LA) and capric acid(CA) were mixed into binary mixture, whose melting temperature was predicted with Schroder’s equation and tested in step cooling curve method. Then latent heat was tested by DSC, and T-history method was used to test thermal conductivity of binary mixtures, heating and cooling characteristics were studied through expanded perlite(EP) adsorption of binary mixtures. Results show that Schroder’s equation can be used to predict melting temperature of fatty acid, and binary mixture prepared of 6:4 molar ratio has a high latent heat and its temperature is within a range that meets indoor comfort temperature. Thermal conductivity and the heating and cooling characteristics of the mixtures reveals that the thermal conductivity of fatty acid phase change material(PCM) is low, which restricts its latent heat release rate.

Molecular determinants for the line tension of coexisting liquid phases in monolayers

The line tension (λ) in biphasic membranes has been determined in monolayers and bilayers using a variety of techniques. In this work we present a novel approach to the determination of λ in monolayers with liquid/liquid phase coexistence, overcoming several of the drawbacks of current techniques. Using our method, we determined the line tension of liquid/liquid phases in binary mixtures of different lipids and a molecule similar to cholesterol but less oxidizable. We analyzed the effect of the hydrocarbon chain length and the polar head-group of the non-sterol lipid and found the latter to exert much more influence than the former. The presence of PE led to high λ values, PG to low values and PS and PC to intermediate values. The line tension showed a strong correlation with the critical packing parameter of the phospholipid. The spontaneous curvature displayed by the phases constituted by a particular lipid appears to be an important parameter for determining the line tension in mixed films.

Formation of smectic phases in binary liquid crystal mixtures with a huge length ratio

A system of two liquid-crystalline phenylpyrimidines differing strongly in molecular length was studied. The phase diagram of these two chemically similar mesogens, with a length ratio of 2, was investigated, and detailed X-ray diffraction and electrooptical measurements were performed. The phase diagram revealed a destabilization of the nematic phase, which is present in the pure short compound, while the smectic state was stabilized. The short compound forms smectic A and smectic C phases, whereas the longer compound forms a broad smectic C phase and a narrow higher-ordered smectic phase. Nevertheless, in the mixtures, the smectic C phase is destabilized and disappears rapidly, whereas smectic A is the only stable phase observed over a broad concentration range. In addition, the smectic translational order parameters as well as the tilt angles of the mixtures are reduced. The higher-ordered smectic phase of the longer mesogen was identified as a smectic F phase.

Atomistic simulations of liquid crystal mixtures of alkoxy substituted phenylpyrimidines 2PhP and PhP14

We study liquid crystal mixtures of alkoxy substituted phenylpyrimidines 2-[4-(butyloxy)phenyl]-5-(octyloxy)pyrimidine (2PhP) and 2-[4-(tetradecyloxy)phenyl]-5-(tetradecyloxy)pyrimidine (PhP14) using molecular dynamics simulations at the all atom level. The molecular length of PhP14 is 1.8 times that of 2PhP, resulting in an interesting binary mixture phase diagram. Our simulations are composed of 1000-1600 molecules for a total of 80,000-130,000 atomic sites, with total simulation times of 60-100 ns. We first show that a pure 2PhP system self-assembles into isotropic, nematic, smectic A and smectic C phases, and a pure PhP14 system self-assembles into isotropic and smectic C phases. Binary mixtures of PhP14 and 2PhP display a stabilization of the smectic A phase at the expense of the smectic C and nematic phases. We determine that the concentration-induced phase transition from the smectic C to the smectic A phase in the mixture is driven by an out-of-layer fluctuation arrangement of the molecules. We also observe that the tilt angle in the smectic C phases formed in the mixtures is concentration dependent. The results of our simulations are in good agreement with the experimental findings of Kapernaum et al. [J. Org. Chem. 5, 65 (2009)], thus showing that atomistic simulations are capable of reproducing the phase behavior of liquid crystal mixtures and can also provide microscopic details regarding the mechanisms that govern phase stability.

Thermotropic Liquid Crystalline Phases in Binary Mixture of Nonmesogenic Compounds

The binary mixture of two nonmesogenic compounds viz., Tetradecyl Trimethyl Ammonium Bromide (TTAB) and Orthophosphoric acid (H3PO4) exhibits very interesting liquid crystalline smectic phases at large range of concentrations and temperature. The mixture with lower and higher concentrations of TTAB exhibits Sm A, Sm D, Sm B, and Sm E phases, sequentially when the specimen is cooled from its isotropic phase. Different liquid crystalline phases observed in the mixture were studied using DSC, X-ray, and Optical microscopic techniques. The temperature variation of optical anisotropy has also been discussed. Helfrich potential and elastic moduli have been estimated in the smectic phase using Helfrich model.

Kinetically driven self-assembly of a binary solute mixture with controlled phase separation via electro-hydrodynamic flow of corona discharge

This feature article describes a new and facile process to fabricate a variety of thin films of non-volatile binary solute mixtures suitable for high performance organic electronic devices via electro-hydrodynamic flow of conventional corona discharge. Both Corona Discharge Coating (CDC) and a modified version of CDC, Scanning Corona Discharge Coating (SCDC), are based on utilizing directional electric flow, known as corona wind, of the charged uni-polar particles generated by corona discharge between a metallic needle and a bottom plate under a high electric field (5-10 kV cm(-1)). The electric flow rapidly spreads out the binary mixture solution on the bottom plate and subsequently forms a smooth and flat thin film in a large area within a few seconds. In the case of SCDC, the static movement of the bottom electrode on which a binary mixture solution is placed provides further control of thin film formation, giving rise to a film highly uniform over a large area. Interesting phase separation behaviors were observed including nanometer scale phase separation of a polymer-polymer binary mixture and vertical phase separation of a polymer-organic semiconductor mixture. Core-shell type phase separation of either polymer-polymer or polymer-colloidal nanoparticle binary mixtures was also developed with a periodically patterned microstructure when the relative location of the corona wind was controlled to a binary solution droplet on a substrate. We also demonstrate potential applications of thin functional films with controlled microstructures by corona coating to various organic electronic devices such as electroluminescent diodes, field effect transistors and non-volatile polymer memories.

Induced smectic phases in phase diagrams of binary nematic liquid crystal mixtures

To elucidate induced smectic A and smectic B phases in binary nematic liquid crystal mixtures, a generalized thermodynamic model has been developed in the framework of a combined Flory-Huggins free energy for isotropic mixing, Maier-Saupe free energy for orientational ordering, McMillan free energy for smectic ordering, Chandrasekhar-Clark free energy for hexagonal ordering, and phase field free energy for crystal solidification. Although nematic constituents have no smectic phase, the complexation between these constituent liquid crystal molecules in their mixture resulted in a more stable ordered phase such as smectic A or B phases. Various phase transitions of crystal-smectic, smectic-nematic, and nematic-isotropic phases have been determined by minimizing the above combined free energies with respect to each order parameter of these mesophases. By changing the strengths of anisotropic interaction and hexagonal interaction parameters, the present model captures the induced smectic A or smectic B phases of the binary nematic mixtures. Of particular importance is the fact that the calculated phase diagrams show remarkable agreement with the experimental phase diagrams of binary nematic liquid crystal mixtures involving induced smectic A or induced smectic B phase.

Effect of Saline on Transitions in Poly(ethylene glycol)-Grafted Succinyl-Phosphoethanolamine Monolayers Bearing C16Aliphatic Chains

To investigate the effect of saline on miscibility, phase, and conformational transitions in binary mixtures of a succinyl-phosphoethanolamine bearing C(16) aliphatic chains, DPPE-succinyl, and a poly(ethylene glycol) (PEG)-phospholipid conjugate with a PEG molecular weight of 2000, DPPE-PEG2000, we have compared the properties of monolayers spread on water and on phosphate buffered saline (PBS). A comparative analysis of monolayer surface pressure, surface potential, compressibility, and epifluorescence microscopy data has revealed that spreading on PBS induces unfavorable interactions between the two phospholipids, which stabilizes immiscible phases in mixed monolayers. Strikingly, the conformational transition in grafted PEG2000 chains on PBS could not be easily described by the existing interpretive schemes. Plausibly, this transition becomes partially impaired due to interactions with PBS. Thus, saline has a significant effect on miscibility, phase, and conformational transitions in these PEG-grafted monolayers bearing C(16) aliphatic chains, which may have implications for understanding the behavior of PEG-grafted phospholipid surfaces in aqueous media of biological relevance.

Twisted Grain Boundary Phases in Binary Mixture of Smectic and Cholesteryl Compounds

A binary mixture of cholesteryl ethyl corbonate (CEC) and terephthal-bis-p-n-tetradecylaniline (TB14A) exhibits a twisted grain boundary (TGB) phase and smectic polymorphic phases. The mixture exhibits TGB-A and TGB-C phases at different concentrations and at different temperatures. Mixtures with higher concentrations of TB14A exhibit I – Ch – TGB-A – TGB-C – Sm A – Sm I – Sm F phases sequentially when the specimen is cooled from its isotropic melt. The existence of different TGB phases and polymorphic smectic phases are confirmed by differential scanning calorimetric (DSC) and optical microscopic studies. The phase diagram is in accordance with the Renn and Lubbensky model.

Alternating Thick and Thin Layers Observed in the Smectic Phase of Binary Mixtures of Rigid-Rod Helical Polysilanes with Different Molecular Lengths

Alternating Thick and Thin Layers Observed in the Smectic Phase of Binary Mixtures of Rigid-Rod Helical Polysilanes with Different Molecular Lengths

Evidence of Coexisting Phases in Binary Mixtures of POPC/ceramide3

Stratum corneum, the uppermost layer of skin epidermis exhibits an unusual lipid composition consisting mostly of long-chain asymmetric ceramides with different head groups, both saturated and unsaturated. Small-angle X-ray scattering (SAXS) was used to investigate the impact of one of the aforementioned ceramides, Ceramide3 (Cer3), on the structure of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) host membranes. Results on the composite model system for three mole ratios Cer3:POPC (5:95; 10:90; 15:85) are presented and compared to properties of the pure systems. All methods applied so far (SAXS, DSC, confocal microscopy) reveal non-ideal miscibility of the two components with macroscopic separation of coexisting phases of different rigidity, indicating a coexistence of two lamellar POPC-rich phases with crystalline Cer3 in all the binary mixtures. An especially developed 4G hybrid approach based on a modified Caille theory was used to model the POPC-rich phases in the temperature range of [0°C, 90°C]. Average structural parameters such as bilayer thickness, lamellar repeat distance and Caille parameter were extracted from the model together with the electron density profile for the coexisting POPC-rich phases. For the crystalline structure of pure Cer3 a distorted orthogonal unit cell was found by indexing. In summary, binary mixtures of Cer3:POPC exhibit a complex arrangement within the lipid matrix that we try to file into a simple model to account for the results.

Imaging cerebroside-rich domains for phase and shape characterization in binary and ternary mixtures

The objective of this paper is to review phase behavior and shape characterization of cerebroside-rich domains in binary and ternary lipid bilayers, as obtained by microscopy techniques. These lipid mixtures provide a format to examine molecular (e.g. headgroup, tail unsaturation, and tail hydroxylation) and thermodynamic (e.g. temperature and mole percentages) factors that determine phase behavior, molecular partitioning, crystal/atomic scale structure, and microstructure/shape (particularly of phase-separated domains). Microscopy can provide excellent spatial (often with high resolution) characterization of cerebroside-rich domains (and their surroundings) to identify, describe or infer with high certainty these characteristics. In the introduction to this review we review briefly the molecular structure, phase behavior, and intermolecular interactions of cerebrosides, in comparison to ceramides and sphingomyelins and in some binary and biological systems. The bulk of the review is then devoted to microscopy investigations of cerebroside-rich domain microstructure and shape dynamics in binary and ternary (one component is cholesterol) systems. Quantitative and/or high-resolution microscopy techniques have been used to interrogate cerebroside-rich domains such as freeze-fracture electron microscopy, atomic force microscopy, imaging elipsometry, two-photon fluorescence microscopy, and LAURDAN generalized polarization in addition to the laboratory workhorse technique of epifluorescence microscopy that allows a quick often qualitative assessment of microstructure and dynamics. We particularly focus on the information these microscopy investigations have revealed with respect to phase behavior, cholesterol partitioning, domain shape, and determinants of domain shape.

Positronium as a probe of structure and stability of solid phases in binary n-alkane mixtures

Annihilation of triplet ortho-positronium (o-Ps) in binary mixture of odd numbered n-alkanes was investigated. Sensitivity of o-Ps lifetime to the size of free volumes in the sample structure allows to distinguish not only the phases of solid but also some details of their structure. It was found that in the rigid phase o-Ps locates in the interlamellar gap. In mixed systems the o-Ps lifetime in that phase is longer than in neat compounds due to the change of molecular arrangements around the gap. In the case of n-tricosane + n-nonadecane mixture a transient structure appears when the n-tricosane content is between 3% and 10%. Directly after the increase of temperature to the range of 285–292 K the sample transforms to the rotator phase, but returns (at least partially) to the previous rigid structure with recovery time constant of many hours. Above 292 K the structure is stable.

Induction of B 1 phase in binary mixtures of rod- and bent-shaped mesomorphic compounds

The miscibility of a rod-shaped (R) and a bent-shaped (BC) compound forming an induced B 1 phase is reported. B 1 phase is not present in both R and BC in the entire phase sequence. R exhibits partially bilayered smectic A d phase with cholesteric and TGB while BC shows a B 2 phase. It is interesting to show that the B 2 phase is totally diminished in low composition (weight%) of BC, B 1 phase is induced at lower temperature range (~90–135 °C). A dielectric study is also incorporated to confirm the induction of B 1 phase in the binary mixture.

Electrostatic Exclusion of Neutral Solutes from Condensed DNA and Other Charged Phases

Motivated by experiments on condensed DNA phases in binary mixtures of water and a low-dielectric solute, we develop a theory for the electrostatic contribution to solute exclusion from a highly charged phase, within the continuum approximation of the medium. Because the electric field is maximum at the surface of each ion, the electrostatic energy is dominated by the Born energy; interactions between charges are of secondary importance. Neglecting interactions and considering only the competition between the Born energy and the free energy of mixing, we predict that low dielectric solutes are excluded from condensed DNA phases in water-cosolvent mixtures. This suggests that the traditional continuum electrostatic approach of modeling binary mixtures with a uniform dielectric constant needs to be modified. The linking of solute exclusion to solute dielectric properties also suggests a mechanism for predicting the electrostatic contribution to preferential hydration of polar and charged surfaces.

Entropically-Driven Formation of Smectic A1, A2, and A3 phases in Binary Mixtures of Rigid-Rod Helical Polysilanes with Different Molecular Weights

The smectic liquid crystal arrangements of binary mixtures of rod-like polymers, i.e., poly[n-decyl-(S)-2-methylbutylsilane]s, with narrow molecular weight distributions, were investigated by synchrotron radiation small-angle X-ray scattering (SR-SAXS) and atomic force microscopy (AFM) analyses. Depending on the molecular weight ratio, r (higher molecular weight/lower molecular weight), and the mixing ratio, three types of smectic phases are formed with different accommodations by two polymers. In the binary mixture of the shorter and longer polymers with the lower r values of 1.0−1.7, the two polymers are randomly mixed within a layer, forming the conventional smectic A1 phase with a layer thickness corresponding to an average length of the two polymers. In contrast, when two kinds of polymers with the higher r values of 1.7−2.8 are mixed, different types of smectic A structures are formed. Upon the addition of the shorter polymer to the abundant longer polymer, a smectic A2 phase in which a pair of smec...

Recovery of a reversed phase sequence in one ternary liquid-crystal-mixture system

The nOHFBBB1M7 (n=10) compound, 10OHF, shows a reversed SmC{FI2}-SmC phase sequence, unique among all known antiferroelectric liquid crystals. This reversed phase sequence is stabilized when 10OHF is doped with 9OTBBB1M7(C9) or 11OTBBB1M7(C11). In contrast, doping of the homologous members ( n=9 , 11, or 12) eliminates the SmC{FI2} phase. One 10OHF/11OHF mixture without the SmC{FI2} phase was selected for further studies. By adding C9 into this particular mixture, the reversed phase sequence is revived. To our surprise, even though 11OHF destabilizes the SmC_{FI2} phase in binary mixtures with 10OHF, it significantly increases the SmC_{FI2} temperature range in the 10OHF/11OHF/C9 ternary mixtures.