Fraction Of Liquid Crystal Research Articles

Dielectric characterization of polymer dispersed liquid crystal film with chitosan biopolymer

Polymer Dispersed Liquid Crystals (PDLC) systems were obtained using chitosan as a biopolymer matrix and the nematic liquid crystal (LC) mixture E7 in various concentrations (30, 40 and 50% E7 in chitosan). Several techniques were used to analyze the obtained films: polarizing optical microscopy (POM), IR spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric spectroscopy (DS). FTIR spectroscopy revealed minor changes for all PDLC films, suggesting weak interactions between LC and chitosan matrix. For each sample a clear segregation of the nematic droplets could be observed by POM. DSC measurements show that the phase transitions have shifted to lower temperature values for PDLC samples with approximately 2.7 °C compare to pure E7. The values of α (fraction of LC in the droplets) for compositions of 30, 40 and 50 wt% E7 in Chitosan were 0.48, 0.55 and 0.61 respectively, that are lower than for E7/PMMA system.The qualitative and quantitative analysis of the permittivity spectra obtained by DS reveals the fact that there are no significant changes in the molecular dynamics attributed to pure LC E7 compared to the PDLC composites, leading to the conclusion of the existence of a weak interaction between the two components, fact confirmed by the findings from the FTIR results.

Polymer (PEO)-liquid crystal (LC E8) composites: The effect from the LC inclusion

The effect from the inclusion of nematic liquid crystal (LC) E8 into the polymer poly(ethylene oxide) (PEO) was inspected by studying of structural and electrical properties of PEO-E8 composites at weight percentage of E8 ranging from 10 % to 50 %. Flexible PEO-E8 films with a thickness of 0.1 mm were structurally characterized by X-ray diffraction and X-ray photo-electron spectroscopy. The results obtained by our analyses indicate that a polymer-LC intermolecular complex is formed by inclusion of E8 LC molecules in the PEO host at a certain their concentration level. The structural properties of PEO-E8 composites were correlated with their electro-conducting properties as depending on the E8 LC concentration. By the amount of the LC fraction one can achieve a controlled modification of the structural and electro-conducting properties of the PEO-E8 material. As compared to PEO, the inclusion of E8 LC in the PEO polymer matrix can lead to a considerably enhanced electrical conductivity of PEO-E8 composites.

Size control of phase-separated liquid crystal droplets in a polymer matrix based on the phase diagram

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Thermal and morphological studies of liquid crystalline materials dispersed in a polymer matrix

Polymer dispersed liquid crystal (PDLC) films have been prepared by a combination of solvent-induced phase separation and thermal-induced phase separation techniques, for three mesogenic materials: 4-(undecyloxy) benzoic acid (UDBA), 4-(decyloxy) benzoic acid (DBA) and 4-(dodecyloxy) benzoic acid (DDBA) in poly(methyl methacrylate) (PMMA) as polymer matrix and tetrahydrofuran (THF) as common solvent. Differential scanning calorimetry and polarising optical microscopy are used for thermal and morphological investigations of prepared PDLCs, and findings are explained with the help of a suitable phase diagram. It is found that isotropic liquid–nematic transition temperature (TIN ) for these mesogens in the PMMA matrix decreases by about 2.8–5.6°C as compared with the pure mesogens. Methods based on the solubility parameter and the fraction of liquid crystal (LC) in LC-rich domains inside the PMMA matrix at different concentrations have been adopted to achieve an optimised condition for uniform dispersion of the film over a larger area. Remarkable changes in the droplet morphology of the mesogens confined in PMMA matrix as compared with their bulk counterparts have also been observed. Bipolar droplets and Maltese-type crosses are observed by POM for 75 and 30 wt% UDBA in the PMMA matrix.

Viscosity Variation During Evaporation of a Vegetable Oil Emulsion Stabilized by Tween 80R

The viscosity during evaporation was determined for emulsions in the system water, vegetable oil, a commercial surfactant, Tween 80R, and the results related to the phases of the emulsion according to the phase diagram. The correlation between the viscosity and the fraction of liquid crystal in the emulsion was pronounced for the emulsions with the oil as the dispersed phase. For the emulsions with oil as the major phase, the effect was significantly less.

Weight fractions in three-phase emulsions with an L α phase

Analytical expressions are given for the weight fractions in emulsions, which contains a lamellar liquid crystalline phase in addition to the two isotropic liquid phases. The fraction of liquid crystal is used to calculate the aqueous phase volume requirements of vesicles formed from the liquid crystal during intense emulsification. It is demonstrated that these requirements become excessive for vesicles with a small ratio of interfacial layer thickness to core radius.

Morphology and orientational order of nematic liquid crystal droplets confined in a polymer matrix

The orientational order of nematic liquid crystal (LC) droplets confined in a polymer matrix is investigated by 13C-NMR. Different morphologies exhibiting various cavity sizes were obtained by changing the LC fraction. The phase diagram has been established by polarized optical microscopy exhibiting a typical upper critical solution temperature shape. The nematic order increases with decreasing droplet size which may result from increased polymer/LC surface contacts in smaller cavities. The nematic fraction of 4-n-pentyl-4'-cyanobiphenyl (5CB) contained in the droplets was calculated by integrating the NMR peaks, then fitted using a simple theoretical model and compared with differential scanning calorimetry results. NMR investigations in the aliphatic region of the spectra have shown that the 2-ethyl hexyl fragment of the polymer chain is partially ordered at the polymer/LC interface due to interdigitation with 5CB molecules. Above the nematic-isotropic transition temperature, a weak pretransitional behavior is shown by the polymer.

A crustally contaminated komatiitic dyke–sill–lava complex, Abitibi greenstone belt, Ontario

Detailed field and laboratory studies indicate the Shaw Dome area of the Abitibi greenstone belt, Ontario, contains a lower horizon of intrusive komatiitic rocks (LKH), komatiitic dykes, and an upper horizon of extrusive komatiitic rocks (UKH). The LKH is 500–1000 m thick and consists of undifferentiated dunite (45–50% MgO), laterally equivalent wehrlite (20–50% MgO), and differentiated wehrlite–amphibole gabbro sills. A differentiated wehrlite–amphibole gabbro dyke intrudes calc-alkalic volcanic rocks and iron-formation. Undifferentiated wehrlite dykes (17–25% MgO) intrude calc-alkalic volcanic rocks and sulphide iron-formations stratigraphically underlying the LKH and contain xenoliths of those rocks. The UKH is 500–3000 m thick and consists of up to 50 m thick, weakly differentiated komatiites that grade laterally and vertically to thinner, undifferentiated and spinifex textured komatiite (20–35% MgO) and komatiitic basalt (5–20% MgO) flows, and host minor nickel sulphide mineralisation. These vertical and lateral variations are interpreted to be primary komatiitic lithofacies variations in a single intrusive–extrusive stratigraphic sequence. This sequence represents a dyke–sill–lava complex and constrains facies models for komatiitic magmatism–volcanism. The vertical and lateral transition from LKH dunite to wehrlite to wehrlite–amphibole gabbro sills represents the transition from proximal dynamic flow conduits to more static, ponded distal facies in a sub-volcanic magma chamber. The LKH is underlain by a largely hidden system of wehrlite dykes, possibly feeders to the overlying sills. The distribution of UKH undifferentiated, spinifex textured, and brecciated komatiite and komatiitic basalt flows represents the transition from proximal channel to distal sheet flow volcanic facies. Geochemical modelling utilising MELTS suggests that the LKH and UKH are related by liquid–crystal fractionation and accumulation of olivine±clinopyroxene from magma that assimilated variable amounts of calc-alkalic volcanic rocks±iron-formation. Furthermore, the modelling results suggest derivation of dunite and wehrlite and komatiite flows from uncontaminated magma and differentiated wehrlite-amphibole gabbro units and komatiitic basalt flows from contaminated magma. This contrast in degree of contamination is explained by intrusion and eruption of uncontaminated komatiite followed by assimilation of fused crustal material adjacent to magma conduits, fractional crystallisation, and eruption of the contaminated magma as komatiitic basalt. Given the generally accepted relationship of contamination and dynamic/static flow transitions to nickel sulphide mineralisation, komatiitic dyke/sill contacts should be sought and targeted in nickel sulphide exploration.

A Study on Thermally Stimulated Current Behaviors of Liquid Crystal/Polymer Composite Films and Liquid Crystal/Monomer Mixtures.

Thermally stimulated current(TSC) behaviors of liquid crystal(LC)/polymer composite films and LC/monomer mixtures have been investigated. The composite films are formed by the photo-polymerization induced phase separation process. The samples used were mixtures of the fluorinated liquid crystals having tolane linking group and the diacrylate monomer, and the composite films after photo-polymerization. In TSC curves of the liquid crystal/monomer mixtures with 65-85mol% of LC fraction, 3 kinds of peaks were observed at -48(peak A), -55(peak B), and -62°C(peak C). The peak A was assigned as the melting point of the monomer-rich phase and the peak C as T g of the liquid crystalline phase, whereas there is no clear-cut explanation for the peak B. TSC curves of LC/polymer composite films showed a tendency similar to the LC/monomer mixtures.

Deglaciation effects on mantle melting under Iceland: results from the northern volcanic zone

A striking feature of Icelandic volcanism is the effect that the last ice age had on volcanic activity. After the final retreat of ice ∼11 kyr BP, the average eruption rate is estimated to have been 20–30 times greater than it is today. This increase has been attributed to the release of pooled magma through differential tectonic movements during the unloading of ice. However recent work has shown that deglaciation can account for the increase in mantle melting by decreasing the pressure in the upper mantle. We present geochemical data and volume estimates of erupted magmas from Iceland's northern neovolcanic zone which show that the average composition of magmas erupted during the last glacial period in Iceland are significantly more enriched in incompatible trace elements than postglacial and interglacial lavas. The difference in light rare earth element concentrations cannot be accounted for by liquid–crystal fractionation. Averaging the compositions of glacial and postglacial magmas also eliminates the likelihood that the compositional change is due to variations in source composition. An increase in mantle melting from deglaciation can account for both the magma eruption rate and observed changes in trace element concentrations. Finite transport times for magma to travel from the source region to the surface can be estimated from the delay in timing of the increased eruption rates and the end of the last glacial period. This gives transport times of about 1–3 kyr and is consistent with estimates from ( 226Ra/ 230Th) activity ratios measured in ocean island and mid-ocean ridge basalts.

Morphology and electro-optic properties of polymer-dispersed liquid-crystal films

An attractive way of making polymer-dispersed liquid-crystal (PDLC) films is through photopolymerization-induced phase separation. The electro-optic properties of these films are determined in large part by the size, shape, and packing of the embedded liquid-crystal drops. We explore the relationships between the conditions of phase separation, morphology, and electro-optic properties. A strikingly strong dependence of electro-optic properties on the fraction of liquid crystal in the film is demonstrated and explained by consideration of the phase separation process. Also, confocal microscopy is shown to be a useful, noninvasive means of obtaining three-dimensional information on PDLC morphology. Not only does it provide very clear images of liquid crystalline drops in the film, but unexpected features were revealed. The drops exhibit a morphology much like a polyhedral foam in the films studied. Polymeric filaments inside the drops were observed as well as a drift in the average size of the drops with proximity to the film substrates. All of these features have important consequences for the electro-optic performance of PDLC films.

A Calorimetric Determination of Fundamental Properties of Polymer-Dispersed Liquid Crystals

Abstract We have developed a combined calorimetric/electron microscopic technique for determining several fundamental properties of polymer-dispersed liquid crystal (PDLC) films. Calorimetry allows us to determine the solubility limit of liquid crystal in the polymer matrix as well as the fraction of liquid crystal which is dispersed in the form of microdroplets. By combining the calorimetry results with electron microscopy measurements of D, the microdroplet diameter, we are able to calculate the functional relationship between the droplet number density and D. All of these parameters are of considerable importance in assessing the behavior of PDLCs. The usefulness of the method is illustrated by applying it to thermally-cured epoxy-based systems.

Aggregation State-Permeation Characteristic Relationships of Self-Supported Liquid Crystalline Membranes

A series of built-up films composed of the blend materials of polymer and liquid crystal(LC) were prepared by a solvent-casting or a water-casting method. The weight fraction of LC in the composite membrane was 60–70%. The thickness and aggregation state in the composite membrane can be controlled by solvents and the concentration of a solution. LC material forms a continuous phase in the three-dimensional spongy network of the matrix polymer. Therefore, LC phase can play a role of a diffusing phase for the permeants, because of very low viscosity of LC. The composite membranes were applied as the permselective membranes for the purpose of oxygen enrichment, molecular filtration, active transports of metal cations and enantioselective transport of amino acid salts.

Novel polymer/liquid crystal composite membrane with unique permselective characteristics

A series of built-up thin films composed of polymer and liquid crystal (LC) was prepared by spreading a single drop of mixture solution on a water surface. The weight fraction of LC in the composite membrane was 60%. The thickness and the aggregation state of the water-cast membrane can be controlled by the kind of solvent and the concentration of the mixture solution. Liquid crystalline material forms a continuous phase in the three-dimensional spongy network of the polymer matrix. Therefore, the liquid crystalline phase can play the role of a low viscous diffusing phase for permeants such as gases or metal ions. The novel polymer/LC composite membranes can be applied to oxygen enrichment, molecular filtration, active transport of metal cations and complete thermocontrol of ion permeation.