Phase behavior of medium-length hydrophobically associating PEO-PPO multiblock copolymers in aqueous media.

Hypothesis: The micellization of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) is driven by the dehydration of PPO at elevated temperatures. At low concentrations, a viscous solution of isolated micelles is obtained, whereas at higher concentrations, crowding of micelles results in an elastic gel. Alternating PEO-PPO multiblock copolymers are expected to exhibit different phase behavior, with altered phase boundaries and thermodynamics, as compared to PEO-PPO-PEO triblock copolymers (Pluronics®) with equal hydrophobicity, thereby proving the pivotal role of copolymer architecture and molecular weight.

Experimental Advances in Nanoparticle-Driven Stabilization of Liquid-Crystalline Blue Phases and Twist-Grain Boundary Phases.

Recent advances in experimental studies of nanoparticle-driven stabilization of chiral liquid-crystalline phases are highlighted. The stabilization is achieved via the nanoparticles' assembly in the defect lattices of the soft liquid-crystalline hosts. This is of significant importance for understanding the interactions of nanoparticles with topological defects and for envisioned technological applications.

Test of Halperin-Lubensky-Ma crossover function at the N-Sm-A transition in liquid crystal binary mixtures via high-resolution birefringence measurements.

We report optical birefringence data for a series of mixtures of the liquid crystals octylcyanobiphenyl (8CB) and decylcyanobiphenyl (10CB). Nematic order parameter S data in the nematic and smectic A phases have been derived from phase angle changes obtained in temperature scans with a rotating analyzer method. These S values have been used to arrive at values for possible entropy discontinuities at the smectic A to nematic phase transition temperature T_{NA}.

The critical behavior of the dielectric constant in the polar + polar binary liquid mixture nitromethane + 3-pentanol: an unusual sign of its critical amplitude in the one-phase region.

Dielectric constant measurements have been carried out in the one- and two-phase regions near the critical point of the polar + polar binary liquid mixture nitromethane + 3-pentanol. In the two-phase region, evidence for the |t|(2β) singularity in the coexistence-curve diameter has been detected, thus confirming the novel predictions of complete scaling theory for liquid-liquid criticality. In the one-phase region, an "unusual" negative sign for the amplitude of the |t|(1-α) singularity has been encountered for the first time in an upper critical solution temperature type of binary liquid mixture at atmospheric pressure.

Large heat capacity anomaly near the consolute point of the binary mixture nitromethane and 3-pentanol.

The large critical anomaly in the isobaric heat capacity C(p,x)(T) of the binary mixture nitromethane + 3-pentanol is measured using high-resolution adiabatic scanning calorimetry. The unique features of this technique provided an alternative approach to the study of the critical behavior of C(p,x)(T), providing further C(p,x)(T) related quantities from which valuable information could be extracted. Our data are in full agreement with the predictions of the Modern Theory of Critical Phenomena; specifically, 3D-Ising model values for the critical exponent α and the universal amplitude ratio values of the leading critical amplitudes, as well as for the first correction-to-scaling ones, provide the optimum fits to represent the experimental data.

Order of phase transitions and tricriticality in mixtures of octyloxycyanobiphenyl and nonyloxycyanobiphenyl liquid crystals: a high-resolution study by adiabatic scanning calorimetry.

A detailed study has been performed for mixtures of octyloxycyanobiphenyl (8OCB) and nonyloxycyanobiphenyl (9OCB) liquid crystals and nine of their mixtures by means of high-resolution adiabatic scanning calorimetry. The isotropic to nematic transitions are weakly first order with latent heat values in the range usually encountered for this transition in other liquid crystals. With the exception of pure 8OCB, for which only an upper limit of 1.

Critical behavior of static properties for nitrobenzene-alkane mixtures.

We present experimental data of the isobaric heat capacity per unit volume C(p,x)V(-1) for mixtures containing nitrobenzene and an alkane (C(N)H(2N+2), with N ranging from 6 to 15) upon approaching their liquid-liquid critical points along a path of constant composition. Values for the critical amplitude A(+) have been determined. They have been combined with the previously reported ones for the leading term of the coexistence-curve width to obtain, with the aid of well-known universal relations, the critical amplitudes of the correlation length and of the osmotic susceptibility.

Nanoparticle-induced widening of the temperature range of liquid-crystalline blue phases.

Liquid-crystalline blue phases exhibit exceptional properties for applications in the display and sensor industry. However, in single component systems, they are stable only for very narrow temperature range between the isotropic and the chiral nematic phase, a feature that severely hinders their applicability. Systematic high-resolution calorimetric studies reveal that blue phase III is effectively stabilized in a wide temperature range by mixing surface-functionalized nanoparticles with chiral liquid crystals.

Dielectric constant of fluids and fluid mixtures at criticality.

The behavior of the dielectric constant epsilon of pure fluids and binary mixtures near liquid-gas and liquid-liquid critical points is studied within the concept of complete scaling of asymmetric fluid-fluid criticality. While mixing of the electric field into the scaling fields plays a role, pressure mixing is crucial as the asymptotic behavior of the coexistence-curve diameter in the epsilon-T plane is concerned. Specifically, it is found that the diameters, characterized by a |T-Tc|1-alpha singularity in the previous scaling formulation [J.

Temperature, concentration, and frequency dependence of the dielectric constant near the critical point of the binary liquid mixture nitrobenzene-tetradecane.

Detailed results are reported for the dielectric constant epsilon as a function of temperature, concentration, and frequency near the upper critical point of the binary liquid mixture nitrobenzene-tetradecane. The data have been analyzed in the context of the recently developed concept of complete scaling. It is shown that the amplitude of the low frequency critical Maxwell-Wagner relaxation (with a relaxation frequency around 10 kHz) along the critical isopleth is consistent with the predictions of a droplet model for the critical fluctuations.

Effects of magnetic nanoparticles with different surface coating on the phase transitions of octylcyanobiphenyl liquid crystal.

The impact of magnetic nanoparticles with different surface coating upon the isotropic-to-nematic and nematic-to-smectic- A phase transitions of the liquid crystal octylcyanobiphenyl is explored by means of high-resolution adiabatic scanning calorimetry. A shrinkage of the nematic range is observed, which is strongly dependent on the surface coating of the nanoparticles. The isotropic-to-nematic transition remains weakly first order while the nematic-to-smectic- A is continuous with the effective critical exponent alpha values (0.

Temperature-driven mixing-demixing behavior of binary mixtures of the ionic liquid choline bis(trifluoromethylsulfonyl)imide and water.

The ionic liquid (2-hydroxyethylammonium)trimethylammonium) bis(trifluoromethylsulfonyl)imide (choline bistriflimide) was obtained as a supercooled liquid at room temperature (melting point=30 degrees C). Crystals of choline bistriflimide suitable for structure determination were grown from the melt in situ on the X-ray diffractometer. The choline cation adopts a folded conformation, whereas the bistriflimide anion exhibits a transoid conformation.

High-resolution calorimetric study of a liquid crystalline organo-siloxane tetrapode with a biaxial nematic phase.

High-resolution adiabatic scanning calorimetry and differential scanning calorimetry have been employed to study the thermal behavior of an organo-siloxane tetrapode reported to exhibit a biaxial nematic phase. No signature of the uniaxial to biaxial nematic phase transition could be retraced in sequential heating and cooling runs under different scanning rates, within the experimental resolution. The results obtained reveal that an extremely small heat should be involved in the uniaxial to biaxial nematic phase transition.

Accelerated dielectric relaxation in the isotropic phase of associating liquid crystals dispersed with aerosils.

The dielectric response of liquid crystals in their nematic phase shows an acceleration of the relaxation associated with the rotation around the short molecular axis when dispersed with aerosils. However, in the isotropic phase, this acceleration is only seen for certain liquid crystalline molecules. In this paper, an associating liquid crystal (5CB) and a shorter monotropic liquid crystalline member of the same homologous series (4CB), a liquid crystal that does not show association (5NCS) and a nonassociating liquid crystal (5O5) have been studied by dielectric spectroscopy in the isotropic phase.

Temperature dependence of the electrical conductivity of imidazolium ionic liquids.

The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393 K on the basis of dielectric measurements in the frequency range from 1 to 10(7) Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain.

Effect of nonmesogenic impurities on the liquid crystalline phase transitions of octylcyanobiphenyl.

The effect of the nonmesogenic solutes cyclohexane (CH), biphenyl (BP), and water (W) on the nematic-isotropic (N-I) and the nematic-smectic- A (N-SmA) phase transitions in the liquid crystal octylcyanobiphenyl (8CB) has been studied by means of adiabatic scanning calorimetry. For BP and CH a linear decrease of both transition temperatures was observed with increasing solute mole fraction. For water the transition temperature stayed nearly constant (after a slight decrease for mole fractions of water up to 0.

Task-specific ionic liquid for solubilizing metal oxides.

Protonated betaine bis(trifluoromethylsulfonyl)imide is an ionic liquid with the ability to dissolve large quantities of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium(II) oxide, mercury(II) oxide, nickel(II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide, manganese(II) oxide, and silver(I) oxide.

Effect of nonmesogenic impurities on the order of the nematic to smectic-A phase transition in liquid crystals.

By means of adiabatic scanning calorimetry, we have studied the effect of the nonmesogenic solutes cyclohexane (CH) and biphenyl (BP) on the nematic-smectic-A phase transition in the liquid crystal octylcyanobiphenyl (8CB). For all concentrations of BP studied, the transition remains second-order. For 8CB+CH, however, crossover from second-order to first-order is observed at a tricritical point of the mole fraction x of CH around 0.

Echocardiographic strain and strain-rate imaging: a new tool to study regional myocardial function.

Ultrasonic imaging is the noninvasive clinical imaging modality of choice for diagnosing heart disease. At present, two-dimensional ultrasonic grayscale images provide a relatively cheap, fast, bedside method to study the morphology of the heart. Several methods have been proposed to assess myocardial function.

Experimental investigation of leaky lamb modes by an optically induced grating.

By removing the symmetry of a free plate configuration, fluid loading significantly modifies the nature of acoustic waves travelling along a plate, and it even gives existence to new acoustic modes. We present theoretical predictions for the existence, dispersive behavior, and spatial distribution of leaky Lamb waves in a fluid-loaded film. Although Lamb modes are often investigated by studying the radiated fluid waves resulting from their leakage, here their properties are assessed by detecting the wave displacements directly using laser beam deflection.

Two-dimensional ultrasonic strain rate measurement of the human heart in vivo.

A study is presented in which the feasibility of two-dimensional strain rate estimation of the human heart in vivo has been demonstrated. To do this, ultrasonic B-mode data were captured at a high temporal resolution of 3.8 ms and processed off-line.

Phase transitions in the starch-water system studied by adiabatic scanning calorimetry.

We report high-precision measurements of phase transitions in the starch-water system by using for the first time adiabatic scanning calorimetry (ASC). Potato starch and nixtamalized corn flours were studied by this technique as a function of the moisture content. We calculated the percentage of gelatinized starch granules, as a function of the temperature, for both flours.

Nonlinearity of acoustic waves at solid-liquid interfaces.

The small-amplitude and finite-amplitude propagation characteristics of laser line source excited and laser detected Scholte waves are investigated. Acoustic waves with Mach numbers up to 0.054 are observed at the interface between water and glass.