Influence of electric field on the phase transitions of the hexagonal cylinder phase of diblock copolymers.

We have used the cell dynamic simulations (CDS) method to study the evolution of asymmetric and symmetric diblock copolymers under electric fields. For symmetric diblock copolymers, long-range-ordered lamellar phases form readily under electric fields. For asymmetric diblock copolymers, sphere-to-cylinder phase transitions occur rapidly when strong electric fields are applied, but it takes longer for the system to form hexagonal cylinder structures. The results of these simulations suggest that the sphere phase is stable under weak electric fields, but a threshold electric intensity exists for the sphere-to-cylinder phase transition. In addition, we also studied the kinetic pathways of the transition of the lamellar phase to the hexagonal cylinder phase of the asymmetric diblock copolymers under electric fields. Hexagonal cylinder structures form when the lamellar phase is subjected to a sudden temperature jump. The scattering functions suggest that the hexagonal cylinder structures are very regular and possess very few flaws.     

Spectroscopic studies on the effect of field strength upon the curie transition of a VDF/TrFE copolymer

Infrared spectroscopic studies of the effects of field strength upon the ferroelectric phase transition behavior of a VDF/TrFE (75/25) copolymer upon heating and cooling in an electric field have revealed new findings. The paraelectric phase in the absence of an electric field resembles the α phase of PVDF with a trace of short trans sequences distributed randomly along the chain axis. The paraelectric phase in a high electric field is very different from that in the absence of an electric field. The paraelectric phase under an electric field has much longer trans sequences. The Curie transition temperature upon heating is a first-order transition temperature (T^↑_c) and is dramatically elevated from 120 to 135°C under the field of more than 0.4 MV/cm. Upon cooling, the paraelectric phase in an electric field does not show a clear transition. The field-induced phase transition and the loss of dipole switchability observed below a cooling temperature of 120°C, and their dependence on time and filed strength when exposed to a cyclic bipolar electric field are discussed. © 1993 John Wiley & Sons, Inc.     

The effect of high electric fields on the structure and dielectric properties of the B2 phase

Dielectric studies are presented of a banana-shaped compound that exhibits the antiferroelectric B₂ phase. Upon application and subsequent removal of strong electric fields the textures and dielectric properties of the phase drastically change. Most notable is the huge increase of the low frequency permittivity. This behaviour would suggest the induction of ferroelectricity by the electric field.     

Isothermal crystallization of poly(vinylidene fluoride) in the presence of high static electric fields. I. Primary nucleation phenomenon

Primary nucleation of poly(vinylidene fluoride) (PVF₂) γ-phase crystals from the melt is affected by the presence of an electric field. Crystallization under the electric field is studied by polarized optical microscopy, thermal analysis, and wide-angle x-ray diffraction. Preliminary results indicate that the γ-phase crystal nucleation rate and content are enhanced by the electric field. A modification of the classical theory of homogeneous nucleation of a crystalline phase is proposed to account for the experimental observations. Electrostatic interaction between the nucleus total polarization and the electric field contributes to the free energy of nucleation to a very large extent at low undercooling. Theoretical predictions indicate that a static electric field will increase the nucleation rate of a polar phase and will decrease the nucleation rate of a nonpolar phase. Confirmation of the former fact is observed experimentally.     

Biaxial order and a rotation of the minor director in the nematic phase of an organo-siloxane tetrapode by the electric field

Biaxiality in the nematic phase for a liquid crystalline tetrapode made up of organo-siloxanes mesogens is investigated using polarized infrared spectroscopy. An ordering of the minor director for the homeotropically aligned sample is found to depend on the amplitude of the in-plane electric field. On increasing the in-plane electric field, the minor director, lying initially along the rubbing direction, rotates to the direction of the applied field. The scalar order parameters of the second rank tensor are found to depend significantly on the strength of the electric field. A most significant increase is found in the nematic order parameter and in the parameter that characterizes the phase biaxiality.     

Bistable electro-optical switching in the smectic I* phase of a ferroelectric liquid crystal

The ferroelectric switching behaviour of the highly ordered smectic I* phase has been investigated in the mixture which shows a S*_I phase at room temperature. The bistability was obtained in a 3.5μm thick cell. Director switching and the reorientation processes have been studied by applying symmetric square and triangular wave pulses. It has been found that an asymmetric switching occurs in the smectic I* phase for low electric fields due to the hexagonal ordering of the molecules in the layer. This asymmetric switching was confirmed by optical microscopy and four stable states have been observed for low electric field. For higher electric fields only one state is stabilized which results in symmetric switching by both methods in the smectic I* phase.     

Phase transition of nanotube-confined water driven by electric field

The effects of electric field on the phase behaviors of water encapsulated in a thick single-walled carbon nanotube (SWCNT) (diameter = 1.2 nm) have been studied by performing extensive molecular dynamics simulations at atmospheric pressure. We found that liquid water can freeze continuously into either pentagonal or helical solidlike ice nanotube in SWCNT, depending on the strengths of the external electric field applied along the tube axis. Remarkably, the helical one is new ice phase which was not observed previously in the same size of SWCNT in the absence of electric field. Furthermore, a discontinuous solid-solid phase transition is observed between pentagonal and helical ice nanotubes as the strengths of the external electric field changes. The mechanism of electric-field-induced phase transition is discussed. The dependence of ice structures on the chiralities of SWCNTs is also investigated. Finally, we present a phase diagram of confined water in the electric field-temperature plane.     

Flow splitting at the inlet electrode as a method for decreasing the electric current in electric field assisted liquid chromatography

The combination of pressurized flow and electric field offers, with the use of capillary columns, several options for retention control. However, it has been shown that the utility of this technique is strongly limited by the high electric current that is generated at the high electric field strengths that are needed. We have earlier shown that the high current is a result of locally increased mobile phase ion concentration in the electric field, particularly around the inlet electrode. In this paper, we report that by splitting the mobile phase flow around the inlet electrode a relatively constant ion concentration around the electrode can be obtained and the high currents are there by reduced.     

The effects of anionic surfactants on the conductivity of a water-in-oil emulsion in a dielectric hydrophobic capillary

The effect of anionic surfactants on the conductivity of a water-in-crude oil emulsion in a laminar flow inside a dielectric hydrophobic capillary is experimentally investigated in an alternating electric field with strengths ranging from 4 to 10 kV/cm and a frequency of 50 Hz. Conductivity is analyzed as a function of aqueous phase concentration, electric field strength, and surfactant concentration in the dispersed phase.     

Effect of electric field on phase separation of polymer dispersed liquid crystal

The kinetics of the polymerization induced phase separation of liquid crystal (LC)/monomer mixture has been investigated by means of depolarized light intensity technique and polarized light microscope (PLM). To examine the effect of the electric field, a DC electric field was applied across the mixtures during the phase separation process. The kinetic study indicates that the phase separation process is accelerated when the electric field is applied. The morphologies of the formed polymer dispersed liquid crystal (PDLC) films were observed by PLM. The electric field applied during the phase separation process yields the PDLC with small LC domains and fine morphologies. The clearing temperature (T_NI) of the formed PDLC films was measured by the PLM and it is found that the T_NI increases with the applied electric field intensity.     

Frequency dependence of the electrorheological effect in the nematic phase of pentyl cyanobiphenyl

The effect of an electric field on the viscosity, the electrorheological (ER) effect, is studied as a function of the frequency of the electric field for the nematic phase of 4-n-pentyl-4'- cyanobiphenyl (5CB). In the frequency region between 10Hz and 1kHz, a gradual change of the ER effect is observed, with its behaviour depending on the shear rate and the amplitude of the electric field. On the basis of a calculation of the orientational motion of the director and its effect on the viscosity, the observed frequency dependence is suggested to occur as a result of an orientational relaxation of the director.     

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarising optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system. On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single-handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 μm to 15 μm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/μm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail.     

Phase behavior of polarizable spherocylinders in external fields

Applied electric fields are known to induce significant changes in the properties of systems of polarizable molecules or particles. For rod-shaped molecules, the field-induced behavior can be rather surprising, as in the case of the negative electric birefringence of concentrated solutions of rodlike polyelectrolytes. We have investigated the interplay of shape anisotropy and field-induced anisotropy in molecular dynamics simulations of systems of polarizable soft spherocylinders in an electric field, in the limit of infinitely anisotropic polarizability, taking full account of mutual induction effects. We find a novel crystalline structure (K(2)) in the high-field limit, whose formation is driven by interactions between induced dipoles. For high pressures, the phase diagram exhibits a polar nematic phase between the hexagonal close-packed crystal phase and the K(2) phase. We also compare this system with an analogous system of spherocylinders with permanent electric dipoles and find that qualitatively similar behavior is obtained in the limit of strong coupling of the permanent dipoles to the external field.     

Effect of an electric field applied during the injection procedure on the pretilt angle of a nematic liquid crystal

We examined the effect of an electric field applied during the injection procedure on the polar pretilt angle of a nematic liquid crystal (LC). The pretilt angle of the sample injected at 25°C gradually increased as the electric field was increased. On the other hand, the pretilt angle of a sample injected at 90°C (which is above the nematic-isotropic phase transition temperature of LC) showed a sudden increase in the presence of the electric field and also increased with a greater electric field. We think the alignment layer might be swollen with LC molecules, and the rotation of the immersed LC molecules by the electric field induces a deformation of the alignment layer. These results imply LC and the alignment layer were coupled, and their cooperation had an influence on determining the bulk pretilt angle.     

Measurement of the Kerr effect in cholesteric blue phases

The electric field induced birefringence within the blue phases and the isotropic phase of several different liquid crystals has been measured. The temperature dependences within the blue phases are found to be strong, characteristically different for each phase, and unlike what is predicted by simple theoretical arguments.     

Permanent electric dipole moments of four tryptamine conformers in the gas phase: a new diagnostic of structure and dynamics

Rotationally resolved electronic spectroscopy in the gas phase, in the absence and presence of an applied electric field, has been used to determine the charge distribution of a cross section of the energy landscape of tryptamine (TRA). We report the magnitude and direction of the permanent electric dipole moments of the four TRA conformers GPyout, GPyup, GPhup, and Antiup in their S0 and S1 electronic states. Each dipole moment is unique, providing a powerful new tool for the conformational analysis of biomolecules in the gas phase. A comparison of the results for the different conformers of TRA reveals that the position and orientation of the ethylamine side chain play a major role in determining both the permanent and induced electric dipole moments of the different species in both electronic states.     

Observation of an electric field-induced metastable blue phase in supercooled liquid crystalline systems

In this preliminary communication, the influence of an electric field on the metastable blue phase BPS is reported. Experiments involved both supercooling of the BPI at constant applied field and increasing the electric field strength applied to BPS at constant temperature, and resulted in the observation of a new field induced metastable phase BPES.     

Protein diffusion across the interface in aqueous two-phase systems

We present a detailed study of the diffusive transport of proteins across a fluid phase boundary within aqueous two-phase systems. The aim of the work is to investigate whether local effects at the phase boundary cause a retardation of the diffusive transport between the phases. Possible modifications of interfacial mass transfer could be due to protein adsorption at the phase boundary or local electric fields from electric double layers. Experiments with a microfluidic system have been performed in which protein diffusion (bovine serum albumin and ovalbumin) within a bilaminated configuration of two phases containing polyethylene glycol and dextran is analyzed. A one-dimensional model incorporating phase-specific diffusion constants and the difference in chemical potential between the phases has been formulated. A comparison of experimental and simulation data shows a good overall agreement and suggests that a potential local influence of the phase boundary on protein transport is insignificant for the systems under investigation.     

Molecular Dynamics Simulation: Influence of External Electric Field on Bubble Interface in Air Flotation Process

Molecular dynamics(MD) simulation was performed to investigate the influence of external electric field on the vapour-liquid interface of the bubble during the process of toluene separation by air flotation. The physicochemical properties of vapour-liquid interface, surface tension, probability of a hydrogen bonding near the vapour-liquid interface and the viscosity of liquid phase caused by external electric field were analyzed. The results show that the angle between the water molecule dipole moment and the normal z axis in the vapour phase changes smaller when the external electric field is applied. The surface tension and the probability of hydrogen bonding near the vapour-liquid interface increase with the increase of electric field strength. And the viscosity also increases under an external electric field. The results confirm that the external electric field has a positive effect on the performance of bubbles in air flotation, which may provide useful guidance for the combination of electric field and air flotation technology.