Effect of electrooptical memory in suspensions of carbon nanotubes in liquid crystals

Electrooptical response and microstructure of dispersions of multiwall carbon nanotubes in N-(4-ethoxybenzilidene)-4-n-butyl aniline nematic liquid crystal (LC) are studied. Irreversible response on the applied electric field (electrooptical memory) was revealed in oriented layers of such suspensions. The essence of this effect consists in the fact that, after the switch-on and subsequent switch-off of the field, the optical transmittance of suspension layer placed between two crossed polarizers substantially increases compared to the initial value which is typical for homeotropic orientation of LC. The efficiency of electrooptical memory nonmonotonically depends on the concentration of nanotubes in suspension, c _CNT, reaching its maximum at c _CNT = 0.02–0.05 wt %. It is shown that the memory of suspensions is caused by the incomplete relaxation of LC molecules from planar to initial homeotropic state after the electric field switch-off. The model is proposed and substantiated, according to which the planar state of LC is stabilized by the network of nanotubes formed upon the disintegration of aggregates under the action of electrohydrodynamic flows. The disclosed memory effect is rather common; it is brought about in the suspensions of carbon nanotubes based on other LCs in which electrohydrodynamic instabilities are developed.     

Electrooptics of β-FeOOH Particles in Aqueous Media: 1. Reversing-Pulse Electric Birefringence in the Low Field Region

Reversing-pulse electric birefringence (RPEB) of a nearly monodisperse iron(III) hydroxide oxide sample in the β-form (β-FeOOH) was measured at 25°C and at a wavelength of 633 nm in aqueous media in the presence of NaCl. The concentrations of β-FeOOH and added NaCl varied between 0.00111 and 0.0555 g/L and 0.03 and 2.0 mM, respectively. Except for the suspensions with high salt concentrations, each RPEB signal showed a dip or minimum in the reverse process upon electric field reversal, together with a smooth rise in the buildup and a fall in the decay process. The observed signals were analyzed with a new RPEB theory, which takes into account not only the permanent electric dipole moment (μ) but also the root-mean-square ionic dipole moment (m^21/2) due to the ion fluctuation in ion atmosphere, in addition to the field-induced electronic (covalent) dipole moment Δα′ E. The results showed that the slowly fluctuating moment of m^21/2 is by far the most predominant one for the field orientation of the β-FeOOH particle, though the permanent dipole moment μ may not be completely excluded. The rotational relaxation time of the whole particle was evaluated from the decay signal, while the relaxation time for fluctuating ions was estimated from RPEB signal fitting. The sign of the steady-state birefringence for β-FeOOH suspensions was positive without exception under the present conditions. The birefringence signals in the steady state (δ/d) were proportional to the second power of the applied field strength (E) in the low field region; thus, the Kerr law was verified to hold for β-FeOOH suspensions. The specific Kerr constant was evaluated for each suspension by extrapolating the values of δ/d to zero field (E→0).     

<Emphasis Type="Italic">E. coli</Emphasis>, <Emphasis Type="Italic">P. aeruginosa</Emphasis>, and <Emphasis Type="Italic">B. cereus</Emphasis> Bacteria Sterilization Using Afterglow of Non-Thermal Plasma at Atmospheric Pressure

We developed and employed a new geometrical structure of dielectric barrier discharge in atmospheric pressure for bacterial broad spectrum sterilization. We utilized a plasma source having an AC power supply at 50 HZ and 5,400 V (rms value). We prepared suspensions of the Gram-negative bacteria species (Escherichia coli, Pseudomonas aeruginosa) and a Gram-positive of Bacillus cereus with Luria–Bertani broth media up to OD_600 nm = 0.25 of McFarland standard. Afterglow of non-thermal atmospheric pressure plasma treated these suspensions. The influence of the atmospheric plasma afterglow on the species was assayed in different time durations 5, 10, and 15 min. The spectroscopic results of this investigation indicated that the survival reduction of the species can reach to 100% for P. aeruginosa in an exposure time of 10 min, E. coli and B. cereus in an exposure time of 15 min.     

Orientation mechanism of palygorskite and kaolinite derived from the electric reversing pulse technique

Summary The investigation of electrooptical effects (birefringence, light scattering, dichroism) by the electric reversing pulse technique gives information on the directions of the electric moments of the particles. In case of Palygorskite and Kaolinite the experimental curves show a maximum at the instant when the field changes its polarity. The existence of this maximum demonstrates that the electric moments (permanent and induced moment) are oriented perpendicular to each other. The electric polarizability is parallel oriented to the long axis of the particles and the permanent dipole moment perpendicular to it. From the maximum the mean rotational diffusion coefficient of the particles has been calculated and the ratio of both electric moments in the case of Palygorskite after the theory ofI. Tinoco et al. andK. Yoshioka et al. has been obtained.

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Zusammenfassung Die Untersuchung elektrooptischer Effekte (Doppelbrechung, Lichtstreuung, Dichroismus) im elektrischen Feld mit rechteckförmigen Impulsen wechselnder Polarität gibt die Möglichkeit, die Richtung der elektrischen Momente der Teilchen zu ermitteln. Im Fall von Palygorskit und Kaolinit zeigen die experimentellen Kurven der Doppelbrechung ein Maximum beim Wechsel der Polarität des Feldes. Dieses Maximum bedeutet, daß die elektrischen Momente (permanentes und induziertes) senkrecht zueinander orientiert sind. Die elektrische Polarisierbarkeit liegt parallel zur langen Achse der Teilchen und das permanente Dipolmoment senkrecht dazu. Aus dem Maximum der Doppelbrechung ergibt sich für Palygorskit nach der Theorie vonI. Tinoco et al. und vonK. Yoshioka et al. die mittlere Rotations-Diffusionskonstante der Teilchen und das Verhältnis beider elektrischer Momente.

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With 2 figures     

Complex electrooptic research of nano-particle parameters in colloids

A research of some colloids has been carried out by means of dynamic light scattering, electrooptical and magnetooptical techniques. Intensity autocorrelation functions of scattered light have been compared to the relaxation curves of electrooptical effect for colloid particles of different shapes. The results of complex research confirm that the complicated character of light scattering by particles allows us to use the methods of birefringence and dichroism only formally when studying most colloid systems. Very thin nano-disperse structures are an exception to this rule. The investigation of polydispersity of some colloids was carried out by magnetooptical and two electrooptical techniques. Size distribution functions resulted from the different techniques agree. This justifies the suppositions about particle light scattering that are required for the use of the methods.     

Mechanisms and kinetics of living radical polymerizations

The polymerization rates and activation processes of several variants of living radical polymerization (LRP) are discussed on the basis of recent experimental and theoretical results. Because of bimolecular termination, which is inevitable in LRP as well as in conventional radical polymerization, the time‐conversion curves of LRP have several characteristic features depending on the experimental conditions, such as the presence or absence of conventional initiation. Despite the presence of termination (and initiation, in some cases), polymers obtained by LRP can have a low polydispersity, provided that the number of terminated chains is small compared to the number of potentially active chains. A large rate constant of activation, k_act, is another fundamental requisite for low polydispersities. Systematic experimental investigation into k_act has clarified the exact mechanisms of activation in several LRP systems. The magnitudes of k_act was found to largely differ from system to system.     

On the relationship between the nonlinear dielectric properties and respiratory activity of the obligately aerobic bacterium Micrococcus luteus

We have recently described the construction of a dual-cell, nonlinear dielectric spectrometer, and its application to the study of cell suspensions of S. cerevisiae (A.M. Woodward and D.B. Kell, Bioelectrochem. Bioenerg., 24 (1990) 83). Substantial, odd harmonics were generated by these cells when stimulated by very modest sinusoidal electrical fields, within fairly sharp voltage- and frequency windows (ca. 0.8–2.5 V cm⁻¹, 1–50 Hz). Resting cells were found to generate only odd-numbered harmonics. In the present work, we have simultaneously applied two sinusoidal frequencies which were individually of unsuitable frequency and/or amplitude for the generation of harmonics when applied to suspensions of S. cerevisiae. Strong “sidebands” or “beat frequencies” were observed which were the (odd-numbered) sums and differences of the exciting frequencies (viz. ƒ₁±2ƒ₂, ƒ₂±2ƒ₁). The generation of these beat frequencies was strongly inhibited by low concentrations of sodium metavanadate, suggesting that they may be ascribed largely to the H⁺-ATPase present in the plasma membranes of these cells. We show that the ability of dc fields to inhibit the manifestation of nonlinear dielectric behaviour by these cells is explicable in terms of their ability to act as a field of zero Hz, forcing the excitation out of the amplitude window. When the cells were allowed to glycolyse, beat frequencies of even order (ƒ₁±ƒ₂, ƒ₁±3ƒ₂) were observed. The present approach provides a novel and powerful approach to the registration of nonlinear dielectric spectra, which, due to the greater precision inherent in the discrimination of frequencies rather than voltages may be expected to provide a more sensitive means of detecting nonlinear dielectric properties in biological systems. If the transduction of exogenous electrical field energy recorded by this method is representative of the natural turnover of the H⁺-ATPase in vivo, it may be calculated that the efficiency of the capture of electric field energy by this enzyme is some 3%.     

Effect of Particle Size Distribution on the Rheology of Dispersed Systems

The rheological properties of aqueous polystyrene latex dispersions from three synthetic batches, with nearly the same z-average particle sizes, 400 nm, but varying degrees of polydispersity, 0.085, 0.301, and 0.485, respectively, were systematically investigated using steady-state shear and oscillatory shear measurements. The particles were sized with photon correlation spectroscopy and transmission electron microscopy and were stabilized sterically with PEO–PPO–PEO triblock copolymer (Synperonic F127). Results from steady-state shear measurements show that the viscosities of the systems exhibit shear-thinning behavior at high solid fractions. However, the degree of shear thinning depends on the breadth of particle size distribution, with the narrowest distribution suspension exhibiting the highest degree of shear thinning. The Herschel–Bulkley relationship best describes the flow curves. The relative viscosities as a function of volume fraction data were compared, and it was found that the broadest distribution suspension had the lowest viscosity for a given volume fraction. In addition, the data were fitted to the Krieger–Dougherty equation for hard spheres. A reasonable agreement of theory with experiment is observed, particularly and surprisingly for the very broad distribution. However, when the contribution to the volume due to the adsorbed polymer layer is considered, the agreement between experiment and theory becomes closer for all the suspensions, although the agreement for the broad distribution suspension is now worse. Fitting the Dougherty–Krieger theory to the experimental data based on our experimental maximum packing fractions gives very good agreement for all the systems studied. From oscillatory shear measurements, the moduli were obtained as a function of frequency at various latex volume fractions. The results show general change of the dispersions from viscous (G" > G′) at low volume fractions (0.25–0.30) to moderately elastic (G′ > G") at moderately high volume fractions (0.41–0.45). The change at this concentration level is likely due to some compression and interpenetration of the stabilizing polymer chain at the periphery, indicating the dominance of the interparticle forces. Overall, the very broad distribution was found to have the lowest elastic modulus for a given volume fraction.     

Bacterial inactivation via microfluidic electroporation device with insulating micropillars

Electroporation is a promising method to inactivate cells and it has wide applications in medical science, biology and environmental health. Here, we investigate the bacteria inactivation performance of two different microfluidic electroporation devices with rhombus and circular micropillars used for generating locally enhanced electric field strength. Experiments are carried out to characterize the inactivation performance (i.e., the log removal efficiency) of two types of bacteria: Escherichia coli (E. coli, gram-negative) and Enterococcus faecalis (E. faecalis, gram-positive) in these two microfluidic devices. We find that under the same applied electric field, the device with rhombus micropillars performs better than the device with circular micropillars for both E. coli and E. faecalis. Numerical simulations show that due to the corner-induced singularity effect, the maximum electric field enhancement is higher in the device with rhombus micropillars than that in the device with circular micropillars. We also study the effects of DC and AC electric fields and flowrate. Our experiments demonstrate that the use of the DC field achieves higher log removal efficiencies than the use of AC field.     

Self-stabilization of aqueous suspensions of alumina nanoparticles obtained by electrical explosion

The particle-size distribution, electrooptical potential, and acid properties of the surface of Al₂O₃ nanoparticles in aqueous media were studied by dynamic light scattering, electroacoustic spectral analysis, and potentiometric titration. The nanopowder with the mean particle size 22 nm was obtained by the oxidation of aluminum wire in the vapor phase using electrical explosion in oxygen-argon mixture. In spite of the presence of aggregates, aqueous suspensions of nanoparticles, as distinct from suspensions of micropowders, are stable without the addition of special stabilizers because of the spontaneous formation of a double electrical layer on their surface, the electrokinetic potential of which is positive and exceeds 30 mV. The most probable reason for electrostatic self-stabilization of suspensions of nanopowders is the adsorption of Al ions formed in the hydrolysis of aluminum nitrates, small amounts of which are produced in electrical discharges during preparation.     

Electrooptical properties of polarization holographic gratings formed in liquid-crystal composites

The results of experimental study of the electrooptical properties of polarization holographic gratings formed in a liquid-crystal composite by polarization holography are presented. The influence of the formation conditions, the parameters of the controlling ac electric field, and the composite geometry on the diffraction efficiency of such gratings is considered.     

Computational Insights into the Role of External and Local Electric Fields in Macrocyclic Chemical and Biological Systems

The investigation of the role of the electric field in systems of widespread interest employing computational techniques is an emerging area of research. The outcome of applying an oriented external electric field (OEEF) on the geometric and electronic properties of the chemically unique π-conjugated cyclic carbon ring compounds has been explored with density functional theory (DFT). Distinct changes in the structural and electronic features of such ring compounds are observed upon the application of OEEFs. Importantly, the calculations indicate that a mixed aliphatic-aromatic conjugated ring converts from a singlet to a triplet after the application of an OEEF, suggesting potential applications in optoelectronics for such molecules, without the need for photochemically induced change in the spin state. Furthermore, the influence of built-in local electric fields (LEFs) present in naturally occurring macrocyclic systems such as valinomycin has also been explored. Static and ab initio molecular dynamics (AIMD) calculations indicate that LEFs are the primary driving factor in determining the energetically favoured position of counter anions such as chloride (Cl⁻) in the potassium (K⁺) and sodium (Na⁺) coordinated valinomycin macrocycle structures: they exist inside the cage in the case of K⁺ sequestration by valinomycin and outside for Na⁺. This divergence has been proposed to be the determining factor for the selectivity of the valinomycin macrocycle for binding a K⁺ cation over Na⁺.     

Bactericidal effect of an electrodialysis system on E. coli cells

Using a new electrodialysis system with both cation- and anion-exchange membranes, the bactericidal effect on Escherichia coli has been investigated in detail from the standpoint of electrochemistry. Various electrolyte solutions containing E. coli (10⁸ cells/cm³) were passed through a desalting chamber at a flow rate of 3 cm³/min under varying current densities, and the viability of the cell (%) and the pH changes in the effluents were measured. When a 0.1 M NaCl aqueous suspension was used, a disinfection effect emerged in the vicinity of the limiting current density (LCD 0.81 A/dm²) and increased with an increase in the current density. The pH value of the suspensions decreased owing to the dissociation of water to H⁺ and OH⁻ ions by the well-known “neutrality disturbance phenomenon” in the region beyond the LCD. These tendencies were also observed when other electrolyte suspensions were used. Concerning the effect of the various species on the disinfection of E. coli cells, ionic systems in which a LCD was easily attained were found to have a strong effect.The germicidal effect may be due to a synergistic effect of acidic H⁺ and basic OH⁻ ions which are produced on the anion-exchange membrane and cation-exchange membrane, respectively, of the desalting chamber.     

Microcalorimetric Evaluation of the Effect of Kanamycin： An Analysis Based on the Median-Effect Principle

A study of the effect of drug, kanamycin, on the growth metabolism of recombinant Escherichia coli B 1 was carded out by microcalorimeter monitoring of the metabolic activity of treated cells. Power-time curves of growing recombinant Escherichia coli cell suspensions, treated with different kanamycin doses, were recorded. The extent of the effect was evaluated by changes in the slopes of the microcalorimetric curves and the kinetics of the drug action was interpreted from the time at which these changes reached their maximum values and maintained their maximum values. Experimental dose-effect relationships conform to the median-effect principle of the mass-action law： fa/（1-fa）=（D/D50）^m. A plot of y=lg[（fa）^1-1]^-1 versus x=lg D gives the slope m, D50 and R∞. The experimental results revealed that high concentration of kanamycin had an inhibitory effect on the growth of recombinant Escherichia coli B 1 in the lg phase, and had a promoting effect in the stationary period. Moreover, it was demonstrated that microcalorimetry was a reliable method for the detection of modulatory effects in biology.     

Trapping Radial Electric Field Optimization in Compensated FTICR Cells

Herein, we present the theoretical and experimental study of the recently introduced FTICR cell designs. We developed an approach that determines the electric field inside the cell, based on the measurement of calibration coefficients as a function of post-excitation radius and other conditions. Using the radial electric field divided by radius (E _r /r) as a criterion of the cell harmonization, we compare the compensated cell approach with alternative designs and discuss practical implications of the cell compensation.     

Statistical thermodynamics in the framework of the lattice fluid model, 2. Binary mixture of polydisperse polymers of special distribution

In this paper, the Gibbs free energy, the equation of state and the chemical potentials of polydisperse multicomponent polymer mixtures are derived. For general binary mixtures of polydisperse polymers, we also give the Gibbs free energy, the equation of state and the chemical potentials and derive the stability criteria and spinodal. Furthermore, binary polydisperse polymer mixtures of special distribution, i.e., Flory distribution, uniform distribution and Schulz distribution, are discussed and the influence of polydispersity on the interaction energy parameter is considered. For these special-distribution systems, the spinodal curves are simulated and the influence of chain length and polydispersity on the spinodal curves is discussed. The results suggest that the spinodal temperature of the mixture with a given volume fraction of one component decreases with increasing polydispersity and the extent of the shift decreases with increasing degree of polymerization when η = M̄_w/M̄_n is given. In addition, the variations of the spinodal curves with polydispersity and chain length are shown and they are qualitatively compared with the experimental results.     

Microdielectrometric monitoring of film preparation process with oriented domains for hydroxypropyl cellulose cast from isotropic aqueous solution under the sinusoidal electric field with large amplitude

Microdielectrometry was applied to macroscopically anisotropic media. The distribution and effective portion of the electrostatic energy density, w ₁₄ and J ₁₄, respectively, were calculated, considering the additive contributions of four pairs of microelectrodes. The electric field lines were calculated numerically and investigated experimentally with polarised optical microscopy using thin layers of a nematic liquid crystal with a positive dielectric anisotropy. The applicability of microdielectrometry was investigated using the nematic liquid crystal. Microdielectrometric monitoring was also performed during the preparation process for a solid film with oriented domains with long axes perpendicular to the electric filed cast from an isotropic aqueous solution of hydroxypropyl cellulose under the sinusoidal electric field with large amplitude of 2.0 kV mm^?1 and frequency of 10⁵ Hz. In the logarithmic relation between the dielectric constant and loss factor divided by J ₁₄, the two dielectric parameters measured for different film thicknesses at 2.0 kV mm^?1 were superposed on a single curve. The curve for the electrically oriented domains was considrably different from that for a randomly oriented polydomain texture found under the electric field with small amplitude of 0.05 kV mm^?1 and the same frequency.     

Synthesis and characterization of well‐defined optically active methacrylic diblock copolymers

A new, simple, and cost‐effective approach toward the development of well‐defined optically active diblock copolymers based on methacrylate monomers is described for the first time. Starting from the low‐cost optically active (S)‐(?)‐2‐methyl‐1‐butanol, a new optically active methacrylic monomer, namely, (S)‐(+)‐2‐methyl‐1‐butyl methacrylate [(S)‐(+)‐MBuMA], was synthesized. Reversible addition fragmentation chain transfer polymerization was then used for preparing well‐defined poly[(S)‐(+)‐MBuMA] homopolymers and water‐soluble diblock copolymers based on [(S)‐(+)‐MBuMA] and the hydrophilic and ionizable monomer 2‐(dimethyl amino)ethyl methacrylate (DMAEMA). The respective homopolymers and diblock copolymers were characterized in terms of their molecular weights, polydispersity indices, and compositions by size exclusion chromatography and ¹H NMR spectroscopy. Polarimetry measurements were used to determine the specific optical rotations of these systems. The structural and compositional characteristics of micellar nanostructures possessing an optically active core generated by p((S)‐(+)‐MBuMA)‐b‐p(DMAEMA) chains characterized by predetermined molecular characteristics may be easily tuned to match biological constructs. Consequently, the aggregation behavior of the p[(S)‐(+)‐MBuMA]‐b‐p[DMAEMA] diblock copolymers was investigated in aqueous media by means of dynamic light scattering and atomic force microscopy, which revealed the formation of micelles in neutral and acidified aqueous solutions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effects of ELF Magnetic Field in Combination with Iron(III) Chloride (FeCl3) on Cellular Growth and Surface Morphology of Escherichia coli (E. coli)

This study investigated the effects of extremely low frequency (ELF) magnetic field with/without iron(III) chloride (FeCl₃) on bacterial growth and morphology. The ELF exposures were carried out using a pair of Helmholtz coil-based ELF exposure system which was designed to generate 50 Hz sinusoidal magnetic field. The field was approximately uniform throughout the axis of the coil pair. The samples which were treated or non-treated with different concentrations FeCl₃ were exposed to 50 Hz, 2 millitesla (mT) magnetic field for 24 h. ELF effect on viability was assessed in terms of viable colony counts (in colony-forming unit per milliliter) with the standard plate count technique. Scanning electron microscopy was used to investigate the magnetic field effect on surface morphology of Escherichia coli. No significant results were seen in terms of cell viability between ELF and sham-exposed bacterial strains. Similarly, FeCl₃ treatment did not change cell viability of E. coli samples. However, we observed some morphological changes on E. coli cell surfaces. Pore formations and membrane destruction were seen on the surface of 24 h ELF field-exposed cells. We concluded that ELF magnetic field exposure at 2 mT does not affect cell viability; however, it may affect bacterial surface morphology.     

Model Studies of Nitroxide‐Mediated Styrene Miniemulsion Polymerization – Opportunities for Process Improvement

Modeling studies were performed to investigate how persulfate‐initiated nitroxide‐mediated styrene miniemulsion polymerizations are influenced by changes to the polymerization recipe. By manipulating the initial concentrations of potassium persulfate and nitroxide, and the aqueous phase volume, trends in the predicted polymerization time, number average molecular weight, polydispersity and degree of polymer livingness were identified that indicate operating conditions for improved process performance. Specifically, our model predicts the existence of experimental conditions that simultaneously minimize polymer polydispersity and maximize the livingness of the polymer. The mechanisms responsible for the predicted trends were identified from the predicted molecular weight distributions of the living and dead polymer chains.

Predicted number MWDs at 20% monomer conversion for styrene NMMP systems employing various levels of [KPS]_aq,0. Dormant KPS‐initiated polymer radicals.