Protein dielectrophoresis: Key dielectric parameters and evolving theory

Globular proteins exhibit dielectrophoresis (DEP) responses in experiments where the applied field gradient factor ∇E² appears far too small, according to standard DEP theory, to overcome dispersive forces associated with the thermal energy kT of disorder. To address this a DEP force equation is proposed that replaces a previous empirical relationship between the macroscopic and microscopic forms of the Clausius–Mossotti factor. This equation relates the DEP response of a protein directly to the dielectric increment δε⁺ and decrement δε⁻ that characterize its β-dispersion at radio frequencies, and also indirectly to its intrinsic dipole moment by way of providing a measure of the protein's effective volume. A parameter Γ_pw, taken as a measure of cross-correlated dipole interactions between the protein and its water molecules of hydration, is included in this equation. For 9 of the 12 proteins, for which an evaluation can presently be made, Γ_pw has a value of ≈4600 ± 120. These conclusions follow an analysis of the failure of macroscopic dielectric mixture (effective medium) theories to predict the dielectric properties of solvated proteins. The implication of a polarizability greatly exceeding the intrinsic value for a protein might reflect the formation of relaxor ferroelectric nanodomains in its hydration shell.     

On the structure of the microscopic dielectric tensor in incommensurate crystals

A microscopic model for calculating the optical response of incommensurately modulated phases in insulating crystals is presented. The dominant contribution to the dielectric permittivity tensor is shown to originate from the lowest-index reciprocal lattice vectors, thus proving the validity of the mesoscopic approach developed in several earlier studies. The expression for the mesoscopic Fourier component of the dielectric tensor is obtained. These results may be useful in relation to the controversial problem of the optical activity observed in the incommensurate phases of some A₂BX₄ family crystals.     

Induced twisted-grain-boundary phases in the binary mixtures of a cholesteric and a nematic compound

Thermodynamical, optical-texture and dielectric studies have been performed to study the phase diagram of the binary system of 5-cholesten-3β-ol-octanoate and 4-n-nonyloxybenzoic acid. It is observed that low concentrations of 5-cholesten-3β-ol-octanoate (2–30?mol?%) in 4-n-nonyloxybenzoic acid induce a mean-field phase diagram derived by Renn within the framework of the chiral Chen–Lubenski model. Various optical textures of the twisted-grain-boundary (TGB) phases under different conditions of molecular anchoring have been observed. Weak transitions related to the TGB phases have been detected by temperature dependent dielectric spectroscopy.     

Phase transitions and metastable states in TlGaSe2

The results of measurements of the dielectric constant of TlGaSe₂ in temperature range of successive phase transitions are presented. An anomaly in the temperature dependence of the real part of dielectric constant in TlGaSe₂ has been observed at about 242?K in addition to anomalies at 115, 108, and also near 65?K as reported in previous publications. The presence of temperature hysteresis effects in temperature interval between 115 and 242?K allowed making a conclusion about possible existence of an incommensurate phase in the mentioned temperature range. A model of succession of the structural phase transitions in TlGaSe₂ has been suggested.     

Proteins as functional interlayer in organic field-effect transistor

The paper summarizes and discusses the recent advances of proteins as functional interlayers in organic field-effect transistors (OFETs). Specific focus is given on the proteins integrated into the device structure, either to act as dielectric materials or to perform as the functional interlayer between the dielectric and the organic semiconductor (OSC). The main emphasis is give to the location and the specific effect of protein layers in the structure of OFETs. Besides, the possibility of amyloid serving as useful building blocks for OFET is discussed.     

Crystal structure,physical properties and bond valence analysis of NaLuP2O7

Single crystals of a diphosphate NaLuP₂O₇ have been synthesized by the flux method and characterized by single-crystal X-Ray diffraction. NaLuP₂O₇ crystallizes in the monoclinic system with P2₁/n space group with cell parameters: a = 8.9985(8) Å, b = 5.3473(5) Å, c = 12.756(1) Å, β = 103.174° (1), V = 597.67 (9) Å³, Z = 4. Its structure consists of a three-dimensional framework of P₂O₇ units that are corner-shared by LuO₆ octahedra, forming tunnels running parallel to [010] which are occupied by Na atoms. NaLuP₂O₇ powder was characterized by XRD, SEM, FTIR and Raman spectroscopy. The activation energy of (1.49 eV) obtained by electrical measurements suggests the charge carriers to be the sodium cations. The activation energies obtained from impedance and loss spectra were analyzed in order to explain the mechanism of conduction. The correlation between ionic conductivity of NaLuP₂O₇ and its crystallographic structure was investigated and the most probable transport pathway model was determined.     

Effective permittivity of liquid crystal nanodispersions and composites with different pore structure

The volume filling fraction dependence of the effective permittivity of the nematic liquid crystal 4-n-pentyl-4’-cyanobiphenyl embedded in different porous membranes and dispersed with aerosil nanoparticles was determined using broadband dielectric spectroscopy in the frequency range from 10⁶ to 10⁹ Hz. The experimental data were analyzed and compared with some existing theories based on the effective medium approximation and their modifications. The obtained effective permittivities as a function of the volume filling fraction lie between the lower limits of the Wiener and Hashin–Shtrikman bounds. The observed shift of the experimental points reflects the changes in the structure of the investigated composites.     

Multiferroicity in La1/2Nd1/2FeO3 nanoparticles

Nano-sized La_1/2Nd_1/2FeO₃ (LNF) powder is synthesized by the sol–gel citrate method. The Rietveld refinement of the X-ray diffraction profile of the sample at room temperature (303 K) shows the orthorhombic phase with Pbnm symmetry. The particle size is obtained by transmission electron microscope. The antiferromagnetic nature of the sample is explained using zero field cooled and field cooled magnetisation and the corresponding hysteresis loop. A signature of weak ferromagnetic phase is observed in LNF at low temperature which is explained on the basis of spin glass like behaviour of surface spins. The dielectric relaxation of the sample has been investigated using impedance spectroscopy in the frequency range from 42 Hz to 1 MHz and in the temperature range from 303 K to 513 K. The Cole–Cole model is used to analyse the dielectric relaxation of LNF. The frequency dependent conductivity spectra follow the power law. The magneto capacitance measurement of the sample confirms its multiferroic behaviour.     

Effect of B-site isovalent doping on electrical and ferroelectric properties of lead free bismuth titanate ceramics

In the present work, zirconium modified bismuth titanate ceramics have been studied as potential lead-free ferroelectric materials over a broad temperature range (RT – 800 °C). Polycrystalline samples of Bi₄Ti_3−xZr_xO₁₂ (x=0.2, 0.4, 0.6) (BZrT) with high electrical resistivity were prepared using the solution combustion technique. The effect of Zr doping on the crystalline structure, ferroelectric properties and electrical conduction characteristics of BZrT ceramics were explored. Addition of zirconium to bismuth titanate enhances its dielectric constant and reduces the loss factor as it introduces orthorhombic distortion in bismuth titanate lattice which is exhibited by the growth along (0010) lattice plane. Activation energy due to relaxation is found to be greater than that due to conduction thus confirming that electrical conduction in these ceramics is not due to relaxation of dipoles. Remanent polarization of the doped samples increases as the Zirconium content increases.     

Spectral,Optical and Mechanical studies on pure and thiourea doped ammonium di-hydrogen phosphate NLO single crystals

Pure and thiourea substituted single crystals of ammonium di-hydrogen phosphate have been grown from aqueous solution by isothermal solvent evaporation technique. Doped crystal exhibits prominent changes in physical and chemical properties. Single crystal XRD analyses of the samples are carried out and the results are compared. FTIR and UV–vis–NIR spectral analyses have been employed to identify the presence of various functional groups and the UV cut-off range in the grown crystals. Density measurements have been made and Photoconductivity studies revealed the negative photo conducting nature. Hardness measurement shows that the mechanical strength of the doped crystal is high when compared to pure ammonium di-hydrogen phosphate. The dielectric response of the samples has been studied in the frequency range 100 Hz–5 MHz at room temperature and the results are discussed.