Low AC Electric Field Research Articles

Diffusion-based culture and real-time impedance monitoring of tumor spheroids in hydrogel microwells of a suspended membrane under microfluidic conditions

Tumor spheroids are widely studied for in vitro modeling of tumor growth and responses to anticancer drugs. However, current methods are mostly limited to static and perfusion-based cultures, which can be improved by more accurately mimicking pathological conditions. Here, we developed a diffusion-based dynamic culture system for tumor spheroids studies using a thin membrane of hydrogel microwells and a microfluidic device. This allows for effective exchange of nutrients and metabolites between the tumors and the culture medium flowing underneath, resulting in uniform tumor spheroids. To monitor the growth and drug response of the spheroids in real-time, we performed spectroscopic analyses of the system's impedance, demonstrating a close correlation between the tumor size and the resistance and capacitance of the system. Our results also indicate an enhanced drug effect on the tumor spheroids in the presence of a low AC electric field, suggesting a weakening mechanism of the spheroids induced by external perturbation.

Streamers in transformer oil initiated by partial discharge in a bubble at low AC electric fields

Streamers in transformer oil initiated by partial discharge in a bubble at low AC electric fields

The effect of fatty acids, ionic strength, and electric fields on the microscopic dynamics of BSA aggregates

This paper presents the microscopic dynamics of the concentrated suspensions of bovine serum albumin (BSA) proteins and their aggregates by dynamic light scattering (DLS) experiments. The effects of fatty acids binding to BSA, as well as the ionic strength and weak electric field, are discussed for affecting the stability of BSA suspensions against calcium-induced aggregation. By variation of the ionic strength, in the absence of an external electric field, DLS experiments show that monomer–BSA interactions (in the essentially fatty acid-free case) are overall repulsive but that, nevertheless, aggregation occurs to some extent. Also, the diffusive properties of different types of BSA are explored under an applied low-AC electric field by means of in situ electric small-angle depolarized DLS experiments, which reveal a significant decrease of the translational BSA–monomer diffusion coefficient with increasing frequency, while the aggregates indicate orientational motion via rotation on applying an electric field. These observations are interpreted in terms of (localized) orientation interactions obtained as oscillations in the intermediate scattering correlation function, as well as the anomalous slower relaxations as resulting in effective (collective) dynamics between monomeric BSA and their protein aggregates.

Electric field effects on phase transitions in the 8CB liquid crystal doped with ferroelectric nanoparticles.

The influence of a low ac electric field on phase transitions is discussed in the case of a nematic liquid crystal 4-n-octyl-4^{'}-cyanobiphenyl (8CB) doped with Sn_{2}P_{2}S_{6} ferroelectric nanoparticles. The phase-transition temperatures obtained from temperature-dependent dielectric measurements were higher than those determined by the calorimetric method. This difference is explained by the presence of the measuring electric field which induces two effects. The first one is the amplification of the interactions between the nanoparticle polarization and the liquid-crystal order parameter. The second one is the field-induced disaggregation or aggregation process at high nanoparticle concentrations.

Charged Colloidal Rods Out of Equilibrium

This article is a comprehensive overview of the ongoing research of the author on charged colloidal rods out of equilibrium, under external electric fields and at high concentrations around the glass transition. The suspensions of fd-virus particles are used as a model system for charged colloidal rods, which exhibit several disorder-order (and liquid-crystalline) phase transitions. When a low AC electric field is applied to suspensions in isotropic-nematic coexistence concentration, with frequencies that are sufficiently low to polarize the electric double layer and the layer of condensed ions, various phases/states are induced: a chiral nematic, a dynamical state where nematic domains persistently melt and form, and a uniform homeotropic phase. A point in the field-amplitude versus frequency diagram, where various transitions lines meet, can be identified as a non-equilibrium critical point. Without an electric field, at high concentrations of charged fd-rods, various self-assembled orientation textures are found beyond the isotropic-nematic coexistence regions, and a glass transition is observed on approach and within the glass state that are probed. The presented system exhibits transient behaviors of repulsive glasses and slow dynamics out of equilibrium.

Behavior of carbon cone particle dispersions in electric and magnetic fields

The behavior of carbon cone (CC) particle dispersions in electric and magnetic fields is presented. The behavior of CC dispersions in an ac electric field was studied by the use of electrorheological (ER) measurements. Low ac electric fields were sufficient for fibrilar structures to form. However the structures formed were relatively weak as determined by ER measurements and this was attributed to the high conductivity of the particles. This is also consistent with the low relaxation frequency found by impedance spectroscopy. The behavior of a dispersion of CC added ferrofluid was studied using magnetorheological measurements. The relative increase in viscosity was found to be around 1.2–1.5 for low magnetic fields and low shear rates. This was attributed to purely hydrodynamic effects caused by CC particle–particle interactions.

Directional growth by low electric-field-controlled crystallization of bulk amorphous lithium tetraborate

Highly oriented rod-shaped crystals were grown during crystallization of bulk amorphous Li2B4O7 under a low ac electric field of ∼5V∕mm. The crystal c axis that is the long direction of rods and perpendicular to the flat surface of the sample is parallel to the applied electric-field direction. The oriented crystals, with an alignment within a declined angle of ∼15°, are so long along the c direction compared with those of other directions that the geometrical structure of each rod is quasi-one-dimensional. The measured electromechanical coupling coefficient of kt=0.47 is comparable to that of single-crystal Li2B4O7.

Electrooptic Effects in the Nematic and Isotropic Phases of Aqueous V2O5 Suspensions

In water-based lyotropic liquid crystals (LCs), e.g., aqueous suspensions of V2O5, the electrooptical effects typical of thermotropic mesophases are difficult to observe, owing to the large conductivity and electrochemical reactions of the suspensions. Overcoming these difficulties, the authors demonstrate that V2O5 aqueous nematic suspensions can be aligned and even reoriented in a low AC electric field—in addition to the recently reported slow (30 min) alignment in magnetic fields. The response time of ∼1 s indicates that mineral LCs may be suitable for simple display applications.

A Discrete Change of the Rotation Angle in Twisted Structures

Abstract A forced relaxation of LC molecules placed in an usual twist cell was realised at relative low AC electric field frequencies in a nematic LC material, possesing an inversion of dielectric anisotropy sign upon frequency. Some changes of periodic structures were observed in range of critical frequencies. A discrete change of the rotation angle of the NLC structure was observed. The possibility of the practical use of this penomena is discussed.