Electric response of a cell of hydrogel: Role of the electrodes (original) (raw)
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Influence of the rheological properties on the electrical impedance of hydrogels
Journal of Applied Physics, 2012
We show that the anomalous frequency dependence of the real part of the electrical impedance of hydrogels can be interpreted by taking into account their non-Newtonian character, according to which the effective viscosity, η, depends on the frequency of the imposed deformation. Our experimental results are in good agreement with the Poisson–Nernst–Planck model if the ionic viscosity is taken proportional to the macroscopic one, measured by means of a viscositymeter, and the diffusion coefficient is assumed frequency dependent according to the formula of Stokes D = KBT/(κη), where κ is a shape coefficient. From this result it follows that the non-Newtonian character of complex liquid can be investigated by means of the impedance spectroscopy technique.
Physiological Measurement, 2010
In biomedical applications such as the electroencephalogram, electrocardiogram and electromyogram, usually conductive hydrogels are applied to the skin providing a skin-electrode layer, with the aim of lowering contact impedance and improving the signal/noise ratio. It is important to know the electrical behavior of these materials, obtaining reliable values of their conductivity. It can be extracted by the whole cell impedance, which is affected not only by the bulk but also by the surface properties. The aim of the present work is to characterize the impedance of some currently available conductive hydrogels in the frequency range 5 Hz-1 MHz. For this purpose we have designed a novel cell, with silver electrodes, optical detection of the gap and guard ring. In this paper the results are compared with those obtained by means of a commercial cell with stainless steel electrodes, without a guard ring. In order to extract the different contributions of the bulk and the interface, we fitted the experimental data with a very simple model: the bulk properties are described by a single RC-parallel, whereas the interface is represented by a constant phase element.
Dielectric study of neutral and charged hydrogels during the swelling process
The Journal of Chemical Physics, 2006
Dielectric spectroscopy measurements of conductivity were applied for understanding the change in the internal morphology of the neutral and permanently charged polyacrylamide ͑PAAm͒ hydrogels during the swelling process. For the first time four distinct peaks ͑each corresponding to a different swelling stage͒ in the conductivity of the neutral gel were observed during the swelling of this gel. These peaks are related to the distribution of dense polymer regions ͑they are defined as the "blobs"͒ appearing in a microstructure of the given PAAm gel having at least four average sizes. For the charged gel the heterogeneity decreases due to the internal electric field of the charged sites. Thus, this characteristic behavior in the conductivity becomes almost negligible for the gel charged with permanent SO 3 − groups. It seems this fact causes considerable decrease in amplitude of the peaks and overall decrease the conductivity during the whole swelling process especially at high frequencies.
Thermoporometry and impedance analysis to study dynamics of water and polymer present in hydrogel
International Journal of Biological Macromolecules, 2015
Though various conventional methods are available to explore hydrogels, they have drawbacks such as analysis in solid state and failure to give insights into individual components of hydrogel viz. water (dispersion medium) and hydrophilic polymers (dispersed phase). The combined study of porosity and dielectric nature of hydrogel succeeds, in this context, as it investigates both the components individually. In this study, we have taken well-known hydrogel system gelatin-polyvinyl alcohol (PVA) cross linked with genipin. Thermoporometry has been used to investigate the state of water and porosity whereas Alternative Current (AC) impedance analysis has been used to study about nature of polymers through dielectric properties in hydrogel. The influence of physic-chemical properties was examined with SEM and in vitro drug release using catechin. The study revealed that increasing concentration of PVA to gelatin has retained excessive bound water molecules exhibiting high polarity in each polymeric component. Further, it is shown that reduction in pore size and high reactivity with drug molecules have led to lower initial release and increase total amount of release. We conclude that non-conventional methods such as thermoporometry and AC impedance analysis yield more valuable information about hydrogel, which can aid in designing appropriate biomaterial for intended drug release.
Effect of composition on the dielectric properties of hydrogels for biomedical applications
Physiological Measurement, 2010
Ba(Ti 0.75 Sn 0.25)O 3 • xPbTiO 3 (0 ≤ x ≤ 1) samples prepared by a standard ceramic processing route have been characterized by X-ray diffraction, thermogravimetry, and dielectric, piezoelectric, and pyroelectric measurements. The results demonstrate that the system in question contains solid solutions with the perovskite structure, which have cubic symmetry for x < 0.2 and tetragonal symmetry for x ≥ 0.2. Increasing the percentage of PbTiO 3 in the samples has been shown to cause sequential changes in their dielectric properties in the following sequence: ferroelectric relaxor, reentrant ferroelectric relaxor, ferroelectric with a diffuse phase transition, and conventional ferroelectric.
Impedance properties and comparison effects of different dose safranin doped hydrogels
Journal of Non-crystalline Solids, 2017
Frequency evolution of dielectric characteristics of different dose safranin (SR) doped hydrogels was studied by impedance spectroscopy (IS) at room temperature (RT). Real and imaginary parts of complex dielectric constant, impedance, electric modulus and conductivity of SR doped hydrogels were analyzed in the frequency range of 100 Hz to 40 MHz for pH 5.0 value. Phase angle, capacitance, surface resistivity, tangent factor (tan δ) for all samples were recorded with the same frequency range. Surface and bulk polarization effects were dominant on impedance at low and high frequency regime, respectively. Fluctuation effect of SR doped hydrogels was observed from the dielectric measurements. Tutorial of radio frequency, RF, impedance matching were realized by using the Smith chart. The coulomb interaction between SR-cations and hydrogels may be anticipated to enhance the organic electrical performance. The potential applications of SR doped hydrogels were presented to microbial fuel cells.
Dielectric Characterization of Biopolymer/Poly(ϵ-Caprolactone) Hydrogels
International Journal of Polymer Analysis and Characterization, 2014
The dielectric properties of a series of pure atelocollagen samples and of atelocollagen-based hydrogels long-range cross-linked with bifunctional poly(e-caprolactone) derivative, or further short-range cross-linked by UV irradiation, were discussed in relation to the cross-linking method, composition, and hierarchical assembly. Three main factors with significant influence on the electrical behavior, frequency, temperature, and moisture content, are analyzed in detail.
Dynamic electric-field-induced response of charged spherical colloids in uncharged hydrogels
2009
Embedding colloidal particles in polymeric hydrogels often endows the polymer skeleton with appealing characteristics for microfluidics and biosensing applications. This theoretical study provides a rigorous foundation for interpreting active electrical microrheology and electroacoustic experiments on such materials. In addition to viscoelastic properties of the composites, these techniques sense physicochemical characteristics of the particle–polymer interface. Wang & Hill (Soft Matter, vol. 4, 2008, p.
Electroanalysis, 2009
Microfabricated microdisk electrode arrays (MDEAs) of 50 mm (5184 disks), 100 mm (1296 disks) and 250 mm (207 disks) (d/r ¼ 4; A ¼ 0.1 cm 2 ) were coated with poly(hydroxyethylmethacrylate)-based hydrogel membranes and studied by electrochemical impedance spectroscopy (EIS) in 1.0 mM ferrocene monocarboxylic acid (FcCO 2 H). Equivalent circuit modeling showed an approximate three-fold increase in solution resistance, R sol , and an order of magnitude increase in charge transfer resistance, R ct, resulting from a reduction in apparent diffusivity of FcCO 2 H. Additionally, both resistive parameters decreased while the capacitance (Q) increased with decreasing microdisk diameter; consistent with an increase in effective electroactive area. The hydrogel layer did not compromise enhanced mass transport achieved by the MDEA and thus may be used to advantage in biosensors.