Microwave Dielectric Analysis Research Articles

Microwave Dielectric Analysis on Porous Hydroxyapatite/Starch Composites with Various Ratio of Hydroxyapatite to Starch

This study aims to investigate the dielectric response of the porous hydroxyapatite/starch composites by varying the starch proportion in determining the feasibility of the microwave sample characterization technique in bone tissue engineering. The porous hydroxyapatite/starch composites were fabricated by using natural starch (gelatinization and retrogradation) through the solvent casting and particulate leaching technique. The dielectric constant (ε′) and loss factor (ε′′) of the complex permittivity of the porous hydroxyapatite/starch composites were measured in the Ku band frequency of 12.4-18.0 GHz. ε′ and ε′′ of the porous composites increase with frequency. The highly porous composite that due to higher starch proportion exhibit higher ε′ and ε′′, resulting in the significant dielectric responses.

Influence of point defects in KTaO 3 on low-temperature dielectric relaxation

Substituted KTaO 3 ceramics were synthesized, sintered and studied using low-temperature microwave dielectric analysis and Raman spectroscopy. Because of a fundamentally different nature of aliovalent Mn- and isovalent Na-substitution mechanisms, significant differences in processing and dielectric properties were identified. The properties were correlated to the defect structure of the substituted KTaO 3 lattices. Characteristics of the induced polar domains were clearly different for the two substitutional mechanisms, which further reflects in a significantly different dielectric behavior. Linear response of changes in the Raman spectra corresponds to evidence of the formation of symmetry-breaking regions.

The effect of wet granulation on the erosion behaviour of an HPMC–lactose tablet, used as a rate-controlling component in a pulsatile drug delivery capsule formulation

The purpose of this study was to investigate the variability in the performance of a pulsatile capsule delivery system induced by wet granulation of an erodible HPMC tablet, used to seal the contents within an insoluble capsule body. Erodible tablets containing HPMC and lactose were prepared by direct compression (DC) and wet granulation (WG) techniques and used to seal the model drug propranolol inside an insoluble capsule body. Dissolution testing of capsules was performed. Physical characterisation of the tablets and powder blends used to form the tablets was undertaken using a range of experimental techniques. The wet granulations were also examined using the novel technique of microwave dielectric analysis (MDA). WG tablets eroded slower and produced longer lag-times than those prepared by DC, the greatest difference was observed with low concentrations of HPMC. No anomalous physical characteristics were detected with either the tablets or powder blends. MDA indicated water-dipole relaxation times of 2.9, 5.4 and 7.7×10 −8 ms for 15, 24 and 30% HPMC concentrations, respectively, confirming that less free water was available for chain disentanglement at high concentrations. In conclusion, at low HPMC concentrations water mobility is at its greatest during the granulation process, such formulations are therefore more sensitive to processing techniques. Microwave dielectric analysis can be used to predict the degree of polymer spreading in an aqueous system, by determination of the water-dipole relaxation time.

Properties of saccharides and saccharide derivatives in the dry and partially hydrated states

This study investigates the correlation (if any) between the surface properties of dry mannitol, sorbitol and glucose, as determined using inverse gas chromatography (IGC) and other techniques, with microwave dielectric analysis of the molecular polarisability of water in the hydrated material. Microwave dielectric analysis of the hydrated material (using a circular resonant cavity) showed a transition (ht) in the gradient of imaginary permittivity (e″ at 2.2 GHz) vs. water content for all materials. This transition reflects the appearance of another population of water with enhanced mobility. The gradient below ht (m1) reflects the reorientation mobility of water close to the surface of the solid, and therefore provides one measure of the strength of interaction with each material. Estimates for ht and m1 parallel the IGC data by giving a rank order of affinity as glucose ≥ mannitol ≥ sorbitol. This link suggests that the molecular properties of water and the strength of interaction with the hydrated material are most certainly governed by the acceptor/donor properties of the surface (as determined by IGC). Moreover, it can be inferred that the presence of mobile water (up to the relatively high levels defined by ht) does not change the surface energy of the material.

Composition-dependent dynamical structures of monohydric alcohol-water mixtures studied by microwave dielectric analysis

Dielectric relaxation measurements on methanol (MA)-water, ethanol (EA)-water, and 1-propanol (1PA)-water mixtures were carried out using TDR (Time Domain Refletometry) for the entire concentration range of 0 ≤ X (molar fraction of alcohol) ≤ 1.0 up to 25GHz at 20°C-30°C. We have calculated the excess activation free energy, enthalpy, and entropy of these mixtures, ΔG E , ΔH E , and ΔS E , and the excess partial molar quantities for alcohol, ΔG A E , ΔH A E , and ΔS A E (A = MA, EA, and 1PA) and those for water, ΔG W E , ΔH W E , and Δ S W E from the temperature-dependent relaxation times. There exists boundary above and below which behaviors of the partial molar quantities are quite different. If we call the concentration corresponding to the boundary X b, X b∼0.30, 0.18, and 0.14 for methanol-water, ethanol-water, and 1-propanol-water, respectively. In the region of X ≥ X b, Δ H A E and Δ S A E are nearly zero. This means that, in terms of the activation enthalpy and entropy, alcohol molecules in the mixtures find themselves in not a very different environment from that in pure liquid. In water-rich region, ΔH A E and ΔS A E exhibit two maxima at X 1 and X 2, where X 1∼0.045, 0.04, and 0.03, and X 20.12, 0.08, and 0.06, for methanol-water, ethanol-water, and 1-propanol-water, respectively. This is clearly attributed to hydrophobic hydration. Detailed analysis of the behavior of ΔH A E and ΔS A E (A=MA, EA, and 1PA) suggests the formation of two kinds of saturated hydration structures and their transition; the clathrate hydration shells with tetrahededral local arrangements of water molecules around X∼ X 1 and non-clathrate shells with large cavities with three-coordinated local arrangements around X∼ X 2.

Hydrophobic hydration and molecular association in methanol–water mixtures studied by microwave dielectric analysis

Dielectric relaxation measurements on the methanol–water mixtures for the entire concentration range were carried out using time domain reflectometry in the frequency range from 500 MHz to 25 GHz at 20, 25, and 30 °C. The excess partial molar activation free energy, enthalpy, and entropy for methanol, ΔGMAE, ΔHMAE, and ΔSMAE, and those for water, ΔGWE, ΔHWE, and ΔSWE, were calculated from accurately measured concentration and temperature dependence of the dielectric relaxation time of the mixtures. The behavior of the excess partial molar quantities in the regions below and above X (molar fraction of methanol) ∼0.3 are quite different from each other. In a water-rich region, ΔHMAE and ΔSMAE exhibit two maxima at X∼0.045 and X∼0.12, which is clearly attributed to structural enhancement of the hydrogen bond network of water, the so-called hydrophobic hydration. Appearance of two maxima in ΔHMAE and ΔSMAE implies that water molecules surround methanol molecules in qualitatively different manners around the two points. In the concentrated region of X⩾0.3, the values of ΔHMAE and ΔSMAE become nearly zero, which means that methanol molecules in the mixtures find themselves in not a very different environment from that in pure methanol, associated and forming chainlike clusters. Water molecules seem to exothermically attach to the hydrophilic site of methanol.

Protein hydration in solution. By high-resolution microwave dielectric analysis method.

Protein hydration in solution. By high-resolution microwave dielectric analysis method.

A method of measuring surface permittivity by microwave dielectric analysis

A method for controlling skin depth by microwave dielectric analysis using an open end cell is presented here. The correlation between the measured permittivity, the electric length of the cell, and the permittivity depth profile has been shown from time domain reflectometry measurements on a sample with known depth profile of permittivity. This skin depth controlling method is exceedingly useful for dielectric analysis of water in living organisms and related food products.

Hydration Study of Proteins in Solution by Microwave Dielectric Analysis

We propose a method for evaluating protein hydration which enables one to evaluate the amount of restrained water and distinguish between “weakly” and “strongly” restrained water on proteins in an aqueous solution using microwave dielectric measurement. Measurements were taken with a precision microwave network analyzer and a thermostated glass cell at 20.0 ± 0.01 °C with an open-end flat-surface coaxial probe. Examined proteins were cytochrome c, myoglobin, ovalbumin, bovine serum albumin, and hemoglobin. The present method is based on the Wagner equation and the Hanai equation for emulsion analysis and assumes that there is “weakly” restrained water on proteins which has a simple Debye-type relaxation in the gigahertz region and that the dielectric constants of hydrated solutes at high-frequency limits are given by the electron polarizations of atom groups. This analysis enabled us to characterize more precisely the hydration state of proteins in water.