Dielectric analysis of PMMA microcapsules containing an aqueous KCl solution to derive a distribution function of the release rate of KCl

Release of KCl from a batch of PMMA microcapsules containing an aqueous 3 mM KCl solution was studied with the following two methods: 1) dielectric measurements of suspensions of the microcapsules in distilled water. The electrical conductivity of capsule interior was estimated with this method. 2) Measurements of the conductivity of suspending medium of the microcapsule suspensions. These two kinds of experiments provided us with information about the amount of KCl remaining in the capsules and that diffused outside. Results of these experiments showed that the microcapsules varied in their release rate of KCl. A distribution function of the release rates was derived from the results of the dielectric measurements. That distribution function was successful in explaining the results of the measurements of the conductivity of suspending medium. Furrther examination revealed that the release rate increased with the increase in the thickness of capsule wall.     

Analysis of dielectric observations of KCl-charged poly(methyl methacrylate) microcapsules using a two-component model consisting of KCl-permeable and KCl-impermeable capsules

Dielectric measurements were carried out on aqueous suspensions of poly(methyl methacrylate) microcapsules charged with KCl solutions to examine the KCl permeability of the microcapsules. The specimens exhibited three kinds of dielectric relaxation. Two kinds of dielectric relaxation were observed immediately after washing the specimens with distilled water. These overlapped each other when the specimen was left standing in the measuring cell for a long time. Their relaxation frequencies were affected by the KCl concentration of the suspending medium in which the specimen was kept before washing. Another relaxation was observed distinctly when the spepcimens were washed thoroughly with distilled water. Its relaxation frequency was affected by the KCl concentration of the charged solution. These results were explained by assuming that the specimens were mixtures of KCl-permeable and KCl-impermeable capsules. The theoretical analysis procedure was devised in the light of dielectric theory of interfacial polarization to estimate the parameters which characterize the structure of the specimens.     

Dilatometric study of glass transition kinetics in polyisoprene

From dielectric measurements the thermal dependence and the distribution function of the relaxation times can be determined. In the present contribution we are testing the correspondence between the relaxation times obtained from the dielectric measurement and the dilatometric behavior of the material in the vicinity of the glass transition temperature. The experimental data used for the comparison were obtained for the sample of polyisoprene.     

反渗透膜UTC-70在水溶液中的介电谱及其解析

根据平面层状体系介电弛豫理论研究了反渗透膜UTC-70在各种浓度氯化钠和氯化钾溶液中的介电弛豫行为.利用计算机拟合的方法得到膜/溶液体系的介电参数,并由此计算得到了UTC-70膜相和水溶液相的相参数,获得了反映反渗透膜UTC-70荷电情况的信息及其与电解质溶液浓度的关系,介电解析的结果解释了介电弛豫的产生机制.     

Chain dynamic parameters for some acrylic polymers

The dielectric relaxation data of Ishida et al. on a number of acrylic polymers are represented in terms of the relaxation function proposed by Havriliak and Negami using the multi-response techniques developed by Havriliak and Watts. Two of the parameters of this function are interpreted in terms of a temperature dependent distribution of relaxation times. In this method of interpretation the breadth of the distribution function is temperature-dependent while the skewness is not. The temperature dependence of the breadth of the distribution function is similar for most of these acrylic polymers.The parameters of the relaxation function are also interpreted in terms of Mansfield's model which represents intra- and inter-molecular interactions in terms of springs and dash pots. Briefly, increasing the side chain length for the methacrylate series increases the inter-molecular relaxation time which may be due to an increase in the entropy of activation for the orientation process. The difference between the one acrylate in this study and the four methacrylates of the series is a reduction in the intra-molecular relaxation time, apparently due to the lack of the alpha methyl group.     

DC dielectric study of polyethylene/CaCO3 composites

The dielectric properties of composite samples prepared by polymerizing ethylene on the surface of filler are compared to those of mechanical mixtures consisting of CaCO₃ and ultra high molecular weight polyethylene. After presenting the normalized master curves of AC dispersion and loss measured at different relative humidities, the field strength dependence of the 50 Hz AC and DC responses were studied. With one exception, the effect is small. Thermally stimulated polarization (TSP) and depolarization (TSD) curves are presented; the peak appearing on the TSP curves of the samples stored under ambient conditions is interpreted as a result of water desorption. The high temperature DC conductivity and the depolarization current density are higher in the composites and mechanical mixtures than in the matrix. The dielectric properties of the wet filler particles were calculated from the measured composite and matrix data using various mixture formulae. The results can be understood and interpreted if the dielectric properties of adsorbed water are described by the cluster theory of dielectric relaxation.     

Amorphous solid-like distribution of polydisperse particles of colloidal clay and microcrystalline cellulose in deionized suspension

A metallurgical microscope is used to directly observe the amorphous solid-like structures of deionized suspensions of highly polydispersed colloids in sedimentation equilibrium. The colloids used are colloidal clay of bentonite and microcrystalline cellulose (MCC). The two-dimensional distance distribution functions of the amorphous solid-like structures at relatively diluted and concentrated suspensions resemble those of the liquid-like and gas-like structures of monodispersed spheres, respectively. The center-to-center interparticle distances (D) in the amorphous solid-like structures are explained by the effective hard-sphere model; a colloidal particle is coated with electrical double layers. The maximum length of the width of the double layers (Debye length,D ₁) observed is ca. 1n at very dilute suspensions.D andD ₁ continue to decrease as the initial concentration of the particles increases, and from these data rigidities are estimated to be 0.12 and 0.09 Pa for bentonite and MCC suspensions, respectively. The log [viscosity] of bentonite suspensions begins to increase linearly as log [shear rate] decreases with a slope close to –1, which supports the solid-like nature of the suspensions. These experimental results show that electrostatic interparticle repulsion and the elongated Debye-screening length around the particles are both essential for the appearance of the amorphous solid-like structures.     

Studies of polymer solvation by dielectric relaxation spectroscopy I: polyvinyl pyrrolidone in propylene carbonate,dimethyl sulfoxide and tetramethyl urea

The dielectric relaxation behavior of the title solutions of PVP 40000 is measured in the frequency domain (50 MHz to 36 GHz) at 20 °C. The polymer content of the solutions (up to 0.25 mole fraction of monomer units) is such that it does not yet contribute significantly to dielectric loss. The solvent relaxation shows in all cases a bulk and a slowed down contribution, both characterized by concentration-independent relaxation times. The slow contribution is ascribed to the solvate. Solvation numbers for dilute solutions roughly range between 2 and 4 per PVP repeat unit.     

Dielectric analysis of macroporous anion-exchange resin beads suspensions

Dielectric measurements were carried out for suspensions of D354 anion-exchange beads dispersed in electrolyte solutions at different concentrations, and distinct Maxwell-Wagner dielectric relaxations were observed around 10(6) Hz. Through fitting the experimental data we obtained the dielectric parameters of the suspensions, and then we calculated the phase parameters from the dielectric parameters and the measured volume fractions by Hanai's method. In light of the present understanding of the interfacial properties, and with the information obtained from the phase parameters, we satisfactorily interpreted the concentration dependences of the dielectric parameters. It is concluded that Hanai's method is an effective tool for obtaining the properties of dispersed particles; the properties of the electrical double layer, which are mainly decided by the properties of the electrolyte solution, predict the dielectric behavior of suspensions with conducting particles. The dielectric relaxation spectroscopy (DRS), based on the M-W mechanism, is also a very sensitive tool for probing the properties of the liquid/solid interface.     

Recent development in dielectric relaxation spectroscopy of polymers

An evaluation strategy for dielectric measurements in the frequency and/or time domain is presented which provides complete information about a relaxation mechanism (intensity, position, and shape of the relaxation function) independent of overlapping with neighboring mechanisms. As an example results on poly-(ethyleneterephthalate) are given.     

Dielectric relaxation spectroscopy of aqueous micellar electrolyte solutions: A novel application to infer Dukhin number and zeta potential of a micelle

The complex permittivities of aqueous SDS solutions, with and without the addition of sodium chloride (NaCl), are measured in the frequency range from 200 MHz to 14 GHz. The SDS concentrations are chosen such that the SDS molecules aggregate to micelles. In this frequency range, the measured spectra allow for the identification of two different relaxation processes. That is, the relaxation of the water molecules at frequencies above 1 GHz and the micellar relaxation at frequencies lower than 1 GHz. It is found that the addition of NaCl to the system mostly affects the micellar relaxation process. In detail, the time constant as well as the amplitude of the relaxation decrease by adding NaCl. These effects are attributed to the change in the solution conductivity that changes the properties of the micelle's electrical double layer. We also extract the Dukhin number of the micelles as a function of surfactant and electrolyte content from the measurements. The Dukhin number is a dimensionless group that describes the influence of the surface conductivity on a phenomena. A regression between Dukhin numbers and free sodium ions is found so that all data collapses on a single curve independent of the surfactant concentration. The surface conductivity is a manifestation of the electrical double layer and we use the Bikerman equation to infer the zeta potential of the micelles. Comparison to literature data shows very good agreement and proves that dielectric relaxation spectroscopy can be engaged to infer the zeta potential of micelles. Abbreviations: CMC critical micelle concentration, DRS dielectric relaxation spectroscopy, EDL electrical double layer     

The rheology and microstructure of charged colloidal suspensions

The effects of electric charge interation and particle correlations on suspension rheology are examined. A one-component fluid analysis using a Smoluchowski equation for the equilibrium structure is applied to charged suspensions of spherical colloids under shear. The frequency dependent modulus and viscosity, predicted as functions of particle and added salt concentrations, are compared with published rheological measurements on model suspensions. Recent improvements in the statistical mechanical theories for the equilibrium microstructure, its nonequilibrium deformation, and the bulk shear stresses are included. The direct electrostatic interaction is found to drive the divergence in the shear viscosity near the liquid-solid phase transition. Extensions of the theory predict the elastic modulus of binary mixtures of charged colloids. Estimates of the primary electroviscous effect, hydrodynamic interactions, and errors in the Yukawa limiting form for the potential and applications of asymptotic theories are presented. Predictions for the rheology based on effective hard-sphere models are found to be reasonable when using a parameter fit from the equilibrium phase behavior. Mean-field mode coupling theories predict larger relaxation times than calculated from the Smoluchowski equation (=SE). A study of binary mixing effects on elasticity shows non-ideal behavior. It is noted that equilibrium structural information can be used to resolve discrepancies between the theoretical predictions and the measured rheology.     

Microscopic observation of ordered colloids in sedimentation equilibrium and the importance of the Debye-screening length. 9. Compressed crystals of giant colloidal spheres (diam. 2–66 μm)

Compressed crystal-like structures of very large polystyrene spheres (specific gravity=1.05, diameter=2–66 m) are observed directly by a metallurgical microscope in sedimentation equilibrium and in deionized aquueous and 20 vol % methanol aqueous suspensions. Spheres of 2–42 m in diameter float above the cover glass apart from each other. The center-to-center intersphere distance decreases as the initial concentration of spheres increases, from which Young's elastic moduli (G) for the crystal-like structures are estimated to be between 1 to 10 dyn/cm², irrespective of the spheres size.G's in aqueous suspension are smaller than those in methanol aqueous mixtures. The crystal-like structures are compressed substantially by the gravitational field. These results are consistent with the significant role of the electrical double layers under the influence of purely electrostatic repulsive forces in the effective hard-sphere model.     

Electrolytic conductivity of poly(1,3-propylene phosphate) solutions containing mono- and divalent-counterions

The results of conductivity measurements for aqueous solutions of poly(1,3-propylene phosphate) (PPP), which can be considered as a synthetic analogue of naturally occurring teichoic acids, are reported. Experiments were carried out with oligomeric fractions of a polymer in acidic, sodium, potassium, magnesium and calcium forms. The concentration and molecular weight dependence of the equivalent conductivity of PPP was analysed and the limiting equivalent conductivity determined. From the conductivity data, the polyion-counterion interaction parameter F and the equivalent conductivity of a polyion _p were calculated. It was shown that both F and _p depend on polyelectrolyte solution concentration and molecular weight of PPP. Conclusions concerning mono- and divalent metal ions binding to PPP are drawn.     

Broadband dielectric spectroscopy on a discotic liquid crystalline polymer

Broadband dielectric spectroscopy is employed for the first time to study the molecular dynamics in discotic liquid crystalline polymers. One dielectric relaxation process is found which is strongly broadened and asymmetric. It is assigned a local hindered rotation of the ester groups attaching the spacer to the discotic mesogen. This assignment is supported by NMR measurements on the identical substance.Dedicated to Prof. E. W. Fischer on the occasion of his 60th birthday.     

The complex rheological behavior of an aqueous cationic surfactant solution investigated in a Couette-type viscometer

In this paper the behavior of an aqueous surfactant solution in a rotational Couette viscometer is investigated. It is shown that this behavior depends strongly upon time, upon the way in which the flow curve is obtained (with increasing or decreasing shear rate), upon the temperature, and upon the concentration of the solution. Furthermore, the results also reveal a pronounced dependence upon the size of the actual measuring system used. It is shown that the slip-velocity concept is not applicable to explain this dependence.     

Kinetic study of ion exchange reaction between lysozyme and carboxymethyl Sephadex C-25

The ion-exchange reaction of lysozyme with carboxymethyl Sephadex C-25 was followed by conductivity change as a function of time just after the rapid mixing of the protein solution with the Sephadex suspension. A single relaxation process was observed; the conductivity increased exponentially with time in the 100 s scale. In this process, protons were released from the Sephadex C-25 in the same time scale. The relaxation process slowed down with an increase in the lysozyme concentration, but it quickened upon the addition of HCl. On the other hand, the potential on the Sephadex C-25 surface changed from a negative value to a positive one with an increase in the amount of lysozyme adsorbed on the surface. On the basis of these data, the relaxation process was attributed to the ion-exchange reaction of lysozyme with several protons of carboxymethyl groups of the Sephadex.     

Limiting equivalent electrical conductivity of inorganic salt solutions and dielectric properties of a polar solvent

A relation has been found to exist between the limiting equivalent electrical conductivity of inorganic salt solutions, viscosity, temperature, and dielectric properties of the solvent. As temperature rises, the limiting equivalent electrical conductivity of aqueous solution of an inorganic salt has been shown to increase in direct proportion to the ratio of the dielectric permittivity to the dipole dielectric relaxation time, i.e., the limiting high-frequency electrical conductivity of the polar solvent. Expressions have been derived to be used in ascertaining the limiting equivalent electrical conductivities of inorganic salt solutions proceeding from the dielectric properties of the solvent.     

Microscopic observation of ordered colloids in sedimentation equilibrium and the importance of Debye-screening length. 8. Unsymmetrical ordering and inclusion of anisotropic particles

Unsymmetrical crystal-like ordering of anisotropic-shaped particles are observed directly by a metallurgical microscope in sedimentation equilibrium and in deionized suspensions. The anisotropic colloids are polydispersed gold sols, rectangular tungstic acid, ellipsoidal poly(tetrafluoroethylene)(PTFE), aggregated (dimer, trimer, ...) polystyrene spheres, and bowl-shaped polymers. The distribution of the particles is analyzed by the two-dimensional distance distribution function. The interparticle distance continues to decrease as the initial concentration of the particles increases. Young's elastic modulus for the crystal-like structures is estimated to be 3.1 Pa for PTFE particles. The transformation from the unsymmetrical ordering to the symmetrical (hexagonal) array takes place as the concentration of diffusible ions decreases, which shows that the electrostatic interparticle repulsion and the elongated Debye-screening length around the particles play a key role. Furthermore, a bowl-shaped particle is observed to include a sphere in its cavity. This inclusional association is influenced greatly by the delicate changes in the effective sizes of the host and guest molecules containing the electrical double layers. These results show that electrostatic interparticle repulsion and the elongated Debye-screening length around the particles are essential for the ordering.     

非导电微球悬浊系的介电谱——弛豫机制的考察和界面信息的解析

研究了不同浓度电解质溶液中聚苯乙烯微球悬浊液的介电谱, 发现在40 Hz～110 MHz频率范围内出现了两个明显的弛豫. 在介电模型基础上对弛豫原因的理论分析结果表明, 千赫兹频域出现的弛豫是由粒子附近双电层中对离子的扩散所致, 兆赫兹附近出现的弛豫源于空间电荷在固/液界面的累积. 应用Hanai方法计算出体系内部的相参数, 获得了微球/溶液界面的电信息, 并给出了合理解释. 理论计算结果验证了模型和方法的适用性. 实验采用透析法调制样品, 有效地防止了体系内部粒子二次团聚的发生.