Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from wh... more Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from which important interfacial electrokinetic properties, for instance their zeta potential, can be deduced. Unfortunately, dielectric spectroscopy measurements are hampered by electrode polarization (EP). In this article, we review several procedures to compensate for this effect. First EP in electrolyte solutions is described: the complex conductivity is derived as function of frequency, for two cell geometries (planar and cylindrical) with blocking electrodes. The corresponding equivalent circuit for the electrolyte solution is given for each geometry. This equivalent circuit model is extended to suspensions. The complex conductivity of a suspension, in the presence of EP, is then calculated from the impedance. Different methods for compensating for EP are critically assessed, with the help of the theoretical findings. Their limit of validity is given in terms of characteristic frequencies. We can identify with one of these frequencies the frequency range within which data uncorrected for EP may be used to assess the dipole moment of colloidal particles. In order to extract this dipole moment from the measured data, two methods are reviewed: one is based on the use of existing models for the complex conductivity of suspensions, the other is the logarithmic derivative method. An extension to multiple relaxations of the logarithmic derivative method is proposed.
7-(Dimethylamino)-1-methylquinolinium tetrafluoroborate (2), a stable color shifting mobilitysens... more 7-(Dimethylamino)-1-methylquinolinium tetrafluoroborate (2), a stable color shifting mobilitysensitive fluorescent probe, was employed for investigating physical aging in amorphous polymers. A linearcorrelation between the emission wavelength of 2 and the specific volume of the polymer was found inpolycarbonate (PC) and poly(methyl methacrylate) (PMMA). The shift in emission wavelength measured duringphysical aging was used to calculate the temperature and time dependence of the effective relaxation time tau_eff ,employing an age-dependent Kohlrausch-Williams-Watts (KWW) equation. From these data and by comparisonwith data obtained by positron annihilation spectroscopy (PALS) in PC and volume relaxation in PC and PMMA,it was concluded that the fluorescence of 2 yields reliable information on physical aging of these polymers. Thefluorescence method, employing a color-shifting probe, offers opportunities for investigating physical aging inpowders and semicrystalline polymers, of specific components in blends and mixtures, and in confined systems.
The dielectric spectra of colloidal systems often contain a typical low frequency dispersion, whi... more The dielectric spectra of colloidal systems often contain a typical low frequency dispersion, which usually remains unnoticed, because of the presence of strong conduction losses. The KK relations offer a means for converting ε ′ into ε ′′ data. This allows us to calculate conduction free ε ′′ spectra in which the l.f. dispersion will show up undisturbed. This interconversion can be done on line with a moving frame of logarithmically spaced ε ′ data. The coefficients of the conversion frames were obtained by kernel matching and by using symbolic differential operators. Logarithmic derivatives and differences of ε ′ and ε ′′ provide another option for conduction free data analysis. These difference-based functions actually derived from approximations to the distribution function, have the additional advantage of improving the resolution power of dielectric studies. A high resolution is important because of the rich relaxation structure of colloidal suspensions. The development of all-in-1 modeling facilitates the conduction free and high resolution data analysis. This mathematical tool allows the apart-together fitting of multiple data and multiple model functions. It proved also useful to go around the KK conversion altogether. This was achieved by the combined approximating ε ′ and ε ′′ data with a complex rational fractional power function. The all-in-1 minimization turned out to be also highly useful for the dielectric modeling of a suspension with the complex dipolar coefficient. It guarantees a secure correction for the electrode polarization, so that the modeling with the help of the differences ε ′ and ε ′′ can zoom in on the genuine colloidal relaxations.
... The curves were calculated by numerical "'P7i-er,tr r = - 2qF@=5L@-L-- __ -1__L__L ... more ... The curves were calculated by numerical "'P7i-er,tr r = - 2qF@=5L@-L-- __ -1__L__L e salea 50 :OR :?E Figure 8. Frequency factor fine-structure diagram of the Gaussian distribution studied. summation of the subprocesses in the Gaussian distribu-tion. ...
10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256), 1999
Previously we focussed on the dielectric properties of laminates and blends consisting of a weakl... more Previously we focussed on the dielectric properties of laminates and blends consisting of a weakly conducting and an insulating phase. Dielectric spectroscopy was used as a tool to obtain information about the dimensions of the conducting phase. With decreasing thickness of the conducting layer in the laminates, the permittivities measured were found to deviate more and more from those predicted
Fluidized beds are a common form of a chemical reactor, in which a deep layer of solid particles ... more Fluidized beds are a common form of a chemical reactor, in which a deep layer of solid particles is set in motion by a stream of gas blowing upward. However, the appearance of gas bubbles can significantly limit the selectivity, conversion, and product properties of gas–solid fluidized beds. We present results on the application of low-intensity electric fields in fluidized beds for reducing the bubble size up to 85% while maintaining the free movement of particles so essential to fluidization, at an energy cost as low as 50 W/m33.An analysis is presented of the qualitative response of particles to electric fields, including both drift and diffusion of charges. On this basis, the influence of particle size and particle conductivity on the overall dipole moment, and therefore the interparticle forces, is discussed. Experimental results in a two-dimensional bed show the predicted response to changes in particle size, while variations in optimal frequency response can be explained on the basis of particle conductivity. A maximum reduction in bubble diameter of 25% is achieved with small particles (77μm), while for large particles (700μm) the bubble diameter can be reduced by as much as 85%.
Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from wh... more Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from which important interfacial electrokinetic properties, for instance their zeta potential, can be deduced. Unfortunately, dielectric spectroscopy measurements are hampered by electrode polarization (EP). In this article, we review several procedures to compensate for this effect. First EP in electrolyte solutions is described: the complex conductivity is derived as function of frequency, for two cell geometries (planar and cylindrical) with blocking electrodes. The corresponding equivalent circuit for the electrolyte solution is given for each geometry. This equivalent circuit model is extended to suspensions. The complex conductivity of a suspension, in the presence of EP, is then calculated from the impedance. Different methods for compensating for EP are critically assessed, with the help of the theoretical findings. Their limit of validity is given in terms of characteristic frequencies. We can identify with one of these frequencies the frequency range within which data uncorrected for EP may be used to assess the dipole moment of colloidal particles. In order to extract this dipole moment from the measured data, two methods are reviewed: one is based on the use of existing models for the complex conductivity of suspensions, the other is the logarithmic derivative method. An extension to multiple relaxations of the logarithmic derivative method is proposed.
7-(Dimethylamino)-1-methylquinolinium tetrafluoroborate (2), a stable color shifting mobilitysens... more 7-(Dimethylamino)-1-methylquinolinium tetrafluoroborate (2), a stable color shifting mobilitysensitive fluorescent probe, was employed for investigating physical aging in amorphous polymers. A linearcorrelation between the emission wavelength of 2 and the specific volume of the polymer was found inpolycarbonate (PC) and poly(methyl methacrylate) (PMMA). The shift in emission wavelength measured duringphysical aging was used to calculate the temperature and time dependence of the effective relaxation time tau_eff ,employing an age-dependent Kohlrausch-Williams-Watts (KWW) equation. From these data and by comparisonwith data obtained by positron annihilation spectroscopy (PALS) in PC and volume relaxation in PC and PMMA,it was concluded that the fluorescence of 2 yields reliable information on physical aging of these polymers. Thefluorescence method, employing a color-shifting probe, offers opportunities for investigating physical aging inpowders and semicrystalline polymers, of specific components in blends and mixtures, and in confined systems.
The dielectric spectra of colloidal systems often contain a typical low frequency dispersion, whi... more The dielectric spectra of colloidal systems often contain a typical low frequency dispersion, which usually remains unnoticed, because of the presence of strong conduction losses. The KK relations offer a means for converting ε ′ into ε ′′ data. This allows us to calculate conduction free ε ′′ spectra in which the l.f. dispersion will show up undisturbed. This interconversion can be done on line with a moving frame of logarithmically spaced ε ′ data. The coefficients of the conversion frames were obtained by kernel matching and by using symbolic differential operators. Logarithmic derivatives and differences of ε ′ and ε ′′ provide another option for conduction free data analysis. These difference-based functions actually derived from approximations to the distribution function, have the additional advantage of improving the resolution power of dielectric studies. A high resolution is important because of the rich relaxation structure of colloidal suspensions. The development of all-in-1 modeling facilitates the conduction free and high resolution data analysis. This mathematical tool allows the apart-together fitting of multiple data and multiple model functions. It proved also useful to go around the KK conversion altogether. This was achieved by the combined approximating ε ′ and ε ′′ data with a complex rational fractional power function. The all-in-1 minimization turned out to be also highly useful for the dielectric modeling of a suspension with the complex dipolar coefficient. It guarantees a secure correction for the electrode polarization, so that the modeling with the help of the differences ε ′ and ε ′′ can zoom in on the genuine colloidal relaxations.
... The curves were calculated by numerical "'P7i-er,tr r = - 2qF@=5L@-L-- __ -1__L__L ... more ... The curves were calculated by numerical "'P7i-er,tr r = - 2qF@=5L@-L-- __ -1__L__L e salea 50 :OR :?E Figure 8. Frequency factor fine-structure diagram of the Gaussian distribution studied. summation of the subprocesses in the Gaussian distribu-tion. ...
10th International Symposium on Electrets (ISE 10). Proceedings (Cat. No.99 CH36256), 1999
Previously we focussed on the dielectric properties of laminates and blends consisting of a weakl... more Previously we focussed on the dielectric properties of laminates and blends consisting of a weakly conducting and an insulating phase. Dielectric spectroscopy was used as a tool to obtain information about the dimensions of the conducting phase. With decreasing thickness of the conducting layer in the laminates, the permittivities measured were found to deviate more and more from those predicted
Fluidized beds are a common form of a chemical reactor, in which a deep layer of solid particles ... more Fluidized beds are a common form of a chemical reactor, in which a deep layer of solid particles is set in motion by a stream of gas blowing upward. However, the appearance of gas bubbles can significantly limit the selectivity, conversion, and product properties of gas–solid fluidized beds. We present results on the application of low-intensity electric fields in fluidized beds for reducing the bubble size up to 85% while maintaining the free movement of particles so essential to fluidization, at an energy cost as low as 50 W/m33.An analysis is presented of the qualitative response of particles to electric fields, including both drift and diffusion of charges. On this basis, the influence of particle size and particle conductivity on the overall dipole moment, and therefore the interparticle forces, is discussed. Experimental results in a two-dimensional bed show the predicted response to changes in particle size, while variations in optimal frequency response can be explained on the basis of particle conductivity. A maximum reduction in bubble diameter of 25% is achieved with small particles (77μm), while for large particles (700μm) the bubble diameter can be reduced by as much as 85%.
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tau_eff ,employing an age-dependent Kohlrausch-Williams-Watts (KWW) equation. From these data and by comparisonwith data obtained by positron annihilation spectroscopy (PALS) in PC and volume relaxation in PC and PMMA,it was concluded that the fluorescence of 2 yields reliable information on physical aging of these polymers. Thefluorescence method, employing a color-shifting probe, offers opportunities for investigating physical aging inpowders and semicrystalline polymers, of specific components in blends and mixtures, and in confined systems.
tau_eff ,employing an age-dependent Kohlrausch-Williams-Watts (KWW) equation. From these data and by comparisonwith data obtained by positron annihilation spectroscopy (PALS) in PC and volume relaxation in PC and PMMA,it was concluded that the fluorescence of 2 yields reliable information on physical aging of these polymers. Thefluorescence method, employing a color-shifting probe, offers opportunities for investigating physical aging inpowders and semicrystalline polymers, of specific components in blends and mixtures, and in confined systems.