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Electrokinetic data were measured for dilute aqueous dispersions of amorphous silica nanoparticles of various size via capillary electrophoresis with borate buffers containing either Li + , Na + , K + , or guanidinium as a counterion. Taking the mobility-dependent relaxation effect into account (modified analytic approximation developed by Ohshima), reliable values are obtained for the electrokinetic potential and the electrokinetic charge density dependent on the type of cation and the concentration of buffer. The reliability was confirmed by comparison of the results obtained for the nanoparticles with those values obtained for the planar-limiting case (fused-silica capillary inner wall/electrolyte interface). Regarding the inner part of the electrical double layer as a (mono)layer of unspecifically adsorbed counterions, we calculate (together with data gained by Brown et al. on the same type of nanoparticles via in situ photoelectron spectroscopy and potentiometric titration) the charge density at the outer Helmholtz plane and the fraction of charge included in the Stern layer for electrolytes containing the alkali ions Li + , Na + , or K + . This approach explains differences in the electrokinetic charge density as a result of differences in the properties of the Stern layer due to differences in the size of the hydrated cation and the hydration state of the silica surface.

In this study, we use aqueous dispersions of amorphous silica nanoparticles of various sizes to investigate whether electropherograms recorded from capillary electrophoresis experiments can be converted directly into exact number-based particle radius distributions, provided that there is a relaxation effect-based size selectivity of the electrophoretic mobility and provided that the electrokinetic potential ζ of the particles can be regarded to be homogeneous over the surface of the particles, independent of the particle size. The results of this conversion procedure are compared with number-based particle radius distributions obtained from a large set of transmission electron microscopy (TEM) data. For this specific example, it is shown that the modified analytic approximation developed by Ohshima adequately describes the mobility-dependent relaxation effect and the electrophoretic mobility of the particle as a function of the reduced hydrodynamic radius and electrokinetic potential, which is a prerequisite for the presented procedure. Simultaneously, we confirmed that for the given Debye length/particle diameter ratio the electrokinetic surface charge density can be regarded to be size-invariant (including spherical geometry and planar limiting case). It is shown that the accuracy of the results of the developed method is comparable to that gained by a large set of TEM data, which is important when a precise description of the particle size distribution is needed to deduce conclusions regarding the underlying mechanism(s) of particle growth. The values obtained for the dispersion (width) of the distribution show only a small negative deviation, when compared with the TEM data (4-16%).

In the first part of this work we have measured the electrical conductivity of 4-amino salicylic acid (4-ASA) solution in water, methanol and ethanol at different temperatures (293.16-313.16 K). The experimental results were analyzed using Lee-Wheaton equation (LW) for symmetrical electrolytes (1:1). The conductivity parameters were calculated: the equivalent conductivity at infinite dilution (Λ o), the association constant (K A) and the mean distance values between ions (R) at the best standard deviation σs(Λ). It is found that by increasing the temperature, the values of Λ o increased, in contrast of that the values of K A decreased in ethanol only, R are found to be between (2-29)A o which indicates the formation of solvent separated ion pairs in solution. By Vant Hoff equation we have calculated the thermodynamic parameters (∆G, ∆H and ∆S) of ion association in solution. The second part of this work is the measurement of electrical conductivity of (4-ASA) in water with chlorides of each of nickel, cobalt and manganese at different temperatures (293.16-313.16 K) and calculation of conductivity parameters by Lee-Wheaton equation for unsymmetrical electrolytes (2:1), besides the thermodynamic parameters were also performed. The Walden-product (Λ o η) was also determined and discussed.