Yasuhisa Adachi

Adsorption of anionic surfactant sodium dodecyl sulfate onto alpha alumina with small surface area

Adsorption of sodium dodecyl sulfate (SDS) onto large α-alumina beads was systematically analyzed as functions of pH and NaCl concentration. The maximum adsorption density of SDS onto α-Al2O3 increases with decreasing pH due to the increase in equilibrium surface charge. Adsorption isotherms at different salt concentrations demonstrated a common intersection point (CIP) corresponding to charge neutralization. The obtained comprehensive data clarified the applicability of two-step adsorption and four-region models to describe the adsorption isotherms of SDS onto α-Al2O3 beads. Also, proton adsorption isotherms upon SDS uptake onto α-Al2O3 can be fitted by two-step adsorption model with almost the same parameters of surfactant adsorption for 0.001 and 0.01xa0M NaCl. Our finding indicates that proton adsorption takes place onto the adsorbed SDS. After passing through CIP, proton adsorption onto α-Al2O3 increases at low ionic strength while the amount of proton adsorption does not change for 0.1xa0M NaCl. Adsorption amount of proton as a function of SDS adsorption shows that only hemimicelles are plausible for case of low ionic strength. The increase in the proton adsorption is not significant at high ionic strength, suggesting the presence of admicelles on the surface of α-Al2O3 beads.

Adsorption characteristics of anionic azo dye onto large α-alumina beads

Adsorption of anionic azo dye, new coccine (NC), onto large α-alumina beads in aqueous media was systematically investigated as functions of pH and NaCl concentration. Adsorption amounts of NC decrease with increasing pH of solutions due to less positive charges of α-Al2O3 surface at high pH. At a fixed pH, the NC adsorption increases with decreasing NaCl concentration, indicating that NC molecules mainly adsorb onto α-Al2O3 by electrostatic attraction. Experimental results of NC adsorption isotherms onto α-Al2O3 at different pH, and ionic strength can be represented well by two-step adsorption model. The effects of NC on surface charge and surface modification of α-Al2O3 at the plateau adsorption are evaluated by streaming potential and Fourier transform infrared spectroscopy with attenuated total reflection technique (FTIR-ATR), respectively. On the basis of adsorption isotherms, surface charge effect, and surface modification, we suggested that the formation of a bridged bidentate complex between aluminum ions of α-Al2O3 and two oxygen atoms of a sulfonic group induced the adsorption of NC onto α-Al2O3.

Adsorption of Polyanion onto Large Alpha Alumina Beads with Variably Charged Surface

Adsorption of strong polyelectrolyte, poly(styrenesulfonate), PSS, of different molecular weights onto large α-Al2O3 beads was systematically investigated as functions of pH and NaCl concentrations. The ultraviolet (UV) absorption spectra of PSS at different pH and salt concentrations confirmed that the structure of PSS is independent of pH. With the change of molecular weight from 70u2009kg/mol (PSS 70) to 1000u2009kg/mol (PSS 1000), adsorption amount of PSS increases and proton coadsorption on the surface of α-Al2O3 decreases at given pH and salt concentration. It suggests that higher molecular weight of PSS was less flat conformation than lower one. The adsorption density of PSS 70 and PSS 1000 decreases with decreasing salt concentrations, indicating that both electrostatic and nonelectrostatic interactions are involved. Experimental results of both PSS 70 and PSS 1000 adsorption isotherms onto α-Al2O3 at different pH and salt concentrations can be represented well by two-step adsorption model. The effects of molecular weight and salt concentration are explained by structure of adsorbed PSS onto α-Al2O3. The influence of added SDS on the isotherms is evaluated from the sequential adsorption. The SDS uptake onto α-Al2O3 in the presence of hemimicelles can prevent the adsorption of PSS at low concentration so that adsorption of PSS reduces with preadsorbed SDS.

Cluster-cluster aggregation simulation in a concentrated suspension.

The collision radius of a floc is an indispensable parameter for the precise description of the rate of aggregation during the development of particle flocs with a wide size distribution. Herein, we report on the characteristics of the collision radius of fractal aggregates formed by off-lattice diffusion-limited cluster-cluster aggregation (DLCCA) simulations, and discuss aggregation kinetics based on the value of the estimated collision radius. The collision radius has a fractal relationship with the number of primary particles that compose the floc. Further, the obtained fractal dimensions of flocs increase from the normally accepted value of 1.6-1.8 to a value of ~2.5 when the initial volume fraction is above 8%. From an assessment of the partial radial distribution function of the particles, the increase of the fractal dimensions determined by the collision radius can be attributed to a change in the spatial distribution of neighboring particles. The DLCCA simulation also reveals an apparent increase in the rate of aggregation upon an increase in the initial volume fraction. For a relatively low initial volume fraction, the enhancement of the aggregation rate is expressed by a population balance equation taking into account additional factors, i.e., transient collision flux among particles/flocs, excluded volumes, and polydispersed features of flocs. However, for cases with high initial volume fractions, the population balance model that accounts for these three factors overestimates the aggregation rate, which supports the concept of a caging effect.

Dielectric and electrophoretic response of montmorillonite particles as function of ionic strength.

Montmorillonite is a sheet-like clay mineral. The surface charge of the faces is always negative, whereas the surface charges of the edges depend on pH. In this study, pH is around 6.5 implying that the edges are slightly positive; however, the overall charge of the particle appears to be negative as the surface of the faces is 50 times larger than the edges. In the presence of an applied electric field, montmorillonite particles and their double layer will polarize. This polarization affects the electrokinetic response of the particles. In this article, we investigated the effect of ionic strength on the electrokinetic response of montmorillonite particles using the dielectric spectroscopy and electrophoretic mobility. The experimental dipole coefficient found by dielectric spectroscopy was compared to the semi-analytical formula presented by Chassagne [C. Chassagne, J. Colloid Interface Sci. 326 (2008)]. The amplitude of the dipole coefficient of montmorillonite particles increased and the relaxation frequency shifted to lower frequencies with decreasing ionic strength. This tendency is in qualitative agreement with the theoretical prediction. A better agreement between the experimental and theoretical amplitudes of the dipole coefficient and between the high-frequency experimental and theoretical mobilities was obtained when a Stern layer conductivity is introduced. The same values for the zeta potential and Stern layer conductivities were used in both measurement sets. The relaxation frequencies were not changed by addition of a Stern layer. This discrepancy between experimental and theoretical relaxation frequencies are due to the limitation of the theory that is not valid at low κa, as discussed in the conclusion.

Comparison between the electrokinetic properties of kaolinite and montmorillonite suspensions at different volume fractions

We have investigated the electrokinetic responses of two different kinds of clay particles, kaolinite and montmorillonite. The dielectric permittivity of kaolinite suspensions is linearly proportional to volume fraction up to volume fractions of 20%, whereas that of montmorillonite is deviating from a linear relationship, for volume fractions below 0.5%. This indicates that the montmorillonite particles experience a particle-particle interaction at these low volume fractions. The complex dipole coefficients of both clays estimated by experimental data are, however, within experimental error in good approximation independent on volume fraction and agree with the theoretical predictions. The relaxation frequency in clay-water system at low ionic strength is almost determined by the relaxation of the double layer for both kaolinite and montmorillonite. For volume fractions larger than 0.5% for montmorillonite, we find that the zeta potential measured by electroacoustic methods starts to depend strongly on volume fraction. It is expected that for these high volume fractions, the dipole coefficients will also become volume-fraction dependent.

Morphology and Breaking of Latex Particle Deposits at a Cylindrical Collector in a Microfluidic Chamber

We report an analysis for the morphology and breaking behavior of deposits of spherical latex particles (1 and 3.6 μm in diameter) at a cylindrical collector in a microfluidic channel fabricated by soft-lithography. In-situ observation of particle deposition over a large range of flow rate conditions evidence the relationship between deposit morphology and mode of particle transport toward the collector. For low Péclet number (Pe), particle deposits are nearly uniform all over the collector surface except at the rear where particles do not attach. Upon increase of Pe, deposits gradually adopt a columnar morphology at the collector stagnation point. These results are qualitatively consistent with previously reported Monte Carlo simulations of deposits formation in stagnation point flow systems. However, these simulations fail to quantitatively predict the observed deposition at the rear of the collector for sufficiently high flow rate. Additional deposit breaking experiments together with numerical evaluations of particle flux around the collector suggest that such anomalous deposition at large Pe is significantly governed by concomitant detachment of deposited particles at the stagnation point and the presence of recirculation flow at the collector rear. Finally, kinetics of deposition are discussed in connection with particle size-dependence of deposit breaking features.

Electric Charging and Colloid Stability of Fabricated Nedle-Like TiO2 Nanoparticles

Charging and stability of needle-like TiO(_{2})xa0nanoparticles were studied. Measured isoelectric point (IEP) was pH~4xa0and lower than that of spherical ones pH~6. Heat treatment atxa0400(text{r{}})C changed the IEP from 4 to 6. The shift is probably due to shapexa0controller (ethylenediamine). The particles aggregate around IEP and thusxa0are charge-stabilized. Experimental hydrodynamic diameters of needle-likexa0particles showed a reasonably good agreement with the theoretical diameter.xa0That is, the particles can be dispersed to primary particles. 1pK Stern andxa0standard electrokinetic models describe electrophoretic mobility ofxa0needle-like TiO(_{2}), indicating that double layer relaxation isxa0significant for needle-like TiO(_{2}).