Effects of pH and ionic strength on electrokinetic properties of imogolite

Tsuchida, H.; Ooi, Setsuo; Nakaishi, Katsuya; Adachi, Yasuhisa

doi:10.1016/j.colsurfa.2004.10.136

Cited by 26 publications

(17 citation statements)

References 14 publications

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“…39 However, INTs have a strong tendency to form instantaneously transparent gels or to bundle irreversibly in bulky flocs at alkaline pH or for high ionic strength. [39][40][41][42] For instance, it has long been recognized that addition of a concentrated ammonia solution (typically 30 wt%) leads to the formation of gels, 29 then, this mixture is placed into an oven at 95°C for 5 days. At the end of the ageing process, the suspension was recovered at room temperature and subsequently dialyzed (Spectra/Por, cut-off 10 kDa, Spectrum) against ultrapure water until the conductivity dropped below 5 µS.cm -1 .…”

Section: Introductionmentioning

confidence: 99%

Colloidal Stability of Imogolite Nanotube Dispersions: A Phase Diagram Study

et al. 2019

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In this article, we revisit the colloidal stability of clay imogolite nanotubes by studying the effect of electrostatic interactions on geo-inspired synthetic nanotubes in aqueous dispersions. The nanotubes in question are double-walled aluminogermanate imogolite nanotubes (Ge-DWINTs) with a well-defined diameter (4.3 nm) and with an aspect ratio around 4. Surface charge properties are assessed by electrophoretic measurements, revealing that the outer surfaces of Ge-DWINT are positively charged up to high pH values. A series of Ge-DWINT dispersions have been prepared by osmotic stress to control both the ionic strength of the dispersion and the volume fraction in nanotubes. Optical observations coupled to small and wide-angle X-ray scattering (SAXS/WAXS) experiments allow us to unravel different nanotube organizations. At low ionic strength (IS < 10–2 mol L–1), Ge-DWINTs are fully dispersed in water while they form an arrested gel phase above a given concentration threshold, which shifts toward higher volume fraction with increasing ionic strength. The swelling law, derived from the evolution of the mean intertube distance as a function of the nanotube concentration, evidences a transition from isotropic swelling at low volume fractions to one-dimensional swelling at higher volume fractions. These results show that the colloidal stability of Ge-DWINT is driven by repulsive interactions for ionic strengths lower than 10–2 mol L–1. By contrast, higher salt concentrations lead to attractive interactions that destabilize the colloid suspension, inducing nanotube coagulation into larger structures that settle over time or form opaque gels. Detailed simulations of the WAXS diagram reveal that aggregates are mainly formed by an isotropic distribution of small bundles (less than four nanotubes) in which the nanotubes organized themselves in parallel orientation. Altogether, these measurements allow us to give the first overview of the phase diagram of colloidal dispersions based on geo-inspired imogolite-like nanotubes.

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Section: Introductionmentioning

confidence: 99%

Colloidal Stability of Imogolite Nanotube Dispersions: A Phase Diagram Study

et al. 2019

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“…Imogolite is a thin nano tube with an inner diameter of 1 nm, an outer diameter of 2 nm, and a length of several micrometers [13,17]. It has an IEP at pH > 8.5, and thus, has positive charges over a wide range of pH values [13,15,18,19]. Although the EPM of imogolite is not zero, imogolite coagulates in both neutral and alkaline solutions at pH values greater than 6-7 [15,16,[20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Coagulation and charging of latex particles in the presence of imogolite

Kobayashi

Nitanai

Satta

et al. 2013

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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“…Karube et al (1992) reported that the mobility of imogolite toward the positive electrode was difficult to detect using a Briggs-cell due to the flocculation of the fibrous particles. Harsh et al (2002) and Tsuchida et al (2005) mentioned that cations may enter the tube and effectively neutralize the negative charge. Ma and Karube (2007) examined the effects of imogolite addition on the colloidal stability of montmorillonite and kaolinite, and confirmed that imogolite has no surface charge under alkaline conditions.…”

Section: Introductionmentioning

confidence: 99%

Imogolite flocculation under alkaline conditions

Karube

2013

Soil Science and Plant Nutrition

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Imogolite flocculates under alkaline conditions even though the net charge is considerably negative. To clarify the reason for this contradiction, we measured the charge characteristics of imogolite with an ion-exchange method using sodium ions (Na þ ) and chloride ions (Cl À ) as index ions, and estimated its electric field intensity at the outer surface using Gauss' law and the structural model of imogolite. The result showed that the electric field intensity of negative charge at the outer surface was about half of that at the inner surface. Further, we discussed that if cations could easily enter the imogolite tube, the electric field of negative charge would be drastically weakened due to the neighboring cations and, consequently, the outer surface would become electrically indifferent. If so, not only the reason for imogolite flocculation under alkaline conditions, but also the reason for imogolite dispersion at the point of zero net charge would be explained consistently. The reason for imogolite dispersion at the point of zero net charge was considered to be that the colloidal stability of imogolite would be affected only by the positive charges that appear on the outer surface of the tube. Finally, the hydrated sodium ions were considered to move in and out of the imogolite tube freely.

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Effects of pH and ionic strength on electrokinetic properties of imogolite

Cited by 26 publications

References 14 publications

Colloidal Stability of Imogolite Nanotube Dispersions: A Phase Diagram Study

Colloidal Stability of Imogolite Nanotube Dispersions: A Phase Diagram Study

Coagulation and charging of latex particles in the presence of imogolite

Imogolite flocculation under alkaline conditions

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