A Small-Angle X-ray Scattering Study of the Structure of Aqueous Laponite Dispersions

Abstract

Two Laponite clays, of general formula [M n+ ] x/n [Li x Mg 6-x Si 8 O 20 F y (OH) 4-y ], were prepared with different Li + levels (0.57 and 0.70% w/w) and Flevels (9.5 and 9.9% w/w). The clays were characterized by measurements of nitrogen adsorption isotherms, cation exchange capacity, and conductometric titration data. The clay with higher Li + and Flevels had a higher (more negative) face charge and a lower (less negative) edge charge. Small-angle X-ray scattering (SAXS) data obtained from dilute aqueous dispersions indicate that both clays are of similar particle size (diameter ca. 40 nm and thickness ca. 3.5 nm). Experimental structure factors for concentrated Laponite dispersions were calculated using the ratio of scattered X-ray intensities from concentrated and dilute dispersions. Maxima in the experimental structure factors were observed at scattering angles of 0.14-0.2 nm -1 under favorable solution conditions (pH g 9 and ionic strength ca. 5 × 10 -3 mol dm -3 ) for one of the Laponite clays. These results are interpreted in terms of an ordered, aligned structure where the particles' face and edge electrical double layers are expanded and negative in sign. This is in contrast to a "house-of-cards" structure which results when particle aggregation is promoted by lower pH, higher ionic strength, or a lower particle edge charge.

Smectite clay – inorganic nanoparticle mixed suspensions: phase behaviour and rheology

“…Closely related, but with signicantly different properties, is Laponite B a uoro-hectorite in which uorine ions replace hydroxyl groups in the octahedral layers. 18,26 Smectites have a layer charge between 0.2e and 0.6e per half unit cell (corresponding to a surface charge ranging from À0.07 to À0.21 C m À2 ) arising from isomorphic substitutions in the octahedral or tetrahedral sheets. In hectorite, the substitution is of Mg 2+ by Li + in the octahedral sheet.…”

A new and generic preparation method of mesoporous clay composites containing dispersed metal oxide nanoparticles

“…Previous works have revealed that the delamination of clays could enhance significantly their surface areas as well as pore volumes [26]. In addition, because the laponite platelets are very small, the edge areas in this type of clay can contribute significantly to the total surface areas [25,29]. Thus the increased edge surfaces generated from the part breakdown of the clay platelets are also partially responsible for the enhancement of the specific surface areas.…”

“…The silicate platelet of laponite clays consists of an octahedral MgO 6 sheet sandwiched between two tetrahedral SiO 4 sheets [14,25]. After reacting with acidic metal precursors, the content of magnesium decreased ( Table 1), indicating that a large number of magnesium atoms leached out as a result of the break of Mg-O bond induced by protons.…”

Thickness and Surface Characteristics of Colloidal 2:1 Aluminosilicates Using an Indirect Fourier Transform of Small-Angle X-Ray Scattering Data

“…These studies have both theoretical and industrial significance. The thickness, interparticle spacing in hydrated states, and the influence of interparticle forces fall into the characterization length scale of SAXS and have been investigated by this method in the past (Hight et al, 1960(Hight et al, , 1962Taylor and Schmidt, 1969;Morvan et aL, 1994;Pignon et al, 1997;Saunders et al, 1999).…”

“…Hight et al, 1960;Saunders et al, 1999), well-characterized smectites were used in thickness determinations with the SAXS method based on an assumed particle shape. This approach has limited application in the determination of thickness of natural clay minerals which often do not have the required regular dimension in at least two coordinates.…”