Aqueous Suspensions of Natural Swelling Clay Minerals. 1. Structure and Electrostatic Interactions

Abstract

In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10(-3) M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order.

Bottom-up and top-down manipulations for multi-order photonic crystallinity in a graphene-oxide colloid

“…30,38,45 However, freeze-dried samples usually lose the original GO assembly structure in a wet colloid and are restructured during freezing; 36,37 small angle X-ray scattering peaks in colloidal nematic phases are commonly sharper than those of small-molecular nematic phases owing to weaker thermal fluctuation, and the types of patterns are commonly interpreted as characteristic patterns of the nematic phase rather than the lamellar phase in clay suspensions. 41,42,46 Hence, these results do not directly confirm the lamellar mesophase of the GO dispersion. In lamellar phases such as lipid bilayer lamellar phases and the smectic phases of small molecules, a long-range single layer that is composed of many particles should first be defined.…”

“…30,40 This broad, diffuse peak indicates that the GO liquid crystal has liquid-like positional local order in a globally nematic phase, which is not considered a lamellar mesophase with a long-range positional order. 41,42 Hence, it is reasonable to consider the GO photonic crystal as a nematic phase rather than a lamellar mesophase. Figure 2 shows that the reflectance of the GO photonic crystal was~3%, which is much lower than the usual photonic crystal structure (~31% for the CLC cell in Figure 3f).…”

In-Depth Insights into the Key Steps of Delamination of Charged 2D Nanomaterials

“…by sedimentation or centrifugation, to solid contents where liquid crystalline (LC) phases are observed. For kinetic reasons during the concentration procedure equilibrium structures might not be readily achieved (18 [Si 8 ]O 20 F 4 (two formula units per unit cell and therefore abbreviated as Na 0.5 -hectorite) that has been synthesized from the melt at temperatures well above 1000 K (19). The material does not require any purification and shows a very homogeneous intracrystalline reactivity.…”

Formation and Restacking of Disordered Smectite Osmotic Hydrates

“…Several groups have used SAXS to explore the average distances between layers in completely exfoliated smectite as a function of solution conditions (e.g. Paineau et al, 2011). Interpretation of SAXS data beyond quantification of mean interlayer spacings is very model dependent, however, and direct observations of layer disorder, useful for validating proposed models, have not been reported to date.…”