Isotropic/nematic and sol/gel transitions in aqueous suspensions of size selected nontronite NAu1

Abstract

The phase behaviour of aqueous suspensions of NAu1 nontronite was studied on size-selected particles by combining osmotic pressure measurements, visual observations under polarized light, rheological experiments and Small Angle X-ray Scattering (SAXS). NAu1 suspensions display a liquid crystalline behaviour as they exhibit a Isotropic/Nematic (I/N) transition that occurs before the sol/gel transition for ionic strengths below 10–3 M/L. This I/N transition shifts towards lower volume fractions for increasing particle anisotropy and its position in the phase diagram agrees well with the theoretical predictions for platelets. SAXS measurements reveal the presence of characteristic interparticular distances in the isotropic, nematic and gel phases. In the gel phase a local lamellar order is observed which shows that the “house of cards” model is not appropriate for describing the gel structure in swelling clay materials at low ionic strength. Furthermore, by combining results from osmotic pressure measurements and X-ray scattering, it appears that the pressure of the system can be well described using a simple Poisson-Boltzmann treatment based on the repulsion between charged infinite parallel planes. In terms of rheological properties, even if the thermodynamical status of the sol/gel transition remains partially unclear, the yield stress and elasticity of the gels can be easily renormalized for all particle sizes on the basis of the volume of the particles. Furthermore, rheological modelling of the flow curves shows that for all the particles an approach based on excluded volume effects captures most features of nontronite suspensions.

Superflexibility of graphene oxide

“…A second-order peak is even observed in the TH integration at a wave vector twice the wave vector of the first-order diffraction peak. The present data are characteristic of a lamellar phase, as previously observed in graphene suspensions at rest (39,49) and in other inorganic platelet systems (50,51). This is why the present phase can be considered as a pseudosmectic or pseudolamellar phase in such concentrated regimes.…”

Shear-thinning in concentrated rigid fiber suspensions: Aggregation induced by adhesive interactions

“…The internal aggregate volume fraction ϕ i [Eq. (14)] also shows a monotonic increase with the shear rate [ Fig. 7b] related to the fact that more compact aggregates (with higher contact densities) better resist to increasing shear forces.…”

“…Thus, the final approximate expression is obtained for the resultant correction factor for the hydrodynamic force: These two corrections imply the following slight modifications of Eqs. (14), (15) and (27) of the manuscript:…”

“…3. In attractive systems with colloidal nanoparticles, the interplay between the electrostatic repulsion and the van der Waals attraction governs the degree of particle flocculation and yielding behavior [13][14][15]. At the same time, adhesive interactions produce a moderate shear thinning in suspensions of rigid micron-sized rod-like particles, such as polyamide [16,17], ceramic particles [18], wollastonite [19].…”

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

“…The links to the underlying physical chemistry and the associated microstructure of the suspensions/gels is oen clear qualitatively but it has proved a challenge to obtain quantitative predictive theoretical physicochemical models for understanding and predicting the observed rheology in a similar fashion that has been achieved for polymer systems. [121][122][123][124][125][126] However, recently some progress in this direction has been made with so-called effective geometrical models, 102,109,[127][128][129][130] which quantify some of the ideas expressed in this review on the role of the hydrodynamic volume in determining the rheological behaviour of clay systems. These, and related particle simulations, [131][132][133][134] should form the basis of more rigorous theoretical understanding and modelling of the rheology of clay-based suspensions and gels in the near future.…”