Aggregation of Plate-like Colloids Induced by Charged Polymer Chains: Organization at the Nanometer Scale Tuned by Polymer Charge Density

Abstract

We may distinguish two regimes as a function of clay and ionene polymer charge densities (ρ c and ρ p respectively). The first regime applies to ρ p > ρ c and ρ p ∼ ρ c , i.e. for highly and "matching" charged chains. Under these conditions the intercalated chains lie in a flat conformation within the tactoids, irrespective of the ionic strength (within the range studied, i.e. up to 0.05M NaBr). For weakly charged chains, ρ p < ρ c , undulation of the ionene chains within the tactoid is seen. The degree of undulation increases with ionic strength, due to the decreasing persistence length of the ionene chains. The extent of stacking (5-10 platelets per tactoid) is a general feature of all the systems and its origin remains unknown. The system corresponding to the closest match in charge separations on the clay surface and on the polymer chain (ρ p ∼ ρ c) features the highest abundance of tactoids. This coincides with the highest macroscopic density as deduced from simple visual inspection of sediment volumes. This leads to the open question regarding the link between the density at the nanoscale and the macroscopic density and sedimentation behaviour of the aggregate.

Organisation of clay nanoplatelets in a polyelectrolyte-based hydrogel

“…tactoid formation) within the gel structure can be tuned via the nature and the valency of clay-compensating cations. With Ca 2+ and La 3+ clay counterions, the clay platelets are inserted in the form of tactoids, with an inter-layer distance comparable to three 715 water layers [15]. This distance is the same as for clay tactoids formed in the presence of inorganic salts (Ca(NO 3 ) 2 and La(NO 3 ) 3 ) [43].…”

“…Indeed, at 30g/L of 6-Cl mod ionene, the average interparticle distance d is 18 nm whatever the clay volume fraction. This interparticle distance is much higher than the interlamellar distance of 1.43-1.46 nm in clay/ionene tactoids [15] and lower than if the platelets only experienced electrostatic or steric repulsions as in the nematic clay suspensions at volume fractions of the same order of magnitude (around φ = 0.5%) [38]. Another important feature that we need to emphasize is the intensity upturn in the low q region.…”

“…The polyelectrolytes can wrap around clay platelets, be intercalated inside clay layers, induce flocculation or exfoliation of the platelets [10, 35 11, 12]. A set of key parameters influences this structure including the molecular weight [13,14], the chain-charge density and the concentration of the polyelectrolyte [15]; the size [16], the clay concentration [7], and the type [17] of the clay platelets. Nonetheless the set of requirements 40 to obtain one or another structure remains unclear.…”

“…Ionenes have already proved their ability to act as a flocculating agent for clay suspensions in a liquid state [27,15]. Introduction of benzene and amide moieties into the ionene backbone can lead to several possible interactions with clay.…”

Real time observation of the interaction between aluminium salts and sweat under microfluidic conditions

“…8 b, the simulations show that only highly concentrated species with a hydrodynamic radius smaller than 2–3 nm can significantly diffuse and build a plug localized inside sweat channel. This rule explains why cationic organic polymers of large molecular weight such as ionenes 37 do not form plugs inside sweat channels (see Supplementary Information S I3 ), although they are known to aggregate polyanionic molecules or colloids by electrostatic mechanisms in bulk solution 38 .…”