Effect of particle size and Debye length on order parameters of colloidal silica suspensions under confinement

Abstract

Using atomic force microscopy (AFM) and small angle X-ray scattering (SAXS), we show a full comparison between structuring of nanoparticles in confinement and in bulk in order to explain the effect of confinement on characteristic lengths and the scaling law of the characteristic lengths. Three different-sized particle suspensions are used to check the generalization and the correlation between the characteristic lengths and the system parameters, like particle diameter and Debye length. The two characteristic lengths obtained from AFM force curves, the oscillatory wavelength l, which is related to the average particle distance, and the decay length x, which measures how far particle correlates to obtain periodic oscillations, are in good agreement with the mean particle distance 2p/q max and the correlation length 2/Dq in bulk, respectively, obtained from the structure peaks of SAXS diagrams. Although confinement causes layering of nanoparticles parallel to the confining surfaces, the characteristic lengths in the direction perpendicular to the confining surfaces follow the bulk behavior. The wavelength scales as r À1/3 with the particle number density r irrespective of the particle size and the ionic strength and shows a pure volume effect. Upon comparing with literature results, the l ¼ r À1/3 scaling law can be applied more generally for charged particles, as long as the repulsive interaction is sufficiently long-ranged, than the previous expression of l ¼ 2(R + k À1 ), which only approaches the value of average particle distance under specific conditions. The decay length x is controlled both by the particle size and the ionic strength of the suspensions, and x ¼ R + k À1 is proposed in the paper. In addition, the interaction strength, the force amplitude and maximum scattering intensity, increases linearly with particle concentration. On the other hand, the Monte Carlo (MC) simulations and approximate hypernetted chain (HNC) closure calculation based on Derjaguin-Landau-VerweyOverbeek (DLVO) potential are employed to study the characteristic lengths from the theoretical point of view. The experimental wavelengths are in good agreement with the theoretical counterparts and the experimental decay lengths show the same qualitative behavior as theoretical ones on the particle size and ionic strength.

Depinning and heterogeneous dynamics of colloidal crystal layers under shear flow

“…Similar to previous studies [16,18], we here employed a set of system parameters pertaining to a realistic system of charged silica particles [13,26,40]. Thus, our predictions can, in principle, be tested by experiments.…”

“…The particle interaction parameters are set according to experimental setups for particles with diameter d ≈ 26 nm and valency Z = 35 [26,40], yielding κd ≈ 3.2. For the two-component system, an additional small particle species is introduced with diameter d 2 = 0.42d and valency Z 2 = 0.17Z, which are set according to experimental setups [40], where we set κd ≈ 3.3 for all particles. The number density ρd 3 = 1.226 and the slit-pore width L z = 2.65d of the two-component system are chosen such that the volume density is comparable to the one-component system.…”

Bridging interactions of proteins with silica nanoparticles: The influence of pH, ionic strength and protein concentration

“…10 nm to 1 nm when the ionic strength is increased from 1 mM to 100 mM. 29 The layer of the adsorbed protein has a thickness of a few nanometers. Hence in a 1 mM salt solution the electric double layer extends beyond the layer of the adsorbed protein, but at 100 mM salt the protein layer shields the surface-protein contact region from the solution.…”

Can charged colloidal particles increase the thermoelectric energy conversion efficiency?

“…The activity coefficients for the ferro-/ferri-cyanide redox couple in water are well documented for a wide range of ionic strengths. 28 As the ionic strength of a charged colloidal solution is known to depend on the presence of all ions (free salts and counterions surrounding the charged colloidal particles), 29,30 the inclusion of charged nanoparticles (and their concentration) will modify the thermogalvanic contribution to the overall Seebeck coefficient. The second term in eqn (1) is a thermodiffusion term.…”