Structure, Ion Transport, and Rheology of Nanoparticle Salts

Abstract

Above a critical surface chemistry-dependent particle loading associated with nanoscale interparticle spacing, ligand−ligand interactionsboth electrostatic and stericcome into play and govern the structure and dynamics of charged oligomer-functionalized nanoparticle suspensions. We report in particular on the structure, ion transport, and rheology of suspensions of nanoparticle salts created by cofunctionalization of silica particles with tethered sulfonate salts and oligomers. Dispersion of the hairy ionic particles into medium and high dielectric constant liquids yields electrolytes with unique structure and transport properties. We find that electrostatic repulsion imparted by ion dissociation can be tuned to control the dispersion state and rheology through counterion size (i.e., Li + , Na + , and K + ) and dielectric properties of the dispersing medium. Analysis of small-angle X-ray scattering (SAXS) structure factors and the mechanical modulus shows that when the interparticle spacing approaches nanometer dimensions, weakly entangled anchored ligands experience strong and long-lived topological constraints analogous to those normally found in well-entangled polymeric fluids. This finding provides insight into the molecular origins of the surprisingly similar rubbery plateau moduli observed in hairy nanoparticle suspensions and entangled polymers of the same chemistry as the tethered ligands. Additionally, we find that a time−composition superposition (TCS) principle exists for the suspensions, which can be used to substantially extend the observation time over which dynamics are observed in jammed, soft glassy suspensions. Application of TCS reveals dynamical similarities between the suspensions and entangled solutions of linear polymer chains; i.e., a hairy particle trapped in a cage appears to exhibit analogous dynamics to a long polymer chain confined to a tube.

Polycarbosilane-Grafted Nanoparticles: Free-Flowing Hairy Nanoparticle Liquids That Convert to Ceramic

“…The maximum packing volume fraction for all three HNP samples is ∼0.06–0.07. The inverse of the intrinsic viscosity is equivalent to the overlap volume fraction, ϕ*, and this value is ∼25 times smaller than the typical hard-sphere suspension . This behavior indicates that both the polymer corona and silica sphere contribute to an effective core volume, ϕ eff , as follows , For these samples, the silica particle radius, a c , was set to be 7.5 nm, as the diameter of the silica spheres ranges from 10 to 20 nm.…”

Exploring the validity of time-concentration superposition in glassy colloids: Experiments and simulations

“…while the authors did not recognize this, it suggests to us an important regime where TCS was not investigated. More recently, Archer and co-workers studied soft colloidal particle systems to examine the validity of time-concentration superposition [24,25]. They argued for its validity over a large range of concentrations and very broad (reduced) frequency regime, despite the clear emergence of a high frequency β-relaxation.…”

“…While the use of superposition principles in polymeric systems is widespread, there has been much less exploration of such behavior in colloidal systems [22][23][24][25][26][27][28][29]. In polymeric glass-formers, the time-temperature superposition or time-concentration superposition principles discussed above have been used as practical and useful tools to construct maps of material dynamics.…”

Interpenetration of fractal clusters drives elasticity in colloidal gels formed upon flow cessation

“…This is not what we observe here, for the rescaling of the viscoelastic spectrum requires a shift along the frequency axis and a shift along the viscoelastic moduli. Such behavior has, however, been observed in different systems and still attributed to a superposition principle such as in colloidal low-methoxyl pectin [55] in the context of gelling time/relaxation time superposition, protein condensates [56] in the context of aging Maxwell fluids, in triblock copolymer solutions [57] in the context of time-composition superposition, and in soft colloidal glasses [58,59] in the context of time-concentration su-…”