Depletion Stabilization in Nanoparticle–Polymer Suspensions: Multi-Length-Scale Analysis of Microstructure

Abstract

We study the mechanism of depletion stabilization and the resultant microstructure of aqueous suspensions of nanosized silica and poly(vinyl alcohol) (PVA). Rheology, small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS) techniques enable us to analyze the microstructure at broad length scale from single particle size to the size of a cluster of aggregated particles. As PVA concentration increases, the microstructure evolves from bridging flocculation, steric stabilization, depletion flocculation to depletion stabilization. To our surprise, when depletion stabilization occurs, the suspension shows the stabilization at the cluster length scale, while maintaining fractal aggregates at the particle length scale. This sharply contrasts previously reported studies on the depletion stabilization of microsized particle and polymer suspensions, which exhibits the stabilization at the particle length scale. On the basis of the evaluation of depletion interaction, we propose that the depletion energy barrier exists between clusters rather than particles due to the comparable size of silica particle and the radius gyration of PVA.

Exploring the frontiers of colloidal behaviour where polymers and particles meet

“…This same sequential ordering of colloidal stability states with increasing functional ingredient concentration (i.e. bridging / stability / depletion / stability) has been systematically demonstrated in model emulsions containing sodium caseinate (Dickinson, 1999b;Dickinson, Golding, & Povey, 1997), as well as in model colloidal dispersions of nanoparticles þ synthetic polymers (Kim, Hyun, Moon, Clasen, & Ahn, 2015). The stabilization of liquid droplets by a layer of nanoparticles or microparticles located at the droplet surface is generally known as Pickering stabilization (Binks & Horozov, 2006).…”

Particle Dispersion in Silica-Poly(vinyl alcohol) Coatings: Role of Particle-Polymer Interaction

“…When PVOH increased from 4.5 wt.% to 5 wt.%, viscosity decreased at the whole range of shear rate, and finally became a Newtonian fluid at PVOH = 7.5 wt.%. This indicated that the cluster size reduced when PVOH increased above 4.5 wt.% (Kim et al 2015). The clustered structure was further characterized by the frequency sweep test.…”

“…2a, at pH 3 the sedimentation was fastest at PVOH = 0.5 wt.%, but became slow as PVOH increased. In a previous study about the  measurement as a function of PVOH and the dispersion stability at pH 3, the authors found the dispersion stability improved as  increased, owing to steric stabilization as a result of adsorbed PVOH (Kim et al 2015). The study showed that  increases as PVOH increases, and the system approaches the plateau level at around PVOH = 3 wt.%.…”

“…Finally, the significant reduction of both G' and G" was observed at PVOH = 7.5 wt.%, which implied reduced cluster size. The cluster formation probed by rheological measurement could be further understood by the measurement of a small angle x-ray scattering and a small angle light scattering intensity for SiNP-PVOH suspension of pH 3 (Kim et al 2015). The scattering intensity showed the formation of SiNP clusters were mainly dominated by depletion flocculation below PVOH = 4 wt.%, whereas it was dominated by depletion stabilization above PVOH = 4wt.%.…”

Formation of size-tuneable biodegradable polymeric nanoparticles by solvent displacement method using micro-engineered membranes fabricated by laser drilling and electroforming

“…Further increase in C PVA above 1 wt% would stabilize the particles again, which is termed as depletion stabilization [49]. However, high PVA concentrations in the aqueous phase lead to large particle size, due to high viscosity of the aqueous phase so the PVA concentrations above 1 wt% were not investigated in this work.…”