Sprecher
Beschreibung
Shake gel is a kind of polymer/nanoparticle mixture with a distinctive solid-liquid switching ability [1]. It is fluid at rest and can rapidly turn into a gel after shear, and then revert to a liquid upon standing. Previous studies have examined how key parameters such as polymer molecular weight, particle size, and polymer/particle ratio affect the gel formation and rheological properties [2,3].
However, a quantitative understanding of how composition and size collectively govern the gelation boundary remains elusive. Herein, we systematically investigated the phase behavior of shake gels formed by mixing polyethylene glycol(PEG) polymers of various radii of gyration (Rg) with silica nanoparticles of different diameters (d) in water. A series of phase diagrams were constructed with the silica volume fraction ϕsilica as the abscissa and the PEG volume fraction ϕPEG as the ordinate.
Two types of constraints governing gelation were revealed. First, ϕsilica and ϕPEG obey an inverse relationship, (ϕPEG-ϕPEG, c) ⋅ (ϕsilica-ϕsilica, c) ≥ k, where ϕsilica, c and ϕPEG, c are the absolute minimum concentrations of the two components. The concentrations can compensate each other but neither can be infinitely low; otherwise, the system fails to develop a percolating network. Second, the concentration ratio is constrained by a coverage parameter θ = (ϕPEG/ϕsilica) ⋅ (d/Rg). A shake gel forms only when θmin ≤ θ ≤ θmax, corresponding to PEG adsorption on silica surfaces that meets a minimum threshold without reaching saturation. Furthermore, the critical parameters ϕsilica, c, ϕPEG, c, and k all exhibit scaling relations with the dimensionless quantity d/Rg. This result demonstrates that d/Rg is the key scaling variable governing the gelation behavior of PEG/silica systems.
By unifying complex multi-parameter phase diagrams into a single-parameter universal form, we provide a predictive framework that bridges phenomenological observations and scaling theory for polymer-mediated colloidal gelation.
[1] J. Zebrowski, et. al, Colloids Surf. A, 213, 189-197 (2003).
[2] M. Mar Ramos-Tejada, et. al, Colloids Surf. A, 471, 164-169 (2015).
[3] S. Sato, et. al, Molecules, 28, 3555 (2023).