Mechanical Properties of Colloidal Gels

Abstract

A colloidal suspension can be either dispersed or flocculated depending on the interaction between the colloidal particles. If the interaction is repulsive, particles can relax to the minimum of the potential due to their neighboring particles, and the system can reach an equilibrium dispersed state. In the case of attractive interaction, particles form aggregates that settle to the bottom of the container. As the concentration of particles is increased, the overcrowding of the aggregates produces a continuous network throughout the suspension before they settle and a colloidal gel is formed. A major difference between a colloidal gel and a colloidal suspension is that the gel can sustain finite stress and is therefore viscoelastic. Previously we studied the storage modulus and the yield strain of boehmite gels and found that they are related to the particle concentration in a power-law fashion [1]. Similar scaling behavior of the shear modulus was found for other colloidal particulate networks by Buscall et al. [2]. We developed a scaling theory [1] which successfully explains the experimental results on boehmite gels. The theory further predicts that there can be two types of power-law behavior depending on the relative elastic strength of the clusters to that of the links between clusters within the gel network. Furthermore, there can be a crossover from one type of behavior to the other as the particle concentration is varied.

Elastic and Yield Behavior of Strongly Flocculated Colloids

“…[31][32][33] If a short-range repulsion energy 33 or an electrostatic repulsion energy is considered, 31,32 ⑀ yield is estimated using the inflection point of the interparticle interaction energy in the radial direction 31,32 or using a characteristic distance beyond which the interaction energy is larger than a certain value. 33 ⑀ yield values obtained by such analyses are typically <1%, 18,33 unable to explain the large ⑀ yield value observed in the boehmite, 23,24,28 silica, 24 polystyrene, 18,30 and coatedalumina 29 systems.…”

“…Suspensions of smaller particles usually exhibit a larger ⑀ yield than suspensions of larger particles. For example, ⑀ yield of small boehmite 23,24,28 and silica 24 particles of ∼10 nm in size is ∼10%, whereas the ⑀ yield of alumina particles of ∼400 nm in size is <1%. 28 Figures 2 and 3 show measured GЈ and G Љ versus ⑀ for a boehmite gel of 4.5 vol% (10 nm in size) at pH 3.5 with 0.244M KCl (from Ref.…”

“…20 Another way to characterize the yield behavior of a suspension is to do constant-strain measurements with a dynamic rheometer. [23][24][25][26][27] With respect to the strain amplitude ⑀, the storage modulus GЈ and the loss modulus G Љ are measured, where GЈ is proportional to the shear modulus of the particulate network and G Љ proportional to the suspension viscosity. If the concentration is high enough, a flocculated suspension may exhibit as many as three distinctive regimes in such measurements, as schematically shown in Fig.…”

Direct Writing of Three-Dimensional Polymer Scaffolds Using Colloidal Gels

“…[15,20] The shear-reversible control of colloidal structure makes these gel-based inks well suited for flow through a deposition nozzle with low viscosity and the rapid recovery of elasticity required to maintain the shape of the deposited filament even as it spans gaps in the underlying layers. [21][22][23][24][25][26][27][28][29][30][31][32] …”

Three‐Dimensional Periodic Structures

“…The equilibrium mechanical properties of colloidal gels are governed by two parameters: u, which is representative of the interparticle bond density, and u gel , which scales inversely with bond strength. As the interparticle forces are made more attractive, colloidal gels (of constant u) experience a significant and controllable rise in their elastic properties [18][19][20][21][22][23][24][25][26] (see Fig. 3).…”