title: Sudden collapse of a colloidal gel.
abstract: Metastable gels formed by weakly attractive colloidal particles display a distinctive two-stage time-dependent settling behavior under their own weight. Initially, a space-spanning network is formed that, for a characteristic time, which we define as the lag time τ(d), resists compaction. This solidlike behavior persists only for a limited time. Gels whose age t(w) is greater than τ(d) yield and suddenly collapse. We use a combination of confocal microscopy, rheology, and time-lapse video imaging to investigate both the process of sudden collapse and its microscopic origin in a refractive-index matched emulsion-polymer system. We show that the height h of the gel in the early stages of collapse is well described by the surprisingly simple expression, h(τ)=h(0)-Aτ(3/2), with h(0) the initial height and τ=t(w)-τ(d) the time counted from the instant where the gel first yields. We propose that this unexpected result arises because the colloidal network progressively builds up internal stress as a consequence of localized rearrangement events, which leads ultimately to collapse as thermal equilibrium is reestablished.
authors.affiliation: School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom. p.bartlett@bristol.ac.uk
authors.forename: Paul
authors.initials: P
authors.lastname: Bartlett
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Teece
authors.forename: Malcolm A
authors.initials: MA
authors.lastname: Faers
mesh_terms: D003102:Colloids / Q000737:chemistry*; D019245:Compressive Strength; D003198:Computer Simulation; D005782:Gels / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D014783:Viscosity
chemical_list: D003102:Colloids; D005782:Gels