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Issue 22, 2012
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Ergodicity breaking and aging dynamics in Laponite–Montmorillonite mixed clay dispersions

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Abstract

Ergodicity breaking and aging dynamics in a mixture of colloidal clays, Laponite (L) and Montmorillonite (MMT), were investigated. The intensity of the light scattered off L-MMT dispersions scaled with solid volume fraction (ϕ) as, Iϕα, with α = 1.49, for Laponite α = 0.95, for 2 × 10−4 < ϕ < 8 × 10−3, and it remained invariant above ϕ = 8 × 10−3. For MMT, α = 1.38 and no such invariance was noticed. Ergodic to non-ergodic transitions were observed in aged samples with a characteristic ergodicity breaking time, τEB ≈ 102 − 105 s. Dynamic structure factor, g1(q,t) exhibited two-mode relaxation, g1(q,t) = a exp(−t/τ1) + (1 − a) exp−(t/τ2)β. The stretching parameter, β was found to decrease linearly with aging time, tw whereas slow mode relaxation time increased as τ2 ∼ exp (btw) and τ1 remained invariant of tw. Spatial dependence of τ1 and τ2 showed, τ1,τ2q−2 in the ergodic phase, considered arising from the diffusive motion. After the ergodicity breaking time (t > τEB), the slow mode relaxation was no more diffusive and revealed τ2q−1, indicating dynamic arrest of the platelets in the glass phase. The temporal evolution of the slow mode relaxation time τ2 in full aging regime i.e. above τEB, followed a power law growth. The τEB was found to decrease with concentration as τEB ∼ exp(−ϕ/ϕ0). A sharp rise in anisotropy, Dp in the L-MMT glass system occurring precisely at the ergodicity breaking time was observed with the overall aging dependence given by Dpt0.46w. Heterogeneity in these samples was probed from the Cole–Cole plot of rheology data. It is concluded that the aging dynamics was governed by the Laponite platelets with the MMT providing a suitable matrix for appropriate interparticle interactions.

Graphical abstract: Ergodicity breaking and aging dynamics in Laponite–Montmorillonite mixed clay dispersions

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Article information


Submitted
15 Feb 2012
Accepted
04 Apr 2012
First published
01 May 2012

Soft Matter, 2012,8, 6120-6127
Article type
Paper

Ergodicity breaking and aging dynamics in Laponite–Montmorillonite mixed clay dispersions

R. K. Pujala and H. B. Bohidar, Soft Matter, 2012, 8, 6120
DOI: 10.1039/C2SM25337B

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