Topological origin of phase separation in hydrated gels

Cheng Zhao; Wei Zhou; Qi Zhou; Zhe Wang; Gaurav Sant; Lijie Guo; Mathieu Bauchy

doi:10.1016/j.jcis.2021.01.068

Topological origin of phase separation in hydrated gels

J Colloid Interface Sci. 2021 May 15:590:199-209. doi: 10.1016/j.jcis.2021.01.068. Epub 2021 Jan 26.

Authors

Cheng Zhao¹, Wei Zhou², Qi Zhou³, Zhe Wang³, Gaurav Sant⁴, Lijie Guo⁵, Mathieu Bauchy⁶

Affiliations

¹ State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China; Physics of AmoRphous and Inorganic Solids Laboratory (PARISlab), Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA.
² State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China. Electronic address: zw_mxx@whu.edu.cn.
³ Physics of AmoRphous and Inorganic Solids Laboratory (PARISlab), Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA.
⁴ Laboratory for the Chemistry of Construction Materials (LC(2)), Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA; California Nanosystems Institute (CNSI), University of California, Los Angeles, CA 90095, USA; Institute for Carbon Management (ICM), University of California, Los Angeles, CA 90095, USA.
⁵ National Centre for International Research on Green Metal Mining, BGRIMM Technology Group, Beijing 100160, China. Electronic address: guolijie@bgrimm.com.
⁶ Physics of AmoRphous and Inorganic Solids Laboratory (PARISlab), Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA; Institute for Carbon Management (ICM), University of California, Los Angeles, CA 90095, USA. Electronic address: bauchy@ucla.edu.

PMID: 33548603
DOI: 10.1016/j.jcis.2021.01.068

Abstract

Hypothesis: Depending on their composition, hydrated gels can be homogeneous or phase-separated, which, in turn, affects their dynamical and mechanical properties. However, the nature of the structural features, if any, that govern the propensity for a given gel to phase-separate remains largely unknown. Here, we argue that the propensity for hydrated gels to phase-separate is topological in nature.

Simulations: We employ reactive molecular dynamics simulations to model the early-age precipitation of calcium-alumino-silicate-hydrate (CASH) gels with varying compositions, i.e., (CaO)_1.7(Al₂O₃)_x(SiO₂)_{1 -}_x(H₂O)_{3.7 +}_x. By adopting topological constraint theory, we investigate the structural origin of phase separation in hydrated gels.

Findings: We report the existence of a homogeneous-to-phase-separated transition, wherein Si-rich (x ≤ 0.10) CASH gels are homogeneous, whereas Al-rich (x > 0.10) CASH gels tend to phase-separate. Furthermore, we demonstrate that this transition is correlated to a topological flexible-to-rigid transition within the atomic network. We reveal that the propensity for topologically-overconstrained gels to phase-separate arises from the existence of some internal stress within their atomic network, which acts as an energy penalty that drives phase separation.

Keywords: Atomic stress; Hydrated colloidal gels; Molecular dynamics; Phase separation; Topological constraint theory.