Zhao Cheng, Zhou Wei, Zhou Qi, Wang Zhe, Sant Gaurav, Guo Lijie, Bauchy Mathieu
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.
State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China.
J Colloid Interface Sci. 2021 May 15;590:199-209. doi: 10.1016/j.jcis.2021.01.068. Epub 2021 Jan 26.
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.
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)(AlO)(SiO)(HO). By adopting topological constraint theory, we investigate the structural origin of phase separation in hydrated gels.
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.
根据其组成，水合凝胶可以是均匀的或相分离的，这反过来又会影响其动力学和力学性能。然而，决定给定凝胶相分离倾向的结构特征（如果有的话）的本质在很大程度上仍然未知。在这里，我们认为水合凝胶相分离的倾向本质上是拓扑性的。
我们采用反应分子动力学模拟来模拟具有不同组成（即（CaO）（AlO）（SiO）（HO））的钙铝硅酸盐水合物（CASH）凝胶的早期沉淀。通过采用拓扑约束理论，我们研究了水合凝胶中相分离的结构起源。
我们报告了从均匀到相分离转变的存在，其中富硅（x≤0.10）的CASH凝胶是均匀的，而富铝（x>0.10）的CASH凝胶倾向于相分离。此外，我们证明这种转变与原子网络内从拓扑柔性到刚性的转变相关。我们揭示了拓扑过度约束的凝胶相分离的倾向源于其原子网络内存在的一些内应力，该内应力充当驱动相分离的能量惩罚。
