A kinetic model of a polyelectrolyte gel undergoing phase separation
A kinetic model of a polyelectrolyte gel undergoing phase separation
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DOI：
10.1016/j.jmps.2021.104771
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发表时间：
2022-02-07
影响因子：
5.3
通讯作者：
Waters, Sarah L.
中科院分区：
文献类型：
--
作者：
Celora, Giulia L.;Hennessy, Matthew G.;Waters, Sarah L.
在这项研究中，我们提出了一种新的相场理论的基础上非平衡态热力学，解决了宏观变形和浸没在离子溶液中的凝胶的内部结构。凝胶的控制方程解释了其电化学响应、其非线性网络的非线性弹性、多组分Stefan-Maxwell扩散和在相分离时形成的内部界面的能量成本。这些方程耦合到周围的离子溶液的流体动力学模型。全时变模型描述了凝胶-溶液体系在多个时间和空间尺度上的演化，揭示了调节凝胶相分离的机械-电化学机制，从而导致复杂空间模式的出现。该系统的丰富的动力学进行了研究的约束凝胶进行单轴变形。我们发现，在凝胶浴系统中的相分离的调节是依赖于两个物理长度尺度之间的竞争：德拜和库恩长度，分别为双电层和扩散界面的厚度。当库恩长度远大于德拜长度时，标准的电中性假设就成立了。在这种情况下，我们表明，大规模的溶剂通量可以导致凝胶的相分离。取决于周围浴中的离子浓度，凝胶的溶胀/去溶胀经由来自凝胶-浴界面的前沿传播或经由前沿传播与亚稳分解组合而发生。在库恩和德拜长度是相称的限制，我们的模型预测一种新的模式相分离，导致在凝胶体组织成空间局部化的稳定的带电域，从德拜层和传播通过整个凝胶。
In this study we propose a novel phase-field theory based on non-equilibrium thermodynamics that resolves both the macroscopic deformations and the internal structure of a polyelectrolyte gel immersed in an ionic solution. The governing equations for the gel account for its electrochemical response, the nonlinear elasticity of its polyelectrolyte network, multi-component Stefan-Maxwell diffusion and the energy cost of internal interfaces that form upon phase separation. These equations are coupled to a hydrodynamic model for the surrounding ionic solution. The full time-dependent model describes the evolution of the gel-solution system across multiple time and spatial scales revealing the mechano-electro-chemical mechanisms that regulate phase separation of the gel, which results in the emergence of complex spatial patterns. The rich dynamics of this system are investigated for a constrained gel undergoing uni-axial deformations. We find that the regulation of phase separation in the gel-bath system is dependent on the competition between two physical length scales: the Debye and Kuhn lengths which characterise the thickness of electric double layers and diffuse interfaces, respectively. When the Kuhn length is much larger than the Debye length, the standard electroneutral assumption can be invoked. In this case, we show that large-scale solvent flux can result in the phase separation of the gel. Depending on the concentration of ions in the surrounding bath, swelling/deswelling of the gel occurs either via propagation of a front from the gel-bath interface or via front propagation combined with spinodal decomposition. In the limit where the Kuhn and Debye length are commensurate, our model predicts a novel mode of phase separation which results in the gel bulk organising into spatially localised stable charged domains that emanate from the Debye layer and propagate through the whole gel.