Yuan Jiaxing, Tateno Michio, Tanaka Hajime
Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
ACS Nano. 2023 Sep 26;17(18):18025-18036. doi: 10.1021/acsnano.3c04657. Epub 2023 Sep 7.
Phase separation is a fundamental phenomenon leading to spatially heterogeneous material distribution, which is critical in nature, biology, material science, and industry. In ordinary phase separation, the minority phase always forms droplets. Contrary to this common belief, even the minority phase can form a network structure in viscoelastic phase separation (VPS). VPS can occur in any mixture with significant mobility differences between their components and is highly relevant to soft matter and biomatter. In contrast to classical phase separation, experiments have shown that VPS in polymer solutions lacks self-similar coarsening, resulting in the absence of a domain-coarsening scaling law. However, the underlying microscopic mechanism of this behavior remains unknown. To this end, we perform fluid particle dynamics simulations of bead-spring polymers, incorporating many-body hydrodynamic interactions between polymers through a solvent. We discover that polymers in the dense-network-forming phase are stretched and store elastic energy when the deformation speed exceeds the polymer dynamics. This self-generated viscoelastic stress mechanically interferes with phase separation and slows its dynamics, disrupting self-similar growth. We also highlight the essential role of many-body hydrodynamic interactions in VPS. The implications of our findings may hold importance in areas such as biological phase separation, porous material formation, and other fields where network structures play a pivotal role.
相分离是一种导致材料在空间上分布不均的基本现象，在自然界、生物学、材料科学和工业领域都至关重要。在普通的相分离中，少数相总是形成液滴。与这种普遍认知相反，在粘弹性相分离（VPS）中，即使是少数相也能形成网络结构。VPS可发生在任何其组分间具有显著迁移率差异的混合物中，并且与软物质和生物物质高度相关。与经典相分离不同，实验表明聚合物溶液中的VPS缺乏自相似粗化，因而不存在域粗化标度律。然而，这种行为背后的微观机制仍然未知。为此，我们对珠簧聚合物进行了流体粒子动力学模拟，通过溶剂纳入了聚合物之间的多体流体动力学相互作用。我们发现，当变形速度超过聚合物动力学时，处于形成致密网络相的聚合物会被拉伸并储存弹性能量。这种自生的粘弹性应力会对相分离产生机械干扰并减缓其动力学过程，破坏自相似生长。我们还强调了多体流体动力学相互作用在VPS中的重要作用。我们的研究结果可能在生物相分离、多孔材料形成以及其他网络结构起关键作用的领域具有重要意义。
