Watanabe Chiho, Yanagisawa Miho
School of Integrated Arts and Sciences, Graduate School of Integrated Sciences for Life, Hiroshima University, Kagamiyama 1-7-1, Higashi-Hiroshima 739-8521, Japan.
Komaba Institute for Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Tokyo 153-8902, Japan.
Life (Basel). 2022 Mar 4;12(3):373. doi: 10.3390/life12030373.
The dextran−PEG system is one of the most famous systems exhibiting phase separation. Various phase behaviors, including the evaporation process of the dextran−PEG system, have been studied in order to understand the physicochemical mechanism of intracellular phase separation and the effect of condensation on the origin of life. However, there have been few studies in dilute regime. In this study, we focused on such regimes and analyzed the pattern formation by evaporation. The specificity of this regime is the slow onset of phase separation due to low initial concentration, and the separated phases can have contrasting wettability to the substrate as evaporation progresses. When the polymer concentration is rather low (<5 wt%), the dextran−PEG droplets form a phase-separated pattern, consisting of PEG at the center and dextran ring of multiple strings pulling from the ring. This pattern formation is explained from the difference in wettability and compatibility between dextran and PEG upon condensation. At the initial dilute stage, the dextran-rich phase with higher wettability accumulates at the contact line of the droplet to form a ring pattern, and then forms multiple domains due to density fluctuation. The less wettable PEG phase recedes and pulls the dextran domains, causing them to deform into strings. Further condensation leads to phase separation, and the condensed PEG with improved wettability stops receding and prevents a formed circular pattern. These findings suggest that evaporation patterns of polymer blend droplets can be manipulated through changes in wettability and compatibility between polymers due to condensation, thus providing the basis to explore origins of life that are unique to the process of condensate formation from dilute systems.
葡聚糖-聚乙二醇体系是最著名的表现出相分离的体系之一。为了理解细胞内相分离的物理化学机制以及凝聚对生命起源的影响，人们对包括葡聚糖-聚乙二醇体系蒸发过程在内的各种相行为进行了研究。然而，在稀溶液体系方面的研究较少。在本研究中，我们聚焦于此类体系，并分析了蒸发过程中的图案形成。该体系的特殊性在于，由于初始浓度低，相分离开始缓慢，并且随着蒸发的进行，分离出的相可能对基底具有不同的润湿性。当聚合物浓度相当低（<5 wt%）时，葡聚糖-聚乙二醇液滴形成一种相分离图案，由中心的聚乙二醇和从环上拉出的多条链状葡聚糖环组成。这种图案形成可以从凝聚时葡聚糖和聚乙二醇之间润湿性和相容性的差异来解释。在初始稀溶液阶段，润湿性较高的富含葡聚糖的相在液滴的接触线处聚集形成环状图案，然后由于密度波动形成多个区域。润湿性较差的聚乙二醇相后退并拉动葡聚糖区域，使其变形为链状。进一步的凝聚导致相分离，润湿性改善的凝聚聚乙二醇停止后退并阻止形成圆形图案。这些发现表明，聚合物共混物液滴的蒸发图案可以通过凝聚导致的聚合物之间润湿性和相容性的变化来操控，从而为探索稀溶液体系凝聚过程特有的生命起源提供了基础。
