Bifurcation structure and collective motions of a self-propelling droplet driven by surfactant

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03855
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 19010:Fluid engineering-related
• Research Institution: Kyoto University
• Principal Investigator: ICHIKAWA Masatoshi 京都大学, 理学研究科, 講師 (40403919)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 自己駆動液滴 / アクティブマター / エマルジョン / マイクロスイマー / 細胞運動

Outline of Final Research Achievements

A self-propelled object is an object that exhibits motion driven by internal forces utilizing the energy inherent in the system. In this study, we focus on micrometer sized self-propelled droplets that show translational swimming motion and elucidate the mechanism of their motion transition through both experimental and theoretical approaches. When the droplets are composed of water and oil, a drift transition occurs from a stationary state to a translational motion state accompanied with size increase of the droplet. We have revealed that this translational motion has a stable solution for the straight motion. Additionally, as the droplets become more larger, a bifurcation occurs where the direction of the quadrupole mode of internal and external convection becomes unstable. This instability leads to weak directional stability of the motion against disturbances or perturbations, resulting in curved motion.

Free Research Field

生命現象の物理学

Academic Significance and Societal Importance of the Research Achievements

本研究は、細胞サイズのスケールでの液滴が示す遊泳運動の流体力学的特性と駆動対流の安定構造を解明しました。これによって、液滴の運動モードやその安定性が、サイズや物性が変化した際にどのように変わるかのメカニズムが明らかになりました。この知見は、化学反応を利用して自らを動かすアクティブ液滴の運動制御技術への応用面として重要です。さらに、初期の生物がどのような生体分子やメカニズムを利用して細胞運動を獲得したのかは未解明な謎ですが、本研究はそれら初期生物が利用したと考えられる物理学的な要件と、運動の多様性を生み出す最も単純な要素を明らかにしたという観点で、発展的な意義があります。