Dissipative structure in granular segregation: cross-talk between rheology and interface dynamics

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K14614
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 13010:Mathematical physics and fundamental theory of condensed matter physics-related
• Research Institution: Kyushu University
• Principal Investigator: Ebata Hiroyuki 九州大学, 理学研究院, 助教 (90723213)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: 粉粒体 / パターン形成 / 相分離

Outline of Final Research Achievements

When granular mixtures of different sizes are fluidized, each species spontaneously separates and condenses to form patterns. Although granular segregation has been extensively studied, the inability to directly observe the time evolution of the internal structure hinders the understanding of the mechanism of segregation dynamics driven by surface flow. In this project, we found rich band dynamics, including a replicating band, in a horizontally shaken granular mixture in a quasi-two-dimensional container where the granules formed steady surface waves. By using the newly developed systems, we performed direct observation of surface flow and segregated internal structure. We found that coupling among segregation, surface flow, and hysteresis in the fluidity of granules is key to understanding complex band dynamics. Based on the experimental observation, we proposed a phenomenological model that reproduced bifurcation from stable band to oscillatory pattern through replicating band.

Free Research Field

非平衡物理学

Academic Significance and Societal Importance of the Research Achievements

異なる種類の粉体粒子は機械的駆動力により相分離することがある。しかし、粉体層内部の相分離の経時変化の測定が難しいことから、分離現象のメカニズムは解明されておらず、混合・分離を予測するために必要な物理量は分かっていなかった。本研究では、粉体層内部の相分離の時間発展を直接観察できる実験系を構築した。新規実験系を用いることで、表面流により駆動される相分離パターンは、サイズ分離現象・表面流・流動性のヒステリシスが相互に影響することで駆動されることを示した。回転ドラムにおけるバンド形成においても同様のメカニズムが存在する可能性があり、粉粒体の一般的な相分離現象のメカニズム解明に寄与する知見が得られた。