Mechanism of Negative Viscosity in Liquid Crystals

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K03872
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13040:Biophysics, chemical physics and soft matter physics-related
• Research Institution: Hokkaido University
• Principal Investigator: Orihara Hiroshi 北海道大学, 工学研究院, 教授 (30177307)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 負の粘度 / 液晶 / トポロジカル欠陥 / 乱流

Outline of Final Research Achievements

Although the search for fluids with negative viscosity has been conducted for a long time, we have succeeded in observing negative viscosity for the first time in liquid crystals to which an electric field is applied, using a rheometer. In this study, we clarify the mechanism of negative viscosity in liquid crystals.
The equations for the orientation field of the liquid crystal, the flow velocity field, and the electric field were derived from Onsager's variational principle, and three-dimensional numerical calculations are performed using the finite element method. It can be reproduced that as the applied voltage is increased, the flow becomes faster and defects are generated. The shear stress under turbulent flow conditions under steady shear flow was calculated, and it was confirmed that the stress was negative, i.e., the viscosity was negative. The negative stress is attributed to the reversal of the velocity gradient near the interfaces.

Free Research Field

ソフトマター物理学

Academic Significance and Societal Importance of the Research Achievements

本研究により、実験で観測されていた負の粘度がシミュレーションにより再現できた。この際に用いた運動方程式は極めて一般性のあるもので、ネマチック液晶であれば他の条件下の現象にも適用できる。また、本研究で負の粘度の発現機構を明らかにした液晶は非平衡状態にある流体で、最近ではアクティブマターと呼ばれ非平衡物理学の恰好な研究対象となっている。本研究の成果はこのようなアクティブマターに関する新たな学問分野の開拓およびその応用へとつながると期待できる。