Negative viscosity induced by electroconvection in a nematic liquid crystal

2022 Fiscal Year Final Research Report

• Project/Area Number: 18H01374
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 19010:Fluid engineering-related
• Research Institution: Oita University
• Principal Investigator: Nagaya Tomoyuki 大分大学, 理工学部, 教授 (00228058)
• Co-Investigator(Kenkyū-buntansha): 岩下 拓哉 大分大学, 理工学部, 准教授 (30789508)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 液晶電気対流 / レオロジー / 負の粘性

Outline of Final Research Achievements

We found that in the electro-turbulent state of MBBA liquid crystals, spontaneous flow arises and the apparent viscosity value becomes negative. When shear stress is controlled and shear rate is measured, a hysteresis is generated in the relationship between the two. This phenomenon is similar to phase transitions in ferroelectrics. In viscosity measurement, shear stress consists of viscous stress and electrical stress, and in the case of this experimental system, the negative electrical stress is considered to be the cause of the negative viscosity. Based on the viscosity theory of liquid crystals, the magnitudes of these stresses were estimated in qualitative agreement with the experimental results.
Viscosity measurements were performed for EBBA, PBBA, and BBBA, which are homologous liquid crystals of MBBA, and it was found that the negative viscosity phenomenon also occurs in these liquid crystals.

Free Research Field

ソフトマター物理学

Academic Significance and Societal Importance of the Research Achievements

負の粘性を示す流体の開発は様々な実験系で行われ，2015年に大腸菌分散溶液において初めて約-0.1 mPa・sの負の粘度を実現した。我々は液晶という均一な非生物系で初めて約-25 mPa・sの負の粘度を達成した。負の粘性の発現と消滅に関わる分岐現象が，強誘電体などの相転移と類似することを明らかにした。これらが学術的に重要な点である。
負の粘性を示す液晶を利用すると，非常に小さいモーターを作成することが可能である。電場を印加するだけで回転を起こすことが可能なため，応用的な観点から社会的意義がある発見といえる。