News Release

New control of liquid–liquid interface through non-equilibrium thermodynamics

Challenge to non-equilibrium thermodynamics based on the maximum entropy production

Peer-Reviewed Publication

Tokyo University of Agriculture and Technology

Change in the pattern of the flow interface when the non-equilibrium degree ε is changed at t = 600 s.

image: Figure: (a) ~ (c) Change in the pattern of the flow interface when the non-equilibrium degree ε is changed at t = 600 s. (a) circular pattern (ε = 0.20)(b) fingering pattern (ε = 0.61) (c) droplet pattern (ε = 0.97) (d) Calculated entropy production curves during the formation of the circular (C), finger (F, black solid curve), and droplet (D, red solid curve) patterns. The associated velocities are shown as dashed lines. The two intersections among the three entropy production curves appear at ε_F=0.217 and ε_D=0.685. view more 

Credit: Credit: Yuichiro Nagatsu/TUAT, Takahiko Ban/ Osaka University

The Japanese collaborative team of Tokyo University of Agriculture and Technology (TUAT) and Osaka University presents a novel method for tuning hydrodynamic interfacial instability through a thermodynamic parameter controlling liquid–liquid phase separation. Furthermore, they succeeded in predicting the pattern changes of a growing interface by using the maximum entropy production principle.

These researchers published their results in The Journal of Physical Chemistry B on June 29th, 2021.

Flow at the interface of a fluid is a very common phenomenon. Recently, people are interested in the flow of fluid interfaces when they are accompanied by physicochemical effects such as chemical reactions, phase changes, and phase separations. “Since it includes both physicochemical and hydrodynamic factors, its control and prediction become more difficult than that when the physicochemical factors are not considered. Therefore, we decided to establish an appropriate control and prediction methods for the flow interface when physicochemical effects are involved” said Dr. Nagatsu, one of the corresponding authors on the paper, Associate Professor in the Department of Chemical Engineering at TUAT.

 “In the equilibrium system, the "principle of increase of entropy" known as the second law of thermodynamics holds. In contrast, the theory of non-equilibrium systems was proposed in the 1950s that the entropy production rate is maximized in a complex system in which two or more irreversible processes interfere. However, this principle was demonstrated only in a very limited complex process. For example, crystal growth pattern formation and thermal convection pattern formation. Hence, testing in other complex processes is needed” said Dr. Ban, one of the corresponding authors on the paper, Associate Professor in the Department of Chemical Engineering at Osaka University.

After conducting experiments, they reported on the hydrodynamic interfacial instability controlled by a thermodynamic parameter driving the liquid–liquid phase separation during fluid displacement in a Hele-Shaw cell. The cell is composed of two closely spaced plane-parallel plates.  This instability remains even when the solution is hydrodynamically stable. Adjusting the salt concentration helps control the miscibility of the solutions and change the pattern of the interface. The researchers observed stable circular, fingering, and droplet formation patterns as the salt concentration is decreased from equilibrium (see figure). “Our team analyzed this interfacial instability using thermodynamic flux, which is determined from the growth rate of the interface. We also provided a theoretical framework to determine the different patterns such as gas, liquid, and solid phases in equilibrium and to quantitatively predict the transition points between the patterns. Interestingly we found that the pattern transition can be explained by higher entropy production,” Ban added.

“This result showed that the degree of non-equilibrium plays a decisive role in the interfacial flow with liquid-liquid phase separation. This provides an important guideline for the effective control of interfacial flow with liquid-liquid phase separation. In addition, this result provides a new example in which the principle of maximum entropy production, whose verification has been limited so far, can be applied. In the future, further research on the maximum entropy production principle is required,” adds Nagatsu.   


Acknowledgements. This study is supported by JSPS KAKENHI Grant No. 19J12553.

For more information about the Nagatsu laboratory, please visit

For more information about the Ban laboratory, please visit


Original publication:

Tunable Hydrodynamic Interfacial Instability by Controlling a Thermodynamic Parameter of Liquid–Liquid Phase Separation

Ryuta X. Suzuki, Shuntaro Kobayashi, Yuichiro Nagatsu, and Takahiko Ban

J. Phys. Chem. B 2021, 125, 27, 7508–7514


About Tokyo University of Agriculture and Technology (TUAT):

TUAT is a distinguished university in Japan dedicated to science and technology. TUAT focuses on agriculture and engineering that form the foundation of industry, and promotes education and research fields that incorporate them. Boasting a history of over 140 years since our founding in 1874, TUAT continues to boldly take on new challenges and steadily promote fields. With high ethics, TUAT fulfills social responsibility in the capacity of transmitting science and technology information towards the construction of a sustainable society where both human beings and nature can thrive in a symbiotic relationship. For more information, please visit


About Osaka University :

Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.  




Yuichiro Nagatsu, Ph.D.

Associate Professor, Department of Chemical Engineering, TUAT, Japan


Takahiko Ban, Ph.D.

Associate Professor, Graduate School of Engineering Science, Osaka University, Japan

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