News Release

New study may revise a theory of flowing viscous liquids that was accepted for 60 years

Discovery of a topological change of an interfacial hydrodynamics by a partial miscibility and creating a cross-disciplinary discipline of chemical thermodynamics and interfacial hydrodynamics

Peer-Reviewed Publication

Tokyo University of Agriculture and Technology

Temporal evolution of multiple droplet formation during VF experiment

video: Temporal evolution of multiple droplet formation during VF experiment view more 

Credit: Yuichiro Nagatsu/TUAT, Takahiko Ban/ Osaka University, Manoranjan Mishra/IIT Ropar

The international collaborative team of Tokyo University of Agriculture and Technology (TUAT) in Japan, Indian Institute of Technology Ropar (IIT Ropar) in India, and Osaka University in Japan has discovered for the first time a topological change of viscous fingering (one of classical interfacial hydrodynamics), which is driven by "a partially miscibility," where the two liquids do not mix completely with finite solubility. This topological change originates from a phase separation and the spontaneous motion driven by it. It is a phenomenon that cannot be seen with completely mixed (fully miscible) system with infinite solubility or immiscible system with no solubility.

The researchers published their results in the Journal of Fluid Mechanics on Jun 30th, 2020.

When a less viscous fluid displaces a more viscous fluid in porous media, the interface between the two fluids becomes hydrodynamically unstable and deforms in a finger shape. This phenomenon is technically called "Viscous fingering (VF)". Since the 1950s, the VF has been studied as one fluid dynamics issue. Then, it is now widely known that the properties can be classified according to weather the two fluids are fully miscible or immiscible. The viscous fingering dynamics helps to understand the process of fluid displacement in porous media in reactions and separation in chemical processes, as well as in enhanced-oil-recovery and CO2 sequestration.

"It has long been pointed out that viscous fingering in partially miscible fluids occurs in underground processes with high-pressure conditions, such as oil recovery and CO2 storage. However, such viscous fingering has been theoretically studied in the last few years," said Dr. Nagatsu, one of the corresponding authors on the paper and Associate Professor in the Department of Chemical Engineering at Tokyo University of Agriculture and Technology (TUAT). "Experimental studies of such VF have not been done at all. One of the reasons is that fluid mechanics researchers did not use experimental conditions that were partially miscible at room temperature and atmospheric pressure."

The research team succeeded in changing the miscibility of the system to fully miscible, immiscible, and partially miscible with little change in the viscosities at room temperature and atmospheric pressure. They used an aqueous two-phase system consisting of polyethylene-glycol (PEG), sodium-sulfate (Na2SO4), and water (see Figure), which were described in the same research team's paper published in 2019. Here, in the partially miscible system, a pure PEG solution and a pure Na2SO4 solution dissolve each other with finite solubility, and as a result, the phase is separated into a PEG-rich phase (phase L) and a Na2SO4-rich phase (phase H) (see Figure).

They have carried out experiments by using this solution system in which a less-viscous liquid displaces a more-viscous one in a Hele-Shaw cell (see Figure) which is a model mimics flow in porous media. "Our team found that topological change is observed in the case where the two liquids are partially miscible (see Figure and Movie). This is the first instance of topological change in viscous fingering although various changes in the pattern due to various physicochemical effects, so far, have been reported when the two fluids are fully miscible or immiscible. We clearly showed this topological change originates from a phase separation occurring between the two fluids and the spontaneous motion driven by it," Nagatsu explains.

"Our result overturns the common understanding of more than 60 years in VF research which began in the 1950s that the characteristics of VF are divided into immiscible and fully miscible cases and it demonstrates the existence and importance of the partially miscible case, which becomes the third classification category. This will open a new cross-disciplinary research area involving hydrodynamics and chemical thermodynamics. Also, the displacement with partial miscibility in a porous medium takes places in the oil recovery process from the formation and the CO2 injection process into the formation. Thus, our finding is expected to create new control methodology of those processes by utilizing the partial miscibility," adds Nagatsu.


This work was supported by PRESTO-JST (No. 25103004 "Phase Interfaces for Highly Efficient Energy Utilization") and JSPS Invitation Fellowships for Research in Japan (No. S15063 and No. L19548).

For more information about the Nagatsu laboratory, please visit

Original publication:

Phase separation effects on a partially miscible viscous fingering dynamics
Ryuta X. Suzuki,* Yuichiro Nagatsu, Manoranjan Mishra, and Takahiko Ban
Journal of Fluid Mechanics 898 A11

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.


About Indian Institute of Technology Ropar (IIT Ropar):

Indian Institute of Technology Ropar (IIT Ropar) is a premier engineering, science, and technology institute in India established in 2008 by the Ministry of Education, Govt. of India (formerly: Ministry of Human Resource Development (MHRD), Govt. of India). IIT Ropar has initiated research on socially relevant problems like water and air pollution, affordable point-of-care healthcare technologies, and artificial intelligence applied to solve future engineering challenges. IIT Ropar has made active research collaborations with the likes of MIT, SUNY, Cardiff University, Cambridge University to name a few. Department of Science of Technology (DST), Govt of India, has established a Technology Innovation Hub (TIH) in the application domain of Agriculture & Water, named as Agriculture and Water Technology Development Hub (AWaDH), at IIT Ropar in the framework of National Mission on Interdisciplinary Cyber-Physical Systems (NM-ICPS). The high standard of research has ensured that year-after-year IIT Ropar has the best research performance amongst newer IITs, in India and in world rankings like the QS Asia rankings (205th) and Times Higher Education World University rankings (301-350). The institute has made significant research investment in Industry 4.0 in partnership with the Government of Taiwan by setting up the Indo-Taiwan Joint Research Centre on Artificial Intelligence and Machine Learning, a one of its kind in India. For more information, please visit


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

Manoranjan Mishra, Ph.D.
Associate Professor, Department of Mathematics, Indian Institute of Technology Ropar, India

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