Background in fluid and cell transport: I have a strong background in fluid mechanics and soft matter physics. This is evident from my master’s degree from NTNU, my Ph.D. degree from the University of Oslo (UiO), and post-doctoral fellowships at Stanford University, UC Santa Barbara and UiO, see Fig.1.
Part (a) adapted from Mossige et al., PRApplied 2018. Part (b) adapted from Mossige et al., Phys. Fluids 2021. Part (c) adapted from Mossige et al., Rev. Mod. Phys. 2023. Image courtesy of Sam Dehaeck. Part (d) adapted from Chandran Suja et al., J. Colloid Interface Sci. 2022.
Microfluidics: Microfluidic filtration: My Ph.D. research at UiO was a joint project with Sintef Digital aimed to characterize a commercial microfluidic filter. I used pressurized fluids to tune the microfluidic flow fields around special trilobite-shaped separation units, and I identified clog-free separation regimes for plastic particles and for live microalgae [1-4] . To describe the hydrodynamical interactions between the particles and the flow fields, I used a combination of micro Particle Image Velocimetry (?PIV) and Particle Tracking Velocimetry (PTV). The particle images were post-processed using an in-house made Matlab PIV-code.
Hydrodynamic Breadboard: These achievements inspired me to develop a construction base for modular microfluidic circuits (“The Hydrodynamic Breadboard” - inspired by the electrical analogue) that is inherently clog-free. Instead of using internal surfaces, it uses ‘virtual obstacles’ made of hydrodynamic flow structures. Specifically, these virtual obstacles are constructed by combinations of flow inlets (sources, ‘+’) and outlets (sinks, ‘-‘) that cannot be clogged because cells cannot adhere to them; Instead, they are deflected. Bigger cells are deflected more, allowing separation by size.
The breadboard as teaching tool: During my post-doctoral fellowship at Stanford University, I was picked to lead a team of five graduate students in Bioengineering as part of a microfluidics manufacturing and laboratory class. In only ten weeks, the “Breadboard-team" created a hydrodynamic post that showed promising separation characteristics. To enable us to deploy Breadboards across the scientific community, I have an international pending patent [5].
Interfacial dynamics:
I maintain a strong collaboration with the Fuller group at Stanford on problems involving gravitational Rayleigh-Taylor (R-T) instabilities in polymer solutions, miscible liquid drops, and drainage and de-wetting dynamics in thin-liquid films.
Our first study [6] recognizes that unstable concentration profiles can be induced in initially homogeneous materials through the action of evaporation, see Fig. 2a. By tuning the viscosity of polymer solutions (though tuning the concentration and molecular weight of the polymer), we were able to tune the onset of a R-T instability, which we predict by a simple scaling analysis. The onset time of the instability shows two limiting behaviors depending on the polymer diffusivity, see Fig. 2b. For high diffusivity polymers, the pluming time follows ?? 
as expected for diffusion stabilized systems. On the other hand, in low diffusivity polymers the pluming time follows a stronger concentration dependence, ?? ～ ?0?1. An effective interfacial tension, like those in immiscible systems, explains this strong concentration dependence.
The second study concerns the shape evolution of miscible (water) drops rising in more viscous liquids such as glycerol and corn syrup, see Fig. 3. The drops display different behavior depending on their transit time: early in their rise, the drops maintain a spherical shape and rise at a constant velocity (immiscible behavior), while at longer times, the drops become more oblate with the velocity decreasing as they start to mix with the ambient liquid through diffusion. We predict the transition between the immiscible behavior at “early times” and the miscible behavior at “late times” by a simple scaling parameter. A follow-up theory paper explains the observed scaling laws for velocity and volume and the underlying mixing dynamics [8].
The last project [9] recognizes that contact lenses alter tear film stability due to the differences in surface properties as compared to the mucus layer of the eye. We characterize the effect of different surface coatings on the thin-film stability by using a dynamic thin-film interferometer developed in the group (Fig. 4). We reveal that despite the wide variations in wetting agent molecular properties like charge and polarity, the time to dewet.
50% of the contact lens linearly scales with the product of the receding contact angle (θr) and the contact angle hysteresis (cos θr ?cos θa). A corollary of this finding is the importance of minimizing contact angle hysteresis for effective wetting performance. Overall, we believe the methodology and results from this study provides a basis for identifying optimal wetting agents to minimize tear film dewetting and maximize patient comfort.
My main contribution to this project was conducting optical thin film interferometry experiments and reporting the obtained drainage and dewetting results directly to the scientific investigators at Johnson and Johnson, who sponsored this joint investigation.
Kitchen Flows:
Instead of conceding to COVID-19, I initiated a collaboration with three young professors in Europe and in the U.S. to write a review paper on “Kitchen Flows”, which is a platform to connect the fields of molecular gastronomy, soft matter physics, chemistry, and fluid dynamics. We wrote a proposal to the editors of Reviews of Modern Physics, and they accepted our proposal and commissioned a review [10]. Meanwhile, I also suggested to organize a session about this fun topic at the APS-DFD meeting in 2020; I wrote an application to the programming committee and they accepted it. It was an honor to invite my colleagues to present cutting edge research on kitchen sink hydraulic jumps, miscible flows, volatile cocktails, granular materials, beer foams, and how to make a perfect pancake. This fun symposium attracted a fair amount of media attention, so we were invited by the journal Physics of Fluids to become guest editors for a Special Topic about Kitchen Flows [11].
[1] Mossige EJ, Jensen A, Mielnik MM, “An experimental characterization of a tunable separation device”, Microfluid. Nanofluid. 20, 160 (2016).
[2] Mossige EJ, Jensen A, Mielnik MM, “Separation and concentration without clogging using a high- throughput tunable filter”, Phys. Rev. Applied 9, 054007, 2018.
[3] Mossige EJ, Edvardsen B, Jensen A, Mielnik MM, “A tunable, microfluidic filter for clog-free concentration and separation of complex algal cells”, Microfluid. Nanofluid., 23(4), 2019.
[4] Mossige, EJ., & Jensen, A (2020). Clog-Free Trilobite Filtration: Tunable Flow Setup and Velocity Measurements. Micromachines, 11(10), 904. Invited contribution.
[5] Mossige EJ, Mathijssen AJTM, “Microfluidic device for hydrodynamic sorting and rheometry measurements of particles”. International patent. Application number: PCT/US2020/021216. Filed on: 3/14/2020.
[6] Mossige EJ, Chandran Suja V, Wheeler S, Islamov M, Fuller GG, 2020 “Evaporation induced Rayleigh- Taylor instabilities in aqueous polymer solutions”. Phil. Trans. R. Soc. A. 378: 20190533. Invited contribution to special issue in honor of Sir Gabriel Stokes’ 200th birthday.
[7] Mossige EJ, Chandran Suja V, Walls DJ, Fuller GG, “Dynamics of Freely Suspended Drops Translating through Miscible Environments”, Physics of Fluids, 33(3), 2021. DOI: 10.1063/5.0041536. Invited contribution to the special issue on ‘Kitchen Flows’ and featured in Physics of Fluids.
[8] Nordbotten, JM., & Mossige, EJL (2023). The dissolution of a miscible drop rising or falling in another liquid at low Reynolds number. Physics of Fluids, 35(1).
[9] Chandran Suja V, Verma A, Mossige EJ, Cui K, Xia V, Zhang Y, Sinha D, Joslin S, and Fuller GG (2022), “Dewetting Characteristics of Contact Lenses Coated with Wetting Agents”. Journal of Colloid and Interface Science, 614, 24-32.
[10] Mathijssen, AJ, Lisicki, M, Prakash, VN, & Mossige, EJ (2023). Culinary fluid mechanics and other currents in food science. Reviews of Modern Physics, 95(2), 025004.
[11] Fuller, GG., Lisicki, M, Mathijssen, AJ, Mossige, EJ, Pasquino, R, Prakash, VN, & Ramos, L (2022). Kitchen flows: Making science more accessible, affordable, and curiosity driven. Physics of Fluids, 34(11).