13:25 - 13:40

Jan Guzowski

Soft-granular materials for microtissue engineering.

Instytut Chemii Fizycznej PAN

Soft granular materials such as emulsions, microgel suspensions or foams are ubiquitous in industry, but their applications in tissue engineering have emerged only recently. In particular, this has been facilitated by the maturation of droplet microfluidics as a tool for precise generation and manipulation of various types of granular mesostructures. In the talk, I will address important challenges associated with such manipulations, discuss the emerging questions regarding the collective dynamic behavior of granular materials in confined geometries, as well propose the possibilities of their application in generation of new types of microcapsules and scaffolds for the culture of living human microtissues and their use as relevant preclinical models, e.g., for testing of toxicity or efficacy of drugs.  

13:40 - 13:55

Tetuko Kurniawan

Formation of droplets at low capillary numbers

Institute of Fundamental Technological Research, Polish Academy of Sciences

I will discuss the droplet formation at a low Capillary number regime, Ca≤ 10-3. In this regime, the droplet-formation mechanism deviates from the commonly known squeezing regime of higher Ca. Firstly, the experiment revealed an explosion in droplet size. Secondly, there is an extension of the neck before pinch-off. I provided mathematical analysis for these phenomena at a very low Ca regime. The classical mathematical model of the squeezing droplet formation has been expanded based on the current analysis. The result promotes a more general understanding of droplet formation in the microfluidic devices.

13:55 - 14:10

Łukasz Klotz

Influence of porous material on the flow behind backward-facing step - experimental study

Faculty of Power and Aeronautical Engineering, Warsaw University of Technology

We investigate effect of porous insert located upstream of the separation edge of backward-facing step (BFS) in early transitional regime as a function of Reynolds number. This is an example of hydrodynamic system that is a combination of separated shear flow with large amplification potential and porous materials known for efficient flow destabilisation. Spectral analysis reveals that dynamics of backward-facing step is dominated by spectral modes that remain globally coherent along the streamwise direction. We detect two branches of characteristic frequencies in the flow and with Hilbert transform we characterise their spatial support. For low Reynolds numbers, the dynamics of the flow is dominated by lower frequency, whereas for high enough Reynolds numbers cross-over to higher frequencies is observed. Increasing permeability of the porous insert results in decrease in Reynolds number value, at which frequency cross-over occurs. By comparing normalized frequencies on each branch with local stability analysis, we attribute Kelvin-Helmholtz and Tollmien-Schlichting instabilities to upper and lower frequency branches, respectively. Finally, our results show that porous inserts enhance Kelvin-Helmholtz instability and promote transition to oscillator-type dynamics. Specifically, we observe that amplitude of vortical (BFS) structures associated with higher frequency branch follows Landau model prediction for all investigated porous inserts. This work has been accepted for publication in the Journal of Fluid Mechanics and partially founded by the National Science Center (Poland) within OPUS-21 project (2021/41/B/ST8/03142).

14:10 - 14:25

Hiroyuki Kitahata

Droplet motion coupled with chemical reaction

Chiba University

When a small droplet of Belousov-Zhabotinsky (BZ) reaction medium is put onto an organic phase, the droplet exhibits a motion coupled with the chemical oscillaton inside the droplet. The interfacial tension change originating from the chemical oscillation induces this motion. The detailed mechanism is discussed considering the low-Reynolds hydrodynamics and Marangoni stress at the droplet interface.

14:25 - 14:40

Yuki Koyano

Spontaneous motion in camphor-water system

Kobe University

The self-propelled motions are ubiquitous in nature, e.g. bird flocks, fish schools, and so on. Such motions has taken attention of physicists and been studied as active matter. To simplify the discussion, non-biological systems has also been proposed and studied. In the presentation, I would like to introduce spontaneous motion of camphor on water surface, and discuss the effect of the confinement by the boundaries of the system and the shape of the camphor particles on the motion.