U. Thiele présentera ses travaux le lundi 7 mars à 14h30 à l’amphithéâtre Agrosciences (UFR STS-ip) sur les bio-films : 

"Thin-film modelling of spreading biofilms and of drops of active liquids”

After a brief introduction, first, we consider thin-film models for spreading biofilms. After reviewing experiments [1,2] and modelling approaches [3] we establish the thin-film hydrodynamics for free surface films of mixtures where capillarity and wettability are incorporated. This passive model is then extended by bioactive terms like bacterial proliferation and biosurfactant production to obtain models for spreading biofilms [4,5]. These are employed to study (i) the arrest of biofilm spreading due to surface forces [4], and (ii) the emergence of fingering instabilities caused by biosurfactant production. As a result we distinguish four dynamical (morphological) modes of biofilm growth [5].
Second, we employ a related thin-film approach to model shallow drops of active liquid resting and moving on a solid substrate [6]. After introducing coupled evolution equations for film thickness and polarization profiles in the form of a gradient dynamics supplemented by active stresses and self-propulsion we discuss the behaviour of the model based on bifurcation analysis and time simulations. In particular, we show that defects in the polarization drastically influence the shape and motility of active droplets and observe a transition from resting to moving drops via the elimination of defects. Furthermore, we discuss drop splitting resulting from strong active contractile stresses. Results are given for one- [6] and two-dimensional [7] substrates.
[1] Fauvart, M. et al., Soft Matter, 2012, 8, 70-76.
[2] Seminara, A. et al., Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 1116-1121.
[3] Tuson, H.; Weibel, D., Soft Matter, 2013, 9, 4368-4380.
[4] Trinschek, S.; John, K.; Lecuyer, S.; Thiele, U., Phys. Rev. Lett. 119, 078003 (2017). http://dx.doi.org/10.1103/PhysRevLett.119.078003
[5] Trinschek, S.; John, K.; Thiele, U., Soft Matter 14, 4464-4476 (2018).  http://dx.doi.org/10.1039/c8sm00422f
[6] Trinschek, S.; Stegemerten, F.; John, K.; Thiele, U., Phys. Rev. E 101, 062802 (2020). http://dx.doi.org/10.1103/PhysRevE.101.062802
[7] Stegemerten, F.;  John, K.; and Thiele, U., preprint (2021), https://arxiv.org/abs/2107.08961