Interaction Between Active And Passive Particles Under Complex Boundary Conditions

The complex boundary provides an environmental habitat for bacteria and other microorganisms,and the living microorganisms also play the feedback to the microenvironment.On the other hand,for example,bacteria obtain their own overall translation and rotation through flagella flapping,as regarded as a type of typical self-driven active particles in the field of soft matter,which is significantly different from the counterparts of passive colloidal particles dominated by thermal motion This thesis focuses on the motile bacteria,and devotes to explore the interaction between active and passive particles under complex boundary conditions.This provides solutions and ideas for the regulation of bacterial behavior in complex environments,the exploration of bacterial movement mechanisms,and the practical application of bacteria.First,it is interesting to find out how passive particles(here Fe₃O₄ magnetic nanoparticles)approach,adsorb on the surface of living bacteria(E.Coli),and finally be swallowed by bacteria,and to understand the interaction mechanism between passive particles and bacteria.By using a closed PDMS microfluidic channel,for the mixing and co-incubation with and passive magnetic nano particles,It turns out that the normal bacteria can capture and successfully of swallow the magnetic nanoparticles,thus verifying the possibility of carrying magnetic nanoparticle by normal bacteria.Quantitatively,it was found that the engulfment rate of bacteria for magnetic particles is size-dependent,and also the engulfment rate increases with time,which provides the feasibility for the conversion of non-magnetic bacteria to artificially regulated magnetic bacteria.Furthermore,through the introduction of antibiotics,drug-resistant bacteria are successfully induced to swallow large-size magnetic nanoparticles(diameter up to 50 nm),which provides a potential application scheme for the magnetic inactivation of drug-resistant bacteria.Then,the upstream behavior and collective motion of mobile bacteria on the complex-shaped interface are studied.In the circular pool,by constructing solid pillars with different sizes and shapes,and adjusting the curvature of the boundary,the collective of bacterial in this environment is demonstrated.The results show that bacteria are more prone to group vortex swimming at the boundary with high curvature,and the number of vortices increases,and the characteristic radius of the associated motion becomes smaller.The exploration of bacterial movement behavior at complex interfaces provides ideas and directions for studying cluster behavior.Finally,in order to investigate the movement behavior of bacteria on real,dynamic and complex interfaces,the silica colloidal deposit drying from its aqueous solution was introduced as a dynamic porous medium to quantitatively study the effect of bacterial swimming.The regulation of internal stress accumulated by drying process is expected with the moving bacteria within the medium.By increasing the incorporation ratio of bacterial active particles,the crack mode in the colloidal deposit differs from the normal results in the literature.For the rapid evaporation process,the cracks form suddenly and propagate very fast,so that the"slow"movement of bacteria(order of tens micrometers per second)has a limited effect on the cracks.However,when the concentration of introduced bacteria is low,the bacterial particles act as“Soft”defects in the deposit and provide flaws for crack,so that the number of cracks increases significantly.When the amount of introduced bacteria is further increased,the softness of the bacteria and the chain-like flagella absorb the internal stress in the solidifying deposit,which reduces the number of cracks in the deposited porous medium.This research shows that the introduction of active particles of soft bacteria provides a new control idea for understanding the cracking of colloidal evaporation film.