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Research focus:

  1. Bullet  Rheology of bacteria suspensions and the run-tumble behavior.

  2. Bullet  Brownian motion in two-dimensional confinement.

  3. Bullet  Self-organization and self-assembly of micro/nano objects, Pattern formation in the interface system.

  4. Bullet  Wetting phenomena on textured surface and the optofluidics.



Microswimmers: E. Coli in microfluidic channels   

  How the E. Coli fight with the surrounding fluid flow (low mean velocity). Collective motion of the bacteria when the concentration increases to a critical value; superfluidic (very low viscosity) due to the motility of the bacterial; 3D tracking of individual bacteria against the flow; active random motion of the run-tumble behavior.


E. Coli (ATCC /RP strains) are used for the understanding of the active rheology and run-tumble behavior in microfluidic channels (PDMS 100um*600um*20mm). a. Sketch of the bacteria with the basic parameters (left-up), micrography under optical microscope by phase contrast (left-bottom), and the active Brownian motion analogy by the run-tumble random motion; b and c. PDMS channels with tubing; d and e. bacterial flow.

 

Drying pattern   

     Drying crack pattern. Experimental observation of the crack formation in the drying deposition is conducting in the recent work. At the same time, a theoretical model based on the concept of spinodal decomposition in Cahn’s theory, is devoted to the explanation of the physical origin of the crack pattern, in particular, concentric circular crack pattern, parallel array cracks, radius-directional cracks, spiral cracks, and the network crack pattern.

   


     Crack pattern from the drying of colloidal suspensions. The versatile arrangements of the cracks form the unique patterns such as the concentric cracks, radius-like cracks, sectional cracks, parallel crack array, network cracks, and the spiral crack.      


Reference:

  1. Origin of crack pattern in the deposition from drying colloidal suspension. Phys. Rev. E 86, 061406 

(2012).  PDF in  arxiv.org

2. Formation of circular crack pattern in deposition self-assembled by drying nanoparticle suspension. J. Phys. Chem. B, 116, 6225 (2012).


  On the other hand, colloid-polymer mixture is subject to evaporation, and demonstrates two phase separation stage: the depletion-induced phase separation between colloid and polymer; and the water drainage from the ‘porous’ like colloidal deposit hindered by the polymer chains. These two process cause the unique crack pattern different that without additive of polymers into the colloidal suspension.


Brownian motion in Hele-Shaw cell

     The dynamics of the Brownian motion of the colloidal particles presents the distinct properties when confined into the two parallel glass plates. We are trying to track the collective motion of the large number of particles, and understand the interaction among the particles on the stochastic behavior.

     
























 

                               


   Reference:

Jun Ma, Guangyin Jing. Coupling motion of colloidal particles in quasi-two-dimensional confinement. New Journal of Physics 16(7): 073025. (2014).



Wetting and dewetting

  1.   Optowetting on the ZnO nanowire arrays by radiation. Transition between superhydrophobic and superhydrophilic surface by decoration of ZnO nanowire array and the light illumination.

  2.   Drag reduction on superoleophobic surface. Is’t possible to increase the slip length by tuning the wettability of the channel wall? Reaction-diffusion dynamics in micro channels and the opto-fluidic aspects.

  3.   The nano-meniscus will play an important role when drying of colloidal suspensions on these ZnO nanowrie-decorated surface.