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SUMMARY:Physicochemical hydrodynamics of droplets in inkjet printing - Det
 lef Lohse (Physics of Fluids Group\, University of Twente)
DTSTART:20240116T130000Z
DTEND:20240116T140000Z
UID:TALK210460@talks.cam.ac.uk
CONTACT:Sarah Loos
DESCRIPTION:Inkjet printing is the most widespread technological applicati
 on of microfluidics. It is characterized by its high drop productivity\, s
 mall volumes and extreme reproducibility. In this talk I will give a synop
 sis of the fluid dynamics of inkjet printing and discusses the main challe
 nges for present and future research [1]. These lie both on the printhead 
 side – namely the detailed flow inside the printhead\, entrained bubbles
 \, the meniscus dynamics\, wetting phenomena at the nozzle plate\, and jet
  formation – and on the receiving substrate side – namely droplet impa
 ct\, merging\, wetting of the substrate\, droplet evaporation\, and drying
 . In most cases the droplets are multicomponent\, displaying rich physicoc
 hemical hydrodynamic phenomena [2]. The challenges on the printhead side a
 nd on the receiving substrate side are interwoven\, as optimizing the proc
 ess and the materials with respect to either the printhead side or the sub
 strate side is not enough: As the same ink (or other jetted liquid) is use
 d and as droplet frequency and size matter on both sides\, the process mus
 t be optimized as a whole. One example for conflicting requirements from t
 he printhead side on the one hand and from the receiving substrate or more
  specifically the paper side on the other hand is the volatility of the in
 k: At the nozzle\, it would be preferable if the evaporation of ink were a
 voided to prevent nozzle clogging\, but on the paper side\, fast evaporati
 on of ink is desirable to enable productive printing and to prevent paper 
 deformation. \nEven such a seemingly simple process as the evaporation of 
 multicomponent droplets keeps surprising us through its richness of phenom
 ena. I will show and explain several of such phenomena\, namely evaporatio
 n-triggered segregation thanks to either weak solutal Marangoni flow or th
 anks to gravitational effects. The dominance of the latter implies that se
 ssile droplets and pending droplets show very different evaporation behavi
 or\, even for Bond number << 1. I will also explain the full phase diagram
  in the Marangoni number vs Rayleigh number phase space\, and show where R
 ayleigh convections rolls prevail\, where Marangoni convection rolls preva
 il\, and where they compete\, and why these processes are very important i
 n piezoacoustic inkjet printing. I will also extend these considerations t
 o ternary and colloidal droplets and show and explain the new\, fascinatin
 g\, and often counter-intuitive phenomena which occur for these case of co
 mplex ink droplets. \n\n[1] Detlef Lohse\, Annu. Rev. Fluid Mech. 54\, 349
 -382 (2022).\n[2] Detlef Lohse and Xuehua Zhang\, Nature Rev. Phys. 2\, 42
 6-443 (2020).\n
LOCATION:Center for Mathematical Sciences\, Lecture room MR4
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