Contact line dynamics of a liquid meniscus advancing into a microchannel with chemical heterogeneities C. Wylock 1, M. Pradas 2, B. Haut 1, P. Colinet 1 and S. Kalliadasis 2 1 Université Libre de Bruxelles – Transfers, Interfaces and Processes 2 Imperial College London – Chemical Engineering Department 63 rd Annual DFD Meeting of the American Physical Society Long Beach, California November 21-23, 2010

Motivation  Contact line dynamics Rapidly growing fields of: ─Microfluidics ─Miniaturisation of chemical devices Small length scale  solid surface properties become crucial Page 2

Goal  Gas-liquid meniscus moving in a "Hele-Shaw cell like " microchannel  Surface chemically heterogeneous  spatial distribution of wetting properties  2 configurations  Effect of chemical heterogeneities on meniscus dynamics ? 2D configuration 3D configuration Page 3

Modelling  Phase field approach  represents the 2 phases Interface at  =0 Page 4

Modelling  Phase field approach  represents the 2 phases Interface at  =0  Equilibrium given by Ginzburg-Landau model Free energy formulation Double-well potential Chemical potential Page 5

Modelling  Phase field approach  represents the 2 phases Interface at  =0  Equilibrium given by Ginzburg-Landau model Free energy formulation Double-well potential Chemical potential Page 6

Modelling  Wetting boundary condition  Conserved dynamic equation Page 7 Standard deviation  = disorder strength with [1] [1] Cahn, J. Chem. Phys. 66 (1977), 3667

Results and discussion  2D configuration Typical simulation result Page 8

Results and discussion  2D configuration Typical simulation result Statistical analysis on several disorder realisations Page 9

Results and discussion  2D configuration Typical simulation result Statistical analysis on several disorder realisations Page 10

Results and discussion  2D configuration Typical simulation result Statistical analysis on several disorder realisations Page 11

Results and discussion  2D configuration Typical simulation result Statistical analysis on several disorder realisations Page 12

Results and discussion  2D configuration Typical simulation result Statistical analysis on several disorder realisations Page 13 Chemical disorder  contact angle hysteresis enhanced by disorder strength

Results and discussion  3D configuration Contact line dynamics: preliminary analysis ─interface width follows fractal dynamics (  scale-invariant growth) Page 14

Results and discussion  3D configuration Contact line dynamics: preliminary analysis ─interface width follows fractal dynamics (  scale-invariant growth) ─pinning-depinning effects and associated avalanche dynamics Page 15 Avalanche site Pinning site

Results and discussion  3D configuration Contact line dynamics: preliminary analysis ─interface width follows fractal dynamics (  scale-invariant growth) ─pinning-depinning effects and associated avalanche dynamics induced by the chemical disorder  Statistical analysis to perform for various disorder configurations Page 16

Conclusion and future plans  Phase field  contact line dynamics in chemically heterogeneous microchannel  Chemical disorder induces 2D: hysteresis of contact angle  hysteresis “jump” function of disorder strength 3D: kinetic roughening process of contact line motion, pinning-depinning effects  Future plans Statistical analysis for 3D configuration: ─Characterization of the scaling growth factors ─Avalanche dynamics Page 17

18

Modelling  Boundary conditions for 2D configuration Page 19

Modelling  Boundary conditions for 3D configuration Page 20

Results and discussion  2D configuration Typical simulation result Statistical analysis on several disorder realisations Page 21 Chemical disorder  contact angle hysteresis enhanced by disorder strength

Results and discussion  3D configuration Typical simulation results Page 22

Results and discussion  3D configuration Typical simulation results Contact line dynamic: preliminary analysis ─interface width growth follows fractal dynamic Page 23