Transition de séchage dans des nanopores et la tension de ligne de l eau

Transcription

1 Transition de séchage dans des nanopores et la tension de ligne de l eau L. Guillemot, T. Biben, A. Gallarneau, G. Vigier, E. Charlaix Laboratoire LiPhy Université Joseph Fourier Laboratoire MATEIS INSA-Lyon Institut Gerhardt, Montpellier

2 Wetting & dewetting of hydrophobic surfaces at a nanoscale Biological matter, hydrophobic interactions Energy applications

3 Micelle-templated silicas (MTS) : model nanopores CTAB + TMB Kresge & al Nature 1992 Hydrophobic MTS : C8-silane grafting n-octyl-dimethylchlorosilane Martin & di Renzo, Stud. Surf. Sci. Catal 2001 Ø 2nm Ø 6.4nm Ø 4nm Ø 10nm

4 MTS: an ideal experimental model to study wetting at a nanoscale ü Well-defined geometry ü Well-controlled physico-chemistry (very low contamination)

5 Intrusion-extrusion experiments mesoporous powder Eroshenko & Fadeev, Colloid J 1995 Water Ø ~ 1-10 nm Hydrophobic grafting Pressure (MPa) R pore < 1 nm 1nm < R pore < 3nm intrusion R pore > 3 nm extrusion intrusion Volume No energy dissipation à Actuator, energy storage Volume Partial energy dissipation à Damper No extrusion Total energy dissipation à Anti-crash device

6 Experimental set-up water+porous material (no air) Temp sensor sample Pressure transmitting liquid Pressure cell Pressure sensor Traction/compression machine for P V cycles

7 MTS: Influence of the pore radius on the intrusion pressure Lefevre et al, J. Chem. Phys. 120, 2004 MCM 41 R p : 1.3 to 5.6 nm Intrusion pressure liquid R p cos θ a = Classical capillarity: P cap advancing angle describes very well intrusion down to R p =1.3nm

8 Influence of the pore radius on extrusion pressure Lefevre et al, Coll Surf. A. 241, 265, Intrusion - 4 extrusion capillary pressure does not control extrusion

9 Dynamics of intrusion-extrusion cycles Guillemot et al, RSI, 83, (2012) Pressure = 1 50 MPa Température = T amb 80 C Frequency f = Hz

10 Déplacement piston

11 Extrusion has a logarithmic kinetics P ext (MPa) C 50 C 40 C 30 C t ext (sec) Guillemot et al, PNAS 109, 19557, (2012)

12 Dewetting : surface-induced 1st order transition P < P int Slow dynamics Fast dynamics requires the nucleation of a 2-meniscii bubble

13 Nucleation model nucleation rate in each pore n = 1 b exp k B T P ext (MPa) C 50 C 40 C 30 C b 1Å s 12 k B T/V nuc Observed nucleation time nlt ext = t ext (sec) pore length Energy barrier = k B T ln(t ext )+Cte P = k BT V nuc ln(t ext )+Cte = PV nuc +surf.terms critical nucleus volume

14 The nucleus volume SBA-15 R p =1.62nm HMS R p =2.27nm MCM-41 R p =1.32nm 10nm

15 Comparison with classical nucleation theory Saugey et al J Chem Phys bubble energy Grand canonical free energy

16 Classical nucleation theory in a cylinder Saugey et al J Chem Phys 2004 /4 LV R 2 p P L R p /2 LV = P L R p /2 LV = =P L V bub + A LV LV + A SV LV cos V bub /R 3 p Grand canonical free energy Energy barrier tabulated functions ' P L K 1 ( )R 3 p + LV K 2 ( )R 2 p

17 Experiments vs classical nucleation theory Guillemot et al, PNAS 109, 19557, (2012) R p =2.27 ±0.5nm R p =1.32 ±0.2nm R p =1.62 ±0.2nm : nitrogen sorption : intrusion pressure Excellent agreement no adjustable parameter

18 1st Conclusion ü Drying of hydrophobic nano-cavities exhibits logarithmic dynamics ü Dynamics is controlled by vapor nucleation. ü Classical capillarity predicts: P ext = k BT V nuc ln t ext t o + P o ext(t ) u Nucleus volume is very well predicted u?

19 Classical theory: Pext(T o )= k BT to L ln V nuc b K2 ( ) K 1 ( ) LV (T ) R p Experiments Classical theory for MCM-41 Classical theory gives much too low cavitation pressure Overestimates energy barrier at least by 200 k B T

20 Can defects favor vapor nucleation? Local non-wetting defect Topographic defect Energy is too small is not filled at maximum pressure reached in experiment Extended non-wetting defect OK for energy, but is not wetted at maximum pressure reached in experiment

21 2nd Conclusion Classical capillarity with homogeneous pore walls overestimates utterly the energy barrier and predicts too low cavitation pressure Wall defects cannot account for the low energy barrier self-consistantly within classical capillarity

22 Effect of long range interactions? Van der Waals disjonction pressure for solid/liquid/vapor interactions: (e) = A SLV 6 e 3 Silica-water Hamaker constant q At the scale of the pore e = R p 0.5 MPa A SLV J negligible q Close to contact line: line tension

23 Line tension effect From Drelich CSA 1996 J.W. Gibbs, 1876 On the equilibrium of heterogeneous surfaces 3-phase line tension: Can be positive or negative a ( ~ 20 pn for water) Numerical simulations: <0 for LJ fluids Andreotti et al POF 2011 No reliable measurements below some 100 pn Checco et al PRL 2006 Mugele et al 2010

24 Line tension effect T. Biben ILM Lyon 3-phase line tension

25 3rd conclusion Line tension changes dramatically the energy barrier for nucleation Some tens of pn account for cavitation pressure Cavitation pressure gives very sensitive determination of line tension (± 0.5 pn)

26 3rd conclusion Line tension lowers dramatically the energy of nanobubbles of water vapor on hydrophobic surfaces Classical capillarity can describe quantitatively the drying of hydrophobic nano-cavities, provided the line tension is taken into account. Values of line tension between -25 pn to -35 pn are found for water on C8-silanized surfaces of various curvature. Good agreement with available theoretical and numerical estimations.

27 ACKNOWLEDGEMENTS Ludivine GUILLEMOT PhD student Anne GALARNEAU Institut Gerhardt, School of Chemistry, Montpellier Thierry BIBEN Institut Lumière Matière, Lyon Gérard VIGIER National Institute of Applied Sciences, Lyon Thierry ABENSUR EADS - Astrium

28 THANK YOU FOR YOUR ATTENTION