Research 15: G Willmott

1. Dynamics at Nano- and Microfluidic Interfaces Geoff Willmott NZIP Conference 19 October 2011

4. Medical Device Technologies (MDT) MTANZ Report April 2011: Large global demand for MDT - Aging population with rising rates of chronic disease - $437 b globally, driven by the USA NZ has an emerging industry … - >$0.61 b revenues FY2010-11 with double-digit growth (wine approx $0.8 b) - 95% exports; <10% of NZ health expenditure is on devices - Good standard of clinicians and medical researchers - Innovative approach to primary health care … but faces challenges - $0.5 b of that revenue is F&P Healthcare - 165 skilled workers required in the next two years - 22 companies looking to raise $44 M capital

5. Nanofluidics : The study and application of fluid flow in and around nanosized objects. Eijkel and van den Berg, Microfluid. Nanofluid. 1, 249 (2005) Branton et al., Nature Biotechnology 26, 1146 (2008) D’Acunzi et al., Faraday Disc. 146, Paper #3 (2010) Schoch, Han and Renaud, Rev. Mod. Phys. 80, 839 (2008) Tas et al., Appl. Phys. Lett. 85, 3274 (2004)

6. Interdisciplinary, Applied Eijkel and van den Berg, Microfluid. Nanofluid. 1, 249 (2005)

7. Micro- and Nanofluidics: Forces and Transport Inertia - low Reynolds number, laminar flow Eijkel and van den Berg, Microfluid. Nanofluid. 1, 249 (2005) Viscosity Surface tension Electrostatics and electrokinetics Surface slip Molecular interactions (e.g. van der Waals, brush polymers) Geometry - because measurement is difficult!! Body forces (e.g. gravity, pressure)

9. Thiolated, roughened copper Laurate solution (applied to any surface) Substrates: Rod Stanley (IRL) Contact angle > 160  Superhydrophobic Surfaces

10. Splash

12. Classical Capillary Uptake No uptake if  c > 90 °

13. Capillary + Droplet Not widely studied in experiments Marmur, J. Colloid Interf. Sci. , 209 ( 1988) Schebarchov and Hendy, Phys Rev E 78, 046309 (2008)

14. Application: Drop-Based Microfluidics Baroud, Gallaire and Dangla, Lab Chip 10, 2032 (2010) Kintses et al., Curr. Opin. Chem. Biol. 14, 548 (2010) Generation Merging

15. Inspiration: Bottom-Up! Schebarchov and Hendy, Nano Letters 8, 2253 (2008) [Talk O14.1]

16. (1) Direction of non-wetting meniscus motion depends on drop size Willmott, Neto and Hendy, Faraday Disc. 146, 233 (2010)

17. (1) Direction of non-wetting meniscus motion depends on drop size A bound on critical drop size for PTFE - consistent with contact angle 107.8  - 110.6  Willmott, Neto and Hendy, Faraday Disc. , 146, 233 (2010)

19. (3) Uptake Speed Depends on Drop Size Willmott, Neto and Hendy, Soft Matter 7, 2357 (2011)

20. 5 modes of interaction Willmott, Neto and Hendy, Faraday Disc. , 146, 233 (2010)

21. Uptake Enhanced by Detachment 0 ms 4.8 ms 0.8 ms 1.6 ms 2.4 ms 3.2 ms 4.0 ms

22. Uptake Enhanced by Detachment Direct correlation between pressure and meniscus motion with < 1 ms precision

23. Pressure Estimates Significant uncertainty: image analysis method Laplace:

24. A Can of Physics Worms (i) Geometry: - drop asphericity, pinning and dynamic shape change - tube entrance and interior (ii) Entrance dynamics: - meniscus reorientation - prelinear inertial acceleration - viscous flow (iii) Surfaces: - Pinning due to chemical / physical heterogeneity - The non-wetting dynamic contact angle (iv) Pre-filled capillaries: - Incl. ‘jet’ vs ‘sink’ flow for filling/drainage applications (v) Electrokinetics: - Electroviscosity and double layer structure (vi) Close to 100 nm: - violation of the non-slip boundary condition - thermal capillary waves - disjoining pressure - thin film precursors to wetting - nanobubbles

26. “ Resistive Pulse Sensing” Membrane Electrolyte “ Translocations” +/- Current Time

27. Motivation: Duration & shape Magnitude Frequency Willmott et al., J. Phys. Cond. Matt. 22, 454116 (2010)

28. A Semi-Analytic Model: R ( z 0 ) Homogeneous resistivity (assume: uniform electric field across width)

29. End Effects Artificial cone: ‘approximate’ or ‘estimate’ - cone pitch agrees with infinite half space result

30. End Effects: Important

31. FEM Comparison: On-Axis Bryan Smith (IRL Auckland): Comsol 3.3, triangular mesh, ~ 60k degs freedom

32. Transport: Nernst-Planck for for z 0 ( t ) Willmott et al., J. Phys. Cond. Matt. 22, 454116 (2010) DIFFUSION ELECTROKINETICS PRESSURE (CONVECTION) OTHER …

34. Summary of Assumptions Homogeneous resistivity Artificial cone end effects Locally cylindrical Azimuthal symmetry Surface charges and electro-osmosis Electrode and electronic effects Particle on-axis Spherical particle Quasi-static Simplified drag in confinement Other transport insignificant

35. Electrophoretic Mobility of a Charged Particle Schoch, Han and Renaud, Rev. Mod. Phys. 80, 839 (2008) a  -1 E v

37. Thanks! Email: G.WILLMOTT@IRL.CRI.NZ Mike Arnold and NMF team , esp. Rod Stanley (surfaces), Bethan Parry, & James ‘Elf’ Eldridge (qNano) U.Syd. : Chiara Neto (surfaces) ESR : Michael Taylor (HSP) Izon Science esp. Robert Vogel, Ben Glossop, Hans van der Voorn U of Q Collaborators