14.05 o15 g willmott

Dynamics at Nano- and Microfluidic Interfaces

Geoff Willmott

NZIP Conference19 October 2011

• Nano- and Microfluidics

• Wetting: Capillaries, Droplets, Surfaces

• Resistive Pulse Sensing

Introduction

Fast Fluidic Microanalysis: compact, portable, user friendly devices

Advantages:

• reduced volumes of sample and waste; power use

• increased speed, resolution, control and safety

• multifunctional/integrated devices

High Growth Areas:

• pharmaceuticals; drug delivery

• analytical/diagnostic devices

• point of care

• veterinary

• food safety

• biosecurity

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Microfluidics

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

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)

Interdisciplinary, Applied

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

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)

• Nano- and Microfluidics

• Wetting: Capillaries, Droplets, Surfaces

• Resistive Pulse Sensing

Introduction

Thiolated, roughened copper Laurate solution (applied to any surface)

Substrates: Rod Stanley (IRL)

Contact angle > 160

Superhydrophobic Surfaces

Splash

Capillary Uptake Experiments

Thanks Rod Stanley (IRL) for making the substrates: Larmour, Bell and Saunders, Angew. Chem. Int. Edit., 1710 (2007)Willmott, Neto and Hendy, Soft Matter 7, 2357 (2011); Faraday Discuss. 146, 233 (2010)

- PTFE capillary (i.d. 300 m)

- drop on a superhydrophobic surface

- slowly brought into contact

No uptake if c > 90°

Classical Capillary Uptake

Not widely studied in experiments

Capillary + Droplet

Marmur, J. Colloid Interf. Sci., 209 (1988)Schebarchov and Hendy, Phys Rev E 78, 046309 (2008)

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

Inspiration: Bottom-Up!

Schebarchov and Hendy, Nano Letters 8, 2253 (2008)

[Talk O14.1]

(1) Direction of non-wetting meniscus motion depends on drop size

Willmott, Neto and Hendy, Faraday Disc. 146, 233 (2010)

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)

(1) Direction of non-wetting meniscus motion depends on drop size

PTFE capillary; drop radius 0.38 mm

(2) Laplace pressure can drive uptake when c > 90°

• Borosilicate glass capillary (diameter 100 micron) • Silanized: contact angle of internal surface with water ~110

Willmott, Neto and Hendy, Soft Matter 7, 2357 (2011)

(3) Uptake Speed Depends on Drop Size

Willmott, Neto and Hendy, Soft Matter 7, 2357 (2011)

5 modes of interaction

Willmott, Neto and Hendy, Faraday Disc., 146, 233 (2010)

Uptake Enhanced by Detachment

0 ms 4.8 ms0.8 ms 1.6 ms 2.4 ms 3.2 ms 4.0 ms

Uptake Enhanced by Detachment

Direct correlation between pressure and meniscus motion with < 1 ms precision

Pressure Estimates

Significant uncertainty: image analysis method

Laplace:

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RRP

(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

A Can of Physics Worms

• Nano- and Microfluidics

• Wetting: Capillaries, Droplets, Surfaces

• Resistive Pulse Sensing

Introduction

“Resistive Pulse Sensing”+/-

Membrane

Electrolyte

Current

Time

“Translocations”

Motivation:

Duration & shape

Magnitude

Frequency

Willmott et al., J. Phys. Cond. Matt. 22, 454116 (2010)

A Semi-Analytic Model: R(z0)

Homogeneous resistivity(assume: uniform electric field across width)

End Effects

Artificial cone: ‘approximate’ or ‘estimate’

- cone pitch agrees with infinite half space result

End Effects: Important

FEM Comparison: On-Axis

Bryan Smith (IRL Auckland): Comsol 3.3, triangular mesh, ~ 60k degs freedom

Transport: Nernst-Planck for for z0(t)

Willmott et al., J. Phys. Cond. Matt. 22, 454116 (2010)

...

magpressure

poreparticle CC

CD JvEJ

DIFFUSION ELECTROKINETICS PRESSURE(CONVECTION)

OTHER …

Half max

Result: Resistive Pulse Shape

Parameters:

pH 8.0a = 465 nm (fit)b = 16.1 m (fit)d = 150 ma’ = 110 nm 0.3 V applied = 0.86 m

q = -1.54 x 10-3 C m-2

Willmott and Parry, J. Appl. Phys, DOI: 10.1063/1.3580283 (2011)

Summary of Assumptions Homogeneous resistivityArtificial cone end effectsLocally cylindricalAzimuthal symmetrySurface charges and electro-osmosisElectrode and electronic effectsParticle on-axisSpherical particleQuasi-staticSimplified drag in confinementOther transport insignificant

Electrophoretic Mobility of a Charged Particle

Schoch, Han and Renaud, Rev. Mod. Phys. 80, 839 (2008)

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Electrophoretic Mobility of a Charged Particle

Smoluchowski + no curvature dependence

Nanoparticle Detection and Charge Quantification Using Tunable Nanopores: Poster 9

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1a

1a Drag + Gauss … point charge aq 4

•Calculation of “effective charge” based on 2nd (classical) method

•Expect for constant surface charge, so

… conceptual difficulty for measurements?

2aq a

Thanks! Email: [email protected]

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