David Fairhurst

Publications (19) View all

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  Available from: David Fairhurst

  Article: The effects of molecular weight, evaporation rate and polymer concentration on pillar formation in drying poly(ethylene oxide) droplets

  K A Baldwin, D J Fairhurst
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  ABSTRACT: Typically, when droplets of dilute suspensions are left to evaporate the final dry deposit is the familiar coffee-ring stain, with nearly all the solute deposited at the initial contact line. Contrastingly, in previous work we have shown that sessile droplets of poly(ethylene oxide) (PEO) solutions form tall central pillars (or monoliths) during a 4-stage drying process. We show that a dimensionless Péclet-type number Pe, a ratio of the competing advective and diffusive motion of the dissolved polymer, which incorporates the effects of evaporation rate, initial concentration c0 and the polymer diffusion coefficient, to determine whether the droplet will form a pillar or a flat deposit. In this work we vary concentration up to c0 = 0.5 and molecular weight Mw between 3.35 kg/mol and 600 kg/mol and find that in ambient conditions with c0 = 0.1 pillars only form for a limited range, 35 ≤ Mw ≤ 200 kg/mol. This observation is in contrast to the the Péclet argument in which high molecular weight polymers with a slow self-diffusion should still form pillars. We present various experimental measurements attempting to resolve this discrepancy: crossover time-scale for viscoelastic behaviour; fast diffusion of an entangled network; and droplet viscosity or contact line friction.
  Colloids and Surfaces A Physicochemical and Engineering Aspects 11/2012; · 2.24 Impact Factor
• Article: Quantitation of MRI sensitivity to Quasi-monodisperse microbubble contrast agents for spatially resolved manometry.

  Martin Bencsik, Amgad Al-Rwaili, Robert Morris, David J Fairhurst, Victoria Mundell, Gareth Cave, Jonathan McKendry, Stephen Evans
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  ABSTRACT: PURPOSE: The direct in-vivo measurement of fluid pressure cannot be achieved with MRI unless it is done with the contribution of a contrast agent. No such contrast agents are currently available commercially, whilst those demonstrated previously only produced qualitative results due to their broad size distribution. Our aim is to quantitate then model the MR sensitivity to the presence of quasi-monodisperse microbubble populations. METHODS: Lipid stabilised microbubble populations with mean radius 1.2 ± 0.8 μm have been produced by mechanical agitation. Contrast agents with increasing volume fraction of bubbles up to 4% were formed and the contribution the bubbles bring to the relaxation rate was quantitated. A periodic pressure change was also continuously applied to the same contrast agent, until MR signal changes were only due to bubble radius change and not due to a change in bubble density. RESULTS: The MR data compared favourably with the prediction of an improved numerical simulation. An excellent MR sensitivity of 23 % bar(-1) has been demonstrated. CONCLUSION: This work opens up the possibility of generating microbubble preparations tailored to specific applications with optimised MR sensitivity, in particular MRI based in-vivo manometry. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
  Magnetic Resonance in Medicine 12/2012; · 2.96 Impact Factor
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  Available from: David Fairhurst

  Article: Drying and deposition of poly(ethylene oxide) droplets determined by Péclet number

  Kyle Anthony Baldwin, a Manon Granjard, b David I. Willmer, a Khellil Sefianeb, David John Fairhurst
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  ABSTRACT: We report results of a detailed experimental investigation into the drying of sessile droplets of aqueous poly(ethylene oxide) (PEO) polymer solutions under various experimental conditions. Samples are prepared with a range of initial concentrations c0 and are filtered to remove traces of undissolved PEO clusters. In typical experiments, droplets with initial volumes between 5 mL and 50 mL are left to evaporate while temperature and relative humidity are monitored. Droplets either form a disk-like solid ‘‘puddle’’ or a tall conical ‘‘pillar’’. The droplet mass is monitored using a microbalance and the droplet profile is recorded regularly using a digital camera. Subsequent processing of the data allows values of droplet volume V, surface area A, base radius R, contact angle q and height h to be determined throughout drying. From these data we identify four stages during pillar formation: pinned drying; pseudo-dewetting; bootstrap building; solid contraction and propose physical models to explain key aspects of each stage and to predict the transition from each stage to the next. The experimental parameters of relative humidity, temperature, pressure, droplet volume and initial contact angle are all systematically varied and observed to influence the drying process and consequently whether the droplet forms a pillar or a puddle. We combine these parameters into a dimensionless Péclet number Pe, which compares the relative effects of evaporation and diffusion, and show that the drying behaviour is only dependent on c0 and Pe.
  Soft Matter 01/2011; 7:7819. · 4.39 Impact Factor
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  Available from: David Fairhurst

  Article: Robust spatially resolved pressure measurements using MRI with novel buoyant advection-free preparations of stable microbubbles in polysaccharide gels.

  Robert H Morris, Martin Bencsik, Nikolaus Nestle, Petrik Galvosas, David Fairhurst, Anil Vangala, Yvonne Perrie, Glen McHale
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  ABSTRACT: MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25 min. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-distearoyl-sn-glycero-3-phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44 bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar.
  Journal of Magnetic Resonance 05/2008; 193(2):159-67. · 2.14 Impact Factor
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  Available from: David Fairhurst

  Article: Imaging internal flows in a drying sessile polymer dispersion drop using Spectral Radar Optical Coherence Tomography (SR-OCT).

  Selin Manukyan, Hans M Sauer, Ilia V Roisman, Kyle A Baldwin, David J Fairhurst, Haida Liang, Joachim Venzmer, Cameron Tropea
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  ABSTRACT: In this work, we present the visualization of the internal flows in a drying sessile polymer dispersion drop on hydrophilic and hydrophobic surfaces with Spectral Radar Optical Coherence Tomography (SR-OCT). We have found that surface features such as the initial contact angle and pinning of the contact line, play a crucial role on the flow direction and final shape of the dried drop. Moreover, imaging through selection of vertical slices using optical coherence tomography offers a feasible alternative compared to imaging through selection of narrow horizontal slices using confocal microscopy for turbid, barely transparent fluids.
  Journal of Colloid and Interface Science 12/2012; · 3.07 Impact Factor