Published online by Cambridge University Press: 23 October 2012
The influence of fluid droplet properties on the droplet-on-demand jetting of a Newtonian model fluid (water–isopropanol–ethylene glycol ternary system) has been studied. The composition of the fluid was adjusted to investigate how the Ohnesorge number (  $\mathit{Oh}$ ) influences droplet formation (morphology and speed) by a microfabricated short-channel shear-mode piezoelectric transducer. The fluid space for satellite-free single droplet formation was indeed found to be bound by upper and lower
 $\mathit{Oh}$ ) influences droplet formation (morphology and speed) by a microfabricated short-channel shear-mode piezoelectric transducer. The fluid space for satellite-free single droplet formation was indeed found to be bound by upper and lower   $\mathit{Oh}$  limits, but these shift approximately linearly with the piezo pulse voltage amplitude
 $\mathit{Oh}$  limits, but these shift approximately linearly with the piezo pulse voltage amplitude   ${V}_{o} $ , which has a stronger influence on jetting characteristics than pulse length. Therefore the jettable fluid space can be depicted on a
 ${V}_{o} $ , which has a stronger influence on jetting characteristics than pulse length. Therefore the jettable fluid space can be depicted on a   ${V}_{o} {{\ndash}}\mathit{Oh}$  diagram. Satellite-free droplets of the model fluid can be jetted over a wide
 ${V}_{o} {{\ndash}}\mathit{Oh}$  diagram. Satellite-free droplets of the model fluid can be jetted over a wide   $\mathit{Oh}$  range, at least 0.025 to 0.5 (corresponding to
 $\mathit{Oh}$  range, at least 0.025 to 0.5 (corresponding to   $Z= {\mathit{Oh}}^{\ensuremath{-} 1} $  of 40 to 2), by adjusting
 $Z= {\mathit{Oh}}^{\ensuremath{-} 1} $  of 40 to 2), by adjusting   ${V}_{o} $  appropriately. Air drag was found to dominate droplet flight, as may be expected. This can be accurately modelled to yield droplet formation time, which turned out to be
 ${V}_{o} $  appropriately. Air drag was found to dominate droplet flight, as may be expected. This can be accurately modelled to yield droplet formation time, which turned out to be   $20\text{{\ndash}} 30~\lrm{\ensuremath{\mu}} \mathrm{s} $  under a wide range of jetting conditions. The corresponding initial droplet speed was found to vary linearly with
 $20\text{{\ndash}} 30~\lrm{\ensuremath{\mu}} \mathrm{s} $  under a wide range of jetting conditions. The corresponding initial droplet speed was found to vary linearly with   ${V}_{o} $ , with a fluid-dependent threshold but a fluid-independent slope, and a minimum speed of about
 ${V}_{o} $ , with a fluid-dependent threshold but a fluid-independent slope, and a minimum speed of about   $2~\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $ . This suggests the existence of iso-velocity lines that run substantially parallel to the lower jetting boundary in the
 $2~\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $ . This suggests the existence of iso-velocity lines that run substantially parallel to the lower jetting boundary in the   ${V}_{o} {{\ndash}}\mathit{Oh}$  diagram.
 ${V}_{o} {{\ndash}}\mathit{Oh}$  diagram.
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               . Adv. Funct. Mater.
               20, 296–303.Google Scholar
                        $150\hspace{0.167em} \textdegree \mathrm{C} $
                     
                  
               . Adv. Funct. Mater.
               20, 296–303.Google Scholar $25~\lrm{\ensuremath{\mu}} \mathrm{m} $
                     
                   wide silver tracks on unstructured polyimide. Phys. Status Solidi A
               206, 1626–1630.Google Scholar
                        $25~\lrm{\ensuremath{\mu}} \mathrm{m} $
                     
                   wide silver tracks on unstructured polyimide. Phys. Status Solidi A
               206, 1626–1630.Google Scholar