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. 2010 Aug 6;7 Suppl 4(Suppl 4):S451-60.
doi: 10.1098/rsif.2010.0092.focus. Epub 2010 Jun 2.

Controlling the thickness of hollow polymeric microspheres prepared by electrohydrodynamic atomization

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Controlling the thickness of hollow polymeric microspheres prepared by electrohydrodynamic atomization

Ming-Wei Chang et al. J R Soc Interface. .

Abstract

In this study, the ability to control the shell thickness of hollow polymeric microspheres prepared using electrohydrodynamic processing at ambient temperature was investigated. Polymethylsilsesquioxane (PMSQ) was used as a model material for the microsphere shell encapsulating a core of liquid perfluorohexane (PFH). The microspheres were characterized by Fourier transform infrared spectroscopy and optical and electron microscopy, and the effects of the processing parameters (flow-rate ratio, polymer concentration and applied voltage) on the mean microsphere diameter (D) and shell thickness (t) were determined. It was found that the mean diameters of the hollow microspheres could be controlled in the range from 310 to 1000 nm while the corresponding mean shell thickness varied from 40 to 95 nm. The results indicate that the ratio D : t varied with polymer concentration, with the largest value of approximately 10 achieved with a solution containing 18 wt% of the polymer, while the smallest value (6.6) was obtained at 36 wt%. For polymer concentrations above 63 wt%, hollow microspheres could not be generated, but instead PMSQ fibres encapsulating PFH liquid were obtained.

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Figures

Figure 1.
Figure 1.
(a) The experimental set-up; (b) dripping and (c) stable jetting behaviour of PMSQ/PFH.
Figure 2.
Figure 2.
Diameter and shell thickness of microspheres versus varying flow rate of PMSQ and with PFH flow rate of 150 µl min−1 (error bars show standard deviation). Line with crosses, D; line with filled circles, t.
Figure 3.
Figure 3.
Effect of PMSQ flow rate on the geometry of the hollow microspheres: (a) 200; (b) 250; (c) 350; (d) 450; (e) 550; and (f) 650 µl min−1.
Figure 4.
Figure 4.
Scanning electron micrograph of a fractured hollow microsphere.
Figure 5.
Figure 5.
Size and shell thickness of microspheres versus PMSQ concentration with inner flow rates of 150 µl min−1 and outer flow rate of 300 µl min−1 (error bars show standard deviation). Line with crosses, D; line with filled circles, t.
Figure 6.
Figure 6.
Effect of 63 wt% PMSQ concentration on the process product: (a) SEM image of PFH-loaded PMSQ fibre; (b) optical image of PFH-loaded PMSQ fibre. Scale bar, (b) 10 µm.
Figure 7.
Figure 7.
Size and shell thickness of microspheres versus applied voltage with inner flow rates of 150 µl min−1 and outer flow rate of 300 µl min−1 (error bars show standard deviation). Line with crosses, D; line with filled circles, t.
Figure 8.
Figure 8.
Mapping of applied voltage and flow rate of PMSQ at different PMSQ concentrations: (a) 18 wt%, (b) 27 wt% and (c) 36 wt%.
Figure 9.
Figure 9.
Variation of D/t ratio (α) with polymer concentration.
Figure 10.
Figure 10.
FTIR spectra of PMSQ and dried hollow microspheres.

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