Abstract
Polymer shells prepared by the microencapsulation technique with perfect sphericity and defect-free surface finish are demanded in inertial confinement fusion (ICF) experiments. The sphericity and surface finish are some of the hardest specifications to fulfill. Driven by the need to improve qualities of the polymer shells to meet the critical specifications, the effects of fluorobenzene (FB) mass transfer rate on sphericity and surface finish were investigated and the mechanisms of the effects of FB mass transfer on sphericity and surface finish of poly-α-methylstyrene (PAMS) were also discussed. The sphericity and surface finish of the PAMS shells are greatly improved by decreasing the FB mass transfer rate. The calculative frequency of the final shells with an out-of-round (δOOR) of less than 2 μm increases from 30% to 80%, while the power spectra density (PSD) plot gets closer to the specification of the national ignition facility (NIF). The tracking experiments show that the curing process is extended and the percolation transition is also postponed by decreasing the FB mass transfer rate. Therefore, the interfacial tension can work sufficiently, helping make double droplets become spherical, since the double droplets’ stay in the liquid state is effectively extended. Moreover, the Marangoni instabilities at the O–W2 boundary are also restrained by controlling the mass transfer, due to the diffusivity of FB being slowed down. Both the results and methods presented in this work provide a more in-depth understanding of the curing process and the mass transfer, to the benefit of fabricating polymer shells with high sphericity and defect-free surface finish used in ICF experiments.
Highlights
Hollow-core polymer shells with diameters ranging from nanometers to millimeters have drawn signi cant attention in the development of polymer science
The sphericity is characterized by the out-of-round, which is de ned as the difference between the maximum and minimum outer radius of a PAMS shell in six directions
When the total quantity of FB is introduced by 96 double droplets combined with 50 O/W2 single droplets, the percentage of PAMS shells with dOOR of less than 2 mm is 80%
Summary
Hollow-core polymer shells with diameters ranging from nanometers to millimeters have drawn signi cant attention in the development of polymer science. These micron-scale polymer shells have wide applications in various elds, such as in the food industry, pharmacy, chemistry and biotechnology science, due to their low density, low coefficients of thermal expansion and so on.[1,2,3,4,5,6,7,8,9] Unlike their uses in common elds, one particular application for such shells is in laser fusion. There are many factors, such as interfacial tension, density matching, viscosity of the external phase, and shear forces from agitation, in uencing the deformation of droplets.[14] Great efforts have been made to precisely optimize these factors to improve the qualities of the PAMS shells and the related mechanisms have been discussed. The effects of molecules of poly(vinyl alcohol) (PVA), which is used as stabilizer on the formation, stability and deformation of W1/O/W2 double droplets, has been
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