Search

Polymer microspheres can be used as fuel containers for laser inertial confinement fusion (ICF) due to their low atomic number, low density, and high thermal stability. The thin‐walled polymer microspheres are prone to cracking due to an increase in the diameter to thickness ratio (diameter/wall thickness). The effect of polystyrene (PS) and Poly (α‐methyl styrene) (PAMS) materials commonly used in ICF experiments on the quality of thin‐walled microspheres is investigated. PS hollow microspheres show better sphericity, smoother surface, and lower cracking rate than PAMS microspheres. Moreover, the heat treatment of solidified PS microspheres can improve the strength so that the cracking rate of the microspheres decreases. The relative mechanism of how the molecular structure affect the quality is also discussed. This study provides some guidance for the preparation of thin‐walled polymer microspheres with high quality for ICF experiments. [ABSTRACT FROM AUTHOR]

Millimeter-scale polymer shells with stringent specifications such as sphericity, wall thickness uniformity and surface finish are needed in inertial confinement fusion (ICF) experiment. In order to meet these stringent specifications, n -hexadecane (n-HD) is introduced in oil phase to improve the sphericity of poly-α-methylstyrene (PAMS) shells. The results show that n-HD decreases the survival rate of the final PAMS shells, since coalescence between W1/O/W2 double droplets occurs owing to phase separation during the curing process. However, characterization results show that the addition of n-HD into O phase leads an increasing interfacial tension at O-W2 interface, which is considered as the only driving force for sphericity. Tracking experiment data indicates that the addition of n-HD can effectively extend the curing process. A percolation threshold is determined at about 58% where PAMS large-scale networking occurs and over where the deformation of the droplets is considered irreversible. So the addition of n-HD can extend the period W1/O/W2 droplets stay in liquid with nice fluidity, where the interfacial tension can work sufficiently and thus improving the final sphericity of polymer shells. Furthermore, when the mass fraction of n-HD is larger than 2.0%, porous PAMS shells can be obtained. [ABSTRACT FROM AUTHOR]

Thick-walled polymer shells with high sphericity are always needed in the inertial confined fusion (ICF) experiments. The introduction of hexadecane (H) into the oil phase (O) was used to explore possible effects in improving the sphericity of polystyrene (PS) shells. The experimental results showed that not only the interfacial tension increased, but also the density matching levels between the inner water phase (W1) and the oil phase, and that between the W1/O compound droplets and the outer water phase (W2) were improved, probably due to the hydrophobic characteristic and low density of H. Therefore, the batch yield of PS shells with the out-of-round ( δ OOR ) values less than 1 μm increased from 16% to 60% with increasing H mass fraction in the O phase from 0 to 0.6%. For wall uniformity, the yield of the PS shells with Δ t w less than 3 μm also increased from 45% to 67%, but there was no further increase when H mass fraction in the O phase was more than 0.2%. However, when the H mass fraction was 1.0%, the PS shells became opaque, since there were many voids in the shells resulting from very low solubility of H in water. Therefore, the H concentrations in the O phase should be controlled according to the requirements of the structure. Obviously, the introduction of H into the O phase provides a novel and effective method for preparing PS shells with high sphericity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Wall thickness uniformity of PS shells is improved by adjusting density matching. [•] The sphericity is much less sensitive to the density matching. [•] Mechanisms of density matching affecting wall thickness uniformity are proposed. [ABSTRACT FROM AUTHOR]

Hollow polyacrylonitrile (PAN) microspheres can be used as fuel carriers in inertial confinement fusion (ICF) experiments due to their high tensile strength, low permeability to hydrogen isotopes, and resistance to tritium radiation corrosion. Monodisperse oil in water in oil (O1/W/O2) compound droplets were fabricated by the microfluidic technique and then monodisperse hollow polyacrylonitrile microspheres were prepared by the solvent evaporation method. The stability of O1/W/O2 compound droplets was improved by the addition of the surfactant (Dow Corning 749), which reduced the interfacial tension between the O2 phase and the W phase as well as the Laplace pressure on the surface of the compound droplets. The sphericity and the surface quality of the microspheres were also improved by the introduction of DMF droplets into the O2 phase to avoid emulsification, decreasing the DMF mass transfer rate. Therefore, fine monodisperse PAN microspheres with the diameter range of 700–800 µm were successfully prepared. Moreover, the size relationship between the compound droplets and the resulting microspheres was also evaluated, which can be used to predict the sizes of the PAN microspheres. The results provide a method for controllable preparation of monodisperse hollow PAN microspheres for ICF experiments. [Display omitted] • Monodisperse hollow polyacrylonitrile microspheres were successfully prepared by the microfluidic technique. • The effect of the surfactants on the stability of the compound droplets and the quality of resulting microspheres was investigated. • The size relationship between the compound droplets and the microspheres was also studied. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract W1-O-W2 composite droplets are prepared using droplet microfluidics and core-hollow poly(α-methylstyrene) (PAMS) shells are fabricated by microencapsulation. This work examines the effects of alkanes on stability and deformation of double droplets. Results manifest that alkanes benefit resisting the deformation of the double droplets and improving the sphericity of the resulting polymer shells. Moreover, with shortening the chain length of the alkane, the deformation of double droplets is resisted and the sphericity of the solidified shells is improved. However, the addition of alkanes promotes the coalescence between the droplets, decreasing the yield of individual shells. The results presented in this work provide a feasible method to fabricate individual polymer shells with high sphericity. [ABSTRACT FROM AUTHOR]