This may be due to high surface area of nanoparticles with spherical morphology in comparison with flake morphology.
The effects of nanoparticles with different shapes on the interface bond energy in a polyimide/KTa0·5Nb0·5O3 composite were investigated using molecular dynamic simulations. The simulation results showed that the bond energy of sphere particles were 20–85 kcal mol−1, whereas the bond energies of three shape nanoparticles surface atoms (cube,cylinder and cone) were 5–30 kcal mol−1. This indicated that Van der Waals force and hydrogen bonds existed between the matrix and the fillers. The bond strengths of the small nanoparticles were more than the larger nanoparticles due to the size effect. At the same doping volume fraction, the bond energy of the sphere nanoclusters was significantly larger than the ones of other shaped nanoparticles. The introduction of sphere nanoparticles and the small-sized nanoparticles has the potential to be an effective way to improve the properties of the polyimide/KTa0·5Nb0·5O3 composites.
See
http://www.tandfonline.com/doi/abs/10.1179/1432891714Z.0000000001095?scroll=top&needAccess=true&journalCode=ymri20
specific surface area S/V= for sphere 3/r , for cylinder 2/r
Best regards.
Considering same average size, it will depend on your final application. Spherical particles are easier to handle. Irregularly-shaped nanoparticles will tend to agglomerate easier as stated by Yuri.
Depends on the application. For some applications (e.g. in coatings and metallic bronzes) a flake shape is preferred as the give good flip and flop properties and align parallel to surfaces on drying.
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