The yield and size distribution of surfactant-free solid lipid nanoparticles (SF-SLNs) formed by hot homogenization were investigated by changing the amount of lipid (palmitic acid). The yield was 100% and monodispersed same-sized particles of 120200nm were formed at the lipid amount ≤2.8 × 10-4 g-lipid (g-water)-1. The yield decreased owing to phase separation, and the size increased "step- likely" to be 200350nm while keeping the monodispersity when the lipid amount was just above ≤2.8 × 10-4 g-lipid (g-water) -1. The size and the lipid amount continued to increase gradually at the lipid amount >2.8 × 10-4 g-lipid (g-water)-1. The results indicate that submicron- sized solid lipid particles can be formed without surfactants and that the decrease of yield and the step-like increase of particle size occur at the same lipid amount. The total surface area of the SF-SLNs was estimated using the experimental data. It is suggested that the total surface area and the lipid amount are correlated to each other.
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