Zetasizer nano model s90

The synthesized nanoemulsions with no phase separation, demonstrating long-term stability, were taken for further analysis as described [28 (link)]. The prepared oregano nanoemulsions (OENE) were diluted in water to observe the characteristic peaks using UV-visible spectrophotometer Jasco V-630 (Jasco, Japan) with a 10-mm path length cuvette. The interior part structure of nano emulsions was characterized by optical microscopy LEICA DM2500 (Leica, Germany). The nanoemulsion droplets were kept on the glass slide and monitored through the optical microscope to determine the shape and size of the particles. The dispersion, homogeneity, and nano emulsion size were observed by dynamic light scattering (DLS) (Zetasizer Nano^Ⓡ Model S90; Malvern Instruments, UK) to determine the polydispersity index (PDI) of nanoemulsions. All measurement calculations were performed in triplicates.

The formulations were prepared by the low-energy phase-inversion method with modifications [45 ]. To prepare the formulations and determine the HLB value, 11 mixtures with different ratios of nonionic surfactants polysorbate 20 (HLB 16.7) and sorbitan monooleate 80 (HLB 4.3) were prepared (Table 5). The nonionic surfactants were added to the essential oil (5% w/w) and homogenized by magnetic stirring at 500 rpm for 30 min at room temperature (25 °C). Then, the aqueous phase was slowly dripped onto the oil phase under the same conditions for 60 min. The parameters for the characterization were average droplet size (in nm) and polydispersity index (PDI), analyzed by the dynamic light scattering (DLS) in a Zetasizer Nano, model S90 device (Malvern Panalytical, UK). The measurements were performed with the samples at room temperature (25 °C) in a 1:50 dilution in distilled water. The required HLB for the M. floribunda essential oil was calculated with Equation (1) [46 ].
$$HLBr=\frac{\left(HLBa\times A\%+HLBb\times B\%\right)}{100}$$
where the required HLBr is the resulting value of two surfactants mixture, HLBa is the more hydrophobic surfactant, A% is the percentage of the hydrophobic surfactant, HLBb is the hydrophilic surfactant, B% is the percentage of the hydrophobic surfactant, and A% + B% = 100.