Effect of acid-base interaction between silica and fragrant oil in the PCL/PEG microcapsules

In this work, the biodegradable poly(E-caprolactone) (PCL)/poly(ethylene glycol) (PEG) microcapsules were prepared in the presence of SiO2 and fragrant oil using emulsion solvent evaporation method. And SiO2 was chemically treated in 30 wt.% hydrochloric acid and sodium hydroxide. The effect of chemical treatment on SiO2 surfaces was studied in terms of pH, acid-base value, and N-2/77 K gas adsorption. Image analyzer and scanning electron microscope (SEM) were used to observe the shape and surface change of the prepared microcapsules. And the variation of surface free energy of microcapsules was characterized by contact angles. The results showed that the average diameter, surface free energy, and fragrant oil release rate of microcapsules were increased with increasing the PEG ratio. Also, it was found that in the case of basic treated SiO2, the fragrant oil adsorption capacity and release rate were decreased due to the decrease of specific surface area or the increase of acid-base interactions between basic SiO2 and acidic fragrant oil. (C) 2004 Elsevier B.V. All rights reserved.