The relation between the interfacial contact and SiO2 coating efficiency and properties in the case of two clarithromycin polymorphs

Two clarithromycin polymorphs with very similar particle size and morphology were coated with silica using a base-catalyzed sol–gel procedure. It was found that the contact angles, evaluated from measured surface free energies, correlate well with coating efficiency. The connection between interfacial contact (described with the contact angle), nucleation kinetics and coating performance was established using the heterogeneous nucleation theory. The resulting coating thickness and morphology were evaluated by means of thermal analysis, X-ray powder diffraction and scanning electron microscopy. Good agreement was found between the theoretical predictions and experimental findings.

Research highlights▶ Coating of particles is an efficient way for protection, controlled release and taste masking of drugs. ▶ Contact angles, evaluated from measured surface energies, correlate well with coating efficiency. ▶ Even slightly different surface characteristics may lead to significantly more efficient coating performance, even though the particle morphology is very much alike. ▶ Interfacial contact can be just as important as the particle morphology. ▶ The connection between interfacial contact, nucleation kinetics and coating performance may be used generally in the design and optimization of coating processes.