An evaluation of a mass transfer rate at the boundary of different release mechanisms in complex liquid dispersion

• The mass transfer modelling at the boundary of release mechanisms.
• A mechanistic model for predicting release rates from complex liquid dispersion.
• The emulsion structure and an external phase mass transfer resistance sensitive model.
• Evaluation criteria for diffusion controlled release process.

The paper focuses on the development of the criteria for modelling mass transfer during release process at the boundary of diffusion and fragmentation in complex liquid dispersion, such as double emulsions. The proposed model for predicting release rates accounts for the effect of mass transfer resistance coupled with the emulsion structure and external release environment. The criteria of the applicability of the proposed model were formulated after verification by studies of drug release from O1/W/O2 emulsions, prepared in a Taylor–Couette flow bioreactor. It has been found that one or more mechanisms may dominate at different release stages, depending on the mixing intensity of the release medium and internal structure of double emulsions. The experimental analysis of release rates and the changes in the emulsion structure during the release process, revealed the existence of three mechanisms: (i) diffusion, (ii) diffusion and fragmentation—loss of the original structure from double emulsions to single emulsions and (iii) fragmentation. The criteria covering the diffusion release model have been formulated, as the shear rate ranges at the boundary of different mechanisms, and correspond to the values of the critical capillary numbers, which seemed to depend on the volume fraction of internal droplets of multiple emulsions.