Structure formation and coarsening kinetics of phase-separated spin-coated ethylcellulose/hydroxypropylcellulose films

Abstract

Porous phase-separated ethylcellulose/hydroxypropylcellulose (EC/HPC) films are used to control drug transport from pharmaceutical pellets. The drug transport rate is determined by the structure of the porous films that are formed...

Cross-sectional structure evolution of phase-separated spin-coated ethylcellulose/hydroxypropylcellulose films during solvent quenching

“…Since the cross-sections studied in this work are replicates of the in-plane lms studied in previous work from this group, we performed the quantitative image analysis in-plane (xy-plane) and extracted the lm thickness from the cross-sections (xzplane) and performed a qualitative analysis of the structure. From the micrographs series in both planes, it appears likely that hydrodynamic coarsening is taking place, as described in Carmona et al 7 From the micrograph at 158 s and particularly for the in-plane micrographs, a secondary phase separation can be observed 39 where small dark EC domains appear in already phase-separated bright HPC domains. During solvent evaporation, the thickness of the lm is decreasing as a function of time going from 7.5 mm at 116 s to 2.3 mm at 263 s, see Fig.…”

“…The relatively slow kinetics of the structure formation allows the structure to go through a percolation-to-clustertransition and to form a discontinuous droplet-like structure. 7 To investigate the differences between the structures for the different EC/HPC ratios, the shrinkage rate was investigated (see Fig. 4 for an explanation of the determination of the shrinkage rate).…”

“…In previous work, the in-plane in situ phase separation structure evolution was extensively described and analyzed. 7 Since the evolution of the phase-separated structure evolves in 3D, it is interesting to investigate how the cross-sectional structure develops and when confinement effects and surfaces starts to influence. Fig.…”

“…In further work, 7 the effect of the EC/HPC ratio (15 to 85 wt% HPC) on the in-plane structure evolution was determined. Bicontinuous structures were found for 30 to 40 wt% HPC and discontinuous structures were found for the fractions 15 to 22 and 45 to 85 wt% HPC.…”

“…1 are droplet-like structures initiated either by nucleation and growth or by spinodal decomposition followed by a percolation-to-cluster transition. 7 Morphology 2 is a typical self-similar pattern caused by spinodal decomposition phase separation. By determining the position of the solution mixture in the phase diagram, it is possible to relate the phase separation mechanisms to the structure and ethanol content.…”