Rapid drug-polymer phase separa on is also clearly evident for the 40% drug loading. Already within 1 min of buffer exposure, both surface-directed and bulk drug-polymer phase separa on has occurred, with both drug-rich (pink) and polymer-rich (green) domains. Again, the water preferen ally associated with the hydrophilic polymer (as revealed by the coefficients plots). At the 40% drug loading, the magenta drug signal is more prominent across the films, and at 1 min the drug layer at the surface is a few micrometers thicker, more uniform and with a higher peak drug concentra on (about 70%) compared to the 20% drug loading. Once again, the phase separa on intensifies over me, and surface-directed waves of alterna ng drug and polymer rich domains develop consistent with surface-directed spinodal decomposi on. At 40% drug loading, the peak drug concentra ons are greater and the drug rich-domains appear more con nuous also within the matrix where bulk phase separa on dominates.