Already within 1 min of buffer exposure, drug-polymer phase separa on has occurred, as evidenced in the false-color SRS images (Figure , second column from right) as drug-rich domains (pink) and polymer-rich domains (green). This is most visible in the false-color image as a thin magenta layer, along the loca on of the original film-air interface. Immediately to the right of drug-enriched interface, the polymer coefficients peak and gradually decrease to the right, deeper into the dissolu on medium. Thus, as the hydrophilic and water-soluble polymer at the film surface preferen ally associates with the buffer by dissolving and diffusing deeper into the dissolu on medium, it leaves behind the hydrophobic drug which self-associates, enriches and forms a new interface matrix in the form of a drug enriched layer.