The rela ve concentra on distribu ons of PVPVA and buffer (or water) at each me point were analyzed (semi-)quan ta vely using line plots (Figure , le ). The average normalized CLS regression coefficients of the PVPVA and buffer signals at each posi on along the length of a rectangle normal to, and crossing over, the ini al film-air interface are presented in (rectangles shown in the corresponding images on right Figure ). As expected, before buffer addi on, the PVPVA coefficients within the film are consistently at unity (represen ng pure PVPVA signal), and then immediately drop to 0 at the film-air interface and remain at 0 on the other side of the interface (due to the presence of air and absence of SRS signal). Within 30 s of buffer addi on, the coefficients of both the PVPVA and buffer are both strongly represented either side of the original film-air interface, revealing substan al diffusion and mixing of the two components. Analysis of the buffer coefficients reveals that the waterfront had penetrated approximately 76 µm and 100 µm into the film a er 0.5 min and 1 min respec vely. The polymer concentra on gradually decreases and water concentra on increases at increasingly posi ve values on the x-axis, across the field of view, revealing con nuous dissolu on and diffusion of the polymer into the buffer and vice versa. These concentra on gradients gradually decrease for both components as a func on of me, revealing an increasingly homogeneous PVPVA-polymer solu on across the imaged area. There are no abrupt changes in coefficient values at any point, and as such there is no evidence of the presence of a defined gel-solu on interface.