Upon buffer addi on, the buffer (or water) signal in cyan color is visible towards the top right-hand corner of the images. Water penetra on into the matrix resulted in an interface that is visible as a discrete change in shade of green towards the bo om le -hand corner of the SRS images at approximately 87 µm and 121 µm from the original interface at 1 and 2 min, respec vely. The coefficients plot reveals that this represents the penetra on of the water front into the film and therefore the glass-gel interface. At this interface, there is a discrete jump of water content from an undetectable level on the glassy side, to about 12% water content on the gel side, while the RTV and PVPVA coeffi cients correspondingly drop by approximately 5% and 7%, respec vely. At later me points, this interface has penetrated further into the film beyond the field of view. The water penetra on into the film and gel forma on causes the film to gradually swell, with the matrix-buffer interface expanding into the buffer region by approximately 23 µm at the 20 min me point.