PROBING INTERNAL STRESS AND CRYSTALLINITY IN WET FOAM VIA RAMAN SPECTROSCOPY

In this paper, we correlate the internal stress and the characteristics of a vibrational mode in wet foam. Using microscope images, we estimate the average size of the bubbles in wet foam, at specific time intervals, over a duration of 24 h. Raman spectra are also recorded at the same time intervals, over the same time frame. We show that the internal stress, originated from the microscopic structural change of foam with aging, can be related to the observed Raman shift of the low-frequency methylene rocking mode of the constituent surfactant molecules in foam. In this paper, we also show the capability of the Raman spectroscopy to reveal the crystallinity in foamy materials, when studied for a longer period of time.