Brillouin scattering study of gelatin gel using a double passed Fabry-Perot spectrometer

The Brillouin spectrum of gelatin gels has been recorded at room temperature as a function of concentration of gelatin, using a double passed Fabry-Perot spectrometer. It was found that both the Brillouin shifts and line-widths increase linearly with concentration. In the case of the line-widths it was shown that the rate of increase was sensitive to the thermal history of the gels, being greater for gels cooled slowly. Explanation of the results in terms of a relaxation phenomenon is improbable. The observations can however be explained in terms of the structure of the gel. Expressing this structure as a number density of crosslinks, which is dependent on the concentration of gelatin, the increase in Brillouin shift is consistent with the change in bulk properties. The increase in line-width is shown to be caused by the crosslinks scattering the sound waves in the gel.