Scattering of Light by Gel Structures. I. Regenerated Cellulose

A low-angle light scattering photometer is described and applied to the study of regenerated cellulose gels. The scattering patterns were recorded over the angular range from 0.5° to ∼75° for the fresh gel in water (F film) and for the same sample solvent exchanged to an imbibition liquid of refractive index 1.543 (PF film). A sharp drop in over-all turbidity was recorded in going from F to PF film, indicating an intimate penetration of the nonswelling imbibition liquid into the cellulose fine structure. The observed scattering for these samples was interpreted in terms of the Debye-Bueche correlation function using the graphical integration method. The size of the regions of correlated variation in refractive index was 5800 Å for the F film and 6500 Å for the PF film; this corresponded to refractive index fluctuations of 0.005 and 0.001, respectively. It is calculated that these fluctuations in refractive index could arise from about a 3% variation in the degree of order over the respective correlation distances. Such structure heterogeneities would then be associated with a second level organization of the fine structure.